1 Introduction

Atractylodes macrocephala is an important perennial medicinal herb widely cultivated in East Asia, especially in China, where its rhizome is used as the traditional medicine “Baizhu” and demand remains high in clinical and pharmaceutical applications (Fan et al., 2024). Because medicinal plants are often cultivated repeatedly on limited suitable land, continuous cropping has become common, yet this practice frequently causes continuous-cropping obstacles characterized by yield decline, quality deterioration, and increased disease incidence (Haq et al., 2023). In A. macrocephala, continuous cultivation is associated with reduced growth, greater susceptibility to pathogen attack, and severe root rot, making replant problems a major constraint on sustainable production. Existing studies indicate that the obstacle is not caused by a single factor, but by the interaction of autotoxicity, soil physicochemical deterioration, enzyme inactivation, microbial imbalance, and soil-borne disease. Field observations in A. macrocephala further show that increasing planting years significantly lowers rhizosphere pH, increases available Fe, Al, and exchangeable Mn, and reduces catalase, urease, and protease activities after two years of cropping. At the same time, bacterial and actinomycete populations decline while fungi increase, suggesting that acidification, metal-ion accumulation, enzyme suppression, and microbial shifts are central components of the continuous-cropping problem in this species. Autotoxic compounds also contribute directly: 2,4-di-tert-butylphenol has been isolated from A. macrocephala root exudates and rhizosphere soil, and it significantly inhibits seed germination while altering systemic acquired resistance-related indicators (Zheng et al., 2018). These findings explain why continuous cropping has become a major bottleneck for stable A. macrocephala production and why soil fertility change must be examined as part of a broader replant-disease syndrome rather than as an isolated nutrient issue.

Research on medicinal plants more broadly shows that continuous cropping reshapes the soil ecosystem through coupled changes in physicochemical properties, nutrient cycling, enzyme activity, root exudates, and microbial community structure (Pervaiz et al., 2020). Root exudates release autotoxins and other secondary metabolites into the rhizosphere, and these compounds can restructure microbiome assembly, suppress beneficial microorganisms, and enrich pathogens, thereby weakening nutrient acquisition and plant vigor. Across medicinal crops, continuous cropping commonly alters soil pH and nutrient status, which then become major drivers of microbial community composition (Ding et al., 2024). In American ginseng, for example, continuous cropping increased soil salt and inorganic nitrogen but decreased pH, C/N ratio, alkaline phosphatase, and cellulase activity, and these shifts were significantly associated with changes in microbial communities. In Panax ginseng, continuous cropping decreased total nitrogen, hydrolyzable nitrogen, organic matter, soil pH, and multiple enzyme activities, while available phosphorus and potassium accumulated, again demonstrating that nutrient imbalance and biochemical dysfunction can coexist in replant soils. Comparable patterns appear in Pinellia ternata and perilla, where continuous cropping reduced pH, disturbed nutrient balance, lowered enzyme activity, decreased beneficial taxa, and increased pathogenic microorganisms. In Dioscorea polystachya, short-term continuous cropping significantly decreased multiple mineral elements and key enzyme activities while enriching pathogenic fungi, showing that even relatively short monocropping periods can rapidly degrade soil fertility. Studies on Atractylodes lancea reach a similar conclusion: continuous cropping altered nutrient content, organic matter, pH, enzyme activity, and both bacterial and fungal community structure, whereas fallow soil approached the condition of unplanted soil. Together, this evidence indicates that the effects of continuous cropping on medicinal plants are fundamentally ecosystem-level changes, in which soil fertility decline emerges from interactions among nutrient transformation, allelochemical accumulation, enzyme-mediated processes, and rhizosphere microbial succession rather than from simple depletion of one or two nutrients.

For A. macrocephala specifically, research on soil fertility change has progressed from early description of rhizosphere physicochemical and microbial shifts to more integrative analyses of fungi, bacteria, disease status, fallow recovery, and regional soil-quality differences. Fungal studies showed that long-term monoculture reduced soil pH, altered rhizosphere and endophytic fungal diversity, and linked fungal community composition to pH, hydrolysis N, electrical conductivity, and Hg, while Fusarium became overrepresented in diseased plants. Bacterial studies similarly found marked structural shifts under continuous cultivation, with declines in beneficial genera such as Bacillus and Novosphingobium and increases in disease-associated taxa including Ralstonia and Pseudomonas; notably, a two-year fallow largely restored microbial communities and soil conditions. Disease-centered work has further shown that root rot severity is associated with lower pH, higher electrical conductivity and available potassium, and reduced endophytic microbial diversity, confirming the close linkage between soil fertility status and plant health outcomes. Regional comparison also suggests that high-quality production areas possess more complex rhizosphere fungal networks, and that pH and organic matter-decomposing fungi are closely related to A. macrocephala biomass and active component accumulation. Even so, current research still lacks a unified framework that links soil nutrient pools, micronutrient toxicity, enzyme dynamics, allelochemical turnover, microbial food-web structure, and crop quality across continuous-cropping years. Future work should therefore integrate multi-omics, long-term field monitoring, and targeted soil management experiments to identify sensitive indicators of fertility decline and to test mitigation strategies such as rotation, intercropping, fallowing, soil amendments, and beneficial microbial inoculation. Against this background, investigating soil fertility changes under continuous cropping of A. macrocephala is necessary both for clarifying the ecological basis of replant failure and for supporting sustainable, high-quality production of this important medicinal plant.

2 Characteristics of Soil Physicochemical Changes under Continuous Cropping of Atractylodes macrocephala

2.1 Dynamic changes in soil pH and salinity

Continuous cropping of Atractylodes macrocephala is consistently associated with rhizosphere acidification, and this appears to be one of the earliest and most influential physicochemical changes in replanted soil. In field observations across 0-, 1-, and 2-year planting histories, rhizosphere pH declined significantly with increasing cropping duration, while the same system also showed marked increases in available Fe, Al, and exchangeable Mn, indicating that acidification was accompanied by a shift in ionic availability and potential metal stress. More recent work further shows that in A. macrocephala soils, pH is not only a chemical indicator but also a biological regulator, because both fungal and bacterial community structures are strongly correlated with pH during continuous cultivation, helping explain why acidified soils are often more disease-prone and less biologically stable (Zhu et al., 2020).

Salinity-related change is reflected mainly through rising electrical conductivity, which interacts with pH decline to reshape the rhizosphere environment. In continuously cropped A. macrocephala, electrical conductivity was significantly correlated with fungal community composition, and this relationship suggests that salinity-associated stress is part of the mechanism by which continuous cropping alters soil ecological function. Evidence from diseased A. macrocephala plants strengthens this interpretation: rhizosphere soil from severely diseased plants had the highest electrical conductivity and the lowest pH, while conductivity and available potassium increased with root-rot severity, indicating that acidification and salt accumulation develop together as the soil environment deteriorates (Fan et al., 2024).

2.2 Changes in soil structure and physical properties

Although direct measurements of bulk density, aggregate stability, or porosity are still limited for A. macrocephala, current evidence indicates that continuous cropping changes soil physical status through its effects on compaction-related properties, ion accumulation, moisture-nutrient relations, and the broader soil microenvironment. Reviews of medicinal plant continuous-cropping systems identify pH, conductivity, water-holding characteristics, cation exchange capacity, compaction, bulk density, and porosity as key physical and physicochemical attributes disturbed by long-term monoculture, suggesting that structural degradation is a common component of replant obstacles rather than an isolated case. In Atractylodes relatives, continuous cropping altered nutrient status, pH, organic matter, and enzyme activity simultaneously, while fallow soils moved back toward uncultivated conditions, implying that deterioration of physical habitat quality accompanies biochemical and microbial imbalance (Wang et al., 2023).

Indirect support from other medicinal-plant systems also suggests that the physical condition of continuously cropped soils becomes less favorable for root growth and rhizosphere functioning. In American ginseng, continuous cropping increased soil salt while reducing pH, and these changes were significantly associated with shifts in microbial communities and enzyme activities, indicating a tighter, less balanced soil environment after repeated planting. More generally, plant species differ in how strongly they remodel rhizosphere microenvironments, but continuous-cropping-sensitive medicinal plants tend to induce major changes in pH, nutrient availability, and enzyme profiles across root-associated compartments, which supports the view that A. macrocephala soil structural degradation should be understood as part of a whole-soil habitat shift rather than as a purely mechanical phenomenon (Yang et al., 2026).

2.3 Changes in soil organic matter and carbon pools

Changes in soil organic matter and carbon pools under continuous cropping of A. macrocephala show a dynamic rather than linear pattern. Early work found that rhizosphere organic matter and total nitrogen first increased and then decreased with longer planting duration, suggesting that short-term residue return and fertilization may temporarily enrich the soil, but that this effect is not sustained as continuous cropping pressure intensifies. Related evidence from A. macrocephala bacterial-community analysis indicates that organic matter is closely linked to microbial recovery during fallow periods and is positively associated with pH and hydrolyzable nitrogen, highlighting its central role in rebuilding soil fertility after continuous cultivation (Xu et al., 2025).

Findings from other medicinal plants suggest that the instability of organic matter in A. macrocephala reflects a broader pattern of carbon-pool dysfunction under continuous cropping. In long-term tobacco monoculture, soil organic carbon declined significantly in continuously cropped treatments and was one of the main factors driving microbial compositional change (Ding et al., 2024). By contrast, some systems show temporary accumulation of organic matter or SOC under continuous cropping, as reported for Amomum villosum and Curcuma kwangsiensis, indicating that carbon inputs can increase while soil function still declines because accumulated carbon is not necessarily efficiently transformed into stable fertility or healthy nutrient cycling. Overall, continuous cropping of A. macrocephala produces a coupled physicochemical shift characterized by acidification, salinity increase, deterioration of the soil microenvironment, and unstable organic matter dynamics. These changes appear to interact with microbial succession and disease development, making soil fertility decline a process of whole-ecosystem imbalance rather than simple nutrient depletion (Figure 1).

3 Effects of Continuous Cropping of Atractylodes macrocephala on Soil Nutrient Availability

3.1 Changes in soil nitrogen cycling and available nitrogen

Continuous cropping of Atractylodes macrocephala disrupts soil nitrogen cycling rather than simply lowering total nitrogen supply. In this species, hydrolyzable nitrogen is one of the key environmental factors shaping rhizosphere bacterial composition during continuous cultivation, indicating that changes in available nitrogen are closely tied to microbial restructuring and fertility decline. More broadly, rhizosphere continuous-cropping obstacles in medicinal plants are understood as plant-soil-microbe processes in which nutrient imbalance and enzyme dysfunction develop together, so nitrogen availability depends not only on fertilizer inputs but also on microbial turnover, mineralization, and rhizosphere biochemical regulation (Liao and Xia, 2024). Available nitrogen under continuous cropping often shows stage-dependent dynamics, which helps explain the mixed patterns reported across medicinal plants and likely applies to A. macrocephala as well. A general framework for bioavailable nitrogen emphasizes that plant-available N emerges from the balance among organic N depolymerization, sorption-desorption on mineral surfaces, and microbial assimilation and mineralization, so small shifts in soil chemistry or microbiota can markedly alter N supply (Daly et al., 2021). Consistent with this, some continuous-cropping systems show short- to medium-term increases in available or inorganic N, such as tobacco and Curcuma kwangsiensis, where available N accumulated despite broader soil deterioration, suggesting that continuous cropping can create nitrogen enrichment in soil while still reducing crop performance and nitrogen-use efficiency.

In other medicinal plants, however, long-term continuous cropping leads to nitrogen depletion or impaired nitrogen transformation, especially when disease pressure intensifies. In ginseng, continuous cropping significantly reduced total nitrogen and hydrolyzable nitrogen relative to uncultivated soil, showing that prolonged monoculture can exhaust or immobilize accessible N pools even when some other nutrients accumulate (Chen et al., 2023). Comparative work in Panax further showed ammonium accumulation alongside suppression of nitrification-related functions in continuous-cropping-sensitive species, supporting the view that nitrogen cycling becomes less balanced and more microbially constrained as replant stress worsens (Yang et al., 2026). These observations suggest that the nitrogen problem in continuously cropped A. macrocephala is best interpreted as a cycling disorder rather than a simple shortage. Nitrogen inputs can accumulate in surface soils under long-term protected cropping, but the same systems may also carry substantial surplus risk, reduced biological conversion efficiency, and declining crop uptake capacity. Accordingly, future work on A. macrocephala should distinguish among total N, hydrolyzable N, ammonium, nitrate, and N-cycling enzyme activity, because similar total nitrogen status can mask very different levels of biological availability and plant usability.

3.2 Changes in soil phosphorus and potassium availability

Continuous cropping of A. macrocephala appears to promote nutrient accumulation patterns that are uneven across elements, and phosphorus and potassium often show enrichment even when overall soil fertility declines. Across medicinal plant systems, continuous cropping commonly affects the availability of major nutrients including phosphorus and potassium, and these shifts are strongly conditioned by rhizosphere acidification and altered cation exchange processes. In continuously cropped A. macrocephala soils, pH decline is well documented, which is important because acidification can change the release, fixation, and plant uptake efficiency of both P and K even before total nutrient stocks visibly decline. Evidence from related medicinal plants shows that available phosphorus and available potassium frequently accumulate under continuous cropping, but this accumulation often reflects imbalance rather than improved nutrition. In ginseng, continuous cropping significantly increased TP, TK, AP, and AK while TN, hydrolyzable N, and organic matter declined, clearly indicating a decoupling between nutrient accumulation and functional fertility. A similar pattern was reported in Curcuma kwangsiensis, where AP and AK rose sharply with cropping years despite yield loss and soil acidification, suggesting that reduced plant uptake, altered microbial transformation, or fertilization residues may drive P and K build-up in the rhizosphere (Huang et al., 2025).

Not all potassium pools respond in the same way, and the distinction between total K and available K is especially important. In tobacco, long-term continuous cropping increased available phosphorus and alkaline nitrogen but reduced available potassium, indicating that exchangeable K can become depleted even when other nutrients accumulate. Patchouli showed another mixed pattern, with declines in total potassium but increases in available potassium, reinforcing that continuous cropping can accelerate mineral weathering or fertilizer-driven release into available pools while simultaneously weakening long-term K reserves. For A. macrocephala, these comparisons suggest that changes in phosphorus and potassium availability are likely nonlinear and form-specific. The main risk is not necessarily absolute deficiency at all stages, but progressive disequilibrium between accumulated available nutrients and the plant’s actual capacity to absorb and use them under acidified, pathogen-prone rhizosphere conditions. This interpretation is also supported by rotation evidence in chrysanthemum, where improved soil health was accompanied by higher ammonium N, available P, and available K than in monoculture, implying that monocropping suppresses the effective utilization of these nutrients even when some pools remain elevated (Chen et al., 2025).

3.3 Changes in micronutrients and nutrient stoichiometric balance

Continuous cropping of A. macrocephala also affects micronutrient behavior and nutrient stoichiometric balance, and these changes likely contribute to hidden fertility decline. In medicinal plants, continuous cropping can significantly alter the availability of micronutrients such as Fe, Mn, Cu, Ca, Mg, and Mo, while acidification modifies their solubility and biological effects. For A. macrocephala specifically, previous observations showed that with increasing cropping years the rhizosphere accumulated available Fe, available Al, and exchangeable Mn, indicating that acidified soil conditions can shift the system from balanced nutrition toward trace-element stress. Comparable systems confirm that micronutrient accumulation under continuous cropping is common but not always beneficial. In American ginseng soils, Fe, Mn, and Cu contents were much higher than in comparison continuous-corn soil, illustrating how medicinal plant monoculture can intensify micronutrient enrichment beyond ordinary field-crop systems. In chrysanthemum, rotation increased available Fe, Zn, and Cu relative to monoculture, which implies that the lower-quality continuous-cropping system had a less favorable micronutrient regime even where some major nutrients remained high.

Stoichiometric imbalance provides a useful framework for understanding why nutrient-rich soils under continuous cropping can still become functionally infertile. Long-term greenhouse continuous cropping increased soil C, N, and P to different degrees and caused a decoupling of P from N and K in plant nutrient use, showing that accumulation of individual elements can distort elemental coordination rather than improve nutritional harmony. At the broader cropping-system scale, elevated C:P and N:P ratios are associated with disrupted microbial nutrient cycling and poorer productivity, supporting the idea that the ratio among nutrients can be as important as their absolute concentrations. Microbial stoichiometry further suggests that phosphorus imbalance is often central to long-term replant problems. In a 12-year continuous-cropping experiment, microbial nutrient demand was generally C- and P-limited rather than N-limited, meaning that soils can contain nitrogen while still functioning under strong phosphorus constraint. Likewise, studies of intercropping show that improved productivity is associated with greater C-N-P stoichiometric stability and reduced microbial P limitation, implying that the stoichiometric disorder created by continuous monoculture is a key mechanism of fertility decline. Overall, continuous cropping of A. macrocephala appears to alter soil nutrient availability through a combined process of nitrogen-cycle disruption, uneven P and K accumulation, micronutrient redistribution, and stoichiometric imbalance. Thus, evaluating soil fertility in this crop should move beyond single nutrient measurements and instead integrate nutrient forms, elemental ratios, and biologically mediated transformation processes.

4 Effects of Continuous Cropping on Soil Biological Fertility of Atractylodes macrocephala

4.1 Changes in soil microbial community structure

Continuous cropping of Atractylodes macrocephala markedly changes the composition and diversity of soil microbial communities, and this shift is a core feature of declining soil biological fertility. Early rhizosphere observations showed that after two years of planting, the numbers of bacteria, actinomycetes, and total microorganisms declined significantly, whereas fungal abundance increased, indicating a transition from a more balanced microbial system toward a fungus-enriched state. High-throughput sequencing studies later confirmed that continuous cultivation significantly reshaped both rhizospheric and endophytic bacterial communities and increased plant susceptibility to disease.

Fungal community change follows the same general pattern but adds an important disease dimension. In A. macrocephala, continuous cropping reduced rhizospheric fungal alpha diversity, and lower diversity was associated with diseased tissues and soils, suggesting that microbial simplification weakens ecological resistance in the rhizosphere (Zhu et al., 2020). Diseased plants also showed reduced endophytic bacterial and fungal richness together with enrichment of Proteobacteria and Ascomycota and depletion of Firmicutes, Bacteroidetes, Actinobacteria, and Basidiomycota, demonstrating that root rot is accompanied by broad community reassembly rather than the appearance of a single pathogen alone (Fan et al., 2024).

4.2 Changes in soil enzyme activities and nutrient transformation capacity

Continuous cropping also weakens soil enzyme activity, which directly limits biological nutrient transformation. In the rhizosphere of A. macrocephala, catalase, urease, and protease activities were significantly lower after two years of continuous planting than in unplanted control soil, indicating reduced capacity for oxidative balance, nitrogen conversion, and protein decomposition. More broadly across medicinal plants, continuous-cropping obstacles are characterized by coupled declines in beneficial microorganisms, nutrient balance, and enzyme activity, showing that enzyme suppression is part of a whole-soil biological degradation process rather than an isolated biochemical symptom.

Evidence from related medicinal plants shows that enzyme responses can vary in direction, but altered enzyme activity consistently signals disturbed nutrient turnover capacity. In American ginseng, alkaline phosphatase and cellulase activities declined significantly in soils affected by continuous cropping and were closely associated with changes in microbial community composition. By contrast, in Amomum villosum, urease and acid phosphatase tended to increase with longer cropping duration, suggesting accelerated substrate conversion under stress, but this increase occurred alongside reduced microbial diversity and therefore does not indicate stable biological fertility (Wang et al., 2022).

4.3 Rhizosphere microecology and nutrient cycling processes

At the rhizosphere scale, continuous cropping of A. macrocephala appears to reorganize the plant-soil-microbe interaction network that governs nutrient cycling. Soil pH, hydrolyzable nitrogen, electrical conductivity, and Hg were significantly correlated with fungal community composition during continuous cropping, showing that nutrient cycling processes are mediated through a chemically altered microbial habitat rather than through nutrients alone. Bacterial community composition was likewise shaped by pH, hydrolyzable nitrogen, and mercury, indicating that both fungal and bacterial nutrient-transforming guilds respond to the same disturbed rhizosphere filters.

This rhizosphere rewiring is driven in part by autotoxic compounds and by instability in microbial interaction networks. In medicinal plants, accumulated root exudate autotoxins disrupt rhizospheric microbial balance, increase pathogenic microorganisms, and reduce beneficial taxa, thereby altering microbiome assembly and nutrient acquisition processes. For A. macrocephala specifically, 2,4-di-tert-butylphenol was identified from root exudates and rhizosphere soil as an autotoxic compound that inhibited seed germination, while evidence from other medicinal systems shows that continuous cropping can make bacteria-fungi interaction networks less dense and stable, which helps explain why nutrient cycling becomes less resilient under repeated monoculture (Liu et al., 2024). Overall, continuous cropping reduces the soil biological fertility of A. macrocephala by shifting microbial communities toward lower diversity and higher pathogen pressure, by disturbing enzyme-mediated nutrient transformation, and by destabilizing rhizosphere ecological interactions. These biological changes help explain why fertility decline under continuous cropping is a process of ecological dysfunction, not merely a decrease in soil nutrient content.

5 Mechanisms of Soil Fertility Degradation under Continuous Cropping of Atractylodes macrocephala

5.1 Mechanisms of soil nutrient depletion and imbalance between input and output

The nutrient mechanism of soil fertility degradation under continuous cropping of Atractylodes macrocephala is not simple exhaustion of total nutrients, but a progressive imbalance between selective crop uptake, fertilizer input, and biological transformation. Continuous cropping amplifies the preference of single crops for particular elements, which accelerates nutrient imbalance and simultaneously alters the physicochemical environment that microorganisms depend on. In A. macrocephala itself, increasing planting years were accompanied by declining pH, a first-increase-then-decrease pattern in organic matter and total N, and a gradual rise in available K, showing that nutrient pools shift asynchronously rather than uniformly during repeated cultivation. This imbalance further reflects a decoupling between nutrient quantity and nutrient usability. Continuous cropping can reduce the effectiveness of some nutrients by lowering soil buffering capacity and ionic balance, especially when management relies mainly on N, P, and K fertilizers while neglecting organic inputs and trace elements. Evidence from other continuous-cropping systems shows that long-term monoculture often depresses key nutrients and cation exchange capacity, with reductions in N and P occurring together with moderate limitations in organic carbon, indicating that nutrient depletion is closely tied to declining retention and supply capacity rather than to one-time removal alone (Kartini et al., 2024).

A second part of the mechanism is that nutrient input and output become biologically mismatched as soil conditions deteriorate. In A. macrocephala, bacterial community composition is strongly associated with pH and hydrolyzable nitrogen, indicating that nitrogen availability is regulated through microbial mediation rather than fertilizer presence alone. Broader work on medicinal plants shows that nutrient imbalance is coupled with reduced enzyme activity and loss of beneficial microorganisms, so even where some available nutrient pools accumulate, transformation, uptake, and recycling processes become less efficient. Long-term continuous cropping therefore creates a feedback loop of inefficient fertilization. Selective nutrient absorption by the crop and improper fertilization can cause trace-element imbalance, nutritional deficiency, and reduced root absorption capacity, which in turn worsens fertility decline and plant performance. In continuous-cropping systems more generally, toxic metabolites, salts, and acids accumulate while mineralization, active carbon, and nutrient contents decline, indicating that the soil loses the capacity to convert external nutrient inputs into stable productive fertility (Pervaiz et al., 2020).

5.2 Mechanisms of autotoxic compound accumulation and soil functional degradation

Autotoxic compound accumulation is another core mechanism of fertility degradation in continuously cropped A. macrocephala, because root-derived secondary metabolites progressively alter the rhizosphere environment. Reviews of medicinal plants show that under continuous cropping, root exudates release autotoxins that change soil physicochemical properties and microbial community structure, thereby driving nutrient imbalance and enzyme dysfunction. In A. macrocephala, 2,4-di-tert-butylphenol has been identified from root exudates and rhizosphere soil as an autotoxic compound with significant inhibitory effects on seed germination, confirming that the crop itself can generate biologically active compounds that contribute to replant stress. The key point is that autotoxicity does not act only on the plant; it also degrades soil function. In Atractylodes lancea, autotoxic allelochemicals released from roots caused soil acidification, pathogen enrichment, and reduced microbiota diversity, and these changes jointly deteriorated the soil microenvironment and produced replant problems (Wang et al., 2023). Comparable metagenomic-metabolomic evidence from other monoculture systems shows that continuous cropping promotes the accumulation of allelopathic metabolites that correlate with pathogenic fungi enrichment and beneficial-microbe decline, supporting a general mechanism in which metabolite buildup reshapes soil function through ecological feedbacks.

Autotoxic accumulation also appears to be a threshold process that becomes more damaging with time. In continuous-cropping medicinal plants, elevated autotoxin levels exert stronger growth inhibition, and early-stage rhizosphere changes may remain limited until exudates accumulate enough to produce observable biological effects. This staged pattern is consistent with evidence that short-term continuous cropping can leave microbial communities relatively stable, whereas longer-term cropping shifts communities toward pathogenic and saprophytic functions while slowing soil carbon turnover and reducing disease resistance. A further mechanism is that autotoxic compounds interfere with the soil’s own self-remediation capacity. Soil microorganisms can decompose toxic compounds, but they can also transform allelopathic residues into additional phytotoxic products, so the balance of the microbial community determines whether detoxification or further toxicity dominates. In diseased rhizosphere microbiomes, specific metabolites can weaken the bacterial function of autotoxin degradation while promoting alternative metabolic pathways associated with disease development, showing how autotoxicity and functional degradation reinforce one another (Wen et al., 2022).

5.3 Microbial imbalance-driven mechanisms of soil degradation

Microbial imbalance is the most direct biological mechanism linking continuous cropping to declining soil fertility in A. macrocephala. Continuous cropping altered both rhizospheric and endophytic fungal communities in A. macrocephala, reduced fungal diversity, and enriched Fusarium in root-rot-associated plants, indicating that the rhizosphere shifts from a balanced nutrient-transforming community toward a disease-prone state. A parallel bacterial response has also been documented: beneficial genera such as Bacillus and Novosphingobium declined, whereas Ralstonia and Pseudomonas increased under continuous cultivation, directly linking microbial succession to soil health decline. This imbalance matters because microorganisms are the main agents of nutrient cycling, organic matter turnover, toxin degradation, and soil structure maintenance. When continuous cropping changes the number and composition of soil microorganisms, these core ecological processes are impaired, and soil fertility declines even before all nutrient pools are visibly depleted. Reviews focused on continuous cropping therefore identify rhizosphere microecological imbalance as the most crucial cause of cropping obstacles, precisely because it disrupts the microbial food web that supports nutrient cycling and soil health.

The microbial mechanism is not just a loss of diversity; it is a functional shift toward stress tolerance and pathogenicity. In continuously cultivated medicinal-plant rhizospheres, microbial competition intensifies, functional redundancy declines, and fungal communities shift from saprophytic dominance toward coexistence of pathogenic and symbiotic types, while bacterial carbon and nitrogen cycling functions decrease (Jia et al., 2026). Similar evidence from continuous tobacco cropping shows increased ureolysis and manganese oxidation but decreased nitrate reduction and chitinolysis, indicating that microbial functional profiles are reorganized in ways that weaken balanced nutrient cycling. Microbial imbalance is also reinforced by interactions with soil chemistry and plant metabolites. In A. macrocephala, fungal community composition is strongly correlated with pH, hydrolysis N, electrical conductivity, and Hg content, showing that microbial succession is driven by a disturbed chemical habitat. At the same time, studies of replant disease in A. macrocephala indicate that reduced beneficial bacteria and increased pathogens are closely associated with microecological imbalance in the rhizosphere, supporting the view that soil degradation arises from a coupled plant-soil-microbe feedback rather than from any single pathogen or nutrient defect (Yuan et al., 2019). Overall, soil fertility degradation under continuous cropping of A. macrocephala is driven by the interaction of nutrient imbalance, autotoxic accumulation, and microbial dysbiosis. These mechanisms are mutually reinforcing, so the decline in fertility is best understood as a progressive breakdown of rhizosphere ecological function rather than as simple nutrient loss alone.

6 Regulation Strategies for Improving Soil Fertility under Continuous Cropping of Atractylodes macrocephala

6.1 Effects of crop rotation and fallow practices on soil fertility restoration

Crop rotation remains one of the most established agronomic measures for alleviating continuous-cropping obstacles because it helps rebalance nutrient use, interrupts pathogen cycles, and improves the soil microecological environment. In medicinal-plant systems, rotation is regarded as a cost-effective and eco-friendly approach, and its fertility benefits are linked not only to higher yield but also to improved microbial biomass and soil organic carbon stability. Evidence from field studies shows that the fertility-restoring effect of rotation becomes stronger when it is combined with biologically supportive management. In a 12-year experiment, rotation plus organic fertilizer increased crop production by at least 40% relative to other management combinations and simultaneously improved soil organic matter, decomposer abundance, and microbial network stability (Jiang et al., 2022). Rotation also reduced the abundance of potential fungal pathogens by at least 20% and relieved microbial resource limitation, indicating that restored fertility depends on both nutrient pools and microbial functioning (Figure 2).

Fallow is another effective strategy, especially where continuous cropping has already caused strong rhizosphere deterioration. In Atractylodes lancea, natural fallow restored the OTU numbers of bacterial and fungal communities that had declined under continuous cropping (Wang et al., 2023). The same study showed that the biochemical properties, nutrient status, organic matter, pH, and enzyme activity of fallow soil moved closer to those of unplanted soil, suggesting real recovery of soil function rather than short-term symptom relief. Broader evidence supports using fallow as a fertility-restoration phase rather than leaving soil idle without purpose. Increasing seasonal fallow intensity raised soil organic carbon, total nitrogen, and C- and N-acquiring enzyme activities, while green-manure fallow partly alleviated microbial phosphorus limitation. More generally, complex rotations that include perennial forage or fallow phases improve nutrient-cycle efficiency and help maintain stable soil C, N, and P dynamics, which is highly relevant for restoring degraded A. macrocephala soils (Mosier et al., 2021).

6.2 Regulation effects of organic fertilizers and bio-organic fertilizers

Organic fertilizers improve soil fertility under continuous cropping primarily by replenishing organic matter, enhancing nutrient retention, and creating a more favorable habitat for beneficial microorganisms. In medicinal-plant systems, organic amendments are considered effective substitutes for harsher controls because they improve physicochemical properties and support constructive microorganisms involved in disease suppression. This broader pattern is consistent with evidence that organic amendments sustainably enhance soil fertility, suppress soil-borne pathogens, and improve microbial community structure in monoculture soils. Bio-organic fertilizers often produce stronger effects than ordinary organic fertilizers because they combine organic substrates with functional microorganisms. In an 8-year watermelon continuous-cropping system, bio-organic fertilizer improved soil mineral levels, especially available iron, and also enhanced microbial resistance and community stability. In cotton monoculture, bio-organic fertilizer increased soil nutrients, reduced Fusarium, and promoted a more complex rhizosphere microbial network, indicating simultaneous recovery of fertility and ecological resilience (Yu et al., 2025).

The fertility benefits of organic inputs also involve improvements in soil physical organization and functional microbiology. Long-term organic fertilization increased soil C, N, and P within macro-aggregates and promoted crop productivity by increasing the proportion of macro-aggregates, showing that fertility restoration is partly mediated through better soil structure (Tian et al., 2022). Biochar-organic amendments likewise increased organic matter and nutrient-related indicators while supporting pH recovery and microbial habitats, which is relevant where A. macrocephala soils have become acidified and carbon-depleted. Not all organic inputs are equally effective, and combined strategies generally outperform single amendments. Long-term evidence shows that organic fertilizer combined with rotation maintained soil health and production better than either practice alone. Similarly, combined biochar and organic fertilizer increased agroecosystem multifunctionality by 18.7–30.1% and enriched microbial taxa involved in C, N, P, and S cycling, suggesting that integrated amendment programs are more likely to restore nutrient transformation capacity in continuously cropped soils.

6.3 Application of microbial inoculants and soil ecological restoration technologies

Microbial inoculants provide a more targeted way to restore soil fertility because they act directly on rhizosphere ecological processes such as nutrient activation, pathogen suppression, and microbiome assembly. In continuous-cropping systems, microbial agents and microbial fertilizers can improve soil quality and restore rhizosphere equilibrium by reducing soil-borne disease pressure and supporting beneficial microbial abundance (Ahsan et al., 2023). This strategy is especially relevant where A. macrocephala soils show microbial imbalance as a central mechanism of fertility decline. Experimental evidence indicates that inoculants can restore disease-suppressive capacity when they are designed around missing native functions. In peanut, monocropping depleted key rhizosphere taxa and weakened the ability of soil to suppress root rot, whereas supplementation with depleted native strains restored resistance to pathogen invasion. More broadly, microbial inoculants can serve as biofertilizers, biocontrol agents, or soil-improvement tools, but their success depends on ecological fit, formulation quality, and rigorous field validation (O’Callaghan et al., 2022).

In practice, inoculants often work best by reshaping the rhizosphere community rather than by supplying nutrients directly. In tobacco monoculture, a Bacillus*-based inoculant improved yield and disease resistance and enriched rhizosphere biomarkers such as Rhizobium, Pseudomonas, and Sphingomonadaceae while altering the soil metabolite spectrum. In eggplant, inoculant effects were strongly strain-specific: one treatment significantly increased SOC, SOM, total N, and available N, while another showed limited effects, indicating that strain selection is critical for fertility restoration. Soil ecological restoration technologies should therefore emphasize microbiome-guided integration rather than single-input replacement. Reviews of rhizosphere engineering support the use of indigenous consortia and engineered exogenous inoculants for sustainable crop production. At the same time, microbiome-informed biocontrol frameworks stress persistence, ecological compatibility, and the use of precision-designed microbial consortia, which suggests that future management of A. macrocephala continuous-cropping soils should combine inoculants with rotation, organic amendments, and local soil-specific ecological diagnosis. Overall, improving soil fertility under continuous cropping of A. macrocephala requires integrated regulation centered on rhizosphere recovery. Rotation or fallow rebuilds ecological balance, organic and bio-organic fertilizers restore carbon and nutrient functions, and microbial inoculants help re-establish disease suppression and nutrient cycling in degraded soils.

7 Case Study: Effects of Long-Term Continuous Cropping on Soil Fertility Changes in Atractylodes macrocephala

7.1 Case study of soil fertility indicator changes under different continuous cropping years

A representative year-gradient case study of A. macrocephala rhizosphere soil showed that continuous cropping produced a clear temporal shift in several fertility indicators. With increasing planting years from 0 to 2 years, soil pH declined significantly, organic matter and total nitrogen showed a pattern of first increasing and then decreasing, available potassium rose gradually, and available phosphorus changed only slightly. In the same case, available Fe, available Al, and exchangeable Mn increased markedly relative to unplanted soil, indicating that long-term cropping changed not only nutrient status but also the ionic environment associated with declining soil quality. Later case evidence refined this temporal pattern by showing that the fertility decline was linked to threshold-like deterioration rather than a uniform year-by-year loss. In continuous-cultivation plots, soil pH fell to as low as 4.49, well below the reported optimal range of 5.1-6.6 for A. macrocephala, which would be expected to increase disease susceptibility and weaken root-zone function. A broader synthesis of continuous cropping systems supports this interpretation, because long-term monoculture commonly increases acids, salts, and toxic metabolites while reducing mineralization, soil organic matter, active carbon, and nutrient contents, so the A. macrocephala case fits a wider degradation trajectory rather than an isolated local anomaly (Pervaiz et al., 2020).

A second pattern emerging from these case studies is that some nutrient pools do not decline monotonically even while fertility worsens. In A. macrocephala continuous cropping soils, higher hydrolysis N, available P, and available K often reflect fertilizer input rather than stable biological fertility, which means apparent nutrient enrichment can coexist with poorer soil function. This interpretation is consistent with root-rot field comparisons showing that alkali-hydrolyzable N and available P were similar among healthy and diseased plants grown in the same field, even though plant health and rhizosphere condition differed substantially. Taken together, these year-based case data suggest that the most informative fertility indicators in A. macrocephala are composite rather than single-factor measures. Continuous cropping altered pH, nitrogen status, potassium accumulation, and metal-ion availability at the same time, and the original field study explicitly linked severe acidification, metal accumulation, enzyme inactivation, and microflora alteration to the cropping obstacle. More generally, continuous cropping is known to deplete major nutrients and essential minerals while also reducing beneficial organisms, so the best case-based interpretation is that fertility decline reflects coordinated physicochemical and biological imbalance rather than one depleted element alone (Figure 3).

7.2 Case study of continuous cropping effects on rhizosphere microecology and nutrient cycling

Case studies of the A. macrocephala rhizosphere consistently show that long-term continuous cropping restructures the microbial community in ways that undermine nutrient cycling. In the early field microbiological survey, two years of continuous cropping significantly reduced bacteria, actinomycetes, and total microbial numbers, while fungal abundance increased, indicating a shift away from a balanced decomposer community. Sequencing-based analysis later confirmed that continuous cultivation significantly reshaped both rhizospheric and endophytic bacterial communities, with beneficial genera such as Bacillus and Novosphingobium declining and disease-associated taxa increasing. Fungal case evidence points in the same direction and links microecological change directly to rhizosphere chemistry. Continuous cropping decreased fungal diversity in A. macrocephala, and fungal community composition was strongly correlated with pH, hydrolysis N, electrical conductivity, and Hg content, showing that nutrient cycling processes were being filtered through a chemically altered rhizosphere (Zhu et al., 2020). In diseased plants, root rot was associated with increased rhizosphere Proteobacteria and Ascomycota and reduced Firmicutes, Bacteroidetes, Actinobacteria, and Basidiomycota, which indicates that nutrient-transforming and disease-suppressive groups were lost as the soil environment deteriorated.

These community shifts were accompanied by functional evidence of weakened nutrient transformation. In the original continuous-cropping case study, catalase, urease, and protease activities were significantly lower after two years of planting than in unplanted control soil, indicating reduced capacity for oxidative regulation and organic N transformation. A parallel replant-disease case study found that diseased rhizosphere soil had altered phosphatase activity and pronounced microbial-community imbalance, leading to the conclusion that rhizosphere microecological imbalance was the primary cause of replant disease.The case evidence therefore supports a rhizosphere mechanism in which long-term continuous cropping progressively shifts microbial function from nutrient cycling toward stress and disease association. Work in another continuously cultivated medicinal plant showed that soil multifunctionality fell by about 46.19% from years 1 to 4, while bacterial carbon and nitrogen cycling functions declined and microbial competition intensified, providing a useful functional analogue for interpreting the A. macrocephala pattern. This is also consistent with the broader principle that rhizosphere microorganisms are major determinants of medicinal-plant quality and metabolite accumulation, so disruption of rhizosphere microecology in A. macrocephala likely affects both soil fertility and medicinal quality formation (Song et al., 2023).

7.3 Case study of comprehensive evaluation of soil quality and improvement effects in continuous cropping systems

Comprehensive evaluation of long-term continuous-cropping soils in A. macrocephala indicates that soil quality should be judged by integrating physicochemical, biological, and plant-health indicators rather than by nutrient concentrations alone. In one recent field case, healthy and diseased plants grown under the same management still showed significant differences in soil physicochemical properties and microbial community characteristics, demonstrating that soil quality divergence can emerge within the same field once root-zone degradation begins. Region-comparison evidence adds that higher-quality production areas had more complex rhizosphere fungal networks, and fungi involved in organic matter decomposition were linked to better plant quality, suggesting that network structure can serve as part of a comprehensive soil-quality evaluation framework. Improvement case studies further show that soil-quality restoration is possible when management targets both nutrients and microecology. In A. macrocephala, a two-year fallow period gradually restored bacterial diversity toward unplanted-soil levels, increased organic matter, and returned essential soil elements closer to baseline, indicating substantial recovery of biological fertility (Xu et al., 2025). The same study concluded that a two-year fallow was effective for alleviating continuous-cultivation problems, making it one of the clearest case demonstrations of soil-quality improvement in this crop.

Organic amendment case studies support the same conclusion from a different management angle. Vermicompost-based organic fertilizer significantly increased available phosphorus and several soil enzyme activities, while also increasing soil fungal diversity, indicating simultaneous improvement in nutrient availability and biological function. More generally, vermicompost is reported to enhance soil structure, fertility, aeration, drainage, and water-holding capacity, which makes it relevant as a restorative tool where continuous cropping has impaired both physical and biological dimensions of soil quality (Sun et al., 2024). Overall, the case-study evidence shows that long-term continuous cropping of A. macrocephala causes a multidimensional decline in soil quality involving acidification, nutrient imbalance, enzyme suppression, microbial-community shifts, and greater disease susceptibility. The same evidence also shows that comprehensive improvement is achievable through fallow and organic ecological management, especially when success is evaluated by combined indicators of chemistry, biology, and rhizosphere network stability rather than by single nutrient values alone.

8 Future Research Directions and Development Trends

8.1 Application of multi-omics technologies for elucidating continuous cropping obstacle mechanisms

Future research on continuous cropping of A. macrocephala should move from single-factor analyses to integrated multi-omics frameworks that jointly resolve soil chemistry, root exudates, microbial community structure, and functional gene expression. Current reviews of medicinal-plant continuous cropping already identify genome-wide transcriptomes, microbial-community composition, candidate genes, and related molecular pathways as central targets for future work. More recent methodological syntheses show that DNA-based approaches now extend beyond marker-gene surveys to metagenomics, metatranscriptomics, metaproteomics, metabolomics, ionomics, and phenomics, making it increasingly feasible to study rhizosphere fertility decline as a multi-layer biological system rather than as isolated changes in nutrients or taxa.For A. macrocephala, the most important advance will be to use multi-omics to identify the causal chain linking root metabolites, microbial succession, and nutrient-cycling dysfunction across different cropping years. Chronosequence work in another long-term medicinal cropping system used combined metagenomics and non-targeted metabolomics to reveal dynamic changes in physicochemical properties, root metabolites, microbial functions, and their tripartite interactions under continuous cropping. Similar 2026 rhizosphere studies in Rehmannia glutinosa and plant-microbiome interaction research indicate that early microecological shifts can be captured before severe obstacle symptoms fully appear, which is especially relevant for A. macrocephala because preventative diagnosis is likely to be more effective than late-stage remediation (Yusuf et al., 2025).

Another priority is to connect multi-omics data with microbiome engineering and functional strain design. Reviews on rhizosphere engineering emphasize that metagenomics, biochemical profiling, genome sequencing, and downstream transcriptomic or proteomic validation can be used to isolate and optimize beneficial strains for nutrient acquisition, stress resilience, and biocontrol. This direction is reinforced by broader multi-omics syntheses showing that mechanistic plant-microbe insight can support synthetic microbial communities, soil-health biomarkers, and field management strategies that reduce dependence on fertilizers and pesticides. A further development trend is the construction of standardized, cross-scale analytical pipelines for medicinal-plant rhizospheres. Multi-omics studies increasingly stress that the field needs standardized workflows, stronger causal inference across scales, and integration of molecular diagnostics with sensing and analytics. For A. macrocephala, this means future experiments should combine year-gradient field sampling, rhizosphere compartment differentiation, and omics-linked phenotyping of soil fertility, disease incidence, and medicinal quality, so that the mechanisms of continuous-cropping obstacles can be translated into actionable thresholds rather than remaining descriptive patterns.

8.2 Intelligent soil fertility monitoring and precision management

Research on A. macrocephala soil fertility should increasingly adopt intelligent monitoring systems that can track nutrient status, pH, salinity, moisture, and crop responses in real time. Recent IoT-based platforms can already monitor temperature, moisture, salinity, EC, pH, and major nutrients simultaneously, then use AI-supported interfaces to guide fertilization, irrigation, and disease management decisions. Precision-agriculture reviews likewise show that AI and IoT integration is transforming crop monitoring by combining remote sensing, high-throughput phenotyping, and automated decision support into operational management tools. For continuous-cropping systems, the key advantage of these technologies is not only convenience but dynamic diagnosis of heterogeneity and risk. Precision management in specialty crops increasingly relies on site-specific diagnosis of nutrient and water status at high spatial and temporal resolution, followed by variable-rate application strategies instead of uniform inputs (Khoddamzadeh et al., 2026). UAV-GIS nutrient-monitoring systems now show that multi-source fusion of hyperspectral, multispectral, and ground-sensor data can reduce prediction error for N, P, and K by 43-70% and cut fertilizer inputs by 18-27% while still increasing yield, which is directly relevant for A. macrocephala fields where continuous cropping produces strong within-field spatial variability.

Future work should also emphasize accessible field-scale tools rather than only high-end platforms. Portable embedded-sensor systems coupled with machine learning can already measure pH, moisture, temperature, EC, and N-P-K, classify soil fertility, and generate explainable crop recommendations, with strong agreement against commercial soil testers. Related IoT crop-recommendation systems show that low-cost sensor networks combined with cloud analytics can provide real-time pH and nutrient guidance, improve fertilizer targeting, and remain scalable across both small and large farms. The main development trend is therefore toward closed-loop precision management, in which diagnostics, modeling, and prescriptions are integrated. Recent multi-omics and precision-agriculture syntheses describe a pipeline that links sequencing, sensing, feature extraction, edge-cloud computing, and variable-rate actions, while other reviews emphasize interoperability, AI optimization, and scalable decision-support systems as the next bottlenecks. For A. macrocephala, future precision management should target not only fertilization rates but also early warning of continuous-cropping stress, allowing nutrient management to be coordinated with disease prevention and rhizosphere restoration.

8.3 Sustainable production strategies for Atractylodes macrocephala under ecological agriculture systems

Long-term production of A. macrocephala will depend on ecological intensification rather than continued reliance on high external inputs. Broad sustainability reviews show that maintaining soil health is central to future agriculture, and that precision farming, conservation practices, integrated pest management, and carbon-conscious management are all being positioned as core pathways for improving fertility, structure, and biodiversity (Sharma et al., 2024). The same literature also stresses that excessive synthetic fertilizer and pesticide use drives land degradation, so sustainable systems must raise productivity while maintaining agroecosystem integrity. For A. macrocephala, sustainable production strategies should prioritize rotation, diversification, and biologically based soil restoration. Reviews of crop rotation show that diversified systems improve structure, organic matter, and nutrient cycling, and can be further optimized through legume integration and cover crops (Al-Musawi et al., 2025). Large field evidence also shows that diversified rotations can increase equivalent yield by up to 38%, increase soil organic carbon by 8%, and improve overall soil health by 45%, supporting rotation-based redesign as a realistic pathway for medicinal-plant systems facing continuous-cropping decline.

Organic and ecological management will likely be another major direction, especially when combined with modern technologies. Organic farming is widely framed as a way to reduce disruption of nutrient cycles and ecological processes, while combining organic practices with new technologies is considered essential for overcoming the limits of low-input systems. Soil-restoration research further indicates that regenerative gains often require time, that targeted organic inputs can offset some yield penalties, and that restoration measures should be evaluated locally because effectiveness depends strongly on site conditions. A final trend is to build region-specific ecological production models for A. macrocephala. Rotation research now explicitly calls for remote sensing, machine learning, long-term ecological quantification, and farmer-led adaptation to optimize region-specific strategies (Al-Musawi et al., 2025). Evidence from degraded-land restoration also shows that introducing diversified crop rotations with perennial grasses, pulses, and other functional crops can restore fertility and raise output, suggesting that future A. macrocephala systems should be designed as locally adapted ecological rotations rather than simple monoculture replacements. Overall, future research on A. macrocephala should integrate multi-omics mechanism discovery, intelligent monitoring, and ecological system redesign. The most promising development trend is not a single technology, but a coordinated framework in which rhizosphere diagnosis, precision management, and sustainable agronomy are linked to restore soil fertility and reduce continuous-cropping risk.

9 Conclusions

Continuous cropping of Atractylodes macrocephala causes a systematic decline in soil fertility that is expressed through coordinated changes in physical, chemical, and biological properties. At the physicochemical level, the most common features include soil acidification, nutrient imbalance, fluctuations in organic matter, and disturbance of micronutrient availability. These changes do not always appear as a simple uniform decrease in all nutrients; rather, some nutrient elements may temporarily accumulate under repeated fertilization, while the overall capacity of soil to supply, buffer, and cycle nutrients gradually weakens. As a result, the soil environment becomes less favorable for healthy root growth and stable plant development. At the biological level, continuous cropping strongly alters soil microbial community structure, enzyme activity, and rhizosphere ecological processes. Beneficial microorganisms tend to decline, while harmful or stress-tolerant microbial groups may become enriched, leading to reduced microbial diversity and weakened ecological stability. Soil enzymes related to nutrient turnover, organic matter decomposition, and nitrogen or phosphorus transformation are often inhibited or imbalanced, which further limits nutrient availability and biological fertility. Therefore, the fertility decline observed under continuous cropping is not merely a question of nutrient shortage, but a broader process of rhizosphere functional degradation. From a temporal perspective, the effects of continuous cropping on soil fertility usually intensify with increasing planting years. In the early stage, changes may be relatively moderate and sometimes masked by fertilizer inputs or short-term increases in certain nutrient indicators. However, with prolonged monoculture, negative effects gradually accumulate, and the soil shifts from partial stress to more comprehensive degradation involving acidity increase, metal ion imbalance, microbial dysbiosis, and increasing susceptibility to disease. This progressive nature explains why continuous cropping obstacles often become more serious after several years rather than appearing immediately. Overall, the main characteristics of soil fertility change under continuous cropping of A. macrocephala can be summarized as cumulative, interactive, and multidimensional. Soil chemical degradation, biological imbalance, and rhizosphere dysfunction do not occur independently, but reinforce one another through feedback relationships. Consequently, long-term continuous cropping reduces not only current soil productivity, but also the resilience and self-regulation capacity of the soil ecosystem. This makes the maintenance of sustainable production increasingly difficult if no effective ecological intervention is applied.

The key driving factors responsible for soil degradation under continuous cropping of A. macrocephala are mainly concentrated in three closely related aspects: nutrient depletion and imbalance, autotoxic compound accumulation, and rhizosphere microecological disorder. First, long-term planting of the same crop causes repeated selective uptake of similar nutrient elements, which gradually breaks the balance between nutrient input and output. When fertilization management is unreasonable, especially when excessive dependence is placed on chemical fertilizers and insufficient attention is given to organic matter replenishment and trace elements, the soil nutrient system becomes increasingly unbalanced. This not only affects nutrient availability directly, but also weakens soil buffering capacity and intensifies acidification. Second, autotoxic substances released from roots or formed during residue decomposition play an important role in the development of continuous cropping obstacles. These compounds can accumulate in the rhizosphere over time and exert inhibitory effects on seed germination, root growth, and soil biological activity. More importantly, autotoxic compounds do not act independently; they also reshape the microbial environment, promote the proliferation of harmful microorganisms, and suppress beneficial microbial populations. In this way, chemical stress caused by autotoxicity is transformed into a broader ecological disturbance that accelerates soil functional decline. A third major driver is the disruption of the soil microbial community and the loss of rhizosphere ecological balance. Microorganisms are central to nutrient cycling, organic matter turnover, detoxification, and soil structure maintenance, so any long-term disturbance in community structure can have broad consequences for soil fertility. Under continuous cropping conditions, beneficial bacteria and fungi that contribute to nutrient transformation and disease suppression often decline, while pathogenic or opportunistic taxa increase. This shift reduces microbial functional diversity, lowers the efficiency of nutrient cycling, and weakens the natural resistance of the soil ecosystem to stress and disease invasion. These driving factors are not isolated, but mutually reinforcing. Nutrient imbalance can alter root exudation and microbial habitats, autotoxic compounds can further disrupt microbial communities, and microbial imbalance can reduce nutrient transformation and toxin degradation capacity. As these processes interact, the rhizosphere enters a negative feedback loop in which soil conditions become progressively less suitable for healthy plant growth. Therefore, soil degradation under continuous cropping should be understood as the result of coupled physicochemical and biological mechanisms rather than any single causal factor.

Improving soil fertility in continuous cropping systems of A. macrocephala requires integrated regulation strategies centered on restoring rhizosphere ecological function. Agronomic measures such as crop rotation and fallow can interrupt pathogen accumulation, reduce autotoxic stress, and gradually rebuild soil biological balance. At the same time, the application of organic fertilizers and bio-organic fertilizers can replenish soil organic matter, improve nutrient retention, stimulate beneficial microbial activity, and enhance enzyme-mediated nutrient transformation. Compared with single chemical-input approaches, these ecological regulation strategies are more consistent with the long-term restoration of soil fertility and sustainability of medicinal-plant production. Microbial inoculants and soil ecological restoration technologies also show broad application potential. Functional microbial agents can help reconstruct beneficial rhizosphere communities, suppress soil-borne pathogens, and improve nutrient cycling efficiency. However, their effectiveness often depends on strain adaptability, soil background conditions, and compatibility with other management measures. Therefore, future soil improvement should not rely on isolated technical interventions, but rather on coordinated combinations of rotation, organic amendment, microbial regulation, and site-specific management. Only by restoring the overall ecological integrity of the soil can the continuous cropping obstacle be fundamentally alleviated. Future research should place greater emphasis on mechanistic and precision-oriented approaches. Multi-omics technologies, including metagenomics, metabolomics, and transcriptomics, can be used to clarify the interactions among root exudates, soil microorganisms, nutrient transformation, and disease development. These approaches will help reveal the key regulatory pathways and functional indicators associated with soil fertility decline under continuous cropping. In addition, intelligent monitoring technologies based on sensors, digital agriculture, and data analysis should be strengthened so that dynamic changes in soil fertility can be diagnosed more accurately and management decisions can become more precise and timely. In the long run, the sustainable production of A. macrocephala depends on the transition from simple continuous monoculture toward ecologically optimized cultivation systems. This includes the integration of rotation, organic management, biological regulation, precision fertilization, and regionalized ecological planning. Future studies should also pay more attention to long-term field experiments, regional differences, and the coordination between soil health, crop yield, and medicinal quality. In conclusion, the soil fertility changes caused by continuous cropping of A. macrocephala are complex but manageable, and effective restoration will depend on combining deeper mechanistic understanding with practical ecological management strategies.

Acknowledgments

I extend my sincere gratitude to the anonymous reviewers for their valuable and insightful comments, which have greatly strengthened this paper.

Conflict of Interest Disclosure

The author affirms that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.

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