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Aims In the production of the natural medicinal plant American ginseng, replantation typically fails due to continuous cropping obstacles. However, the cause is still not clear and needs more research. Methods Soil samples were collected from (a) maize fields where American ginseng had never been planted, (b) fields where American ginseng had just been harvested, and (c) fields where maize had been planted for 2, 4 and 6 years respectively after American ginseng. We investigated the physicochemical properties, the enzymatic activities, and the soil microbial community structure and composition of the samples. Results We found that the content of soil salt, NH 4 + -N, and NO 3 − -N increased significantly in samples associated with the production of American ginseng, whereas the soil pH, carbon-to-nitrogen ratio, alkaline phosphatase, and cellulase activity all significantly decreased and gradually recovered to the pre-planting level. Moreover, the bacterial diversity decreased, while fungal diversity and richness increased; fungal richness continued to increase in farmlands replanted maize. The relative abundance of some microbial communities was changed significantly and was gradually restored with a longer time to replant maize. Pearson’s correlation analysis shown that significantly changed microbial communities were significantly associated with changes in soil pH, soil salt and nitrogen content, alkaline phosphatase, and cellulase activity. Conclusions Changes in soil pH, soil salt and nitrogen content caused changes in microbial community structure and composition, as well as cellulase and alkaline phosphatase activity. These changes may cause the continuous cropping obstacles of American ginseng and may be improved by planting maize.

Tobacco belongs to the family Solanaceae, which easily forms continuous cropping obstacles. Continuous cropping exacerbates the accumulation of autotoxins in tobacco rhizospheric soil, affects the normal metabolism and growth of plants, changes soil microecology, and severely reduces the yield and quality of tobacco. In this study, the types and composition of tobacco autotoxins under continuous cropping systems are summarized, and a model is proposed, suggesting that autotoxins can cause toxicity to tobacco plants at the cell level, plant-growth level, and physiological process level, negatively affecting soil microbial life activities, population number, and community structure and disrupting soil microecology. A combined strategy for managing tobacco autotoxicity is proposed based on the breeding of superior varieties, and this approach can be combined with adjustments to cropping systems, the induction of plant immunity, and the optimization of cultivation and biological control measures. Additionally, future research directions are suggested and challenges associated with autotoxicity are provided. This study aims to serve as a reference and provide inspirations needed to develop green and sustainable strategies and alleviate the continuous cropping obstacles of tobacco. It also acts as a reference for resolving continuous cropping challenges in other crops.

Background Healthy soil is crucial for maintaining the sustainability of soil ecosystem services and ensuring food security. The soil microbiome serves as a key indicator of soil health. However, long-term continuous monoculture significantly adversely affects the diversity and functioning of soil microbial communities, posing a serious threat to sustainable agricultural development. Therefore, making it crucial to understand the microbial mechanisms underlying these challenges. Methods In this study, tobacco was subjected to different planting durations: 1 year (CR), 5 years (CC5), 10 years (CC10), and 15 years (CC15). The rhizosphere microbial community assembly process, composition, keystone taxa, and their relationship to continuous cropping challenges were analyzed. Results The rhizosphere bacterial community structure of tobacco after 5 years of continuous cropping was significantly separated from other treatments, while no significant separation was observed in the fungal community. Further investigation into the assembly processes of microbial communities under different continuous cropping durations revealed that bacterial community assembly processes exhibited differences, whereas no significant differences were observed in fungal community assembly processes. Specifically, the rhizosphere bacterial community in CC5 was predominantly shaped by deterministic assembly processes, explaining its structural distinctiveness from other treatments. Co-occurrence network analysis revealed that the number of nodes and edges in bacterial-fungal interactions decreased by 22.70% and 79.86%, respectively, in CC5 compared with CR. Differential microbial abundance identified a significant decline in key microbes ( Rhodanobacter , Ellin6067 , Frankiales , and Setophoma ) alongside a marked increase in the abundance of genus Verticillium in CC5 relative to CR. RDA indicated these bacterial genera correlated negatively with pathogen accumulation and disease incidence but postively with yield These relationships potentially constituted the primary driver for exacerbated continuous cropping obstacles in CC5. In CC10, bacterial community assembly was primarily dominated by stochastic processes. Although the number of network nodes and edges increased by 21.96% and 204.73%, respectively, compared to CC5, they remained lower than those in CR. By extending the continuous cropping to 15 years, the bacterial community assembly was shaped by stochastic processes. Compared with CC5, the number of network nodes and edges in CC15 increased by 34.39% and 405.44%, respectively, with beneficial microbes ( Rhodanobacter , Ellin6067 , Frankiales , and Setophoma ) showing remarkable abundance recovery and pathogenic fungi like Verticillium declining, ultimately resulting in microbial community characteristics approximating those observed in the CR. Conclusions The bacterial community in CC5 was driven by deterministic assembly processes, resulting in a distinct structure. The complexity and stability of the co-occurrence network significantly decreased, accompanied by a higher abundance of harmful microbes and a lower abundance of beneficial microbes, which exacerbated the continuous cropping obstacles. In contrast, after 15 years of continuous cropping, the bacterial community assembly shifted to stochastic processes and trans-kingdom co-occurrence network complexity and stability strengthened, beneficial microbes increased, and continuous cropping challenges alleviated.

American ginseng is an important herbal medicinal crop in China. In recent years, there has been an increasing market demand for ginseng, but the production area has been shrinking due to problems associated with continuous monocropping. We analyzed the microbiome in bulk soils to assess whether and, if so, what changes in the bulk soil microbiome are associated with continuous American ginseng cropping. The alpha diversity of fungi and bacteria was significantly lower in the soils planted with American ginseng than the virgin (non-planted) land. The relative abundance of Fusarium spp. and Ilyonectria spp., known plant root pathogens, was much higher in the soils cropped with American ginseng than the non-planted. On the other hand, a number of bacteria with biodegradation function, such as Methylibium spp., Sphingomonas spp., Variovorax spp., and Rubrivivax spp., had lower abundance in the soils cropped with American ginseng than the non-cropped. In addition, soil pH was lower in the field planted with American ginseng than the non-planted. Accumulation of fungal root pathogens and reduction of soil pH may, therefore, have contributed to the problems associated with continuous monocropping of American ginseng.

In order to evaluate the effects of continuous cropping of millet on soil nutrients and soil enzyme activities, the present study was based on four treatments of 2 years of continuous cropping (T1), 3 years of continuous cropping (T2), 4 years of continuous cropping (T3) and rotational cropping (CK), based on 4 years of no fertilizer positioning experiments, and the soil nutrients, soil enzyme activities and millets yields were determined, respectively. The results showed that with the increase of continuous cropping years, the millet yield decreased and was significantly lower than that of rotating with legume crops, and compared with CK, the yields of T1, T2 and T3 treatments were reduced by 8.92%, 13.73% and 37.60%, respectively; the soil nitrogen and phosphorus contents were reduced, the quick-acting potassium content did not change obviously, and the soil pH was increased; Soil urease, alkaline phosphatase, sucrase and catalase activities generally showed a decreasing trend and the decrease was more significant with the increase in the number of years of continuous cropping. Therefore, in order to maintain the soil fertility and increase the millet yield, it is necessary to practice crop rotation and stubble reversal between millets and leguminous crops such as kidney beans, and to apply certain fertilizers.

Background Soil microbial community and diversity are key in sustaining soil ecosystem health. In recent years, the health of soil ecosystems has been severely threatened by the large input of synthetic fertilizers and the continuous monocropping in greenhouse-based intensive production systems. As a result, the N utilization efficiency has significantly decreased, which has had adverse impacts on soil, water, and the atmosphere. Additionally, soil-borne plant diseases are more frequent in greenhouse-based intensive vegetable systems. Shifts in the microbial community structure and diversity largely account for these continuous cropping problems in vegetable agricultural soils. Scope In this review, soil microbial deterioration, including microbial activities, C source utilization patterns, nitrification, microbial community composition, and arbuscular mycorrhizal fungi are summarized. Soil microbial deterioration is due to the excessive use of fertilizers, which have caused soil secondary salinization and acidification, pollutants brought on by intensive vegetable agriculture, and principally continuous cropping of same or similar vegetable species. Conclusions Therefore, measures must be taken to restore soil microbial communities, including rational fertilization, rotation or intercropping, cultivation of catch or cover crops, and reductive soil disinfestation. Rational fertilization, such as the reduction in chemical N fertilization levels, substitution of chemical fertilizer by organic manure, and the use of bio-fertilizer and bio-organic fertilizer, is of decisive importance. This review provides a better understanding of ecosystem health in vegetable agricultural soils and recommends effective measures to improve the health of these ecosystems.

Sugar beet is vulnerable to years of continuous cropping, and allelopathy is one of the important factors leading to continuous cropping disorder. To explore the physiological and molecular mechanisms behind continuous cropping obstacles on sugar beet, this study combined transcriptomics and metabolomics to analyze the effects of different years of continuous cropping on metabolite changes, differential gene expression, and root exudate regulation in sugar beet. We collected sugar beet’s root samples from 1–, 3–, and 5-year continuous cropping systems for metabolome and transcriptome analyses. Our data revealed that T3 and T5 had 50 and 33 metabolites significantly different from T1, respectively. The autotoxic substance salicylaldehyde was found to continuously accumulate in root exudates with increasing years of continuous cropping. Sucrose was highly reduced in T3 (4.05-fold decrease) and T5 (2.01-fold decrease) compared to T1. Respectively, 2,660 and 3,515 differentially expressed genes (DEGs) were significantly regulated in T3 and T5 compared to T1. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that metabolic pathways and biosynthesis of secondary metabolites were perturbed in T3 and T5 vs. T1. Integrated metabolomics analyses identified 73 DEGs involved in enriched metabolic pathways, all of which were the oxidation-reduction process pathways. In conclusion, this study provides evidence that continuous cropping obstacles can change the metabolome and transcriptome of sugar beet, affecting its growth and quality.

Aims The accumulation of organic acids in soil can trigger autotoxicity, resulting in the continuous cropping obstacles (CCOs) for Panax notoginseng under conventional management systems. However, limited information is available about the threshold value of organic acids representing the CCOs in the soil of P. notoginseng from the forest understorey. Methods In this study, mixed organic acids at different concentrations were exogenously applied to simulate the P. notoginseng CCO. The plant growth, edaphic factors, soil extracellular enzyme activity, and bacterial/fungal abundances and diversity in the rhizospheric soil were assessed in the P. notoginseng from the forest understorey. Results High concentrations (>150 mg/kg) rather than low concentrations (<150 mg/kg) of organic acid decreased the dry and fresh weight of plants (1.99%-1.98%), edaphic properties (2.75%-1.03%) and soil extracellular enzyme activities (3.38%-1.05%). Under high organic acid concentrations, the fungal abundance increased by 2.37%, whereas the bacterial abundance decreased by 4.56%. Moreover, the abundance of Pseudomonadales , Xanthomonadales , and Ilyonectria as pathogenic bacteria tended to increase. Compared to bacteria, the fungal community structure varied significantly, and the fungal core flora was more abundant. The SEM results showed that the direct and indirect factors affecting the α-diversity in the rhizosphere of P. notoginseng were increased under the high organic acid concentrations. Conclusion Organic acid concentrations greater than 150 mg/kg in P. notoginseng soils are detrimental to the relationships among plant growth, soil environment, and microbiomes, which implies the occurrence of the CCOs in P. notoginseng ; and therefore, we recommend that P. notoginseng should not be planted again.

Despite the known influence of continuous cropping on soil microorganisms, little is known about the associated difference in the effects of continuous cropping on the community compositions of soil bacteria and fungi. Here, we assessed soil physicochemical property, as well as bacterial and fungal compositions across different years (Uncropped control, 1, 6, 11, 16, and 21 years) and in the watermelon system of a gravel mulch field in the Loess Plateau of China. Our results showed that long-term continuous cropping led to substantial shifts in soil bacterial and fungal compositions. The relative abundances of dominant bacterial and fungal genera (average relative abundance > 1.0%) significantly varied among different continuous cropping years ( P  < 0.05). Structural equation models demonstrated that continuous cropping alter soil bacterial and fungal compositions mainly by causing substantial variations in soil attributes. Variations in soil pH, nutrient, salinity, and moisture content jointly explained 73% and 64% of the variation in soil bacterial and fungal compositions, respectively. Variations in soil moisture content and pH caused by continuous cropping drove the shifts in soil bacterial and fungal compositions, respectively (Mantel R  = 0.74 and 0.54, P  < 0.01). Furthermore, the variation in soil bacterial and fungal composition showed significant correlation with watermelon yield reduction ( P  < 0.01). Together, long-term continuous cropping can alter soil microbial composition, and thereby influencing watermelon yield. Our findings are useful for alleviating continuous cropping obstacles and guiding agricultural production.

Continuous cropping obstacles caused by the over-cultivation of a single crop trigger soil degradation, yield reduction and the occurrence of plant disease. However, the relationships among stability, complexity and the assembly process of soil microbial community with continuous cropping obstacles remains unclear. In this study, molecular ecological networks analysis (MENs) and inter-domain ecological networks analysis (IDENs), and a new index named cohesion tools were used to calculate the stability and complexity of soil microbial communities from eight potato cultivars grown under a continuous cropping regime by using the high-throughput sequencing data. The results showed that the stability ( i.e. , robustness index) of the bacterial and fungal communities for cultivar ZS5 was significantly higher, and that the complexity ( i.e. , cohesion values) was also significantly higher in the bacterial, fungal and inter-domain communities ( i.e. , bacterial-fungal community) of cultivar ZS5 than other cultivars. Network analysis also revealed that Actinobacteria and Ascomycota were the dominant phyla within intra-domain networks of continuous cropping potato soil communities, while the phyla Proteobacteria and Ascomycota dominated the correlation of the bacterial-fungal network. Infer community assembly mechanism by phylogenetic-bin-based null model analysis (iCAMP) tools were used to calculate the soil bacterial and fungal communities’ assembly processes of the eight potato cultivars under continuous cropping regime, and the results showed that the bacterial community was mainly dominated by deterministic processes (64.19% - 81.31%) while the fungal community was mainly dominated by stochastic processes (78.28% - 98.99%), indicating that the continuous-cropping regime mainly influenced the potato soil bacterial community assembly process. Moreover, cultivar ZS5 possessed a relatively lower homogeneous selection, and a higher TP, TN, AP and yield than other cultivars. Our results indicated that the soil microbial network stability and complexity, and community assemble might be associated with yield and soil properties, which would be helpful in the study for resistance to potato continuous cropping obstacles.