| The Chinese herb Yanhusuo is one of the "Eight Flavours of Zhejiang",which is widely used in the treatment of various diseases.However,after years of cultivation by herbalists,it has been found that the yield and quality of the herb are significantly reduced after continuous cultivation.To ensure the supply of the herb to the market and the quality of the herb,it is necessary to study the factors that create obstacles to continuous cultivation of the herb.Therefore,we investigated the effect of continuous crop of Yanhusuo on soil microbial community structure,soil physicochemical environment and the growth of Yanhusuo itself by using the research method of dynamic testing in outdoor field simulation experiments under different years of continuous crop and planting density.The main findings are as follows:(1)The structure of the soil microbial community was significantly altered after short-term crop succession,with the top-ranked probiotic bacteria(Green Campylobacter,slow-growing rhizobia)significantly reduced in abundance after short-term crop succession.while there was a significant increase in pathogenic bacteria(Nocardia),a significant increase in loamy enzymes adapted to harsh environments such as high salt and heavy metals,and a significant increase in pathogenic bacteria as well as resistant microorganisms.An important manifestation of the deterioration of the soil environment when native probiotic bacteria are reduced;the number of fungal viruses increases significantly after short-term crop succession,and the soil is initially transformed from "bacterial" to "fungal".The virulent phage virus has shown a significant increase after a short period of continuous crop.The virulence factors with a low initial abundance in the soil gradually increased after the first crop and after continuous crop when the microbial community structure was changed and the virulence effect of the infestation on the plant was altered.(2)Alkanes were most abundant in fallow soils,accounting for 28.51% of the total;ketones were significantly increased in soils after short-term continuous cropping,The percentage of ketones reached 79.86% after continuous cropping,while alkanes decreased by 24.0% after a short period of continuous cropping.The ketones in the soil are mainly1-methyl-2-pyrrolidone,which is over-enriched in the continuous crop soil and will be transferred to the stalk,and the enrichment of 1-methyl-2-pyrrolidone in the stalk reaches51.6%,much higher than the rest of the organic matter.The stalks were also enriched in 18.8% of other ketones.There were significant differences in the types and numbers of organic matter released into the soil from the different tissue remains of Yanhusuo,with the stems releasing mainly ketones and alcohols,the leaves and tubers releasing alcohols and ketones,and the shell releasing bases and phenols.(3)Short-term continuous cropping had a significant effect on soil fertility and element supply;soil organic carbon varied considerably throughout the reproductive period of the Yanhusuo,with the organic carbon content of the continuous crop treatment significantly lower than that of the first crop treatment,and showed a significant decrease after increasing the planting density.The difference in organic carbon content at the end of a round of planting was lower than before and after planting.The short-term continuous crop and high density planting also significantly reduced alkaline nitrogen and fast-acting phosphorus;fast-acting potassium was significantly higher in the late stage of Yanhusuo fertility in the short-term continuous crop than in the first crop treatment,and effective sulphur was higher in the early stage of Yanhusuo fertility in the short-term continuous crop than in the first crop treatment.After one round of planting,the soil alkaline N and fast-acting phosphorus content decreased significantly,fast-acting potassium increased significantly,and the effective sulphur content was the same as before planting.Both the short term continuous crop and high density planting treatments resulted in a significant reduction in soil p H in the early stages of the crop,with an extreme difference in p H of up to 2.76 throughout the crop period.Short-term continuous cropping significantly increased urease and phosphatase activities in the soil,while sucrase was significantly lower than the first crop after continuous cropping;urease and sucrase activities increased significantly at the end of the round(compared to fallow),while phosphatase activity decreased significantly.The soil micronutrients Zn,Cu and Mo were significantly lower after the first crop and slightly rebounded after the short-term continuous crop,but were still lower than in CK,as affected by the planting of Yanhusuo.B increased significantly after the high planting density treatment.Soil nitrogen and carbon were not significantly affected by the first crop and short-term continuous cropping,while phosphorus,sodium,calcium and magnesium decreased significantly after the first crop and increased slightly after continuous cropping,but were still lower than in CK.In the absence of significant external sources of heavy metal contamination,soil heavy metal content was significantly reduced after planting with Yanhusuo,showing a significant positive correlation between heavy metals.(4)The photosynthetic pigments in the leaves of Yanhusuo showed large differences VIat different planting densities.The photosynthetic pigments in the leaves of Yanhusuo with higher planting densities were more stable and showed a significant positive correlation between chlorophyll a and b.Short-term continuous cropping did not change the chlorophyll a/b values.Some of the enzyme activities(peroxidase,catalase,superoxide dismutase)in the leaves were significantly lower than in the continuous crop treatment after a short period of continuous cropping,with a subsequent significant reduction in leaf enzyme activity after increasing planting density.The malondialdehyde content of the leaves was low at seedling stage,lower in the first crop treatment than in the continuous crop treatment,and increased significantly at flowering stage.Yields varied between treatment groups,with significantly lower yields in the high-density planting short-term continuous crop treatment group,with a 6.0 g reduction per pit compared to the corresponding density treatment group.The total alkaloid content of the herb was significantly reduced after short-term continuous cropping,and the proportion of medicinal components showed significant differences between the first crop and after short-term continuous cropping.Short-term continuous cropping significantly reduced the proportion of safranin hydrochloride,while the proportion of dehydrocorydaline increased significantly in the short-term continuous cropping treatment group.Three heavy metals,chromium,mercury and lead,were at risk values in the high-density short-term continuous crop treatment group,and subsequent plantings need to strictly control these three sources of heavy metals.Conclusion: From the analysis of the above results,it was concluded that the soil microenvironment was greatly transformed by the successive cropping of Yanhusuo,which was affected by the release of various chemosensitive substances from various types of Yanhusuo plants.Soil microbial community structure from "bacterial" to "fungal",soil microbial community structure imbalance,soil enzyme activity and elemental ratio structure change.A significant increase in the risk of disease in Yanhusuo plants;increased elemental antagonism due to nutrient deficiencies as a result of changes in the structure of soil elemental ratios.Causes of succession disorders: the release of chemosensitive substances from the rooting system of the plant leads to a change in the structure of the soil microbial community,a surge in the number of fungi,an increase in the number of virulent viruses and a disruption of the soil bio-ecological balance;the change in microbial species hinders the circulation of soil material and,together with the elemental absorption preferences of the plant,further aggravates the antagonism between soil elements.The excessive accumulation of chemosensitive substances,the disruption of the ecological balance of microorganisms,the intensification of antagonism between elements and the reduction of the nutrient supply capacity of the soil all combine to form a barrier to continuous cropping.Subsequent successive cultivation of Yanhusuo in herb fields has resulted in a sharp increase in plant disease and impaired nutrient uptake,significantly affecting the yield and quality of the herb.To alleviate the problems of increased crop barriers and reduced fertility,the fields need to be sterilised,the soil needs to be replenished with nutrients and suitable crops need to be selected for crop rotation/intercropping. |
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