Soil Microbial Community And Crop Yield Changes With Cropping System Conversions In North China Plain

There has been great decline in environmental quality,biodiversity and agricultural production due to excessive inputs of agrochemicals（e.g.,fertilizers）and simplification of wheat（Triticum aestivum L.）-maize（Zea mays L.）cropping systems in North China Plain.The inclusion of soybean or green manure in the rotation system are alternative strategies to increase the diversity of crops and straw returning to the field and reduce the use of mineral fertilizers.Soil microbial community structure is affected by crop rotation,crop type and green manure management,but the changes of soil microbial community and its functions on the conversion of crop rotation systems,especially the effects on grain crop yield,are still poorly understood.Therefore,based on long-term field experiments established in North China Plain（Xinxiang of Henan Province,Wenshang of Shandong Province and Yongcheng of Henan Province）,this study carried out the multi-year grain crop rotation systems and green manure replacement systems.Using the amplicon sequencing,high throughput q PCR techniques,Functional Annotation of Prokaryotic Taxa（FAPROTAX）,Functional Annotation of Fungal Taxa（FUNGuild）,network analysis and path analysis,the objectives of this study are based on long-term field experiments established at North China Plain 1)to analyze the short and long effects of crop yield,soil properties,bacterial and fungal communities and functional communities under multi-year grain crop rotation systems,and identify their relations;2)to determine the short-term effects of the conversion from the conventional wheat–maize rotation system to the new green manure systems on the soil fungal diversity and community composition,and compare the effects of the cover crop on the soil fungal community under a succession of maize and soybean;3)to determine the effects of crop yield,soil properties,bacterial and fungal communities and function on soil types after 1-year green manure returning;and find the main soil properties that drive the change in s bacterial and fungal communities in green manure replacement systems;4)to determine the four-year effects of the conversion from the conventional wheat–maize rotation system to the new green manure systems on soil carbon,nitrogen,phosphorus and sulfur cycling microbial communities and their effects on grain crop yield in Xinxiang experimental area,reveal the effects of the green manure replacement systems on the soil carbon,nitrogen,phosphorus and sulfur cycling microbial communities,and identify their relations.The main results are as follows:（1）Clarify the microbial regulation ways of crop yield under multi-year grain crop rotation systems.Diversified crop rotations increased crop yield,and changed soil bacterial,fungal communities and function.The microbial regulation pathways of maize and soybean（Glycine max（L.）Merr.）yield increase are opposite.Compared to WM₈,WS₄+WM₄increased maize yield from 2017 to 2021,and wheat yield in 2021.Compared to WS₈,WM₄+WS₄ increased wheat and soybean yield from 2017 to 2021.Compared to WM₈,WS₄+WM₄ decreased soil water content and nitrate nitrogen content,increased soil organic carbon,total nitrogen and soluble carbon content,decreased the bacterial alpha diversity,significantly changed the bacterial and fungal beta diversity,and led to the increase of the relative abundance of carbon cycling functional bacteria and saprotrophs.These processes contributed to increase the maize yield.Compared to WS₈,WM₄+WS₄ increased soil water content and organic carbon content,decreased ammonium nitrogen,nitrate nitrogen and soluble carbon content,increased the diversity of fungal alpha,and decreased the relative abundance of carbon cycling functional bacteria and saprotrophs,which promoted the wheat and soybean yield.（2）Reveal the short-term changes of soil microbial community structure and functional composition in the initial conversion of wheat-maize cropping to green manure replacement systems.Soil microbial and functional composition changed rapidly after the initial conversion of manure replacement systems.Compared to the wheat–maize rotation system with fertilization,green manure replacement systems increased the soil fungal alpha diversity and suppressed pathotrophs by reducing the soil NH₄⁺,NO₃^-,available K,and available P contents in the first year.Different manures（leguminous vetch（Vicia villosa Roth）,a mixture of vetch and rye（Secale cereale L.）,and winter fallow）changed the fungal community composition,but their effect was overwhelmed by the strong effect of succeeding soybean,which induced minor shifts among the manure treatments under soybean than maize.The Vetch–soybean system exhibited the highest fungal diversity,which have been due to an increase of symbiotrophs.Replacing wheat with mixed vetch and rye most greatly suppressed the pathotrophs,and this suppression effect was stronger when succeeded by maize than by soya.（3）Determine the key environmental factors affecting soil microbial diversity,community structure and function under different soil types of green manure replacement systems.Soil type,green manure returning and their interaction significantly changed the beta-diversity of soil bacteria and fungi,and soil texture（sand,clay and silt）,soil p H,wter content,organic carbon,total nitrigen content,nitrate nitrogen content and available phosphorus content were the key environmental factors that affect the change of soil bacteria and fungi.Soil microbial functional composition among soil types were different.The abundance of nitrogen cycling bacteria in Xinxiang（Fluvo-aquic soil）and Yongcheng were（black soil）significantly higher than that in Wenshang（Yellow soil）,while the abundances of pathogenic bacteria in Xinxiang and Yongcheng were significantly lower than that in Wenshang.The abundances of pathotrophs and symbiotrophs in Xinxiang and Wenshang were significantly higher than that in Yongcheng.The effects of green manure replacement systems on the microbial functional composition were different under different soil types.In Xinxiang,the abundances of saprotrophs and symbiotrophs in the Vetch-Maize and Wheat-Maize/Hb systems were higher than that in the Wheat-Maize rotation,but the abundances of pathotrophs were opposite.In Yongcheng,the abundances of saprotrophs in the Vetch-Maize and Wheat-Maize/Hb systems were higher than that in the Wheat-Maize rotation,but the abundances of nitrogen cycling bacteria and pathogenic bacteria were opposite.In Yongcheng,the abundances of saprotrophs and pathotrophs in the Vetch-Maize and Wheat-Maize/Hb systems were higher than that in the Wheat-Maize rotation,but the abundances of nitrogen cycling bacteria were opposite.（4）Determine the long-term effects of green manure replacement systems on crop yield,and soil microbial functional composition.In Xinxiang,green manure replacement systems increased gradually the wheat and maize yields after 4-year conversing,and the vetch-maize rotation system was the best.Compared with wheat–maize rotation system without fertilization,Vetch-Maize rotation system and Wheat–Maize/Hb（Hbean,Glycine soja Sieb.et Zucc）both increased agricultural nitrogen input and reduced carbon input,resulting in the increase of carbon fixation functional microbes（acs A,pcc A）to participate in straw decomposition and soil organic matter formation,thus increasing soil organic carbon and total nitrogen content.These processes contribute to the gradual recovery of wheat and corn yields.Additionally,Vetch-Maize rotation system required a large amount of available nitrogen during the straw decomposition,and thus reduced soil available nitrogen and denitrification functional microbe（nar G,nos Z1 and nos Z2）.In Wheat–Maize/Hb systems,the high soil C/N inhibited the growth of non-symbiotic nitrogen fixing microorganisms（nif H）under Wheat–Maize/Hb,and the nitrogen fixing effect of herbage bean may inhibit the growth of non-symbiotic nitrogen fixing microbes.