Characteristics Of Soil Microbial Communities And Soil Nutrients Under Different Forage-crop Rotations In The Longdong Loess Plateau

Multiple cropping and forage-crop rotation can improve land productivity and natural resource use efficiency in the traditional summer cropping system in dry-farming areas.To determine the soil microbial community characteristics and its influencing factors under different forage-crop rotations in the Longdong Loess Plateau,a field experiment was conducted at the Qingyang Experimental Station of Lanzhou University from 2015 to 2017.Seven crop rotation systems were designed:winter wheat-fallow-winter wheat?W-F-W?,winter wheat-rapeseed-winter wheat?W-R-W?,winter wheat-common vetch-winter wheat?W-V-W?,winter wheat-lucerne-lucerne?W-L-L?,winter wheat-fallow-maize?W-F-M?,winter wheat-rapeseed-maize?W-R-M?,winter wheat-common vetch-maize?W-V-M?,and continuous fallow?F-F-F?was set as control.The crop yield and soil nutrients were measured,and the composition and diversity of soil microbial communities were analyzed by Hiseq platform to the relationships among crop,soil and microorganism under the crop rotation systems.The main results of this study are as follows:1.In winter wheat continuous cropping and winter wheat-maize rotation system,both stalk yield and grain yield remained stable after multiple cropping rapeseed and common vetch in summer.Compared with W-F-W,total yield of W-R-W and W-V-W multiple cropping systems increased by 6.62 and 13.27%,respectively.The total yield of W-R-M and W-V-M multiple cropping systems increased by 25.24%and 53.36%compared with W-F-M?P<0.05?.The NO₃-N,NH₄-N content and soil water use efficiency increased under different multiple cropping and rotation forage models.The soil SOM and TN content increased under the multiple cropping rapeseed.2.Hiseq platform technique test results showed that the dominant bacterial phylums in each rotation model were Proteobacteria,Actinobacteria and Firmicutes.The composition of bacterial community is dominated by Arthrobacter,Sphingomonas,Bacillus and Bryobacter in genus level,while dominanted by Bradyrhizobium_elkanii,Phyllobacterium_myrsinacearum,Klebsiella_variicola and Nitrospira_japonica in specie level.They are all involved in soil nitrogen transformation,nitrogen fixation and phosphorus-solution.In W-F-W rotation,Xanthomonas is a pathogen of wheat black gallbladder,Pseudomonas fluorescens can prevent and control wheat whole rot disease effectively.Exiguobacterium and Pseudomonas syringae were found in the rotation of rapeseed.The former can inhibit the root rot of rapeseed caused by Rhizoctonia solani,the latter can cause bacterial black spot disease in cruciferous vegetables.In Common vetch participating crop rotations,Candidatus_Nitrotoga,Flavisolibacter,Acinetobacter and Gemmatimonas mainly involve in the soil nitrogen cycle.Fimbriimonas,Anaeromyxobacter and Paenibacillus?soil-specific bacteria?are related to nitrogen fixation in the W-L-L,which are biocontrol bacteria of winter wheat diseases.The Alpha diversity of soil bacterial community was highest in the W-R-W and W-F-M rotation.3.The soil dominant fungal in phylum of each crop rotation were Ascomycota,Zygomycota and Basidiomycota.The fungal community composition in the genus level are dominated by Gibberella,Fusarium and Mortierella.The main fungal community composition in specie level are Gibberella intrican,Gibberella acuminata and Mortierella alpina,most of which cause plant fungal diseases.The plant pathogen Phytophthora is the specific fungus under continuous fallow.Gaeumannomyces,Camarosporium and Ascochyta found in W-F-W and W-F-M can cause cereal crop brown spot.Alternaria,Leptosphaeria and Verticillium found in multiple cropping rapeseed were the pathogens causing black leg disease and black shank disease.Chrysosporium in multiple cropping common vetch is involved in nitrogen metabolism,which contributes to post-crop develop resistance to Fusarium graminearum.Colletotrichum was associated with anthrax or black spot disease in legumes in the W-L-L rotation,Penicillium can be used as antibacterial fertilizer and can antagonize Sclerotinia scleroterum infected with leguminous crops.The lowest Alpha diversity and highest bacterial/fungal values,which indicates better soil condition,were observed in the W-R-W and W-F-M rotation.4.The abundances of soil bacteria and fungi community were corelated to total nitrogen?TN?,soil organic matter?SOM?,total phosphorus?TP?,ammonium nitrogen?NH₄-N?,nitrate nitrogen?NO₃-N?,available phosphorus?AP?and the pH.In the winter wheat-forage multiple cropping rotation and winter wheat-forage-maize rotations,the seven soil nutrient factors explained 52.42%and 70.09%of soil bacteria distribution and 44.29%and 46.49%of fungi distribution respectively.In winter wheat-forage multiple cropping rotation models,the distribution of soil bacterial species?DSBS?was mainly related to SOM,NH₄-N and pH?R=0.31?,among which SOM was extremely significant effect on DSBS?P=0.0005?.The fungal community species distribution was significantly associated with NH₄-N and pH?R=0.29,P=0.0005?.The distribution of soil bacteria and fungi was significantly affected by soil TN?P=0.0005,P=0.007?in winter wheat-forage-maize.