Influence Mechanism Of Erosion On Soil Microbial Diversity In Yellow-red Soil

Soil erosion not only changes soil quality,threatens food security,but also affects the cycle of global biogenic elements and global change.Soil microorganisms play a crucial part in the material circulation and flow of soil ecosystem,biochemical geocirculation and water and soil conservation in ecologically fragile areas.However,many factors have important influence on soil microbial diversity in the objective environment.It is difficult to determine the direct relationship of soil erosion-soil microbial diversity.In order to eliminate the influence of terrain,climate factors and ground vegetation on soil microorganisms,this study was based on the artificial simulated erosion plots with different erosion depths(the erosion depth was 0,5,10,20,30 and 40 cm,respectively)constructed in the Yuanjiang-Red River basin by the method of soil cutting-mixing in the previous period.Illumina Mi Seq second-generation highthroughput sequencing technology was used for analysis of the variation characteristics in soil bacterial(including the archaea)(The following bacteria including archaea)and fungal communities among different erosion depth in dry and rainy season,and clarify the relationships of soil bacterial and fungal communities and physicochemical properties,and clear the influence mechanism of soil erosion on soil microbial diversity.The main conclusions of the study are as follows:(1)The contents of soil sand,silt,clay,soil moisture and soil bulk density had no significant difference among different erosion depths.Soil bulk density and soil moisture increased with soil erosion depths.Soil organic carbon,dissolved organic carbon,total nitrogen,ammonia nitrogen,nitrate nitrogen,total phosphorus,available phosphorus,total potassium and available potassium had significantly differences among different erosion depths,and decreased significantly with soil erosion depth in dry and rainy season.(2)The OTU number of soil bacteria and fungi decreased gradually with erosion depth in dry and rainy season.The dominant phyla of soil bacteria were Acidobacteria,Proteobacteria,Chloroflexi,Actinobacteria,Bacteroidetes and Firmicutes.The dominant phyla of soil fungi were Ascomycota,Mortierellomycota,Basidiomycota,Chytridiomycota,Mucoromycota and Glomeromycota.Shannon,Simpson,Chao1,ACE and Species richness indices of bacteria and fungi decreased significantly with soil erosion depth in dry and rainy season.(3)The community structure of soil bacteria and fungi were varied due to soil erosion.Soil bacterial community structure varied significantly when the erosion depth reached 30 cm in both dry and rainy season compared with the control.Thermotogae and Gracilibacteria disappeared in the dry season and Berkelbacteria disappeared in the rainy season when erosion depth reached 30 cm.Soil fungal community structure varied significantly when the erosion depth reached 10 cm in both dry and rainy season compared with the control.Blastocladiomycota and Entorrhizomycota disappeared in dry season while Aphelidiomycota disappeared Olpidiomycota appeared when the erosion depth reached 10 cm in the rainy season.The response of soil fungal to soil erosion was more sensitive than that of bacteria.This may be due to the fact that most of the soil fungi had simpler cell structures than bacteria,and were significantly different from bacteria in their ecological niche,and were more sensitive to the changes of erosion environment.In addition,the community structure of soil bacteria and fungi didn't alter significantly in the rainy season compared with that in the dry season,suggesting that the season(dry and rainy season)didn't alter the community structure of soil bacteria and fungi.The relative abundance of Proteobacteria,Acidobacteria,Actinobacteria,Gemmatimonadetes,Mortierellomycota and Mucoromycota decreased with soil erosion depth in dry and rainy seasons,while the relative abundance of Bacteroidetes,Ascomycota and Chytridiomycota increased with soil erosion depth in dry and rainy seasons.(4)Redundancy analysis(RDA)indicated that available potassium and organic carbon were the main controlling factors affecting soil bacterial communities in dry and rainy season among different erosion depth.C/N was also the main impacting factor of bacterial communities in rainy season.Organic carbon and total phosphorus were the main impacting factors affecting soil fungal communities in dry and rainy season among different erosion depth.Ammonia nitrogen was also the main controlling factor of fungal communities in dry season.Structural equation models(SEM)analysis showed that soil erosion indirectly affected soil bacterial and fungal communities by affecting soil nutrients in dry and rainy season.On the one hand,soil erosion affected bacterial communities indirectly by affecting the contents of TN,AK and C/N in dry season.Soil erosion indirectly affected bacterial communities mainly through influencing the contents of TOC and AP in rainy season.In terms of fungi,soil erosion indirectly affected the fungal communities mainly by affecting the content of AP in dry season.Soil erosion indirectly affected fungal communities mainly by affecting the content of DOC in rainy season.Additionally,soil erosion also can indirectly affect fungal communities by affecting sand content.Soil nutrient variability directly caused by soil erosion had a greater impact on soil microbial communities than that of soil mechanical composition.In conclusion,the experiments of different erosion depth simulated by the method of cutting soil-distribution showed that soil erosion significantly altered the soil microbial community structure.Soil microbial diversity decreased,the relative abundance of soil microorganisms associated with the carbon and nitrogen cycles decreased and some soil microorganisms disappeared at some phyla levels with the increase of erosion depth.Soil erosion indirectly changed soil microbial community composition mainly by changing soil nutrient content.Therefore,it makes great difference to monitor soil nutrients among different erosion depth and develop reasonable land management measures for regulating microbial community structure to fit to land degradation caused by soil erosion.