Effects Of Defoliation,Water And Organic Material Addition On Soil Microbial Community In Grassland

Global climatic change is generally expected to stimulate precipitation and soil organic matter input in grassland of northern China.Grazing is one of the main management methods for grassland in northern China.Soil microbes are the richest and largest number species,which is important for nutrients turnover,material cycle and maintaining soil physical structure of grassland ecosystem.How soil microbial communities respond to grazing,organic matter input and precipitation increase at the same time and are there interactions between interference factors on soil microbial communities? At present,there is no comprehensive study of such issues.This study was conducted in form of controlled experiment,we selected dominant species-Leymus chinensis and associated species-Kalimeris intergrifolia and Artemisia mongolica in Songnen grassland as plant materials,we set up clipping treatments,organic material addition treatments and water gradient treatments,each treatment included multiple levels,the experiment was conducted in Songnen Grassland Research Station,lasted two plant growth seasons.Real-time quantitative PCR technique and HiSeq 2500 sequencing technology were used to detect soil fungal and bacterial numbers,diversity and composition,aimed to find the effects of clipping,organic material addition and changes of soil moisture on soil microbial communities,find the key factors impacting soil microbial communities.This study could provide theoretical basis for understanding and predict changes in soil microbial communities in Songnen grassland on condition of global climate change.We obtained results and conclusions were as follows:(1)Soil bacteria were dominant in this study.Soil fungal gene copies were 3.53 ×104 mean per gram of dry soil,soil bacterial gene copies were 9.98 × 106 mean per gram of dry soil,gene copies of fungal: bacterial ratio were 2.84 × 10-3 mean per gram of dry soil.Clipping and water had significant effects on soil bacterial numbers,there was an interaction between clipping and water.There was a positive correlation between soil bacterial gene copies and soil moisture.Clipping could increase soil bacterial gene copies by increasing soil moisture.(2)Soil bacterial richness index and soil fungal richness index were significantly different under experimental treatments.Clipping reduced soil fungal richness by reducing plant total biomass.Clipping increased soil bacterial richness might resultfrom alterations in plant root exudates quality and quantity.It need further study to explain the negative effect of organic material addition on changing soil bacterial richness.(3)Clipping and water had significant effects on soil bacterial community composition through influence the relative abundance of Actinobacteria,Chloroflexi,Gemmatimonadetes,Verrucomicrobia.The redundancy analysis results showed that soil moisture and soil ammonia nitrogen were the key drivers of soil bacterial community composition,soil ammonia nitrogen was the most important influencing factor.(4)The relative abundance of individual groups of fungi had significantly changed under experimental treatments.Clipping increased the relative abundance of Zygomycota by increasing soil nitrate nitrogen.There was a negative correlation between the relative abundance of Glomeromycota and soil moisture.Clipping reduced the relative abundance of Glomeromycota by increasing soil moisture.In conclusion,soil microbial communities were sensitive to simulated herbivore foraging and water,but organic material addition had no significantly effects on soil microbial communities.Changes in soil moisture directly effected on soil bacterial numbers,herbivore foraging effected on soil bacterial numbers by influence soil moisture.Herbivore foraging influenced soil fungal richness by reducing plant total biomass,there was the interaction between clipping and organic material addition for soil bacterial richness,which needed further study to explain.The changes of precipitation and herbivore foraging effected on individual groups to influence soil microbial communities through changing soil physical and chemical properties.This study confirmed the regulatory effects of water and nutrient on soil microbial communities.The study is helpful for understanding and predicting changes in soil microbial communities in Songnen grassland on condition of global climate change.