Effects Of Soil Community Changes On Nitrogen Mineralization Of Straw And On Rice Growth

Soil communities are complex and diverse,with different organism having distinct body sizes.Body size is one of the most basic life history traits of soil organisms.The relationship between body size and abundance can explain the allocation of resources in ecosystem and link the community composition with ecosystem functioning.Soil organisms interact with each other within soil food webs,and changes in composition or diversity within one trophic group may alter the abundance,diversity,and functioning of another.Soil biodiversity loss is repeatedly reported to impair ecosystem functions,but earlier studies usually focused on specific organism.Therefore,it is necessary to understand how changes in soil community composition and diversity affect ecosystem functioning.Based on body size which is the important biological function traits,combining biodiversity and community composition,this study was attempted to explore the relationship between changes in soil communities and ecosystem functioning(i.e.organic matter mineralization and rice growth).Soil suspensions as inoculum were sieved sequentially and then inoculated to sterilized soil,mixing with 15N-labeled rice straw,with or without planting rice.The main research results showed that:(1)Soil communities of high diversity were conducive to the decomposition of straw and increased soil dissolved organic carbon content.The 15N isotope tracer measurement showed that there was a positive correlation between straw 15N mineralization rate with the ratio of fungi and bacteria(P<0.05),indicating that microbial community composition was a determinant factor.Despite the mineralization pathway of organic matter in paddy soil is mainly manifested as bacterial energy flow,the increase of fungal biomass or fungal mycelium acted as a carrier for bacteria to accelerate the decomposition of straw by bacteria.In the presence of rice planting,15N recovery rate of straw was positively correlated with protozoa abundance(P<0.05),and was negatively correlated with the ratio of fungi and bacteria(P<0.01),indicating that soil microfauna could increase the N retention by feeding on bacteria.(2)Mineral 15N released from straw was negatively correlated with bacterial and fungal richness and nematode abundance(P<0.05),and the ratio of fungi and bacteria(P<0.001).Both rice plant biomass and amino acid concentration were positively correlated with microbial richness and nematode abundance.These results indicated that the more abundant soil communities,and the more frequent interaction between soil microfauna and microbes,promote the N or nutrient uptake by rice and to promote rice growth.Notably,there appeared a trade-off relationship between rice growth and resistance trait.The rice that grown better had less defense signal and less resistance.(3)Simplification and diversity loss of soil community resulted in the decrease of N use efficiency,which led to accumulation of salt ion content and soil acidification.Flooding and submergence of rice paddy soil under acidic conditions could also promote denitrification process and resulting in N loss.(4)Despite some single function such as straw 15N recovery rate,rice biomass and content of rice total nitrogen were not increase linearly with the increase in soil biodiversity,suggesting high functional redundancy from intermediate level of soil biodiversity.But soil biodiversity was positively correlated with ecosystem multifunctionality,confirming diversity was necessary to guarantee more functions.In conclusion,soil community composition,especially the relationship between microfauna and microbes,is a key factor affecting the decomposition of organic matter,N mineralization,plant growth and plant chemistry.The higher the overall biodiversity of complex communities is,the higher capability of resource utilization,as indicated by high ecosystem multifunctionality.