Effects of decadal nitrogen and phosphorus fertilization on microbial taxonomic and functional attributes associated with soil organic carbon decomposition and concentration in an alpine meadow

Abstract

Microorganisms drive many important soil processes and ecosystem functioning; however, the soil microbial community can respond to environmental change, which can alter decomposition and storage of soil organic carbon (SOC). We assessed soil microbial taxonomic and functional attributes linked to SOC decomposition and concentration based on a grassland experiment fertilized with nitrogen (N) and phosphorus (P). There were divergent responses at both the taxonomic and functional level to fertilization, with a greater quantitative response in terms of the taxonomic attributes of bacteria and fungi than the abundance of SOC degradation genes. There was a negative correlation between SOC concentration and the abundance of SOC degradation genes. This indicated that N and P fertilization had the potential to stimulate SOC decomposition through modification of the soil microbial community, particularly by increasing the abundance of SOC degradation genes. Redundancy and variation partitioning analyses, as well as structural equation models revealed that soil total P was a pivotal factor shaping the microbial community both for taxonomic and functional gene attributes in the alpine meadow. The abundance of SOC degrading genes had stronger effects on SOC concentrations than did taxonomic attributes. Quantification of the abundance of SOC degradation genes can provide more direct and effective understanding of SOC decomposition processes and prediction of shifts in soil function as organic C pool in grasslands than a focus on the taxonomy of microbial communities. Given the important role of microbial community in regulating SOC decomposition and lower SOC concentrations under N and P fertilization, we recommend that the alpine meadow should be protected from mineral fertilizers, particularly P alone fertilization, to sustain high grassland ecosystem function as SOC sink in this region.