The Tibetan Plateau is witnessing a warming rate of 0.2 oC per decade, which dwarfing the rate of global warming by a factor of two. Consequently, the precipitation pattern is projected to change in the future. In the past, the effect of warming on plants, animals and soil microbes has been well-documented, but the interactive response of microbial communities to warming and altered precipitation was still obscure in alpine ecosystem, which leads to uncertainty in soil carbon dynamics. To address it, we examine how microbial functional structure, bacterial taxonomic and fungal taxonomic composition, as well as important ecosystem functions, such as soil and ecosystem carbon fluxes, respond to warming (control, +2oC) and precipitation alteration (control, +50%, -50%). Two-way ANOVA based-on mixed-effects models was used to determine the interactive effect of warming and altered precipitation on soil variables, plant variables and microbial communities. In addition, the linkage between microbial communities, plant communities and carbon fluxes were analyzed, using correlation tests. We then tested the relative roles of plant, soil, microbial in controlling soil carbon fluxes by partial Mantel test, linear mixed-effects regression and multiple regressions based on distance matric.
Results/Conclusions
Warming increased gross primary production (GPP) and ecosystem respiration (ER). Combined treatments of warming and drying significantly decreased aboveground net primary production, suggesting that water availability is a limiting factor. Increased precipitation increased net ecosystem exchange and GPP with or without warming, indicating a larger soil carbon sink. There was no interaction of warming of altered precipitation for microbial functional structure and taxonomic composition. Soil CO2 and CH4 fluxes were strongly and significantly (r > 0.70, P < 0.05) correlated with corresponding microbial functional abundances but not overall bacterial or fungal communities, decoupling microbial function from taxonomy. Microbial functional groups associated with carbon cycling and plant communities contributed to soil CO2 flux responses at the comparable levels, while microbial methanogenic and CH4-oxidizing communities were solely responsible for soil CH4 fluxes. As the C balance of cold regions is sensitive to climate changes, quantifying microbial and plant contribution is essential for predicting the direction and strength of future C dynamics. In addition, our results demonstrate that the key level at which to predict soil C fluxes may not be microbial species (by means of rRNA taxonomy), but rather microbial functional communities.