Responses of soil microbial communities to plant diversity and warming in a grassland ecosystem
Despite current advances in our understanding of the effect of warming and biodiversity on plant growth and productivity as well as the microenvironment (e.g., soil/air temperature, humidity, soil moisture), little is known about how soil microbial communities respond to these variables. In this study, we examined the soil microbial taxonomic and functional gene diversities, compositions and structures under temperature and plant diversity gradients at the Biodiversity and Climate (BAC) field experiment located at the Cedar Creek Ecosystem Science Reserve in Minnesota. Soil was sampled from ambient (AT), low (LT; 1-3℃) and high (HT; 3-5℃) temperature subplots, which were nested in plots with 1, 4, 16 and 32 plant species. Microbial communities were analyzed by MiSeq sequencing of 16S rRNA gene amplicons and functional gene arrays (GeoChip 5.0). Correlations between soil geochemical variables (i.e., total carbon, total nitrogen, and nitrate and ammonium contents) and plant biomass were calculated to link the microbial communities with their environment.
Aboveground plant biomass was similar at AT and LT plots but significantly (p<0.05, same for below) higher at HT. As such, further analysis focused on the AT and HT plots. Dissimilarity tests indicated that the soil microbial taxonomic structure with monoculture plant significantly differed from those with higher plant diversities (16 and 32 species), but was not affected by HT. Solirubrobacter, Gp6, Bradyrhizobium and Gp4 were more abundant with higher plant diversity (16 or 32 species), while Spartobacteria genera incertae sedis, Gp1 and Gp3 were more abundant with lower plant diversities (1 and 4 species). Microbial α-diversity was similar across plant diversity gradients under AT and for higher diversities under HT, but was significantly lower under HT for 1 and 4 plant species. Geochip analysis indicated that abundance of carbon fixation genes were significantly increased in higher plant diversities and decreased by HT. Canonical correspondence analysis indicated that multiple environmental factors including total carbon, total nitrogen, carbon and nitrogen ratio and aboveground plant biomass significantly correlated with the microbial community structure. These results provide new insights into the responses of soil microbial communities to plant diversity and elevated temperature.