Successional dynamics of grassland microbial communities in response to warming, precipitation alternation and clipping
Soil microbial communities mediate critical carbon and nutrient cycling in terrestrial ecosystems. However, very little is known about how microbial communities respond to vegetation and multiple climate change factors. We undertook a long-term experiment to examine the effect of climate warming, precipitation alternation, and clipping on soil microbial communities in a temperate grassland of Central Oklahoma (OK). This experiment included three treatments: air warming (control and warming), precipitation alteration (double, normal, and half), and clipping (unclipped and clipped). Surface layer (0-15cm) soil samples from all plots were collected annually at the summer peak plant biomass season (Sep. or Oct.) from 2009 to 2014. To examine bacterial and fungal community changes under multiple treatments, a total of 264 soil samples were collected and analyzed by sequencing of 16S rRNA gene and ITS amplicons and GeoChip hybridization. Various statistical analysis methods were used to detect the effect of year, warming, precipitation alternation and clipping on the diversity, composition, structure, functional potential and dynamics of soil microbial communities.
Soil temperature at a depth of 7.5 cm was 3°C higher (P<0.001) in the warmed plots compared to the control plots. Soil moisture was significantly (P<0.001) lower in the clipped and warmed plots, and higher in the double precipitation plots compared with their controls. Plant biomass significantly (P<0.05) decreased with reduced precipitation. Dissimilarity analysis showed that each treatment alone as well as year affected the bacterial and fungal communities. Permutational analysis indicated that over time, warming became the most influential treatment. The α-diversity of microbial communities was gradually decreased in the warming (P < 0.05) samples over time. The community composition also shifted over time with significantly (P < 0.05) more Firmicutes, and less Deltproteobacteria, Gammaproteobacteria and Acidobacteria in warmed samples in 2014 compared to the control. By 2014, significantly (P < 0.05) more Proteobaceria and Ascomycota and less Basidiomycota were observed in the double precipitation soil samples compared to the half precipitation soils, while in the clipped plots, Planctomycetes were less abundant compared to the unclipped plots. In addition, GeoChip analysis showed that warming, clipping as well as year had significant effects on the functional structure of soil communities. C cycling genes were differentially influenced under different treatments. These results indicate that warming, altered precipitation and clipping have differential effects on the diversity, composition, structure, function and dynamics of soil microbial communities.