Disturbances Consistently Favor Sub-Dominant Bacterial Phyla in Grassland Soil

Different environmental changes may have some consistent effects on soil microbial community, which remains largely unexplored. Here, we report a novel and general pattern that different environmental changes consistently selected for the sub-dominant soil bacterial phyla. We mimicked 16 types of environmental changes relevant to the Eurasian steppe ecosystem, including removing different number of plant functional groups, mowing, nitrogen adding, phosphorus adding, watering, warming, and some of their combinations. While the absolute abundance of each of the four dominant bacteria phyla (Acidobacteria, Actinobacteria, Chloroflexi, and Proteobacteria) did not show a consistent response to these treatments, that of the five sub-dominant phyla (Bacteroidetes, Firmicutes, Gemmatimonadetes, Nitrospirae, and Planctomycetes) showed a consistent increase. The dominant phyla had high abundances of genes responsible for energy production/conversion and transcription, exhibiting oligotrophic traits; in contrast, the sub-dominant phyla had high abundance of 16S rDNA sequences, which could be due to greater rRNA copy number or smaller genomes, showing large growth/propagation potential and copiotrophic trait. Stochastic processes (e.g., random birth, death, colonization) played more important roles in structuring the sub-dominant than dominant phyla, and the treatments promoted the stochastic processes. The copiotrophy and stochasticity of sub-dominant phyla led to their positive responses to the treatments.