Effects of plant interspecific interaction and warming on soil microbial community in root zone soil of two dominant tree species in the subalpine coniferous forest in southwestern China

Aims Soil microbial community composition and structure were regulated by temperature and plant species. Picea asperata and Abies faxoniana were planted in the monoculture and mixture plantations of the subalpine region in southwestern China. However, the effects of these two species and their interactions on soil microbial community under future climate warming remain unclear.
Methods An experiment was conducted to examine the effects of warming and plant species on soil microbial community composition with two levels of temperature (unwarming and warming with infrared heater) and four planting patterns (single A. faxoniana, single P. asperata, mixture of A. faxoniana and P. asperata, and unplanted bare land). Root zone soil of different planting treatments were sampled to estimating the microbial biomass and microbial community composition by the phospholipid fatty acids (PLFAs) content analysis.
Important findings The results indicated that: (1) Both P. asperata and A. faxoniana mono-planting significantly increased the biomass (PLFAs content) of main soil microbial groups and the whole community, regardless of warming, but the PLFAs content was only increased by mixed planting in unwarming plots. On the other hand, warming enhanced fungi (F) in unplanted plots and gram-negative bacteria (GN) in the P. asperata plots, respectively. However, warming significantly decreased soil microbial biomass in A. faxoniana and the mixed planting plots. (2) Principal component analysis (PCA) showed that effects of planting P. asperata and A. faxoniana on soil microbial community composition were greater under unwarming than under warming conditions. All the planting treatments significantly decreased the ratio of gram-positive/gram-negative bacteria (GP/GN) and increased the ratio of fungi/bacteria (F/B) in unwarming plots. However, significant effects on GP/GN and F/B ratios were only observed in A. faxoniana plots under warming condition. (3) PLFAs content was positively correlated with soil organic carbon, and F/B ratio was significantly correlated with soil pH and inorganic N. These results showed that the effects of warming on soil microbial biomass and composition varied among the tree species, and the effects of P. asperata and A. faxoniana were weakened under warming condition than under unwarming condition. Our results provide a vital theoretical basis for further study on the responses of soil microbial communities to vegetation and global climate change in southwestern China.