Tree species richness and identity influence the structure and functioning of soil microbial communities
The relationship between biodiversity and ecosystem function has often been explored by examining species diversity in relation to producer productivity. Despite the importance of soil microbial communities in forest ecosystem functioning (nutrient and carbon cycling), little is known about how these communities respond to changes in aboveground plant species diversity. In the present study we examined how soil microbial communities respond to tree species richness (SR).
We used a common garden experiment of high-density tree communities near Montreal, Canada consisting of conifer and hardwood species mixtures, to characterize microbial communities in both monocultures and species mixtures. We tested the response of the communities along a SR gradient: 1, 2, 4 and 12 species. Phospholipid fatty acid (PLFA) analysis and the MicroRespTMsystem were used to assess community structure and community-level physiological profiles (CLPP).
Our results showed a significant effect of SR on microbial parameters. Basal respiration, glucose-induced respiration (active microbial biomass) and the metabolic quotient (qCO2) were significantly higher in SR mixtures compared to monocultures. Principal component analysis based on CLPP revealed that communities associated with SR mixtures use higher amounts of carbon sources than do monocultures, while communities associated with deciduous trees generally use higher amounts of carbon than those associated with evergreen species. Nevertheless, there were no differences in total PLFA abundances, neither in bacteria, fungi, or any other tested soil microbial PLFA abundances or ratios, between monocultures and SR mixtures. Likewise, there were no differences in microbial structure among monoculture plots, with the exception of Gram positive bacterial species, which were more abundant in certain monoculture plots. These results indicate that the identity of the aboveground species rather than their diversity may influence the soil microbial community structure, while both the identity and diversity drive their functioning.