Soil bacterial and fungal biomass are independent of aboveground plant communities in a rocky island system

Abstract

Soil microbial communities and plants are intimately associated and each can regulate the growth and specific composition of the other through relationships such as competition and symbiosis. Such links between the above and belowground components of soil ecosystems are important as they determine the functioning of key ecosystem processes, including decomposition and nutrient cycling. In the present study, we used structural equation models to investigate the direct and indirect effects of plant community properties (richness, evenness and net primary productivity) and of soil nutrient pools (C, N and P) on the biomass of rhizosphere and non-rhizosphere bacteria and fungi. The biomass of rhizosphere and non-rhizosphere bacteria and fungi was mainly determined by the organic matter content. More importantly, nutrient pools were not modulated by plant communities and we did not find any evidence of a link between aboveground and belowground components of soil systems in this respect. The findings indicate that aboveground and belowground components of the soil system are not directly linked and that any potential relationships will be mediated by the effects of aboveground components in nutrient pools.