Does Forest Stand Relative Density Index Affect Soil Microbial Community Functioning?

Abstract

Forest management aims to maintain a sustainable production of quality so that trees can adapt to climate change which increases competition for resources. In this context, forests have been assigned another major role: carbon sequestration, particularly in soils. The functioning of forest soils depends largely on the interaction between trees and the soil microbial community (SMC). Yet, little is known about the link between forest management and SMC. Many studies have focused on the effect of thinning on the SMC, evidencing contrasted effects. Thinning is only a temporary disturbance, and in perennial forest ecosystems such as forests, attention should be paid to how the final stand density affects SMC. In this study, we hypothesize that relative stand density index (RDI) affects biomass, gene abundance and activity of the SMC. We therefore tested the effect of RDI on SMC according two sylvicultural practices: dynamic (low RDI) and conservative (medium RDI) in a temperate Oak Stand (OS) in Europe Forest. We evidence a decrease in the soil microbial (bacteria, archaea, and fungi) gene abundance in stands where the RDI is lower. At the same time, there is a decrease in the functional microbial diversity, but a global increase in mineralization activity. Our results were incremented with a large number of biotic and abiotic environmental variables to analyze correlations between environment that can impact RDI and SMC interactions. Finally, this highlights that the effect of environmental factors had contrasting effects on SMC, and there is no single factor, including RDI or thinning, to explain all the SMC responses. Our findings strengthen the emerging idea that there is a large network of complex interactions in the forest influencing the SMC, necessitating the promotion of long-term studies considering a maximum of biotic and abiotic factors.

Keywords: forest, relative density index, Soil microbial community, microbial functional diversity, environmental factors