Decline of soil microbial diversity shapes the source of CO2 emission in soil. DIMIMOS_EROSION

It remains unclear whether microbial diversity drives carbon transformations in soil. Assumption prevailing still supports that activity of soil microbial communities does not rely on diversity because of functional redundancy. However this idea is challenged by recent experimental tests, even if mixed results can be found depending on the function investigated or the experimental design deployed. Here, we hypothesized that functional redundancy may decrease with increasing carbon source recalcitrance, and that coupling of diversity with C-cycling may change accordingly. We manipulated microbial diversity in a soil microcosm experiment to examine the functional significance of diversity decrease on the decomposition of easily decomposable (i.e. allochthonous plant residues) vs recalcitrant (i.e. autochthonous organic matter) C-sources. Our study pointed to two main conclusions: (i) the decrease of microbial diversity shapes the source of CO2 emission towards preferential decomposition of most degradable C-compounds, (ii) the significance of the “diversity effect” increases with nutrient availability, and is consequently time dependent in soil ecosystems that receive pulse inputs of plant and rhizodeposites. Altogether, these new findings show that C-cycling in soil may be more vulnerable to microbial diversity changes than expected from previous works, and that concerns for the preservation of biodiversity may consequently also apply for microbial communities.