High microbial diversity promotes soil ecosystem functioning
Résumé
In soil, the link between microbial diversity and carbon transformations is challenged by the concept of functional redundancy. 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 to examine how diversity decrease affects the decomposition of easily degradable (i.e. allochthonous plant residues) vs. recalcitrant (i.e. autochthonous organic matter) C-sources. We found that a decrease in microbial diversity (i) affected the decomposition of both autochthonous and allochthonous carbon sources hence reducing global CO2 emission by up to 40%, and (ii) shaped the source of CO2 emission towards preferential decomposition of most degradable C-sources. Our results also revealed that the significance of the “diversity effect” increases with nutrient availability. Altogether, these findings show that C-cycling in soil may be more vulnerable to microbial diversity changes than expected from previous studies, particularly in ecosystems exposed to nutrient inputs. Thus concern about the preservation microbial diversity may be highly relevant in the current ‘global changes’ context assumed to impact soil biodiversity and the pulse inputs of plant residues and rhizodeposits into the soil.