Positive effects of plant species diversity on organic carbon accumulation in soil aggregates driven by mineral protection in a subtropical forest in southwest China

High plant species diversity (PSD) has been reported to enhance soil organic carbon (SOC) storage, but the mechanisms underlying its stimulative effects on soil aggregates remain poorly understood, especially in terms of the effects on aggregate-associated OC content.

We selected 45 plots in a subtropical forest to determine the pattern of variation of soil aggregate-associated OC along a natural PSD gradient and the effects exerted by PSD.

OC contents of three soil aggregate fractions were significantly and positively correlated with PSD. High PSD could enhance the proportion of macroaggregate OC in bulk OC, but decreased that of silt + clay-associated OC. Our results also revealed that high PSD might increase the OC content in soil aggregates by stimulating plant litter inputs. At the same time, high PSD increased soil minerals, which could enhance mineral protection of OC in soil aggregates.

Along the PSD gradient, the accumulation of OC in soil aggregates was mainly influenced by Ca²⁺/Mg²⁺-mediated mechanisms that protected them in the study area, which is characterized by karst forest soils dominated by dolomite and limestone. Our study provides a better understanding of soil C dynamics in aggregates under varying PSD in forest ecosystems, possibly assisting in making more accurate predictions.