Higher subsoil carbon storage in species-rich than species-poor temperate forests

Abstract

Forest soils contribute ca. 70% to the global soil organic carbon (SOC) pool and thus are an
\nimportant element of the global carbon cycle. Forests also harbour a large part of the global
\nterrestrial biodiversity. It is not clear, however, whether tree species diversity affects SOC. By
\nmeasuring the carbon concentration of different soil particle size fractions separately, we were
\nable to distinguish between effects of fine particle content and tree species composition on the
\nSOC pool in oldgrowth
\nbroadleaved
\nforest plots along a tree diversity gradient (1,
\n3and
\n5species).
\nVariation in clay content explained part of the observed SOC increase from
\nmonospecific to mixed forests, but we show that the carbon concentration per unit clay or fine
\nsilt in the subsoil was by 30–35% higher in mixed than monospecific stands indicating a
\nsignificant species identity or species diversity effect on C stabilization. Underlying causes
\nmay be differences in fine root biomass and turnover, in leaf litter decomposition rate among
\nthe tree species, and/or speciesspecific
\nrhizosphere effects on soil. Our findings may have
\nimportant implications for forestry offering management options through preference of mixed
\nstands that could increase forest SOC pools and mitigate climate warming.