Climate change alters the regional precipitation pattern and causes seasonal droughts that affect forest growth
and belowground carbon cycling. This is expected to create greater oscillations in soil moisture that affect the
stability of the soil organic carbon (SOC) pool. This study examined the effects of the precipitation decline on the
SOC dynamics by experimentally controlling the throughfall in a Pinus massoniana plantation in subtropical
region of China. Soil physicochemical properties were analyzed in topsoil (0–5cm depth) during the dry-cool and
the wet-warm season after five consecutive years of ~30% throughfall reduction. We also assessed the SOC stock
and its stability, as indicated by the easily oxidizable carbon (EOC) pool, SOC mineralization rates, soil aggregate
size distributions and fine root biomass in relation to soil microbial community structure. The throughfall
reduction reduced the soil moisture by 15–20% between sampling dates, with an average 18% during the fiveyear
experiment. With throughfall reduction, topsoil SOC stocks significantly increased by 0.18 kg C m-2 or 10%,
but fine root biomass, EOC content, and the micro-aggregate fraction were significantly higher, suggesting less
stable SOC. The abundance of bacterial r-strategists (e.g. Bacteroidetes, Betaproteobacteria, and Gammaproteobacteria) increased significantly while K-strategists (e.g. Planctomycetes) decreased. Both SOC and EOC mineralization were positively correlated with the abundance of r-strategists, but negatively correlated with the
K-strategists abundance. We posit that micro-aggregates, fine root biomass, and altered microbial strategist ratios
are associated with the decline in SOC stability in forests with less throughfall. Keywords: Soil organic carbon, SOC stability, Subtropical forest, Pinus massoniana, Precipitation manipulation,
Microbial community structure
