Abstract: Study on influence of photosynthetic carbon of early rice on soil organic carbon under double rice cropping system at the annual scale is of great significance for understanding the mechanisms underlying cropland carbon cycling and soil carbon sequestration. The distribution of photosynthetic carbon in early rice and its contribution to soil organic carbon were examined using ¹³C pulse labeling at the panicle differentiation (PD) and grain filling stages (GF) of early rice with a pot experiment. The results showed that photosynthetic ¹³C was transferred to both aboveground and belowground after 1 d of labeling. The recovery rate of PD-labeled carbon was 74% at the harvest time of rice, which was significantly higher than that of GFlabeledcarbon (59%). Moreover, partition of PDlabeled carbon to belowground was higher than that of GFlabeled carbon. In both the early and late rice seasons, the contribution of photosynthetic carbon at early rice PD stage to dissolved soil organic carbon (DOC) was significantly higher than that of GF stage. By the late rice maturity stage, the contribution of photosynthetic carbon at early rice PD stage to DOC was up to 9.4%, being significantly higher than that of GF stage (2.6%). The contribution of photosynthetic carbon at early rice PD stage to total soil organiccarbon was significantly higher than that of GF stage at both harvests, which was 20.7 fold of that of GF stage by late rice maturity. In conclusion, compared with the early rice GF stage, the early rice PD stage can result in more photosynthetic carbon accumulation in soils, with higher contribution to soil organic carbon pool under double rice cropping system.

Key words:  ¹³C pulse labeling, double cropping rice, photosynthetic carbon, soil organic carbon, dissolved soil organic carbon.