[Distribution characteristics of rice photosynthesized carbon in soil aggregates of different size and density].

Rice growth affects the distribution of organic matter in soils and soil fractions, and is thus an important factor to control the storage of soil organic matter. The aims of our study were to quantify the photosynthesized C in soil fraction pools of different size and density during the rice growth, and also to offer data evidence not only in the mechanisms of SOC accumulation, but also in C sequestration potential in paddy soils. Therefore, the microcosm experiment was carried out to quantify the input and distribution of photo-assimilated carbon (C) in soils size and density aggregates pools by using continuous 14C labeling technique. Destructive samplings of rice (Oryza sativa) were conducted after labeling for 80 days. The allocation of 14C-labeled photosynthates in soil C pools was examined in rice-planted soil over the 14C labeling span using the size (250-2 000 microm, 20-250 microm, < 20 microm) and density (light and heavy) fractionation procedure. The amount of 14C in the soil organic C (SOC14) in the 250-2 000 microm particle size was dependent on the soils, ranged from 118.23 mg x kg(-1) to 309.94 mg x kg(-1), accounting for 0.52%-1.55% of its SOC, respectively, which was much larger than those of aggregates with the other two sizes (20-250 microm, < 20 microm). Moreover, the amounts of SOC14 in light fractions of 250-2 000 microm and 20-250 microm particle size aggregate were significantly greater than those in their heavy fractions (P < 0.05). The data suggested that rice photosynthesize C mainly entered into the light fraction of 250-2 000 microm particle size aggregate by rhizodeposition, which enhanced the contents of SOC. There was a significant positive correlation between the light and heavy fraction and 250-2000 microm particle size aggregate, 20-250 microm and < 20 microm particle size aggregate of SOC14, although significant negative correlation between light fractions in < 20 microm, 20-250 microm aggregates was observed.