[Input and distribution of rice photosynthesized carbon in the tillering stage under different nitrogen application following continuous 13C labeling].

The input of rice-photosynthesized carbon (C) into soil plays an important role in soil C cycling. A 13C-labelled microcosm experiment was carried out to quantify the input of photosynthesized C into soil C pools in a rice-soil system during the tillering stage. Growing rice (Oryza sativa L. ) was continuously fed with 13C-labeled CO, ( C-CO, ) in a closed chamber without nitrogen (NO), or at different rates of N supply (N10,N20, N30, N40 or N60). The results showed that there were significant differences in rice shoot (1.58 g plot-1 to 4.35 g plot-1) and root (1.05 g plot-1 to 2.44 g plot-1 ) biomass among the N treatments after labeling for 18 days. The amounts of 13C in shoots and roots ranged from 44.0 g plot-1 to 157.6 g.plot-1 and 8.3 g.plot-1 to 49.4 g.plot-1, respectively, and generally followed the order of N60 > N40 > N20 > N10 > NO. The contents of rice-planted 13C-SOC, 13C-DOC and 13C-MBC in soil carbon pool were much higher than those of CK (without rice and N supply). The amount of 13C-SOC ranged from 11.1 g plot - to 23.7 gplot-1 , depending on the rate of N addition, accounting for 10.2% -18. 1% of the net assimilation. The amounts of 13C-DOC and 13C-MBC ranged from 4. 82-14.51 microg kg-1 and 526. 1-1 478.8 microg kg-1 , both depending on the N application rate. In addition, at 18-day of labeling, the 13C-SOC, 13C-DOC and 13C-MBC concentration was positively correlated with the rice biomass. Therefore, our results suggest that paddy soils can probably sequester more C from the atmosphere if more photosynthesized C enters the soils and N application can stimulate C rhizodeposition during the tillering stage.