[Estimating photosynthesized carbon distribution and inputs into belowground in a maize soil following 13C pulse-labeling].

Evaluating the contribution of maize growth to soil organic carbon is important for the understanding of the relationship of farmland carbon balance and agriculture production. 4 times of 13C pulse-labelling were used to estimate the photosynthesized carbon distribution at different development stages (seedling, elongation, heading and grain-filling) in maize-soil system, and quantify the carbon inputs into each part of belowground in whole growth season. The result indicated that the 13C retained aboveground reached its maximum: 80.01% among net assimilated 13C at grain-filling stage labelling. For the 4 labelling stages, the 13C transferred into belowground is 43.24%, 46.46%, 30.30% and 19.99% respectively, and of the 13C input into belowground, 34.68%-77.56% was respired by rhizosphere, 16.63%-57.02% was remain in roots and 5.05%-8.30% was incorporated into soil organic carbon by rhizodeposition. During the whole growth season of maize, the photosynthesized carbon allocated to aboveground, roots, rhizosphere respiration and soil organic carbon was 62.39%, 17.88%, 17.07% and 2.67% of the net assimilated carbon. At elongation, heading and grain-filling stages, maize's rhizosphere respiration accounted for 67.07%, 63.31% and 28.82% of the total CO2 efflux from the soil respectively, during the same period rhizosphere priming effect led to 31.11%, 79.09% and 120.83% increase of decomposition of original soil organic carbon respectively. Based on the calculation of 18 t x hm(-2) dry matter of maize for farmland production and its C content is 42%, the total carbon transferred into belowground is 4.6 t x hm(-2), among which 2.1 t x hm(-2) was respired by rhizoshphere, 2.2 t x hm(-2) was retained in roots and 0.33 t x hm(-2) was incorporated into soil organic carbon.