用13C脉冲标记法研究玉米光合碳分配及其向地下的输入

研究玉米生长对土壤有机碳的贡献对了解农田碳平衡与农业生产之间的关系具有重要意义.应用4次¹³C脉冲标记对不同生育时期（苗期、拔节、抽雄和灌浆期）玉米光合碳在玉米-土壤系统中的分配特征进行了为期1个生长季的研究.结果表明,留在地上部的¹³C占玉米净吸收¹³C的百分含量,在灌浆期标记时最大,为80.01%.在不同生育时期,玉米向地下转移的¹³C比例分别为43.24%、46.46%、30.30%和19.99%;此部分¹³C中有34.68%～77.56%被根际呼吸消耗,16.63%～57.02%存在于根部,5.05%～8.30%通过根际沉积转化为土壤有机碳.整个生育期内,玉米分配到地上部、根部、根际呼吸和土壤有机碳中的光合碳量,分别占净吸收碳量的62.39%、17.88%、17.07%和2.67%.在拔节、抽雄和灌浆期,玉米的根际呼吸分别占土壤呼吸总量的67.07%、63.31%和28.82%;同时其根际激发效应使土壤原有有机碳分解分别增加了31.11%、79.09%和120.83%.以大田玉米地上部干重18 t·hm^-2、含碳量42%计算,玉米在其生育期内输入到地下的总碳量为4.6 t·hm^-2,其中有2.1 t·hm^-2通过根际呼吸进入大气,2.2 t·hm^-2存在于根中,0.33 t·hm^-2转化为土壤有机碳.

Estimating Photosynthesized Carbon Distribution and Inputs into Belowground in a Maize Soil Following

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.