不同生育期光合碳在水稻-土壤系统中的分配及输入效率

为了研究不同生育期光合碳在水稻-土壤系统中的分配与输入效率,通过盆栽试验,采用13C-CO₂脉冲标记法,定量研究水稻不同生育期(分蘖期、拔节期、抽穗期和灌浆期)内光合碳在水稻-(根际/非根际)土壤系统中的分配及其对根际、非根际土壤有机碳的贡献.结果表明:13C-CO₂脉冲标记6 h后,水稻地上部、根系和根际土中13C的丰度最大值均出现在分蘖期,分别达到1 864.7‰、842.6‰和-8.2‰,显著高于后3个生育期.分蘖期、拔节期、抽穗期、灌浆期这4个生育期水稻光合13C在地上部的分配比例依次增加,而在根部和根际土中的分配比例逐渐减小；不同生育期水稻光合13C在水稻-土壤系统中的总回收率为72.0%～81.0%,在籽粒中的回收率由1.8%逐渐增至40.3%,在根部和土壤中的回收率逐渐下降,表明水稻生育前期光合作用更强,能够向地下部快速输入“新碳”.水稻生长至成熟后,茎叶中光合13C的分配比例由61.0%～93.1%降至32.8%～74.1%,而在籽粒、根部和根际土中的分配比例分别增加了1～2倍,表明水稻植株在生长过程中光合碳向籽粒和地下部传输.根际沉积效率随水稻的生长逐渐由分蘖期的11.0%降至灌浆期的4.1%；光合碳对土壤有机质的贡献也逐渐减低,而且对根际土的贡献显著大于非根际土,表明水稻生长速率决定了光合碳对土壤有机碳的贡献率,而水稻根际沉积效应是根际土壤有机质获得较高光合碳贡献率的主要原因.该研究进一步量化了水稻生长期间光合碳的分配及其对土壤有机碳库的贡献,有助于深入开展水稻土有机质积累持续机制与固碳潜力研究. 

Allocation and Input Efficiency of Assimilated Carbon in Rice-Soil Systems at Different Growth Stages

To quantify the distribution of photo-assimilated carbon in rice-soil systems and its contribution to rhizosphere and non-rhizosphere soil organic matter, an isotopic pulse labeling experiment was conducted in a microcosm system. Rice crops were pulse-labeled with 13C at the tillering, jointing, heading and filling stages. After 6 h of pulse labeling, the maximum δ13C values of aboveground plant organs, roots and rhizosphere soil were 1864.7‰, 842.6‰, and -8.2‰, respectively, at the tillering stage； these values were significantly higher than those at the other three growth stages. The amount of assimilated 13C gradually increased in aboveground organs but gradually decreased in roots and rhizosphere soil during rice growth. The 13C recovery in rice-soil systems was 72.0%-81.0% at the four growth stages； 13C recovery in grain increased from 1.8% to 40.3%, and gradually decreased in roots and soil organic carbon. The results suggested that young rice formed considerably more photosynthates and could transfer high amounts of newly formed C to the soil. After the maturing stage, the distribution of assimilated 13C decreased from 61.0%-93.1% to 32.8%-74.1% in shoots, but increased 1-2-fold in seeds, roots and rhizosphere soil. Rice rhizosphere deposition efficiency gradually decreased from 11% at the tillering stage to 4.1% at the filling stage. The contribution of rice photosynthetic carbon to soil organic matter also decreased gradually, and the contribution to rhizosphere soil was significantly greater than that to bulk soil, indicating that the contribution of photosynthetic carbon was affected by rice growth rate, and that rhizodeposition efficiency played a considerable role in the increase in photosynthate input to rice rhizosphere soil. This study provides new insights into the distribution of photosynthetic carbon during rice growth and its contribution to soil organic carbon, and provides a theoretical basis for research on the carbon cycle in agroecosystems.