生态系统地下碳输入与输出过程是陆地生态系统碳分配和转化的核心, 并直接影响着全球碳循环。了解水稻地下碳输入及其周转对于充分认识稻田生态系统碳循环和固定具有重要意义。之前有关作物地下碳输入的评述往往都集中在旱地作物，对水稻根际沉积碳和地下碳的输入尚未得到全面的总结。
为此，中国科学院亚热带农业生态研究所吴金水研究员团队收集和整理利用碳同位素示踪技术研究水稻光合碳分配和周转的相关文献资料并结合该团队的前期工作，分析整合了水稻光合碳（通过根际沉积作用）的输入量及其在水稻-土壤系统的分配特征，结果表明，水稻光合碳的土壤固持及其在水稻-土壤系统的分配与标记方法有关，在连续标记方法下，最终会有72%的光合碳被固定到水稻地上部，17.1%固定在根系，10.2%固定到土壤，还有1.3%固定在土壤微生物中；而在脉冲标记方法下，分别有79%、13.4%、5.5%和2.1%的光合碳被固定到水稻的茎叶、根系、土壤和土壤微生物（图1）。
此外，该团队还估算了水稻地下碳输入量和根际沉积碳的数量，发现利用连续标记方法，水稻一个生长季地下碳输入总量为1.58Mg ha-1，其中根际沉积碳占0.42Mg ha-1。而利用脉冲标记方法估算的碳输入量则略低（总地下碳输入，1.37Mg ha-1；根际沉积碳，0.35Mg ha-1）。
鉴于同位素示踪技术费用高昂，而且需要专业的知识和特殊的分析设备，因此目前该技术的使用还不是非常普遍，因此该团队还建立了一种快速和简便估算水稻生态系统地下碳和根际沉积碳数量的方法。考虑到水稻不同组织之间以及根系和根际沉积之间相对稳定的比例关系，该团队发现可以一个相对系数来估算水稻生态系统地下碳和根际沉积碳的数量，即用水稻的某个组织的生物量乘以该系数便可大致速算出水稻的地下碳和根际沉积碳的含量。发现，水稻总地下碳量的估算系数为：水稻茎叶生物量的0.24，水稻根系的0.79和水稻总生物量的0.17；而根际沉积碳数量的估算系数为：水稻茎叶生物量的0.06，水稻根系的0.28和水稻总生物量的0.04（图2）
综上，脉冲标记和连续标记法作为估算水稻地下碳输入直接有效的方法，有助于研究根际来源碳的转化和分配，并将其与土壤原有有机质区分开来。在标记后，水稻光合碳固定到茎叶、根系和土壤的比例迅速变化，但在1-2周后保持稳定。连续标记法估算的水稻碳输入量要比脉冲标记法高15%。用该方法测定水稻土中光合碳的输入量为1370-1580 kg ha-1。但无论采用何种标记方法，水稻根际沉积碳约占总地下碳输入量的26%（图3）。
上述结果以Carbon input and allocation by rice into paddy soils: A review为题发表在土壤学Top期刊Soil Biology and Biochemistry上。该研究得到了国家重点研发计划 、国家自然科学基金和研究所青年创新团队的支持。
延伸阅读：该团队近年来发表的水稻光合碳土壤固持及其相关机制的文章
1)Tida Ge, Chang Liu, Hongzhao Yuan, Ziwei Zhao, Xiaohong Wu, Zhenke Zhu, Phil Brookes, Jinshui Wu. Tracking the photosynthesized carbon input into soil organic carbon pools in a rice soil fertilized with nitrogen. Plant and Soil，2015，392: 17–25
2)Tida Ge, Hongzhao Yuan, Hanhua Zhu, Xiaohong Wu, San’an Nie, Chang Liu, Chengli Tong, Jinshui Wu, Phil Brookes. Biological carbon assimilation and dynamics in a flooded rice – soil system. Soil Biology and Biochemistry, 2012, 48: 39-49
3)Tida Ge, Baozhen Li, Zhenke Zhu, Yajun Hu, Hongzhao Yuan, Maxim Dorodnikov, Davey L Jones, Jinshui Wu, Yakov Kuzyakov. Rice rhizodeposition and its utilization by microbial groups depends on N fertilization. Biology and Fertility of Soils. 2017, 53: 37-48
4)Yalong Liu, Tida Ge, Jun Ye, Shoulong Liu, Olga Shibistova, Ping Wang, Jingkuan Wang, Yong Li, Georg Guggenberger, Yakov Kuzyakov, Jinshui Wu. Initial utilization of rhizodeposits with rice growth in paddy soils: Rhizosphere and N fertilization effects. Geoderma. 2019, 338: 30-39
5)Ziwei Zhao, Tida Ge, Anna Gunina, Yuhong Li, Zhenke Zhu, Peiqin Peng, Jinshui Wu, Yakov Kuzyakov. Carbon and nitrogen availability in paddy soil affects rice photosynthate allocation, microbial community composition, and priming: combining continuous 13C labeling with PLFA analysis. Plant and Soil 2018, DOI : 10.1007/s11104-018-3873-5
6)Cornelius Talade Atere, Tida Ge, Zhenke Zhu, Shoulong Liu, Xizhi Huang, Olga Shibsitova, Georg Guggenberger,Jinshui Wu. Assimilate allocation by rice and carbon stabilisation in soil: effect of water management and phosphorus fertilization. Plant and Soil 2018, DOI: 10.1007/s11104-018-03905-x
7)Zhenke Zhu, Tida Ge, Shoulong Liu, Yajun Hu, Rongzhong Ye, Mouliang Xiao, Chengli Tong, Yakov Kuzyakov,Jinshui Wu. Rice rhizodeposits affect organic matter priming in paddy soil: The role of N fertilization and plant growth for enzyme activities, CO2 and CH4 emissions. Soil Biology and Biochemistry. 2018, 116: 369-377
8)Cornelius Talade Atere, Tida Ge, Zhenke Zhu, Chengli Tong, Davey L Jones, Olga Shibistova, Georg Guggenberger,Jinshui Wu. Rice rhizodeposition and carbon stabilisation in paddy soil are regulated via drying-rewetting cycles and nitrogen fertilization. Biology and Fertility of Soils. 2017, 53: 407-417
9)Zhenke Zhu, Tida Ge, Yajun Hu, Ping Zhou, Tingting Wang, Olga Shibistova, Georg Guggenberger, Yirong Su,Jinshui Wu. Fate of rice shoot and root residues, rhizodeposits, and microbial assimilated carbon in paddy soil-part 2: turnover and microbial utilization. Plant and Soil. 2017, 416: 243-257
10)Zhenke Zhu, Tida Ge, Mouliang Xiao, Hongzhao Yuan, Tingting Wang, Shoulong Liu, Cornelius Talade Atere,Jinshui Wu, Yakov Kuzyakov. Belowground carbon allocation and dynamics under rice cultivation depends on soil organic matter content. Plant and Soil. 2017, 410: 247-258
11)Zhenke Zhu, Guanjun Zeng, Tida Ge, Yajun Hu, Chengli Tong, Olga Shibistova, Xinhua He, Juan Wang, Georg Guggenberger, Jinshui Wu. Fate of rice shoot and root residues, rhizodeposits, and microbe-assimilated carbon in paddy soil – Part 1: Decomposition and priming effect Biogeosciences, 2016, 13: 4481-4489
12)Hongzhao Yuan, Zhenke Zhu, Shoulong Liu, Tida Ge, Baozhen Li, Qiong Liu, Tin Mar Lynn, Jinshui Wu, Yakov Kuzyakov. Microbial utilization of rice root exudates: 13C labeling and PLFA composition. Biology and Fertility of Soils, 2016, 52: 615–627
13)Yu Luo, Zhenke Zhu, Shoulong Liu, Peiqin Peng, Jianming Xu, Philip Brookes, Tida Ge, Jinshui Wu, Nitrogen fertilization increases rice rhizodeposition and its stabilization in soil aggregates and the humus fraction, Plant Soil, 2018, doi.org/10.1007/s11104-018-3833-0.
14)Cornelius Talade Atere, Tida Ge, Zhenke Zhu, Liang Wei, Ping Zhou, Xinhua He, Yakov Kuzyakov, Jinshui Wu, Carbon allocation and fate in paddy soil depending on phosphorus fertilization and water management: results of 13C continuous labelling of rice, Canadian Journal of Soil Science, 2018, 98: 469-483
图1 连续标记和脉冲标记方法下，光合碳在水稻-土壤系统中的分配
图2 水稻地下碳和根际沉积碳与水稻不同组织生物量的相对比例（SB：茎叶生物量；RB：根系生物量；WB：总生物量）
图3 连续标记和脉冲标记方法下水稻土壤光合碳输入、分配和根际沉积的概述图
