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Limited potential of harvest index improvement to reduce methane emissions from rice paddies

Jiang, Yu, Qian, Haoyu, Wang, Ling, Feng, Jinfei, Huang, Shan, Hungate, Bruce A., van Kessel, Chris, Horwath, William R., Zhang, Xingyue, Qin, Xiaobo, Li, Yue, Feng, Xiaomin, Zhang, Jun, Deng, Aixing, Zheng, Chenyan, Song, Zhenwei, Hu, Shuijin, van Groenigen, Kees Jan, Zhang, Weijian
Global change biology 2019 v.25 no.2 pp. 686-698
greenhouse gas emissions, harvest index, meta-analysis, methane, microorganisms, plant breeding, rice, root exudates, staple foods, surge irrigation, surveys
Rice is a staple food for nearly half of the world's population, but rice paddies constitute a major source of anthropogenic CH₄ emissions. Root exudates from growing rice plants are an important substrate for methane‐producing microorganisms. Therefore, breeding efforts optimizing rice plant photosynthate allocation to grains, i.e., increasing harvest index (HI), are widely expected to reduce CH₄ emissions with higher yield. Here we show, by combining a series of experiments, meta‐analyses and an expert survey, that the potential of CH₄ mitigation from rice paddies through HI improvement is in fact small. Whereas HI improvement reduced CH₄ emissions under continuously flooded (CF) irrigation, it did not affect CH₄ emissions in systems with intermittent irrigation (II). We estimate that future plant breeding efforts aimed at HI improvement to the theoretical maximum value will reduce CH₄ emissions in CF systems by 4.4%. However, CF systems currently make up only a small fraction of the total rice growing area (i.e., 27% of the Chinese rice paddy area). Thus, to achieve substantial CH₄ mitigation from rice agriculture, alternative plant breeding strategies may be needed, along with alternative management.