SUSIBA2水稻光合碳分配特征及其对土壤有机碳和甲烷排放的影响

Methane is an important greenhouse gas because it has 25 times the global warming potential of carbon dioxide by mass. Flooded rice fields are a significant source of atmospheric methane. Worldwide emission from rice is responsible for about 50-60Tg annual. To meet the increased rice demand of a growing population, rice cultivation must continue to expand at or beyond its current rate and thus to intensify methane emission. Breeding the varieties with low methane emission is fundamental strategy of reducing greenhouse gas emissions. Previous studies we described a ‘high-starch low-methane’ rice variety on Nature, named SUSIBA2 rice, which is produced by adding sugar-signaling gene Hvsusiba2 (a plant-specific transcription factor) from barely, with extremely low methane emissions and high starch contain in both grain and stem. .To get a better understanding of the role of SUSIBA2 rice in methane mitigation, in this project we will take four-pronged approach: 13C pulse labelling performing at different growth stages of SUSIBA2 rice to estimate the contribution of photosynthesized C to MBC and DOC; quantifying methanogenic communities at the rhizosphere; Measuring the phenotypic traits of transgenic rice; Characteristics analysis of carbon allocation and quantifying analysis the expression of carbohydrate metabolism genes. .In additional, for estimating the transgenic rice methane emission reduction efficiency, a series of experiments are designed including comparing of the amount of methane between transgenic rice and non-transgenic rice under different ecological rice field, different soil type and different of rice crop.

甲烷是最重要的温室气体之一，其吸热量高于CO225倍。全球稻田每年甲烷排放量达50-60Tg。不断增加的人口对粮食的需求将导致稻田甲烷排放量加剧上升。培育低甲烷品种是稻田甲烷减排的根本。前期，我们利用大麦Hvsusiba2基因调控光合碳分配的特性，创制了转基因水稻命名为SUSIBA2，SUSIBA2具有甲烷排放量显著下降、粒重增加、籽粒和茎鞘淀粉含量显著上升的特点，研究结果发表于2015年Nature。本研究拟通过13C同位素示踪分析转Hvsusiba2水稻光合同化碳分配特征，研究其发育过程中非结构性碳积累和流向，理解水稻光合碳向土壤碳库输入性变化对土壤有机碳库和相关微生物的影响及其与甲烷排放关系，初步阐明Hvsusiba2对稻田甲烷减排机理。同时继续监测SUSIBA2水稻在不同稻区、不同耕作方式下甲烷减排效率和稳定性。为进一步开展“高产、低甲烷排放”水稻的分子设计奠定基础。

本研究以过表达HSUSIBA2水稻(SUSIBA2水稻)为材料，研究其对稻田甲烷减排的效果及其机理。早稻栽培田甲烷减排达到50.98%，晚稻栽培稻田甲烷减排达到50.97%，冬季稻田的甲烷减排率仅为22.26%。不同品种的SUSIBA2水稻甲烷减排效率也不同，SUSIBA2粳稻的减排率为50.97%，而SUSIBA2籼稻的减排率为30.8%；早稻每生产1克稻谷甲烷排放量为0.04g，而对照是0.12g；单位稻谷产量甲烷排放量为：SUSIBA2早稻每1克稻谷甲烷排放量为0.04g，而对照是0.12g；SUSIBA2晚稻每1克稻谷甲烷排放量为0.04g，而对照为0.08g。.SUSIBA2水稻显著降低了土壤有机碳和CH4相关微生物的丰度，改变了产甲烷和产甲烷营养化群落，表明SUSIBA2水稻向土壤释放的碳量较少，从而降低了CH4的产量。.13C分析SUSIBA2水稻植株生长期间光合碳转运和分配，结果显示SUSIBA2水稻总碳量与对照相比无显著差异；但不同组织的碳占比在生长的不同时期存在显著差异，总体表现为：SUSIBA2水稻地上部总碳含量显著高于对照，地下部的总碳含量低于对照。这说明SUSIBA2植株在碳的分配上存在差异，倾向于将更多的碳留在地上部。.SUSIBA2水稻土壤中13C丰度显著或极显著低于对照，进一步证实了SUSIBA2水稻光合产物向根部输入量显著减少的事实，尤其在生长旺盛期的抽穗期和灌浆期显著受到影响。.综上分析，我们认为SUSIBA2水稻降低稻田甲烷排放的主要机制是HvSUSIBA2基因通过调控水稻淀粉合成相关基因的表达，减少了光合同化物向水稻地下部的分配，SUSIBA2稻田土壤中碳含量发生变化，导致产甲烷菌丰度显著降低，减少了稻田甲烷的产生，进而降低了稻田甲烷排放。