高CO2浓度导致稻米锌营养变劣的机理及其调控

Rising atmospheric CO2 concentration reduces zinc (Zn) concentration and its bioavailability in edible parts of staple food crops, this will put more people under the risk of “hidden hunger”, and poses a serious threat to human nutrition. Thus, understanding the mechanism of high CO2-induced decline of Zn level in grain, especially endosperm, in response to high CO2 concentration and its manipulation becomes an urgent issue. The growth chamber facilities with natural light and the free-air gas concentration enrichment (FACE) system for CO2 fumigation will be used. Firstly, the genotypic variation in rice grain Zn concentration and bioavailability in response to elevated CO2 concentration will be investigated, the contrasting genotypes will be selected for the following studies. Secondly, the physiological mechanisms responsible for Zn concentration decline under elevated CO2 concentration will be studied through examining the key physiological processes determining Zn transport efficiency in xylem, including plant transpiration, xylem sap flow rate and components change. The dynamics of Zn translocate into and distribute in rice endosperm during grain development will be traced by the LA-ICP-MS, facilitated by using stable Zn isotope and ear culture technique. Thirdly，the multi-factor design will be applied to study the influence of changing cultivation measures on Zn concentration and bioavailability in endosperm of rice grain, and find effective agronomical approaches for rice biofortification under elevated CO2 environment. The results of this research will provide new information for understanding physiological mechanism and its regulation for CO2-induced deterioration in rice zinc nutrition, and provide a scientific basis for effectively resolving the problem of human Zn deficiency.

持续增高的大气CO2浓度使主要粮食作物食用部位锌浓度及其有效性普遍下降，这将使更多人口置于“隐性饥饿”的风险之中，给人类营养造成严重威胁。因此，破解高CO2浓度环境中籽粒特别是胚乳锌营养的变劣机理及其调控途径成为急需解决的重要课题。利用开放式CO2熏蒸平台结合人工气候室，首先研明高CO2浓度对水稻籽粒锌浓度及有效性影响的基因型差异；然后选用代表品种，通过离体穗培养、锌稳定同位素与激光剥蚀电感耦合等离子体质谱仪联用技术，动态追踪灌浆期锌进入籽粒胚乳的路径，结合植株蒸腾、锌在木质部的转运等关键生理过程的变化，揭示水稻胚乳锌浓度对高CO2浓度的响应机制；最后设置多因子互作试验，研究改变栽培措施对水稻胚乳锌浓度和有效性的调节效应，探索高CO2浓度环境下胚乳锌生物强化的农艺途径。这一研究有望在高CO2浓度引发主食锌营养变劣的机制及其对策方面取得新认识，从而为有效解决人类锌营养缺乏问题提供科学依据。

人类微量元素锌缺乏是非常突出的公众健康问题，而这主要与水稻等主要粮食作物籽粒中锌浓度较低有关，因此明确不断升高的大气CO2浓度对稻米锌营养的影响对未来粮食安全至关重要。本项目利用根系生长不受限制的大田FACE平台，模拟本世纪中叶的大气CO2浓度，重点研究不同水稻品种籽粒锌浓度与有效性对CO2的响应及其可能原因。高CO2浓度环境下稻米氮和硫浓度表现为确定性下降，但稻米锌浓度的响应随条件变化而有较大变异，表现为减少、不变甚至略增的趋势。FACE研究表明，水稻籽粒锌浓度的这种变异受到供试品种、施氮水平、叶面锌肥配比甚至气候条件（阴晴天）的影响。例如，与肥料供应充足不同，缺氮水稻更易表现出锌浓度的下降。高CO2浓度环境下水稻叶片蒸腾减弱、光合下调以及植株氮浓度下降会减弱锌元素的转运，但根系生长增强和库容增大则有相反的趋势，稻米锌浓度的变化是这些因素共同作用的结果。稻米植酸含量与金属矿质元素的生物有效性密切相关。与糙米不同，高CO2浓度环境下精米部位的植酸浓度表现出明显增加的趋势（平均约5%），说明高CO2浓度下精米微量元素的生物有效性可能降低。另外，高CO2浓度环境下因叶片气孔部分关闭，水稻籽粒锌肥利用率显著下降，籼稻更为明显。结实早期叶面施锌处理使水稻特别是籼型水稻籽粒锌浓度和生物有效性显著增加，叶面锌肥中添加尿素有利于增加稻米的锌浓度。这些结果有助于增进我们对FACE水稻锌吸收和转运机理的理解，可为准确预测气候变化对稻作生产的影响以及制定适应对策提供参考。项目实施期间发表标注基金资助的相关论文18篇，其中SCI收录3篇、中文核心期刊论文11篇；另外，指导完成研究生毕业论文3篇。