禾本科C3和C4植物水力特征及其进化生态位保守性研究

C4 grasses have higher water use efficiency than C3 grasses. However, debates still exist for whether C4 grasses have higher abilities in water uptake and transport than C3 grasses, and the hydraulic traits of stems and roots of Poaceae species remain much unknown. As different clades in Poaceae have different photosynthetic types and contrasting habitat water availability, such divergences suggest the influences of phylogeny on water related traits. If the hydraulic traits are similar among close related species (phylogenetic niche conservatism, PNC), they could be expanded within the same clade. This study is based on the phylogenetic trees, photosynthetic types of huge amounts of species in Poaceae, and a dataset of 548 Poaceae species in southern China. Natural habitat types of as many Poaceae species as possible will be investigated and collected, and about 30 species from 3~4 clades will be selected for drought treatment in the greenhouse. Plant hydraulic traits at cellular, tissue, organ and whole plants levels will be measured, so as to test all the parameters for PNC after building phylogenetic trees. The objectives of this proposal are: (1) to compare the hydraulic conductivity between C3 and C4 grasses, find their correlations and establish hydraulic models for them; (2) to carry out PNC tests and find out which hydraulic traits could be expanded to more species. This study will provide very important data for exploring the hydraulic regulating mechanisms of C3 and C4 plants under variable water conditions, predicting the responses of different clades to future changes in precipitation patterns, and for selecting drought tolerant species in Poaceae.

禾本科C4比C3植物的水分利用效率更高，但两者的水分吸收和运输能力 (根、茎、叶) 仍存在未知和争议。同时，禾本科不同起源类群的光合类型 (C3和C4) 和生境水分条件差异巨大，说明进化背景和水力特征相关。由于近缘物种的相似性 (进化生态位保守性，PNC)，若水力特征具有PNC则可推及同类群其他物种。因此本项目基于禾本科系统进化树、光合类型及华南地区禾本科植物基本资料，拟野外调查选取3~4个类群C3和C4共约30个代表物种进行温室干旱处理实验。通过测定整株植物、叶片、茎秆和根系的水力特征，(1) 研究C3和C4植物在不同器官、组织和细胞层面水力特征的差异和相关性，建立完整的C3和C4植物水力模型；(2) 进行PNC检验，找出可在禾本科内推广的水力特征指标。本项目可为探讨不同水分条件下C3和C4植物的水力调节机制、预测不同类群对未来降水格局改变的响应及禾本科耐旱物种的选育提供重要参考。

禾本科C4比C3植物的水分利用效率更高，但两者的水分吸收和运输能力 (根、茎、叶) 仍存在未知和争议。同时，禾本科不同起源类群的光合类型 (C3和C4) 和生境水分条件差异巨大，说明进化背景和水力特征相关。由于近缘物种的相似性 (进化生态位保守性，PNC)，若水力特征具有PNC则可推及同类群其他物种。因此本项目基于禾本科系统进化树、光合类型及华南地区禾本科植物基本资料，野外调查并选取了4个类群C3和C4共44个代表物种测定其整株、叶片和茎秆的水力特征，并进行温室干旱处理实验，研究它们的抗旱性，并进行进化生态位保守性分析。本研究发现：(1) 光合速率、气孔密度、叶脉密度、叶片大小、干物质含量和膨压丧失点具有很强的系统发育信号，叶片和茎秆的水力特征并没有很强的进化生态位保守性；(2) C3和C4草类水分运输和散失过程中的限制因子在叶片，且其水力调节机制受到进化背景的影响；(3) C3和C4草类虽然具有不同的进化历史和生境差异，它们应对干旱的策略并无明显差异，反而是种间差异显著；(4) 干旱实验发现耐旱性越弱的物种，其叶片气孔应对水气压亏缺越敏感，但是敏感性并不受进化背景和光合类型的影响，表明禾本科植物的水力调节机制取决于物种层面的结构和功能差异。本项目为探讨不同水分条件下C3和C4植物的水力调节机制、预测不同类群对未来降水格局改变的响应及禾本科耐旱物种的选育提供了重要参考。

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