Leaf gas exchange characteristics and water- and nitrogen-use efficiencies of dominant grass and tree species in a West African savanna
Leaf gas exchange characteristics and water- and nitrogen-use efficiencies of dominant grass and tree species in a West African savanna
复制标题
西非稀树草原主要草和树种的叶片气体交换特征以及水和氮的利用效率
作者：
G. Simioni;X. Le Roux;J. Gignoux;A. Walcroft
尽管叶子气体交换特性对于评估全球生态系统中的碳和水通量很重要，但对于稀树草原物种来说，此类信息却很少。在本研究中，对来自西非兰托（科特迪瓦）稀树草原的 2 种 C4 草种（Andropogon canaliculatus 和 Hyparrhenia Diplandra）和 2 种 C3 树种（Crossopteryx febrifuga 和 Cussonia arborea）的气体交换特性进行了实地研究。进行测量是为了提供数据，以便对基于生化的光合作用模型（针对 C4 和 C3 植物代谢类型）和气孔导度进行参数化；并比较共存物种的气体交换特性。在标准环境条件下，草类和树种之间没有发现参考气孔导度或叶表面对入射光或蒸气压不足的气孔响应的系统差异。相反，禾本科植物表现出较高的水（1.5-2倍）和氮（2-5倍）光合利用效率（WUE和NUE，分别为净光合作用与蒸腾和叶片氮的比率）。这些对比归因于 C4 植物的 CO2 浓缩机制。当观察植物生命形式时，草种之间没有发现重要差异。然而，树种之间存在显着差异，Cussonia 比 Crossopteryx 表现出更高的 NUE 和参考气孔导度。这些结果强调在估计生态系统碳和水通量时需要考虑功能多样性。特别是，我们的结果表明，树/草比率以及树层的组成可能会强烈影响西非稀树草原生态系统规模的WUE和NUE。
Whereas leaf gas exchange properties are important to assess carbon and water fluxes in ecosystems worldwide, information of this type is scarce for savanna species. In this study, gas exchange characteristics of 2 C4 grass species (Andropogon canaliculatus and Hyparrhenia diplandra) and 2 C3 tree species (Crossopteryx febrifuga and Cussonia arborea) from the West-African savanna of Lamto (Ivory Coast) were investigated in the field. Measurements were done in order to provide data to allow the parameterization of biochemically-based models of photosynthesis (for C4 and C3 plant metabolic types) and stomatal conductance ; and to compare gas exchange characteristics of coexisting species. No systematic difference was found between grass and tree species for reference stomatal conductance, under standard environmental conditions, or stomatal response to incident light or vapour pressure deficit at leaf surface. Conversely, grass species displayed higher water (1.5-2 fold) and nitrogen (2-5 fold) photosynthetic use efficiencies (WUE and NUE, ratio of net photosynthesis to transpiration and leaf nitrogen, respectively). These contrasts were attributed to the CO2 concentrating mechanism of C4 plants. When looking within plant life forms, no important difference was found between grass species. However, significant contrasts were found between tree species, Cussonia showing higher NUE and reference stomatal conductance than Crossopteryx. These results stress the need to account for functional diversity when estimating ecosystem carbon and water fluxes. In particular, our results suggest that the tree/grass ratio, and also the composition of the tree layer, could strongly affect WUE and NUE at the ecosystem scale in West African savannas.