Hawkesbury Institute for the Environment, Western Sydney University, Penrith NSW, Australia.
Lancaster Environment Centre, University of Lancaster, Lancaster, UK.
J Exp Bot. 2018 Apr 27;69(10):2731-2741. doi: 10.1093/jxb/ery095.
Atmospheric CO2 (ca) has increased since the last glacial period, increasing photosynthetic water use efficiency and improving plant productivity. Evolution of C4 photosynthesis at low ca led to decreased stomatal conductance (gs), which provided an advantage over C3 plants that may be reduced by rising ca. Using controlled environments, we determined how increasing ca affects C4 water use relative to C3 plants. Leaf gas exchange and mass per area (LMA) were measured for four C3 and four C4 annual, crop-related grasses at glacial (200 µmol mol-1), ambient (400 µmol mol-1), and super-ambient (640 µmol mol-1) ca. C4 plants had lower gs, which resulted in a water use efficiency advantage at all ca and was broadly consistent with slower stomatal responses to shade, indicating less pressure on leaf water status. At glacial ca, net CO2 assimilation and LMA were lower for C3 than for C4 leaves, and C3 and C4 grasses decreased leaf hydraulic conductance (Kleaf) similarly, but only C4 leaves decreased osmotic potential at turgor loss. Greater carbon availability in C4 leaves at glacial ca generated a different hydraulic adjustment relative to C3 plants. At current and future ca, C4 grasses have advantages over C3 grasses due to lower gs, lower stomatal sensitivity, and higher absolute water use efficiency.
大气中的二氧化碳（ca）自末次冰期以来一直在增加，提高了光合作用的水分利用效率并改善了植物的生产力。在低 ca 条件下，C4 光合作用的进化导致了气孔导度（gs）的降低，这使得 C4 植物相对于 C3 植物具有优势，而 ca 的增加可能会降低这种优势。我们利用受控环境，确定了 ca 的增加如何影响 C4 相对于 C3 植物的水分利用。我们在冰川（200 µmol mol-1）、环境（400 µmol mol-1）和超环境（640 µmol mol-1）ca 条件下，对四种 C3 和四种 C4 一年生作物相关草的叶片气体交换和比叶面积（LMA）进行了测量。C4 植物的 gs 较低，这使得它们在所有 ca 条件下都具有水分利用效率优势，并且与对遮荫的较慢气孔响应基本一致，表明对叶片水分状况的压力较小。在冰川 ca 条件下，C3 叶片的净 CO2 同化和 LMA 均低于 C4 叶片，C3 和 C4 草的叶片水力导度（Kleaf）下降幅度相似，但只有 C4 叶片的渗透势在膨压损失时下降。在冰川 ca 条件下，C4 叶片中较高的碳可用性导致了与 C3 植物不同的水力调节。在当前和未来的 ca 条件下，由于 gs 较低、气孔敏感性较低以及绝对水分利用效率较高，C4 草具有相对于 C3 草的优势。
