Texas A&M University Agricultural Research and Extention Center, 1619 Garner Field Rd., 78801, Uvalde, TX, USA.
Photosynth Res. 1993 Oct;38(1):41-9. doi: 10.1007/BF00015060.
Single leaf photosynthesis (Pn) and stomatal conductance (Cg) of drought stressed and nonstressed pearl millet [Pennisetum americanum (L.) Leeke] were measured across growth stages to determine if a pattern exists in Pn and Cg during the growing season and to evaluate the influence of air vapor pressure deficit (VPDa) on the seasonal variations of Pn and Cg. Leaf photosynthesis and Cg were measured independently on pearl millet plants grown at the driest (drought stressed) and wettest (nonstressed) ends of a line-source irrigation gradient system. Well defined and predictable variations in both Pn and Cg were found across two growing seasons. Leaf photosynthesis of the nonstressed plants declined from a maximumof 25.8 μmol m(-2) s(-1) at the flag leaf emergence (48 days after planting, DAP) to a minimum of 14.5 μmol m(-2) s(-1) at physiological maturity. Stomatal conductance of the nonstressed plants peaked at the flowering and early grain fill stages and declined as plants approached maturity. In contrast, Pn and Cg of the stressed plants declined from a maximum at flag leaf emergence to a minimum at flowering and increased as plants approached maturity. High VPDa during the flowering and grain fill stages induced stomatal closure and decreased Pn in the stressed plants. High mid-season VPDa did not induce stomatal closure and did not reduce leaf photosynthesis in nonstressed plants. The lack of sensitivity of Pn to VPDa in the nonstressed treatment suggests large air VPD such as that prevalent in southern Arizona does not limit the growth of irrigated pearl millet by limiting CO2 assimilation.
对干旱胁迫和非胁迫条件下的珍珠粟（Pennisetum americanum（L.）Leeke）进行了整个生育期的单叶光合作用（Pn）和气孔导度（Cg）测量，以确定在生长季节中 Pn 和 Cg 是否存在模式，并评估空气蒸气压亏缺（VPDa）对 Pn 和 Cg 季节性变化的影响。在线源灌溉梯度系统的最干燥（干旱胁迫）和最湿润（非胁迫）端生长的珍珠粟植株上，分别独立测量叶片光合作用和 Cg。在两个生长季节中，均发现 Pn 和 Cg 存在明显且可预测的变化。非胁迫植株的叶片光合作用从旗叶出现（种植后 48 天，DAP）时的最大值 25.8 μmol m(-2) s(-1)下降到生理成熟时的最小值 14.5 μmol m(-2) s(-1)。非胁迫植株的气孔导度在开花和早期灌浆阶段达到峰值，并随着植株接近成熟而下降。相比之下，胁迫植株的 Pn 和 Cg 从旗叶出现时的最大值下降到开花时的最小值，并随着植株接近成熟而增加。开花和灌浆阶段高 VPDa 诱导气孔关闭，降低胁迫植株的 Pn。生长中期高 VPDa 不会诱导气孔关闭，也不会降低非胁迫植株的叶片光合作用。非胁迫处理中 Pn 对 VPDa 的不敏感性表明，像亚利桑那州南部那样普遍存在的高空气 VPD 不会通过限制 CO2 同化来限制灌溉珍珠粟的生长。
