叶片光合生理参数变化特征与小麦受旱状态的关系

以小麦为供试作物布设干旱过程试验,研究干旱过程中小麦叶片光合生理参数(包括净光合速率(Pn)、气孔导度(g_(ssat))、胞间CO_2与空气CO_2浓度比(Ci/Ca)、最大羧化速率(Vc_(max))以及最大电子传递速率(J_(max)))的变化特征,并探讨干旱不同阶段Pn与g_(ssat)的关系及其对气孔导度模型斜率的影响。结果表明:土壤有效含水量(ASWC)较大时(0.5),即水分供给充足条件下,小麦叶片光合生理参数随着ASWC的减少保持相对稳定;而当ASWC降至0.5时,g_(ssat)、Ci/Ca以及Pn减小,在ASWC0.3时,Pn与g_(ssat)及Ci/Ca的关系保持相对稳定;当ASWC0.3时,g_(ssat)随ASWC减小呈显著降低趋势,Vc_(max)和J_(max)也在此阶段随ASWC减小而线性降低,而Pn随g_(ssat)的减小降幅明显增大,拟合所获得的气孔导度模型斜率也随之发生改变;当ASWC0.1时,Ci/Ca随ASWC减小呈增大趋势,而Pn随ASWC减小而减小,在该阶段,Ci/Ca与Pn呈相反的变化趋势。根据叶片光合生理参数的变化特征,可将小麦受旱过程划分为4个阶段,即无干旱胁迫或干旱胁迫较轻的阶段、只有气孔因素影响光合生理过程的阶段、非气孔因素和气孔因素同时影响光合生理过程的阶段以及光合器官遭受损坏的阶段。

Relationship between drought severity and leaf photosynthetic physiological parameter variation of spring wheat

Quantifying drought severity plays critical role in agricultural drought monitoring, crop modeling and irrigation scheduling. In this study, dry\|down experiments for spring wheat were carried out in plots and buckets. The responses of several photosynthetic parameters, including net photosynthesis (Pn), stomatal conductance (g_ssat), ratio of intercellular CO₂ to atmospheric CO₂ (Ci/Ca), maximum carboxylation rate of Rubisco (Vc_max) and maximum rate of electron transport (J_max), to water supply condition were analyzed. Meanwhile, the relations between different photosynthetic parameters under different water conditions were also determined, especially the relationship between Pn and gssat and the impacts of drought on parameters for three typical semi\|empirical stomatal conductance models. The results showed that there were no significantly variation for the photosynthetic parameters until available soil water content (ASWC) was less than 0.5. The parameters gssat, Ci/Ca and Pn sequentially decreased as ASWC decreased from 0.5 to 0.3. The relation of Pn, gssat and Ci/Ca were stable while ASWC ranged from 0.5 to 0.3. The parameters gssat, Vc_max and Jmax decreased in linear form with ASWC when ASWC was less than 0.3. Meanwhile, the relationship between Pn and g_ssat changed in the range of ASWC from 0.5 to 0.3, hence the slope of semi\|empirical stomatal conductance model. However, when ASWC was smaller than 0.1, Ci/Ca increased with ASWC, and Pn decreased as Ci/Ca increased. Based on the responses of different photosynthetic parameters to water supply condition, four stages of drought development for spring wheat apparently existed. As ASWC was greater than 0.5 and gssat greater than 0.35 mol·m^-2·s^-1, there was not drought or drought was very slight. The gssat mainly limited Pn during ASWC ranged from 0.3 to 0.5 and gssat varied from 0.15 to 0.35 mol·m^-2·s^-1. However, non\|stomatal conductance started to impact Pn as ASWC changed from 0.1 to 0.3 (gssat ranged from 0.06 to 0.15 mol·m^-2·s^-1). As ASWC was less than 0.1, g_ssat was smaller than 0.06 mol·m^-2·s^-1 and the apparatus for photosynthesis might suffer injury.