高温期间水分对银杏光合作用和光化学效率的影响

Influence of Drought Stress on Photosynthesis and Photochemistry Efficiency in Leaves of Ginkgo biloba during High Temperature Days

对2年生盆栽银杏苗木试验设计了3种水分供应水平(分别相当于田间持水量的80%、40%和25%),研究高温期间水分对其光合作用和光化学效率的影响。结果表明,银杏叶片在快速脱水过程中,当叶片饱和水分亏缺(WSD)增加到25%之前,净光合速率(Pn)随着气孔导度(Gs)的快速下降而急剧下降,两者之间存在显著的线性相关关系(R2=0.816),而实际光化学效率(ΦPSⅡ)保持相对稳定。当WSD增加到25%以后,Pn和Gs都开始缓慢下降,但两者之间相关关系不显著(R2=0.152),ΦPSⅡ则开始快速下降。分析结果表明,WSD增加到25%之前Pn降低的主导因素是气孔限制,而WSD增加到25%之后Pn降低的主导因素是包括光化学活性限制在内的叶肉因素;长期干旱条件下,银杏叶片的光合活性、净光合速率、气孔导度和水分利用效率(WUE)都大幅下降,但Pn下降的主导因素并不在于因气孔因素引起的CO2供应能力的降低,而在于叶肉光合活性的降低;干旱还大大加剧了银杏的光合"午休"程度。

During the course of dehydration of Ginkgo biloba leaves, net photosynthetic rate(Pn), which has a significant correlation with stomatal conductance(Gs) (R2=0.816),went down sharply with the rapid decline of Gs until water saturation deficiency (WSD) up to 25%, whereas actual PSⅡ efficiency (ΦPSⅡ) only went down slightly. However, with further increase of WSD above 25%, Pn and Gs both decreased slowly and slightly and the correlation between them was insignificant (R2=0.152),while ΦPSⅡ descended rapidly and remarkably. Based on the analysis of such concerned parameters as stomatal limitation(Ls), inter cellular CO2 concentration (Ci) and ΦPSⅡ etc., the conclusion could be drawed that the main factor that led to drop of Pn lied in decline of Gs until WSD up to 25% but it lied in decline of photosynthetic activeness in leaves when WSD was above 25%. Under the longterm drought stress in soil, Pn, Gs and water use efficiency (WUE) in Ginkgo leaves went down remarkably. Regardless of Gs went down significantly under drought stress in soil, the decline of Pn did not lie in it but in the decline of photosynthetic activeness in leaves. Also, drought stress in soil led to more severe decline of Pn in midday in Ginkgo leaves.