Effects of drought stress on gas exchange characteristics and protective enzyme activities in Elaeagnus angustifolia and Grewia.biloba G.Don var.parviflora seedlings
摘 要 ：以沙枣和孩儿拳头2年生盆栽苗为材料，采用称重控水的方法设置4个土壤含水量梯度（CK、T1、T2、T3），研究不同干旱胁迫对沙枣和孩儿拳头气体交换特征与保护酶的影响。结果显示：（1）干旱胁迫不仅引起两物种净光合速率、蒸腾速率、气孔导度、胞间 CO2 浓度的下降，而且使其日变化曲线在一定程度上发生改变；在轻度（T1）和中度胁迫（T2）下，两物种净光合速率下降主要是由气孔因素引起的，重度胁迫（T3）下，净光合速率下降主要是非气孔因素引起的。（2）随着干旱胁迫增加，沙枣瞬时水分利用效率呈现增加-下降-再增加趋势，孩儿拳头呈现下降趋势；两物种表观光能利用效率显著下降，重度胁迫下（T3），下降率达50%左右，孩儿拳头表观光能利用效率对干旱胁迫比较敏感；两物种表观CO2利用效率总体呈现下降趋势，沙枣表观CO2利用效率日进程经历了单峰（T1）、双峰（T2）、单峰（T3）的变化，孩儿拳头各处理的表观CO2利用效率日变化均呈现单峰曲线。（3）随着干旱胁迫加剧，两物种叶片的超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）活性先升高后降低，土壤含水量高于12.8%时，两物种SOD酶活性均高于CK，随着土壤含水量的降低，SOD酶活性低于CK；重度胁迫下（T3），沙枣POD酶活性虽然有所下降，但仍高于CK，而孩儿拳头则和CK无显著差异；两物种CAT酶活性在重度胁迫下（T3）显著低于CK；随着干旱胁迫程度的增加，两物种叶片中的丙二醛（MDA）含量均呈现升高趋势，孩儿拳头脂质过氧化程度受干旱胁迫的影响较大。
Abstract:Using E. angustifolia and G.biloba G.Don var.parviflora 2-year-old seedlings, the effects of drought stress on gas exchange and protective enzyme activities were conducted. Four treatments were arranged: control (CK), light drought (T1), moderate drought (T2) and heavy drought (T3). Results showed drought stress not only caused the decline of net photosynthesis rate, transpiration rate, stomatal conductance and intercellular CO2 concentation of two species, but also changed the diurnal pattern to a certain extent. Under light and moderate stress, the decline of net photosynthetic rate of two species was caused by stomatal factors, however, under heavy stress, this mainly by non-stomatal factors.Instantaneous water use efficiency of E. angustifolia showed the tendency of increase -decrease-increase, but G.biloba G.Don var.parviflora always decreased. Apparent light use efficiency of two species decreased by 50%. Apparent light use efficiency of G.biloba G.Don var.parviflora was more sensitive to drought stress. The changing tendency of apparent CO2 use efficiency of two species decreased. The diurnal pattern of apparent CO2 use efficiency of E. angustifolia shifted from a single-peaked curve(T1) to a double-peaked curve(T2),then a single-peaked curve (T3), while it always showed single-peaked curve in G.biloba G.Don var.parviflora. With the drought stress increasing, the activity of superoxide dismutase(SOD), peroxidase(POD), catalase(CAT)of two species first increased and then decreased. When the content of soil moisture was above 128%, the activity of SOD of the two species was higher than that in CK. With soil water content decreasing, the activity of SOD of the two species was lower than CK. Under heavy stress, although the activity of POD in E. angustifolia decreased, it was still higher than CK, but no significant difference was observed between T3 and CK in G.biloba G.Don var.parviflora.The activity of CAT of two species was significantly lower than CK under heavy stress. With the drought stress increasing, the content of malondialdehyde(MDA) of two species in the leaves increased. and the lipid peroxidation of G.biloba G.Don var.parviflora was more impacted by drought stress.