C02浓度倍增对干旱胁迫下黄瓜幼苗光合特性的影响

摘要

[目的]探讨黄瓜幼苗对C02浓度倍增和干旱胁迫的光合响应机理.[方法]以'津优1号'黄瓜水培幼苗为试材,采用裂区设计,主区设大气C02浓度(约380 μmol·μmo(-1))和倍增C02浓度(760±20 μmol·mol(-1))2个C02浓度处理,裂区设对照、中度和重度干旱胁迫3个水分处理,研究C02浓度倍增对干旱胁迫下黄瓜幼苗光合特性的影响.[结果](1)干旱胁迫显著降低了黄瓜幼苗叶片净光合速率(Pn ),蒸腾速率(Tr)和气孔导度(Gs ).在干旱胁迫条件下,C02浓度倍增可显著降低Tr和Gs、显著提高Pn,从而显著提高水分利用效率(WUE),而且C02浓度与干早胁迫对黄瓜幼苗叶片的Pn,Tr,WUE和Gs均有显著的互作效应(P＜0.01);(2)干旱胁迫显著降低了黄瓜幼苗叶片表观量子效率(AQY)、最大同化速率(Amax)、最大竣化速率(Vcmax)、光饱和的电子传递速率(Jmax).磷酸丙搪利用率(TPU)和光饱和点(LSP),提高了光补偿点(LCP).C02浓度倍增能显著提高对照和中度干旱胁迫条件下的AQY和Amax,在重度干旱胁迫条件下差异不显著.C02浓度倍增可显著提高对照条件下的Vcmax、max-和TPU,降低C02补偿点(Γ*)和呼吸速率(Rd ),而在干旱胁迫条件下各项指标之间差异不显著(中度干旱胁迫条件下Γ*显著降低4.9%除外).[结论]中度干旱胁迫条件下黄瓜叶片Pn的降低主要是气孔限制,而重度干旱胁迫条件下则是气孔和非气孔因素共同作用的结果,干旱胁迫可导致黄瓜幼苗光合电子传递和光合磷酸化能力显著降低;C02浓度倍增可通过提高黄瓜叶片的净光合速率和降低蒸腾速率来提高干旱胁迫条件下叶片水分利用效率,在适度的干旱胁迫条件下,C02浓度倍增也可以通过提高叶片表观量子效率和光饱和的最大同化速率而提高光合性能.因此,推测在干旱或半干旱地区,设施C02施肥技术或未来逐渐升高的大气C02浓度可在一定程度上改善作物的水分状况和增强抗旱能力,提高水分利用效率,从而部分缓解干旱胁迫引起的负面效应.%[Objective] The purpose of this study is to explore the photosynthetic response and mechanism of cucumber seedlings to double CO2 concentration combined with drought stresses.[Method] Using split plot design, the effects of doubled CO2 concentration on photosynthesis of cucumber (Cucumis sativus L. ‘Jinyou No. 1 ’) seedlings under drought stresses were investigated.The main plot was two CO2 concentrations (ambient CO2 concentration, ≈380 μmol·mol-1, and doubled CO2 concentration, 760±20 μmol·mol-1), and the split-plot was three water treatments (control, moderate drought stress and severe drought stress) simulated by PEG 6000. [Result] Drought stresses remarkably reduced net photosynthetic rate, transpiration rate and stomatal conductance of leaves of cucumber seedlings. Under the condition of doubled CO2 concentration, net photosynthetic rate dramatically increased while transpiration rate and stomatal conductance decreased, thereby water use efficiency dramatically increased. The interact effects of doubled CO2 concentration and drought stress on net photosynthetic rate, transpiration rate, water use efficiency as well as stomatal conductance were all significant (P＜0.01). Drought stresses significantly reduced apparent quantum efficiency, maximum assimilation rate, maximum rate of carboxylation by Rubisco, PAR-saturated rate of electron transport, rate of triose phosphate utilization and light saturated points of leaves of cucumber seedlings, but enhanced light compensatory points. Under control and mild drought stress conditions, doubled CO2 concentration dramatically improved apparent quantum efficiency and maximum assimilation rate, but there were no significant differences under severe drought stress. Under control condition, doubled CO2 concentration dramatically enhanced maximum rate of carboxylation by Rubisco, PAR-saturated rate of electron transport and rate of triose phosphate utilization, but reduced CO2 compensatory points and respiration rate, there were no significant differences under drought stresses except CO2 compensatory points reduced by 4.9％ under moderate drought stress. [ Conclusion ] The decrease of net photosynthesis under moderate drought stress was due to stoma restriction, while it was due to stoma and non-stoma combined restriction under severe drought stress. Drought stresses resulted in dramatic decline of photosynthetic electron transport and photophosphorylation capacity of cucumber seedlings. Doubled CO2 concentration improved water use efficiency of cucumber seedlings by improving net photosynthetic rate and reducing transpiration rate, and improved apparent quantum efficiency and CO2 assimilation maximum of cucumber seedlings under moderate drought stress condition to meliorate photosynthetic capacity.Therefore, it is speculated that in arid or semi-arid areas, CO2 fertilization in protected agriculture or rising atmospheric CO2 concentration in future could meliorate plant water status, enhance drought resistance ability and improve water use efficiency to some extent, subsequently alleviate the negative effect of drought stresses.