Sellin Arne, Niglas Aigar, Õunapuu-Pikas Eele, Kupper Priit
Institute of Ecology and Earth Sciences, University of Tartu, Lai 40, Tartu 51005, Estonia.
BMC Plant Biol. 2014 Mar 24;14:72. doi: 10.1186/1471-2229-14-72.
Effects of water deficit on plant water status, gas exchange and hydraulic conductance were investigated in Betula pendula under artificially manipulated air humidity in Eastern Estonia. The study was aimed to broaden an understanding of the ability of trees to acclimate with the increasing atmospheric humidity predicted for northern Europe. Rapidly-induced water deficit was imposed by dehydrating cut branches in open-air conditions; long-term water deficit was generated by seasonal drought.
The rapid water deficit quantified by leaf (ΨL) and branch water potentials (ΨB) had a significant (P < 0.001) effect on gas exchange parameters, while inclusion of ΨB in models resulted in a considerably better fit than those including ΨL, which supports the idea that stomatal openness is regulated to prevent stem rather than leaf xylem dysfunction. Under moderate water deficit (ΨL≥-1.55 MPa), leaf conductance to water vapour (gL), transpiration rate and leaf hydraulic conductance (KL) were higher (P < 0.05) and leaf temperature lower in trees grown in elevated air humidity (H treatment) than in control trees (C treatment). Under severe water deficit (ΨL<-1.55 MPa), the treatments showed no difference. The humidification manipulation influenced most of the studied characteristics, while the effect was to a great extent realized through changes in soil water availability, i.e. due to higher soil water potential in H treatment. Two functional characteristics (gL, KL) exhibited higher (P < 0.05) sensitivity to water deficit in trees grown under increased air humidity.
The experiment supported the hypothesis that physiological traits in trees acclimated to higher air humidity exhibit higher sensitivity to rapid water deficit with respect to two characteristics - leaf conductance to water vapour and leaf hydraulic conductance. Disproportionate changes in sensitivity of stomatal versus leaf hydraulic conductance to water deficit will impose greater risk of desiccation-induced hydraulic dysfunction on the plants, grown under high atmospheric humidity, in case of sudden weather fluctuations, and might represent a potential threat in hemiboreal forest ecosystems. There is no trade-off between plant hydraulic capacity and photosynthetic water-use efficiency on short time scale.
在爱沙尼亚东部，通过人工控制空气湿度，研究了水分亏缺对欧洲白桦植物水分状况、气体交换和水力传导率的影响。该研究旨在加深对树木适应北欧预计增加的大气湿度能力的理解。通过在露天条件下使剪下的树枝脱水来造成快速诱导的水分亏缺；通过季节性干旱产生长期水分亏缺。
由叶片（ΨL）和树枝水势（ΨB）量化的快速水分亏缺对气体交换参数有显著（P < 0.001）影响，而在模型中纳入ΨB比纳入ΨL能得到更好的拟合效果，这支持了气孔开度受调节以防止茎而非叶木质部功能障碍的观点。在中度水分亏缺（ΨL≥ -1.55 MPa）下，与对照树（C处理）相比，生长在高空气湿度（H处理）环境中的树木，其叶片水汽导度（gL）、蒸腾速率和叶片水力传导率（KL）更高（P < 0.05），叶片温度更低。在严重水分亏缺（ΨL < -1.55 MPa）下，各处理间无差异。增湿处理影响了大部分研究特征，而这种影响在很大程度上是通过土壤水分有效性的变化实现的，即由于H处理中土壤水势较高。两个功能特征（gL、KL）在生长于增加空气湿度环境中的树木中对水分亏缺表现出更高（P < 0.05）的敏感性。
该实验支持了以下假设：适应较高空气湿度的树木生理特征在叶片水汽导度和叶片水力传导率这两个特征方面对快速水分亏缺表现出更高的敏感性。气孔导度与叶片水力传导率对水分亏缺的敏感性变化不均衡，在天气突然波动时，对于生长在高大气湿度环境下的植物，会使其因干燥诱导的水力功能障碍面临更大风险，这可能对半寒带森林生态系统构成潜在威胁。在短时间尺度上，植物水力能力与光合水分利用效率之间不存在权衡关系。
