Abstract
BackgroundEffects 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.ResultsThe 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.ConclusionsThe 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.
Highlights
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 strongest effects were observed for leaf conductance to water vapour and leaf water potential (ΨL), whereas leaf temperature
Except for leaf hydraulic conductance, KL, inclusion of ΨB into the analysis model resulted in a considerably better fit than inclusion of ΨL
Summary
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. Climate change scenarios predict by the end of the century increases in air temperature by 3.5– 5oC and precipitation by 5–30% in boreal and northern temperate regions of Europe [2,3]. Increase in atmospheric relative humidity (RH), the inevitable result of more frequent rainfall events, will reduce water loss through transpiration [4,5], and affect both the delivery of nutrients to root absorbing surface and nutrient uptake by trees due to diminished water fluxes through the vegetation [6,7]. Plants growing in humid air have less effective stomatal control over transpirational water loss [4,11,12] and demonstrate higher vulnerability to xylem cavitation, i.e. have narrow hydraulic safety margin [13,14]. Okamoto et al [15] demonstrated that high air humidity induces abscisic acid (ABA) 8′-hydroxylase in stomata and vasculature, followed by the reduction of ABA levels − a plant hormone, which promotes stomatal closure under water deficit [16]
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