Elevated temperature altered the reaction norms of stomatal conductance in field-grown grapevine

• DOI: 10.1016/j.agrformet.2012.06.005
• Publication Date: 2012-08-09T13:00:19Z
• Authors: V.O. Sadras; A. Montoro; M.A. Moran; P.J. Aphalo
• Keywords: Stomatal Conductance; Water Use Efficiency

Abstract We measured the effect of elevated temperature, and its interaction with fruit load (exp. 1) and water supply (exp. 2), on the stomatal conductance (gs) of Vitis vinifera, cv. Shiraz. Thermal regimes (control vs. elevated temperature using open-top chambers) were initiated in spring, thus affecting leaf development, and were maintained during the whole growing season. We used a top-down approach where reaction norms were derived that relate gs for each treatment and the mean gs across treatments; the slopes of reaction norms quantify phenotypic plasticity. Stomatal conductance responded to neither the interaction between temperature and fruit load (P = 0.37) nor the interaction between temperature and water regime (P = 0.33). We therefore dealt with each factor separately. Reaction norms of gs under elevated temperature and control treatments diverged, i.e. elevated temperature had no effect on gs under conditions conducive to low conductance (below ∼100 mmol m−2 s−1) but increased gs in relation to controls under conditions favouring high conductance. Stomata density was 159 ± 6.7 mm−2, and was unaffected by temperature. Stomata length increased from 20.6 μm in controls to 23.2 μm in the heated treatment (P We conclude that the responses of stomata derived from transient temperature treatments in fully expanded leaves are unsuitable to model the dynamics of gas exchange in response to projected warming. Our experiments support a conceptual model where current stomatal conductance is a function of (i) the prevailing environmental conditions during early stages of leaf development that set the upper limit of conductance through the modulation of stomatal density and size, (ii) the current environmental conditions and (iii) the source:sink ratio.