Stay wet or else: three ways in which plants can adjust hydraulically to their environment

PABLO H. MASEDA; ROBERTO. J. FERNANDEZ

JOURNAL OF EXPERIMENTAL BOTANY

Año: 2006 vol. 57 p. 3963 - 3977

0022-0957

We review the literature on whole-plant acclimation to drought and propose that leaf-level homeostasis in water status is attained during ontogeny largely thanks to whole-plant changes in physical resistance to liquid-water flow caused by morphological and anatomical adjustments. We show that, in response to water deficits, plant resistance changes at different levels (tissue, organ, individual), levels that are correlated with the time scale of the response. We found that such adjustments apparently tend to increase resistance to flow in the short term and to reduce it in the long term. We provide a critical view of those findings based on the principle that drought-induced changes cannot be analysed separately from the allometric changes that take place through ontogeny, as for example proposed by the widely-cited hydraulic limitation hypothesis. We present a graphic synthetic model according to which developmental responses to water deficits operate largely through reductions in whole-plant water-transport capacity, combined with more or less strong reductions in leaf area (different “hydraulic allometries”), depending on the intrinsic tolerance of leaf tissues to partial desiccation. We use the model to show that, as the result of such adjustments, the water-transport capacity per unit leaf area can decrease, remain constant, or increase, and argue that the expected leaf-level response would be different in each case, respectively involving a decreased, constant, or increased potential for transpiration. We end with a plea to collect the evidence needed to evaluate the occurrence of these three different response types across taxa and their association with different environments, including the reanalysis of existing data.