Vulnerability to drought-induced cavitation in poplars: synthesis and future opportunities.

Vulnerability to drought-induced cavitation is a key trait of plant water relations. Here, we summarize the available literature on vulnerability to drought-induced cavitation in poplars (Populus spp.), a genus of agronomic, ecological and scientific importance. Vulnerability curves and vulnerability parameters (including the water potential inducing 50% loss in hydraulic conductivity, P-50) were collected from 37 studies published between 1991 and 2014, covering a range of 10 species and 12 interspecific hybrid crosses. Results of our meta-analysis confirm that poplars are among the most vulnerable woody species to drought-induced cavitation (mean P-50=-1.44 and -1.55MPa across pure species and hybrids, respectively). Yet, significant variation occurs among species (P-50 range: 1.43MPa) and among hybrid crosses (P-50 range: 1.12MPa), within species and hybrid crosses (max. P-50 range reported: 0.8MPa) as well as in response to environmental factors including nitrogen fertilization, irradiance, temperature and drought (max. P-50 range reported: 0.75MPa). Potential implications and gaps in knowledge are discussed in the context of poplar cultivation, species adaptation and climate modifications. We suggest that poplars represent a valuable model for studies on drought-induced cavitation, especially to elucidate the genetic and molecular basis of cavitation resistance in Angiosperms. Over the last 25 years our knowledge with regard to the anatomical, physiological and ecological aspects of vulnerability to cavitation has grown considerably. It is now clear that vulnerability to drought-induced cavitation is a key trait of plant water-relations. As poplars (Populus spp.) are among the fastest growing temperate hardwood trees and high water consumers, they are particularly sensitive to water limitations and to drought induced cavitation. The Populus genus has therefore been studied quite intensively. In our review contribution we review and synthesize all the data published in the literature since 1991 on drought induced cavitation in poplar. We discuss and analyse the literature data in terms of (i) genetic variations among and within pure species or hybrids, and (ii) acclimation in response to environmental factors (drought, nutrients, light...). We also link the observations from this comprehensive review with other anatomical and ecophysiological traits. Practical implications, actual gaps in knowledge and future research opportunities offered by poplar as a model tree are also presented.