Leaf and whole-plant water relations of the Patagonian conifer Austrocedrus chilensis (D. Don) Pic. Ser. et Bizzarri: implications on its drought resistance capacity

Abstract

-Physiological studies have suggested that A. chilensis would survive during drought avoiding water stress through an early stomatal closure. However, there are no studies that have explored other potential mechanisms related to drought resistance or avoidance. The objectives were: (1) to measure hydraulic resistance, vulnerability to cavitation and leaf water relations, and (2) to compare these characteristics between different provenances. Pressure-volume curves demonstrate that A. chilensis has high osmotic potentials at full turgor, high water potentials at turgor loss point, low modulus of elasticity, and did not present elastic or osmotic adjustments after drought. Compared to other gymnosperms, A. chilensis has a high total plant resistance but also a high vulnerability to cavitation. We found no differences between the studied provenances in these variables. Our results confirm that A. chilensis is a drought-avoidance species, and suggest that phenotypic morphological differentiation between populations allows the species to survive throughout its broad distribution.pressure-volume curves / xylem cavitation / stomatal conductance / drought avoidance / water stress Résumé -Relations hydriques au niveau de la feuille et du plant chez un conifère de Patagonie Austrocedrus chilensis (D. Don) Pic. Ser. et Bizzarri: implications pour sa capacité à résister à la sécheresse. Des études physiologiques suggèrent que l'Austrocedrus chilensis peut survivre aux périodes de sécheresse évitant le stress hydrique grâce à une fermeture stomatique précoce. Cependant, il n'y a pas d'étude qui eut exploré d'autres mécanismes potentiels liés à la résistance ou à l'évitement de la sécheresse. Les objectifs de ce travail ont été : (1) mesurer la résistance hydraulique, la vulnérabilité à la cavitation et les relations hydriques des feuilles et (2) comparer ces caractéristiques avec celles des populations de différentes provenances. Les courbes pression-volume ont démontré que l'Austrocedrus chilensis possède un potentiel osmotique élevé à pleine turgescence, un potentiel hydrique au point de perte de turgescence, un module d'élasticité bas et qu'il ne présente pas de réglage élastique ou osmotique après la sécheresse. En comparaison avec d'autres gymnospermes, l'Austrocedrus chilensis a une résistance totale élevée mais aussi une importantee vulnérabilité à la cavitation. Nous n'avons pas trouvé de différences significatives entre les provenances étudiées dans ces variables. Nos résultats confirment que l'Austrocedrus chilensis est une espèce qui évite la sécheresse, et ils suggèrent que les changements phénotypiques entre populations permettent à cette espèce de survivre dans sa vaste distribution. courbes pression-volume / cavitation du xylème / conductance stomatique / évitement de la sécheresse / tension hydrique

Influence of radiation and drought on gas exchange of Austrocedrus chilensis seedlings

“…However, the low but positive rates of photosynthesis at low stomatal conductances are similar to data reported for several Cedrus and Quercus species (Epron 1997, Fotelli et al 2000, two Mediterranean species able to survive during periodic droughts. Hydraulic resistance measured in whole plants and their compounds showed that the main resistance to water flow in A. chilensis is located at the leaf level (Gyenge et al 2005). Based on these results, it appears that the strategy of A. chilensis seedlings is to sustain favorable water conditions during a drought, by maintaining relatively high water potential by means of an early stomata closure (desiccation avoidance response).…”

“…In addition, high radiation and temperature could damage photosynthetic apparatus when stomata are closed (Epron 1997). Gyenge et al (2005) found that seedlings of A. chilensis had high total plant resistance, with more than 70% of their water hydraulic resistance placed at leaf level. These could imply a low capacity to transport water from the soil to the leaf.…”

The successional status of tropical rainforest tree species is associated with differences in leaf carbon isotope discrimination and functional traits

“…Several studies demonstrated ontogenetic shifts for functional traits such as biomass allocation, SLA or A for tropical [36,43,53] or temperate (e.g. [11]) species, whereas no such shift was observed for hydraulic traits for Patagonian conifers [27]. Our results support the statement that among species differences in the metabolic intrinsic set point for the trade-off between carbon and water fluxes at the leaf level, as reflected by ∆ [13], are maintained over the lifetime of these species.…”

Drought conditioning improves water status, stomatal conductance and survival ofEucalyptus globulussubsp. bicostataseedlings

“…But sometimes, species with a broad geographical distribution does not show physiological variability [17]. Differences in the osmotic adjustment capacity were observed among provenances of several Eucalyptus [25,42], between and within subspecies of E. globulus [15,54], as well as among clones of E. globulus subsp.…”