Functional characteristics of the arborescent genus polylepis along a latitudinal gradient in the high andes

Résumé 0

Polylepis is a genus restricted to the Andean MountainRange, naturally occurring above the upper continuous forestlimit. The purpose of this work was to integrate and comparefunctional characteristics in terms of water and carbon relationsand low temperature resistance mechanisms in differentPolylepis species along a latitudinal gradient. The studiedspecies were P. sericea in Venezuela, P. tarapacana in Boliviaand P. australis in Argentina. Seasonal measurements of leafwater and osmotic potentials, stomatal conductance, CO2 assimilationand respiration rates, and injury and freezing temperatureswere compared. There is a gradient,in terms offunctional attributes, along the environmental range. P. tarapacanais the most tolerant species to water stress, while P. sericeaavoids the less harsh conditions of its habitat through osmoticadjustments and cell wall elasticity changes. Mean CO2assimilation rates were higher in P. australis (9μmol·m‑2·s‑1)campared to P. sericea (5μmol·m-2·s-1) and P. tarapacana(3·μmol·m-2·s-1). Mean night leaf respiration rates were similarfor all species (1-2·μmol·m-2·s-1). In terms of low temperatureresistance, P. sericea shows daily osmotic adjustments and amoderate supercooling capacity (-9ºC). The other two speciesrely on freezing tolerance in order to survive the moreextreme low temperature conditions. The functional attributesdescribed in this study for the different species in a wide environmentalrange may explain some aspects of their successalong the latitudinal and altitudinal gradients.