Seedling drought stress susceptibility in two deciduous Nothofagus species of NW Patagonia

VARELA, S.A.; GYENGE, J.E.; FERNÁNDEZ, M.E.; SCHLICHTER T.

TREES-STRUCTURE AND FUNCTION

SPRINGER

Año: 2010 vol. 24 p. 443 - 453

0931-1890

The physiological capacities of seedlings to cope with drought may be subject to strong selectivepressure in the context of future climate scenarios, threatening the regeneration and sustainability of forests. Characterization of the responses and the variability between species is of interest to breeding and domestication programs. In this study, our main goal was to describe some ofthe physiological mechanisms involved in the drought response of Nothofagus nervosa and N. obliqua, two forest species of ecological and commercial importance (high wood quality) in NW Patagonia. We tested for differences in water status, gas exchange and survival in response to agradually imposed severe drought. Based on cavitation vulnerability curves and hydraulic conductivity measurements, we can conclude that N. obliqua stems have higher specific hydraulic conductivity and somewhat lower vulnerability to cavitation than N. nervosa stems, leading it tosustain higher stomatal conductance under non-severe drought conditions. N. obliqua had higher photosynthetic capacity than N. nervosa, due both to characteristics of its hydraulic architecture and to its higher metabolic capacity. Our results indicate that both species present characteristicsof plants susceptible to water stress. Also, both species showed behavior resembling an  anisohydric response. This behavior results from a lack of stomatal control over transpiration while the soil dehydrates, probably accompanied by very high vulnerability to cavitation. In contrast, both species had similar high stomatal sensitivity to vapor pressure deficit when soil water was limiting.