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

Abstract

Austrocedrus chilensis is a conifer from Patagonia adapted to a wide moisture gradient. In xeric environments, its natural or artificial recruitment only occurs under nurse shrubs during normal rainfall years. In spite of its importance in ecological and economical terms, little information is available about the physiology of this species. Previous field measurements in experimental plantation revealed that seedlings without plant cover had lower survival, photosynthetic rates and predawn water potential than those planted under trees. So, the response of stomata to radiation and vapor pressure deficit, and the effect of drought stress on photosynthesis and transpiration of A. chilensis seedlings were studied under controlled conditions. Even when soil water was not limiting, all seedlings showed an early stomatal closure in response to moderate evaporative demand. Photosynthetic parameters and instantaneous water use efficiency suggested that microenvironments with intermediate shade are the best for A. chilensis CO2 uptake. We suggest that the early stomatal closure could result in damage in leaves or the base of the stem by oveheating, explaining low survival when grown without shade. As a whole, our results may contribute to understanding the need for nurse plants in the establishment of the species.