Variations in the intrinsic water-use efficiency of north Patagonian forests under a present climate change scenario: tree age, site conditions and long-term environmental effects

HELLE, G; HADAD, M A; ARCO MOLINA, J G; ROIG, F A

TREE PHYSIOLOGY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2018

0829-318X

The δ13C signatures in tree-rings were used to track the intrinsic water-use efficiency (iWUE) in old-growth forests of northern Patagonia distributed in a strong gradient of regional precipitation. It is well known that climatic changes in general affect growth performance and physiology of trees but variations in iWUE can also be an indicator of the local conditions, tree ontogeny or both. In this sense, the main objective of this study was to assess the physiological responses of young and adult trees from two open xeric and two moderately dense mesic A. araucana forests to the atmospheric CO2 concentration (Ca) increase and climate changes during the 20th century, and their correlate with tree productivity. The results indicated that the iWUE increased 33% in average during the last century, but tree responses strongly depended on ontogenetic, local and geographical characteristics. Trees from xeric sites presented greater iWUE and lower 13C discrimination (Δ13C) and intercellular CO2 concentration (Ci) values than from mesic ones (Fig. 4). Moreover, iWUE and Δ13C from mesic sites seemed to be mainly affected by temperature and light conditions, while trees from xeric condition appeared to be more affected by other factors, such as precipitation. Adult trees presented higher iWUE values than young trees, indicating that processes related to tree age and/or height induce different responses, mainly in mesic forests. Moreover, some trees presented positive relationships between iWUE and tree growth, while others presented negative or neutral relationships, indicating that other factors negatively influenced tree productivity. Due to the heterogeneous tree responses, more studies are needed to better understand which individuals will be more committed in their growth and development in face to future climate changes and consequently to hypothesize which role the A. araucana old-growth forests would play in the global change.