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

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

TREE PHYSIOLOGY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2019

0829-318X

The carbon isotope composition (δ13C) in tree rings were used to derive the intrinsic water-use efficiency (iWUE) of Araucaria ara-ucana trees of northern Patagonia along a strong precipitation gradient. It is well known that climatic and ontogenetic factorsaffect growth performance of this species but little is known about their influence in the physiological responses, as iWUE. Thus,the main objective of this study was to assess the physiological reactions of young and adult trees from two open xeric and twomoderately dense mesic A. araucana forests to the increases in atmospheric CO2 (Ca) and air temperature during the 20th cen-tury, and to relate these responses with radial tree growth. The results indicated that the iWUE and the intercellular CO2 concen-tration (Ci) increased 33% and 32% in average during the last century, respectively, but carbon isotope discrimination (Δ13C)was more variable between sites and age classes. Trees from xeric sites presented greater iWUE and lower Δ13C and Ci valuesthan those from mesic sites. In general, iWUE was strongly related with Ca and was significantly affected by mean summer max-imum temperature. Δ13C from mesic sites seemed to be mainly affected by summer maximum temperature, while trees from xericconditions did not show any influence. Tree age also presented a significant effect on iWUE. Adult trees showed higher iWUEvalues than young trees, indicating an incidence of the tree age and/or height, mainly in closed mesic forests. Moreover, sometrees presented positive relationships between iWUE and radial tree growth, while others presented negative or no relationships,indicating that other factors may negatively influence tree growth. Broadly, the results demonstrate the incidence of climatic,environmental and ontogenetic variability in the tree responses; however, more studies are needed to better understand whichforests will be more affected by actual and future climate changes.