Poor acclimation to current drier climate of the long-lived tree species Fitzroya cupressoides in the temperate rainforest of southern Chile

Climate change and rising atmospheric CO2 concentrations (ca) are expected to affect forests worldwide. The effects of climate change, however, have not been deeply assessed in humid forest biomes from the southern Hemisphere where climate is not warming but drying. This is the case of the temperate rainforest in southern Chile, where the endemic and threatened long-living gymnosperm Fitzroya cupressoides occurs. We assessed how radial growth, intrinsic water-use efficiency (iWUE) and tree-ring δ18O responded to increasing ca and decreasing precipitation in F. cupressoides and companion species. We hypothesized that F. cupressoides, a long-lived and probably less plastic species, will show less acclimation to global-change effects than co-occurring Nothofagus species which show broader climatic niche. Thus, F. cupressoides should display iWUE increases different from the ci/ca constant scenario, which represents an active mechanism to increase intercellular CO2 concentrations (ci) as ca rises. Although cool and wet conditions during the growing season enhanced growth of all species, particularly in F. cupressoides, growth of F. cupressoides declined noticeably since the 1980s in response to a decrease in precipitation. Current drier conditions led to increased iWUE in Nothofagus species. According to δ18O values, this increased in iWUE should be due to a decrease in stomatal conductance. Fitzroya cupressoides, however, displayed a decrease in iWUE in response to drier conditions, shifting from an active ci/ca scenario to a more passive ci/ca scenario, and maintaining a relatively constant stomatal conductance. Using multiple bodies of evidence, our findings indicate a poor adaptability of the long-lived F. cupessoides to drier conditions despite rising ca. Thus, not all species are having similar and expected responses to increasing ca, which should be a call of attention in the case of long-lived, endangered and narrow-distributed species, like F. cupressoides.