COS 149-5 - CANCELLED - Tree species subjected to a rainfall exclusion experiment: Can they benefit from water availability reductions?

Abstract: Trees are the most long-lived plants on earth and play a crucial role in forest ecosystems. They are involved in every aspect of forest functionality, from carbon stock to water transition and species refuge. Nonetheless, forests and trees are threatened by global change. The consequences of global change can be observed in different woods and ecosystems worldwide. Among them, reductions in precipitation make forest ecosystems susceptible to novel climates that may affect their composition, structure, and persistence. Anticipating this scenario and its effects, in this research, we evaluated the acclimation of understory tree species of the temperate rainforest of Chiloé Island (southern Chile, 42°LS) submitted to an experimental precipitation reduction.

We hypothesized that individuals submitted to a precipitation reduction would acclimate to more conservative physiology and anatomy than trees that obtain natural water input. Thus, eight species, and a total of 96 individuals, were assessed concerning foliar and hydraulic traits. At the foliar level, we measured economic, anatomical, and physiological characteristics: mass-to-area ratio, nitrogen content, stomatal density, and δ13C. At the branch level, we built the hydraulic vulnerability curves of each species and estimated the P50, the water potential at which the xylem losses 50% of its conductivity.

Between the treatments, we found differences at the leaf level but not at the xylem level. Vulnerability curves showed no differences in shape and similar P50 among species in different treatments. Nevertheless, LMA presented differences between treatments but not between single species. Two species had significantly more stomata in the reference treatment than in the exclusion. Finally, treatment and species possess more negative δ13C in the reference than in the exclusion treatment. Together with this last result, nitrogen contents were also higher in the restricted precipitation treatment. Results are against our initial hypothesis, and we discuss them in light of these new outcomes and what they mean to these ecosystems in current times and forecasted precipitation shortages.

In conclusion, conservative physiology is not always the path tree species follow under reduced precipitation. Reductions predicted that would affect these ecosystems of southern South America. We want to acknowledge the Institute of Ecology and Biodiversity (Chile) through the National Agency of Research and Development (ANID) project FB210006 and ANID Doctoral Scholarship 2018 for financing and support.