Adaptation potential of Neotropical montane oaks to drought events: Wood anatomy sensitivity in Quercus delgadoana and Quercus meavei

Climate and local water availability are major evolutionary drivers of adaptive variation and plasticity in the hydraulic architecture of Tropical Montane Cloud Forest (TMCF) tree species. Between-year xylem vessel variability is key to understanding the adaptation potential of wood anatomy of trees to drought. How wood anatomical features have been influenced by the typical TMCF climate and how tree species persist in these environments remain open questions, particularly in the context of predicted extreme climate events in the future. Here, we evaluated the effects of changes in temperature, precipitation and evapotranspiration during drought events on ring-width and anatomical vessel traits (hydraulic diameter, vessel density, vessel grouping index and vulnerability index) for two relict endemic and threatened oak species (Quercus delgadoana and Q. meavei) from a Mexican TMCF. The study species differed in their functional and ecological vessel anatomical traits, and their wood anatomical differences are related to specific environmental requirements. However, the ring-width indices (RWIs) calculated for these species indicate that both have high resistance and recovery, and thus high resilience to drought events. Ring-width and vessel functional traits show differences in the between-year variability of xylem traits associated with the hydraulic efficiency of these oak species, which is crucial to understanding how they avoid drought-induced embolism and cavitation in vessel conduits. These results provide evidence for the existence of specific hydraulic systems that determine functional wood anatomy in response to climatic variation and drought in the study species. Further research assessing the wood anatomical adaptation to different climatic variables and identifying the xylem functional traits that underlie these adaptations, along with the mechanisms allowing tree species persistence in these environments, is essential to gain insight into the responses of TMCF to future drought events. Read the free Plain Language Summary for this article on the Journal blog.