Coordinated hydraulic traits predict the time to critical hydraulic failure in temperate broad-leaved and conifer tree species

Abstract

Temperate forests face increasing tree mortality from extreme droughts, highlighting the need to understand the mechanisms behind tree drought responses. While complex, these responses can be simplified into two distinct phases: a first phase that lasts until stomatal closure (tsc) and a second that extends until reaching lethal xylem hydraulic thresholds (tcrit). We conducted dry-down experiments on 8 temperate broad-leaved and 8 conifer species to estimate tsc and tcrit. We also measured various hydraulic traits, including water potentials at turgor loss point (Ptlp), stomatal closure (Pgs90), and 12%, 50%, and 88% loss of xylem hydraulic conductivity (P12, P50, P88), hydraulic capacitance, and minimum leaf and bark conductance (gmin, gbark). We then tested these traits in a dynamic model to predict tcrit based on functional traits. Our results indicate that tsc dominates the desiccation process and is closely associated to xylem vulnerability to embolism, while tcrit is influenced by water storage and residual conductance traits. Despite differences between conifers and broad-leaved species, our updated multi-trait model accurately predicted tcrit. We show that while drought-response coordination is too complex to be captured by a single-trait approach, it can be effectively described using a concise set of traits, an approach that may inform forest management under climate change.