Staude, I. | bioRxiv Science

bioRxiv2026

Stomatal sensitivity to VPD across 38 tree species reflects past drought responses but is little explained by stomatal and leaf economic traits

Climate change is exposing trees to rising atmospheric water demand. Because stomata regulate plant water loss, understanding stomatal behaviour is critical. However, few comparative studies examine species-specific stomatal responses to atmospheric demand. Here, we quantify stomatal behaviour in 38 temperate tree species (27 broadleaved, 11 conifers) in a German research arboretum during a warm summer without soil drought. We measured the diurnal stomatal conductance (gs) of 787 leaves and modelled gs species-specific responses to leaf-to-air vapour pressure deficit (VPDL). Four descriptors of the gs-VPDL relationship were derived: maximum stomatal conductance (gmax), the VPDL that maximises gs, the VPDL associated with a 50% reduction in gs, and the stomatal closure rate. We relate these metrics to drought-induced shifts of carbon isotope ratios and to leaf functional traits. Large variation in stomatal behaviour exists, ranging from early-closure to VPDL-tolerant strategies. Species maintaining gs at higher VPDL also show weaker physiological responses to past drought. gmax is partly explained by leaf economic traits; other gs-VPDL descriptors are not related to stomatal anatomy and leaf economy. Our interspecific comparison reveals substantial variation in stomatal responses to atmospheric demand that is relevant to drought responses, but cannot be readily inferred from commonly measured leaf traits.

ecology↗

bioRxiv2025

The urban tree of life: quantifying relationships between body size and urban tolerance for more than 30,000 plant and animal species

Urbanization is a major global driver of biodiversity change, with species responses to urban settings ranging from avoidance to exploitation. To better understand these responses, we conducted a global analysis of urban relative affinity inferred from occurrence data across more than 30,000 animal and plant species. Our synthesis showed a consistent pattern across taxa and biogeographic regions: many species are urban avoiders, while few thrive as urban exploiters--a pattern we coin "Species Urbanness Distribution". We then assessed whether body size, an integrative ecological trait fundamental to space use, mobility, metabolism, and environmental sensitivity, showed consistent associations with urban affinity among species and across 371 taxonomic families. Analyses were conducted at the interspecific level and focused primarily on variation among taxonomic families (with an accompanying application to view results available here: https://globalecologyresearchgroup.github.io/body_size_results_visualization/). Larger body sizes were generally associated with greater urban affinity in plants compared to animals, though these size-affinity relationships showed considerable variability among families. Our findings highlight the heterogeneous relationship between body size and urban affinity across the tree of life, underscoring the importance of tailored strategies to support urban biodiversity. This research advances ecological understanding of urban filtering and provides a framework for guiding biodiversity-sensitive urban planning amid accelerating global urbanization.

ecology↗