Phenotypic plasticity in linked plant hydraulic traits: an evaluation of a common-taxa experiment across a climatic gradient in the Western U.S.

Abstract

Increasing drought conditions and variable water availability under climate change impact plant productivity, ecosystem function and the global carbon cycle, with many species-level responses remaining unknown. Variation in response and ability to acclimate to decreased water availability differs among plant species and across biomes. To assess the interactions between acclimation to climate and water availability across a growing season as well as taxa level plasticity, this project utilized a preexisting water deficit trial of horticultural taxa across sites in the Western U.S. Four focal taxa (Cercis occidentalis, Cercis canadensis, Physocarpus ‘Diabolo’ and Physocarpus ‘Little Devil) shared across three locations were measured for physiological and morphological hydraulic traits in response to two irrigation deficit treatments. Full gas exchange, specific leaf area, mean weighted vessel diameter, theoretical hydraulic conductance, stomatal conductance, and ΦPSII were collected and water use efficiencies were calculated for each taxon at each location. Analysis of variance was used to test the effects of trait performance of species between sites as well as across sites, resulting in differing responses depending on species and site. Additionally, impacts of site, treatment, taxa and change across the growing season were analyzed using multivariate methods (RRPP and PERMANOVA). Results show distinctions in water use strategy by climatic location as well as variation between closely related species and cultivars, indicating plasticity to site and among taxa. Additionally, physiological and morphological measurements collected at multiple timepoints during the deficit period indicate measurable physiological acclimation across the growing season. These findings highlight the merits of common-taxa trials over multiple geographic locations to study and identify climate-ready plants. Our results provide novel examples of physiological shifts across the growing season, indicate the importance of experimental location on the ability of different plant taxa to acclimate to water stress, intraspecies level plasticity among horticulturally important species, and contribute to overall knowledge of plant drought responses, knowledge gaps that are crucial to address in the face of anthropogenic climate change.