Elevated growth temperatures alter hydraulic characteristics in trembling aspen (Populus tremuloides) seedlings: Implications for tree drought tolerance

Abstract

Although climate change will alter both soil water availability and evaporative demand, our understanding of how future climate conditions will alter tree hydraulic architecture is limited. Here, we demonstrate that growth at elevated temperatures (ambient +5°C) affects hydraulic traits in seedlings of the deciduous boreal tree species Populus tremuloides, with the strength of the effect varying with the plant organ studied. Temperature altered the partitioning of hydraulic resistance, with greater resistance attributed to stems and less to roots in warm-grown seedlings (P<0.02), and a 46% (but marginally significant, P=0.08) increase in whole plant conductance at elevated temperature. Vulnerability to cavitation was greater in leaves grown at high than at ambient temperatures, but vulnerability in stems was similar between treatments. A soil-plant-atmosphere (SPA) model suggests that these coordinated changes in hydraulic physiology would lead to more frequent drought stress and reduced water-use efficiency in aspen that develop at warmer temperatures. Tissue-specific trade-offs in hydraulic traits in response to high growth temperatures would be difficult to detect when relying solely on whole plant measurements, but may have large-scale ecological implications for plant water use, carbon cycling and, possibly, plant drought survival. We investigated the effect of elevated growth temperatures on hydraulic characteristics of aspen and used the SPA model to predict how the physiological changes we observed might affect tree water use in the face of realistic climate fluctuations. Warming increased aspen growth and altered hydraulic resistance and vulnerability to cavitation in a tissue-dependent manner, such that roots, stems and leaves showed different responses to elevated temperatures. Modeling results showed that aspen that developed at warmer conditions experienced more frequent, severe droughts and had lower water use efficiency than aspen that grew under current temperature regimes. These results indicate that climate warming may increase tree water use due to physiological acclimation of hydraulic and growth traits, which could increase tree susceptibility to drought in future climates. © 2012 Blackwell Publishing Ltd.