Tree water dynamics in a drying and warming world

Abstract

Disentangling the relative impacts of precipitation reduction and vapour pressure deficit (VPD) on plant water dynamics and determining whether acclimation may influence these patterns in the future is an important challenge. Here, we report sap flux density (F ), stomatal conductance (G ), hydraulic conductivity (K ) and xylem anatomy in piñon pine (Pinus edulis) and juniper (Juniperus monosperma) trees subjected to five years of precipitation reduction, atmospheric warming (elevated VPD) and their combined effects. No acclimation occurred under precipitation reduction: lower G and F were found for both species compared to ambient conditions. Warming reduced the sensibility of stomata to VPD for both species but resulted in the maintenance of G and F to ambient levels only for piñon. For juniper, reduced soil moisture under warming negated benefits of stomatal adjustments and resulted in reduced F , G and K . Although reduced stomatal sensitivity to VPD also occurred under combined stresses, reductions in G , F and K took place to similar levels as under single stresses for both species. Our results show that stomatal conductance adjustments to high VPD could minimize but not entirely prevent additive effects of warming and drying on water use and carbon acquisition of trees in semi-arid regions.

Reductions in tree performance during hotter droughts are mitigated by shifts in nitrogen cycling

“…The forest type, piñon‐juniper woodlands, is one of the most widely distributed forests in the southwestern United States (West, ) and has been identified as particularly threatened by hotter droughts in the decades to come (Allen, Macalady, et al, ). Different vulnerabilities to drought in cohabiting piñon pine and juniper trees, including water use regulation (relatively isohydric vs. anisohydric species, respectively; Garcia‐Forner et al, ) and rooting depths (shallow vs. deep rooted species, respectively; Grossiord, Sevanto, Borrego, et al, ), have made these woodlands a useful system for understanding how trees with contrasting survival strategies respond to drought (McDowell et al, ). These recent studies have highlighted a functional and structural advantage of juniper over piñon during droughts, suggesting lower mortality risk during upcoming hot droughts.…”

Detecting the fingerprint of drought across Europe’s forests: do carbon isotope ratios and stem growth rates tell similar stories?

“…At the level of the leaf, C 3 plants (which includes virtually all tree species) respond to low soil moisture availability by closing their stomata to limit water loss through transpiration (Bréda et al 2006;Grossiord et al 2017). One consequence of reduced stomatal conductance is a drop in the intercellular concentration of CO 2 (relative to ambient concentrations outside the leaf), which in turn affects the ratio of 13 C to 12 C -known as δ 13 C -being fixed by RuBisCO (Farquhar et al 1982;Leary 1988;Farquhar et al 1989).…”

“…Yet whether this carbon sink will persist under future climate conditions is unclear (Friend et al 2014), with the likelihood of increasingly frequent and severe droughts and heat waves being a major cause for concern . Consequently, understanding how trees respond to drought is critical to forecasting both short and long-term impacts of climate change on forests (Clark et al 2016;Grossiord et al 2017).…”

Water Balance of Mediterranean Quercus ilex L. and Pinus halepensis Mill. Forests in Semiarid Climates: A Review in A Climate Change Context

“…Indeed, it has been pointed out that plants can adopt two main functional strategies to face drought: isohydric and anisohydric plant responses [30][31][32]. Isohydric plants keep the water potential relatively stable, independently of environmental conditions and soil water fluctuations.…”