title: Stomatal acclimation to vapour pressure deficit doubles transpiration of small tree seedlings with warming.
abstract: Future climate change is expected to increase temperature (T) and atmospheric vapour pressure deficit (VPD) in many regions, but the effect of persistent warming on plant stomatal behaviour is highly uncertain. We investigated the effect of experimental warming of 1.9-5.1 °C and increased VPD of 0.5-1.3 kPa on transpiration and stomatal conductance (gs ) of tree seedlings in the temperate forest understory (Duke Forest, North Carolina, USA). We observed peaked responses of transpiration to VPD in all seedlings, and the optimum VPD for transpiration (Dopt ) shifted proportionally with increasing chamber VPD. Warming increased mean water use of Carya by 140% and Quercus by 150%, but had no significant effect on water use of Acer. Increased water use of ring-porous species was attributed to (1) higher air T and (2) stomatal acclimation to VPD resulting in higher gs and more sensitive stomata, and thereby less efficient water use. Stomatal acclimation maintained homeostasis of leaf T and carbon gain despite increased VPD, revealing that short-term stomatal responses to VPD may not be representative of long-term exposure. Acclimation responses differ from expectations of decreasing gs with increasing VPD and may necessitate revision of current models based on this assumption.
authors.affiliation: Centre for Carbon, Water and Food, University of Sydney, Camden, New South Wales, 2570, Australia. renee.marchin@sydney.edu.au.|Department of Plant Biology, North Carolina State University, Raleigh, NC, 27695-7612, USA. renee.marchin@sydney.edu.au.
authors.forename: Renée M
authors.initials: RM
authors.lastname: Marchin
authors.affiliation: Department of Plant Biology, North Carolina State University, Raleigh, NC, 27695-7612, USA.
authors.forename: Alice A
authors.initials: AA
authors.lastname: Broadhead
authors.affiliation: Department of Plant Biology, North Carolina State University, Raleigh, NC, 27695-7612, USA.
authors.forename: Laura E
authors.initials: LE
authors.lastname: Bostic
authors.affiliation: Department of Applied Ecology and Keck Center for Behavioral Biology, North Carolina State University, Raleigh, NC, 27695-7617, USA.|Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, DK-2100, Copenhagen, Denmark.
authors.forename: Robert R
authors.initials: RR
authors.lastname: Dunn
authors.affiliation: Department of Plant Biology, North Carolina State University, Raleigh, NC, 27695-7612, USA.
authors.forename: William A
authors.initials: WA
authors.lastname: Hoffmann
mesh_terms: D000064:Acclimatization; D057231:Climate Change; D006813:Humidity; D054046:Plant Stomata / Q000378:metabolism / Q000502:physiology; D018526:Plant Transpiration; D036226:Seedlings / Q000378:metabolism / Q000502:physiology*; D013696:Temperature; D014197:Trees / Q000378:metabolism / Q000502:physiology*; D055548:Vapor Pressure
keywords: humidity; sap flux; stomata; stomatal conductance; temperature; warming experiment