title: Responses of two semiarid conifer tree species to reduced precipitation and warming reveal new perspectives for stomatal regulation.
abstract: Relatively anisohydric species are predicted to be more predisposed to hydraulic failure than relatively isohydric species, as they operate with narrower hydraulic safety margins. We subjected co-occurring anisohydric Juniperus monosperma and isohydric Pinus edulis trees to warming, reduced precipitation, or both, and measured their gas exchange and hydraulic responses. We found that reductions in stomatal conductance and assimilation by heat and drought were more frequent during relatively moist periods, but these effects were not exacerbated in the combined heat and drought treatment. Counter to expectations, both species exhibited similar gs temporal dynamics in response to drought. Further, whereas P. edulis exhibited chronic embolism, J. monosperma showed very little embolism due to its conservative stomatal regulation and maintenance of xylem water potential above the embolism entry point. This tight stomatal control and low levels of embolism experienced by juniper refuted the notion that very low water potentials during drought are associated with loose stomatal control and with the hypothesis that anisohydric species are more prone to hydraulic failure than isohydric species. Because direct association of stomatal behaviour with embolism resistance can be misleading, we advocate consideration of stomatal behaviour relative to embolism resistance for classifying species drought response strategies.
authors.affiliation: CREAF, Cerdanyola del Vallès, 08193, Spain.|Universitat Autònoma Barcelona, Cerdanyola del Vallès, 08193, Spain.
authors.forename: Núria
authors.identifier: http://orcid.org/0000-0002-7788-0718
authors.initials: N
authors.lastname: Garcia-Forner
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
authors.forename: Henry D
authors.initials: HD
authors.lastname: Adams
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
authors.forename: Sanna
authors.initials: S
authors.lastname: Sevanto
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
authors.forename: Adam D
authors.initials: AD
authors.lastname: Collins
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
authors.forename: Lee T
authors.identifier: http://orcid.org/0000-0003-3876-7058
authors.initials: LT
authors.lastname: Dickman
authors.affiliation: Department of Biology, University of New Mexico, Albuquerque, NM, 87131, USA.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Hudson
authors.affiliation: Department of Biological Sciences, Macquarie University, Sydney, New South Wales, 2109, Australia.
authors.forename: Melanie J B
authors.initials: MJ
authors.lastname: Zeppel
authors.affiliation: Department of Environmental Studies, University of California, Santa Cruz, California, 95064, USA.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Jenkins
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
authors.forename: Heath
authors.initials: H
authors.lastname: Powers
authors.affiliation: CREAF, Cerdanyola del Vallès, 08193, Spain.|Universitat Autònoma Barcelona, Cerdanyola del Vallès, 08193, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Martínez-Vilalta
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
authors.forename: Nate G
authors.initials: NG
authors.lastname: Mcdowell
mesh_terms: D002244:Carbon / Q000378:metabolism*; D055864:Droughts; D018653:Juniperus / Q000502:physiology*; D008954:Models, Biological; D028223:Pinus / Q000502:physiology*; D018515:Plant Leaves / Q000502:physiology; D054046:Plant Stomata / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology*; D014197:Trees; D014867:Water / Q000502:physiology; D052584:Xylem / Q000502:physiology
chemical_list: D014867:Water; D002244:Carbon
keywords: carbon starvation; drought; global change; hydraulic conductivity; hydraulic failure; increased temperature; iso- versus anisohydric behaviour; mortality; stomatal conductance