title: The role of isohydric and anisohydric species in determining ecosystem-scale response to severe drought.
abstract: Ongoing shifts in the species composition of Eastern US forests necessitate the development of frameworks to explore how species-specific water-use strategies influence ecosystem-scale carbon (C) cycling during drought. Here, we develop a diagnostic framework to classify plant drought-response strategies along a continuum of isohydric to anisohydric regulation of leaf water potential (Ψ(L)). The framework is applied to a 3-year record of weekly leaf-level gas exchange and Ψ measurements collected in the Morgan-Monroe State Forest (Indiana, USA), where continuous observations of the net ecosystem exchange of CO2 (NEE) have been ongoing since 1999. A severe drought that occurred in the middle of the study period reduced the absolute magnitude of NEE by 55%, though species-specific responses to drought conditions varied. Oak species were characterized by anisohydric regulation of Ψ(L) that promoted static gas exchange throughout the study period. In contrast, Ψ(L) of the other canopy dominant species was more isohydric, which limited gas exchange during the drought. Ecosystem-scale estimates of NEE and gross ecosystem productivity derived by upscaling the leaf-level data agreed well with tower-based observations, and highlight how the fraction of isohydric and anisohydric species in forests can mediate net ecosystem C balance.
authors.affiliation: School of Public and Environmental Affairs, Indiana University-Bloomington, 702 North Walnut Grove Avenue, Bloomington, IN, 47405, USA.
authors.forename: D T
authors.initials: DT
authors.lastname: Roman
authors.affiliation: School of Public and Environmental Affairs, Indiana University-Bloomington, 702 North Walnut Grove Avenue, Bloomington, IN, 47405, USA. knovick@indiana.edu.
authors.forename: K A
authors.initials: KA
authors.lastname: Novick
authors.affiliation: Department of Biology, West Virginia University, 53 Campus Drive, Morgantown, WV, 26505, USA.
authors.forename: E R
authors.initials: ER
authors.lastname: Brzostek
authors.affiliation: Department of Geography, Indiana University-Bloomington, 702 North Walnut Grove Avenue, Bloomington, IN, 47405, USA.
authors.forename: D
authors.initials: D
authors.lastname: Dragoni
authors.affiliation: Department of Biology, The University of Texas Rio Grande Valley, 1201 West University Drive, Edinburg, TX, 78539, USA.
authors.forename: F
authors.initials: F
authors.lastname: Rahman
authors.affiliation: Department of Biology, Indiana University-Bloomington, 1001 East Third Street, Bloomington, IN, 47405, USA.
authors.forename: R P
authors.initials: RP
authors.lastname: Phillips
mesh_terms: D000222:Adaptation, Physiological; D002244:Carbon / Q000378:metabolism*; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000378:metabolism; D055864:Droughts; D065928:Forests; D010788:Photosynthesis; D018515:Plant Leaves / Q000502:physiology; D018526:Plant Transpiration; D029963:Quercus / Q000502:physiology; D013045:Species Specificity; D013312:Stress, Physiological; D014197:Trees / Q000502:physiology*; D014867:Water / Q000502:physiology*
chemical_list: D014867:Water; D002245:Carbon Dioxide; D002244:Carbon
keywords: Carbon flux; Eddy covariance; Net ecosystem exchange; Stomatal conductance; Water regulation