title: Drought-induced defoliation and long periods of near-zero gas exchange play a key role in accentuating metabolic decline of Scots pine.
abstract: Drought-induced defoliation has recently been associated with the depletion of carbon reserves and increased mortality risk in Scots pine (Pinus sylvestris). We hypothesize that defoliated individuals are more sensitive to drought, implying that potentially higher gas exchange (per unit of leaf area) during wet periods may not compensate for their reduced photosynthetic area. We measured sap flow, needle water potentials and whole-tree hydraulic conductance to analyse the drought responses of co-occurring defoliated and nondefoliated Scots pines in northeast Spain during typical (2010) and extreme (2011) drought conditions. Defoliated Scots pines showed higher sap flow per unit leaf area during spring, but were more sensitive to summer drought, relative to nondefoliated pines. This pattern was associated with a steeper decline in soil-to-leaf hydraulic conductance with drought and an enhanced sensitivity of canopy conductance to soil water availability. Near-homeostasis in midday water potentials was observed across years and defoliation classes, with minimum values of -2.5 MPa. Enhanced sensitivity to drought and prolonged periods of near-zero gas exchange were consistent with low levels of carbohydrate reserves in defoliated trees. Our results support the critical links between defoliation, water and carbon availability, and their key roles in determining tree survival and recovery under drought.
authors.affiliation: CREAF, Cerdanyola del Vallès, Bellaterra, Barcelona, 08193, Spain.
authors.forename: Rafael
authors.initials: R
authors.lastname: Poyatos
authors.affiliation: CREAF, Cerdanyola del Vallès, Bellaterra, Barcelona, 08193, Spain.|Universitat Autònoma Barcelona, Cerdanyola del Vallès, Bellaterra, Barcelona, 08193, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Aguadé
authors.affiliation: CREAF, Cerdanyola del Vallès, Bellaterra, Barcelona, 08193, Spain.
authors.forename: Lucía
authors.initials: L
authors.lastname: Galiano
authors.affiliation: ICREA at CREAF, Cerdanyola del Vallès, Bellaterra, Barcelona, 08193, Spain.|School of GeoSciences, University of Edinburgh, EH9 3JN, Edinburgh, UK.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Mencuccini
authors.affiliation: CREAF, Cerdanyola del Vallès, Bellaterra, Barcelona, 08193, Spain.|Universitat Autònoma Barcelona, Cerdanyola del Vallès, Bellaterra, Barcelona, 08193, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Martínez-Vilalta
mesh_terms: D002244:Carbon / Q000378:metabolism*; D055864:Droughts; D008962:Models, Theoretical; D010788:Photosynthesis / Q000502:physiology; D041605:Pinus sylvestris / Q000378:metabolism / Q000502:physiology*; D018515:Plant Leaves / Q000378:metabolism / Q000502:physiology; D018520:Plant Shoots / Q000378:metabolism / Q000502:physiology; D054046:Plant Stomata / Q000378:metabolism / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology*; D012621:Seasons; D012987:Soil; D013030:Spain; D014197:Trees; D055548:Vapor Pressure; D014867:Water / Q000502:physiology*; D014934:Wood / Q000378:metabolism / Q000502:physiology
chemical_list: D012987:Soil; D014867:Water; D002244:Carbon
keywords: Pinus sylvestris; canopy defoliation; hydraulic limits; nonstructural carbohydrates; sap flow; stomatal conductance; tree mortality; water potential