Stem hydraulic capacitance decreases with drought stress: implications for modelling tree hydraulics in the Mediterranean oak Quercus ilex.
Hydraulic modelling is a primary tool to predict plant performance in future drier scenarios. However, as most tree models are validated under non-stress conditions, they may fail when water becomes limiting. To simulate tree hydraulic functioning under moist and dry conditions, the current version of a water flow and storage mechanistic model was further developed by implementing equations that describe variation in xylem hydraulic resistance (RX) and stem hydraulic capacitance (CS) with predawn water potential (ΨPD). The model was applied in a Mediterranean forest experiencing intense summer drought, where six Quercus ilex trees were instrumented to monitor stem diameter variations and sap flow, concurrently with measurements of predawn and midday leaf water potential. Best model performance was observed when CSwas allowed to decrease with decreasing ΨPD. Hydraulic capacitance decreased from 62 to 25 kg m-3MPa-1across the growing season. In parallel, tree transpiration decreased to a greater extent than the capacitive water release and the contribution of stored water to transpiration increased from 2.0 to 5.1%. Our results demonstrate the importance of stored water and seasonality in CSfor tree hydraulic functioning, and they suggest that CSshould be considered to predict the drought response of trees with models.
Forest Genetics and Ecophysiology Research Group, E.T.S. Forestry Engineering, Technical University of Madrid, Ciudad Universitaria s/n, 28040, Madrid, Spain.|Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure links, 653-9000, Ghent, Belgium.
Roberto L
http://orcid.org/0000-0003-2674-1731
RL
Salomón
Centre d'Ecologie Fonctionnelle et Evolutive CEFE, CNRS, UMR 5175, 1919 route de Mende, F-34293, Montpellier, Cedex 5, France.
Jean-Marc
JM
Limousin
Centre d'Ecologie Fonctionnelle et Evolutive CEFE, CNRS, UMR 5175, 1919 route de Mende, F-34293, Montpellier, Cedex 5, France.
Jean-Marc
JM
Ourcival
Forest Genetics and Ecophysiology Research Group, E.T.S. Forestry Engineering, Technical University of Madrid, Ciudad Universitaria s/n, 28040, Madrid, Spain.
Jesús
J
Rodríguez-Calcerrada
Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure links, 653-9000, Ghent, Belgium.
Kathy
K
Steppe
D002138:Calibration; D003198:Computer Simulation; D055864:Droughts; D008954:Models, Biological; D018547:Plant Stems / Q000502:physiology*; D029963:Quercus / Q000033:anatomy & histology / Q000502:physiology*; D011891:Rain; D013696:Temperature; D014197:Trees / Q000033:anatomy & histology / Q000502:physiology*; D014867:Water / Q000502:physiology*; D052584:Xylem / Q000502:physiology
D014867:Water
holm oak; hydraulic function; process-based modelling; radial stem growth; stem water storage