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Title: Prolonged experimental drought reduces plant hydraulic conductance and transpiration and increases mortality in a piñon–juniper woodland

Plant hydraulic conductance (k s) is a critical control on whole-plant water use and carbon uptake and, during drought, influences whether plants survive or die. To assess long-term physiological and hydraulic responses of mature trees to water availability, we manipulated ecosystem-scale water availability from 2007 to 2013 in a piñon pine ( Pinus edulis) and juniper ( Juniperus monosperma) woodland. We examined the relationship between k s and subsequent mortality using more than 5 years of physiological observations, and the subsequent impact of reduced hydraulic function and mortality on total woody canopy transpiration (E C) and conductance (G C). For both species, we observed significant reductions in plant transpiration (E) and k s under experimentally imposed drought. Conversely, supplemental water additions increased E and k s in both species. Interestingly, both species exhibited similar declines in k s under the imposed drought conditions, despite their differing stomatal responses and mortality patterns during drought. Reduced whole-plant k s also reduced carbon assimilation in both species, as leaf-level stomatal conductance (g s) and net photosynthesis (A n) declined strongly with decreasing k s. Finally, we observed that chronically low whole-plant k s was associated with greater canopy dieback and mortality for bothmore » piñon and juniper and that subsequent reductions in woody canopy biomass due to mortality had a significant impact on both daily and annual canopy E C and G C. Our data indicate that significant reductions in k s precede drought-related tree mortality events in this system, and the consequence is a significant reduction in canopy gas exchange and carbon fixation. Our results suggest that reductions in productivity and woody plant cover in piñon–juniper woodlands can be expected due to reduced plant hydraulic conductance and increased mortality of both piñon pine and juniper under anticipated future conditions of more frequent and persistent regional drought in the southwestern United States.« less
 [1] ;  [2] ;  [1] ;  [3] ;  [1] ;  [1] ;  [1] ;  [1] ;  [4]
  1. Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Biology.
  2. Université de Montpellier and Université Paul-Valéry Montpellier (France). Centre d'Ecologie Fonctionnelle et Evolutive.
  3. Instituto Tecnológico de Sonora (Mexico). Departamento de Ciencias del Agua y del Medio Ambiente.
  4. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Earth and Environmental Sciences Division.
Publication Date:
Grant/Contract Number:
Published Article
Journal Name:
Ecology and Evolution
Additional Journal Information:
Journal Volume: 5; Journal Issue: 8; Journal ID: ISSN 2045-7758
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
Country of Publication:
United States
54 ENVIRONMENTAL SCIENCES; canopy dieback; climate change; hydraulic failure; net carbon assimilation; plant water stress; precipitation manipulation; stomatal response to drought; tree death
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1212470; OSTI ID: 1295967