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Title: Ten-year variability in ecosystem water use efficiency in an oak-dominated temperate forest under a warming climate

The impacts of extreme weather events on water-carbon (C) coupling and ecosystem-scale water use efficiency (WUE) over a long term are poorly understood. We analyzed the changes in ecosystem water use efficiency (WUE) from 10 years of eddy-covariance measurements (2004-2013) over an oak-dominated temperate forest in Ohio, USA. The aim was to investigate the long-term response of ecosystem WUE to measured changes in site-biophysical conditions and ecosystem attributes. The oak forest produced new plant biomass of 2.5 +/- 0.2 gC kg(-1) of water loss annually. Monthly evapotranspiration (ET) and gross ecosystem production (GEP) were tightly coupled over the 10-year study period (R-2=0.94). Daily WUE had a linear relationship with air temperature (T-a) in low-temperature months and a unimodal relationship with T-a in high-temperature months during the growing season. On average, daily WUE ceased to increase when T-a exceeded 22 degrees C in warm months for both wet and dry years. Monthly WUE had a strong positive linear relationship with leaf area index (LAI), net radiation (R-n), and T-a and weak logarithmic relationship with water vapor pressure deficit (VPD) and precipitation (P) on a growing-season basis. When exploring the regulatory mechanisms on WUE within each season, spring LAI and P, summermore » R-n and T-a, and autumnal VPD and R-n were found to be the main explanatory variables for seasonal variation in WUE. The model developed in this study was able to capture 78% of growing-season variation in WUE on a monthly basis. The negative correlation between WUE and A in spring was mainly due to the high precipitation amounts in spring, decreasing GEP and WUE when LAI was still small, adding ET being observed to increase with high levels of evaporation as a result of high SWC in spring. Summer WUE had a significant decreasing trend across the 10 years mainly due to the combined effect of seasonal drought and increasing potential and available energy increasing ET, but decreasing GEP in summer. We concluded that seasonal dynamics of the interchange between precipitation and drought status of the system was an important variable in controlling seasonal WUE in wet years. In contrast, despite the negative impacts of unfavorable warming, available groundwater and an early start of the growing season were important contributing variables in high seasonal GEP, and thus, high seasonal WUE in dry years. (C) 2015 Elsevier B.V. All rights reserved.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [4] ;  [7] ;  [8] ;  [8] ;  [9] ;  [2] ;  [2] ;  [2]
  1. Beijing Forestry Univ. (China); Beijing Forestry Carbon Sequestration Administration, Beijing (China)
  2. Michigan State Univ., East Lansing, MI (United States)
  3. United States Department of Agriculture (USDA). Raliegh, NC (United States). Southern Research Station
  4. Beijing Forestry Univ. (China)
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  6. Univ. of California, Berkeley, CA (United States)
  7. Henan Univ. (China)
  8. Beijing Forestry Carbon Sequestration Administration, Beijing (China)
  9. Univ. of New Brunswick, Fredericton, NB (Canada)
Publication Date:
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Agricultural and Forest Meteorology
Additional Journal Information:
Journal Volume: 218; Journal ID: ISSN 0168-1923
Publisher:
Elsevier
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; Dryness index; Eddy covariance; Evapotranspiration; Gross ecosystem production; Long-term variability; Water use efficiency; CARBON-DIOXIDE; EDDY COVARIANCE; TERRESTRIAL ECOSYSTEMS; ENVIRONMENTAL CONTROLS; SOIL RESPIRATION; SONIC ANEMOMETER; ASPEN FOREST
OSTI Identifier:
1346640