TY - JOUR
T1 - The carbon balance pivot point of southwestern U.S. semiarid ecosystems
T2 - Insights from the 21st century drought
AU - Scott, Russell L.
AU - Biederman, Joel A.
AU - Hamerlynck, Erik P.
AU - Barron-Gafford, Greg A.
N1 - Funding Information:
Data used in this paper are available at the Ameriflux Data Repository (http://ameriflux.lbl.gov/) or upon request to the corresponding author. This work was supported by USDA-ARS and funding for these Ameriflux Core Sites was provided by the U.S. Department of Energy Berkeley National Labs. Funding for these data sets and maintaining the research infrastructure on Walnut Gulch and the Santa Rita Experimental Range was provided by the USDA-ARS and the University of Arizona. We thank R. Bryant for his expert technical assistance in maintaining the eddy covariance sites. USDA-ARS is an equal opportunity employer.
Publisher Copyright:
© 2015. American Geophysical Union. All Rights Reserved.
PY - 2015/12
Y1 - 2015/12
N2 - Global-scale studies indicate that semiarid regions strongly regulate the terrestrial carbon sink. However, we lack understanding of how climatic shifts, such as decadal drought, impact carbon sequestration across the wide range of structural diversity in semiarid ecosystems. Therefore, we used eddy covariance measurements to quantify how net ecosystem production of carbon dioxide (NEP) differed with relative grass and woody plant abundance over the last decade of drought in four Southwest U.S. ecosystems. We identified a precipitation "pivot point" in the carbon balance for each ecosystem where annual NEP switched from negative to positive. Ecosystems with grass had pivot points closer to the drought period precipitation than the predrought average, making them more likely to be carbon sinks (and a grass-free shrubland, a carbon source) during the current drought. One reason for this is that the grassland located closest to the shrubland supported higher leaf area and photosynthesis at the same water availability. Higher leaf area was associated with a greater proportion of evapotranspiration being transpiration (T/ET), and therefore with higher ecosystem water use efficiency (gross ecosystem photosynthesis/ET). Our findings strongly show that water availability is a primary driver of both gross and net semiarid productivity and illustrate that structural differences may contribute to the speed at which ecosystem carbon cycling adjusts to climatic shifts.
AB - Global-scale studies indicate that semiarid regions strongly regulate the terrestrial carbon sink. However, we lack understanding of how climatic shifts, such as decadal drought, impact carbon sequestration across the wide range of structural diversity in semiarid ecosystems. Therefore, we used eddy covariance measurements to quantify how net ecosystem production of carbon dioxide (NEP) differed with relative grass and woody plant abundance over the last decade of drought in four Southwest U.S. ecosystems. We identified a precipitation "pivot point" in the carbon balance for each ecosystem where annual NEP switched from negative to positive. Ecosystems with grass had pivot points closer to the drought period precipitation than the predrought average, making them more likely to be carbon sinks (and a grass-free shrubland, a carbon source) during the current drought. One reason for this is that the grassland located closest to the shrubland supported higher leaf area and photosynthesis at the same water availability. Higher leaf area was associated with a greater proportion of evapotranspiration being transpiration (T/ET), and therefore with higher ecosystem water use efficiency (gross ecosystem photosynthesis/ET). Our findings strongly show that water availability is a primary driver of both gross and net semiarid productivity and illustrate that structural differences may contribute to the speed at which ecosystem carbon cycling adjusts to climatic shifts.
KW - carbon dioxide
KW - drought
KW - ecosystem
KW - net ecosystem production
KW - semiarid
KW - water
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U2 - 10.1002/2015JG003181
DO - 10.1002/2015JG003181
M3 - Article
AN - SCOPUS:84954381214
VL - 120
SP - 2612
EP - 2624
JO - Journal of Geophysical Research: Biogeosciences
JF - Journal of Geophysical Research: Biogeosciences
SN - 2169-8953
IS - 12
ER -