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Title: Vulnerability of crops and native grasses to summer drying in the U.S. Southern Great Plains

The Southern Great Plains are characterized by a fine-scale mixture of different land-cover types, predominantly winter-wheat and grazed pasture, with relatively small areas of other crops, native prairie, and switchgrass. Recent droughts and predictions of increased drought in the Southern Great Plains, especially during the summer months, raise concern for these ecosystems. We measured ecosystem carbon and water fluxes with eddy-covariance systems over cultivated cropland for 10 years, and over lightly grazed prairie and new switchgrass fields for 2 years each. Growing-season precipitation showed the strongest control over net carbon uptake for all ecosystems, but with a variable effect: grasses (prairie and switchgrass) needed at least 350 mm of precipitation during the growing season to become net carbon sinks, while crops needed only 100 mm. In summer, high temperatures enhanced evaporation and led to higher likelihood of dry soil conditions. Therefore, summer-growing native prairie species and switchgrass experienced more seasonal droughts than spring-growing crops. For wheat, the net reduction in carbon uptake resulted mostly from a decrease in gross primary production rather than an increase in respiration. Flux measurements suggested that management practices for crops were effective in suppressing evapotranspiration and decomposition (by harvesting and removing secondary growth), and inmore » increasing carbon uptake (by fertilizing and conserving summer soil water). In light of future projections for wetter springs and drier and warmer summers in the Southern Great Plains, our study indicates an increased vulnerability in native ecosystems and summer crops over time.« less
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [3] ;  [3] ;  [1]
  1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  2. Univ. of Nebraska, Lincoln, NE (United States). Biological Systems Engineering Dept.
  3. US Dept. of Agriculture, Woodward, OK (United States). Agricultural Research Service, Southern Plains Range Research Station
Publication Date:
OSTI Identifier:
1245476
Grant/Contract Number:
AC02-05CH11231
Type:
Published Article
Journal Name:
Agriculture, Ecosystems and Environment
Additional Journal Information:
Journal Volume: 213; Journal Issue: C; Journal ID: ISSN 0167-8809
Publisher:
Elsevier
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; Agriculture; Drought; Southern Great Plains; Wheat; Switchgrass; Prairie; NEE; GPP; Evapotranspiration