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Multiple constraints cause positive and negative feedbacks limiting grassland soil CO2 efflux under CO2 enrichment.

  • Fay, Philip A1
  • Hui, Dafeng2
  • Jackson, Robert B3
  • Collins, Harold P4
  • Reichmann, Lara G5
  • Aspinwall, Michael J6
  • Jin, Virginia L7
  • Khasanova, Albina R5
  • Heckman, Robert W5
  • Polley, H Wayne4
  • 1 United States Department of Agriculture, Agricultural Research Service (USDA-ARS) Grassland, Soil, and Water Research Lab, Temple, TX 76502; [email protected] , (United States)
  • 2 Department of Biological Sciences, Tennessee State University, Nashville, TN 37209.
  • 3 Department of Earth System Science, Stanford University, Stanford, CA 94305.
  • 4 United States Department of Agriculture, Agricultural Research Service (USDA-ARS) Grassland, Soil, and Water Research Lab, Temple, TX 76502. , (United States)
  • 5 Department of Integrative Biology, The University of Texas at Austin, Austin, TX 78712.
  • 6 School of Forestry and Wildlife Sciences, Auburn University, Auburn, AL 36849.
  • 7 USDA-ARS Agroecosystem Management Research Unit, University of Nebraska, Lincoln, NE 68583.
Published Article
Proceedings of the National Academy of Sciences
Proceedings of the National Academy of Sciences
Publication Date
Jan 12, 2021
DOI: 10.1073/pnas.2008284117
PMID: 33419921


Terrestrial ecosystems are increasingly enriched with resources such as atmospheric CO2 that limit ecosystem processes. The consequences for ecosystem carbon cycling depend on the feedbacks from other limiting resources and plant community change, which remain poorly understood for soil CO2 efflux, JCO2, a primary carbon flux from the biosphere to the atmosphere. We applied a unique CO2 enrichment gradient (250 to 500 µL L-1) for eight years to grassland plant communities on soils from different landscape positions. We identified the trajectory of JCO2 responses and feedbacks from other resources, plant diversity [effective species richness, exp(H)], and community change (plant species turnover). We found linear increases in JCO2 on an alluvial sandy loam and a lowland clay soil, and an asymptotic increase on an upland silty clay soil. Structural equation modeling identified CO2 as the dominant limitation on JCO2 on the clay soil. In contrast with theory predicting limitation from a single limiting factor, the linear JCO2 response on the sandy loam was reinforced by positive feedbacks from aboveground net primary productivity and exp(H), while the asymptotic JCO2 response on the silty clay arose from a net negative feedback among exp(H), species turnover, and soil water potential. These findings support a multiple resource limitation view of the effects of global change drivers on grassland ecosystem carbon cycling and highlight a crucial role for positive or negative feedbacks between limiting resources and plant community structure. Incorporating these feedbacks will improve models of terrestrial carbon sequestration and ecosystem services.

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