Multiple constraints cause positive and negative feedbacks limiting grassland soil CO2efflux under CO2enrichment

Authors

Philip A. Fay, United States Department of AgricultureFollow
Dafeng Hui, Tennessee State University
Robert B. Jackson, Stanford University
Harold P. Collins, United States Department of Agriculture
Lara G. Reichmann, The University of Texas at Austin
Michael J. Aspinwall, Auburn University
Virginia L. Jin, University of Nebraska–Lincoln
Albina R. Khasanova, The University of Texas at Austin
Robert W. Heckman, The University of Texas at Austin
H. Wayne Polley, United States Department of Agriculture

ORCID IDs

Philip A. Fay https://orcid.org/0000-0002-8291-6316

Dafeng Hui https://orcid.org/0000-0002-5284-2897

Robert B. Jackson https://orcid.org/0000-0001-8846-7147

Harold P. Collins https://orcid.org/0000-0002-6473-8894

Michael J. Aspinwall https://orcid.org/0000-0003-0199-2972

Virginia L. Jin https://orcid.org/0000-0003-4146-8497

Albina R. Khasanova https://orcid.org/0000-0001-6652-012X

Robert W. Heckman https://orcid.org/0000-0002-2281-3091

H. Wayne Polley https://orcid.org/0000-0002-1197-8800

Date of this Version

1-12-2021

Citation

PNAS 2021 Vol. 118 No. 2 e2008284117

https://doi.org/10.1073/pnas.2008284117

Comments

U.S. government work

Abstract

Terrestrial ecosystems are increasingly enriched with resources such as atmospheric CO2that 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 CO2efflux, JCO2, a primary carbon flux from the biosphere to the atmosphere. We applied a unique CO2enrichment 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 JCO2responses and feedbacks from other resources, plant diversity [effective species richness, exp(H)], and community change (plant species turnover). We found linear increases in JCO2on an alluvial sandy loam and a lowland clay soil, and an asymptotic increase on an upland silty clay soil. Structural equation modeling identified CO2as the dominant limitation on JCO2on the clay soil. In contrast with theory predicting limitation from a single limiting factor, the linear JCO2response on the sandy loam was reinforced by positive feedbacks from aboveground net primary productivity and exp(H), while the asymptotic JCO2response 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.