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ARS Home » Plains Area » Temple, Texas » Grassland Soil and Water Research Laboratory » Research » Publications at this Location » Publication #342963
Title: CO2 enrichment and soil type additively regulate grassland productivity

Author
item Polley, Herbert
item ASPINWALL, MICHAEL - Western Sydney University
item Collins, Harold
item Gibson, Anne
item GILL, RICHARD - Brigham Young University
item JACKSON, ROBERT - Stanford University
item Jin, Virginia
item KHASANOVA, ALBINA - University Of Texas
item REICHMANN, LARA - University Of California
item Fay, Philip

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2018
Publication Date: 4/1/2019
Citation: Polley, H.W., Aspinwall, M.J., Collins, H.P., Gibson, A.E., Gill, R.H., Jackson, R.B., Jin, V.L., Khasanova, A.R., Reichmann, L.G., Fay, P.A. 2019. CO2 enrichment and soil type additively regulate grassland productivity. New Phytologist. 222(1):183-192. https://doi.org/10.1111/nph.15562.
DOI: https://doi.org/10.1111/nph.15562

Interpretive Summary: The concentration of carbon dioxide gas (CO2) in air has risen by 40% since industrialization and is anticipated to reach double the pre-industrial level this century. Higher CO2 concentrations typically increase plant biomass production of mixed-species grasslands by increasing plant growth per unit of water loss through leaves via the process of transpiration. This increase in plant water use efficiency is expected to boost growth relatively more at locations or during years when water availability to plants is limiting than plentiful. This expectation is not always realized, however, likely because CO2 and water availability influence additional regulators of grassland growth response to CO2. ARS scientists at Temple, TX together with university collaborators used the unique Lysimeter CO2 Gradient facility to expose mixtures of perennial forb and grass species grown on clay, sandy loam, and silty clay soil types to CO2 concentrations that ranged from pre-industrial to elevated levels. Over 10 years and across soil types, we found that increasing CO2 increased grassland productivity more when soil water was relatively plentiful than limiting, opposite expectation. Greater water availability increased productivity by both stimulating plant carbon uptake directly and amplifying an increase in abundance of a productive tallgrass species. Our results indicate that assessments that fail to account for positive water effects and compositional shifts may underestimate the magnitude of past and future CO2 effects on grassland productivity and forage production.

Technical Abstract: Atmospheric carbon dioxide (CO2) concentration has risen by 40% since industrialization and is projected to exceed 2X the pre-industrial level this century. Across regional gradients in precipitation, elevated CO2 stimulates grassland primary productivity more when precipitation is relatively scarce. At local scales, however, the productivity-CO2 response to seasonal or inter-annual declines in water input may be positive, negative, or neutral, dependent on variation in other mediators of ecosystem CO2 responses. Integrating regulators of CO2 responses, such as soil texture and plant species abundances, into predictive models is crucial to forecasting primary productivity and ecosystem carbon balance at the spatial and temporal scales at which land managers operate. We show that, in contrast with results from across spatial gradients in precipitation, increasing atmospheric CO2 from pre-industrial to elevated concentrations increased aboveground net primary productivity (ANPP) of perennial C3/C4 grassland communities grown on clay, sandy loam, and silty clay soil types more when soil water was relatively plentiful. Greater water availability contributed to increase ANPP by as much as 50% at elevated CO2 by both directly stimulating ANPP and amplifying an increase in abundance of a productive C4 tallgrass species, Sorghastrum nutans. Combined, positive effects of species shifts and greater water availability outweighed a negative legacy effect of prior-year ANPP on the ANPP-CO2 response across soil types and a decade of CO2 treatment. Assessments that fail to account for positive water effects and compositional shifts may underestimate the magnitude of past and future CO2 effects on grassland productivity and carbon cycling.