A CO2 concentration gradient facility for testing CO2 enrichment and soil effects on grassland ecosystem function

Authors: Fay, Philip; REICHMANN, LARA - University Of Texas; ASPINWALL, MICHAEL - Western Sydney University; KHASANOVA, ALBINA - University Of Texas; Polley, Herbert

Submitted to: Journal of Visualized Experiments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2015
Publication Date: 11/21/2015
Publication URL: http://handle.nal.usda.gov/10113/62448
Citation: Fay, P.A., Reichmann, L.G., Aspinwall, M.J., Khasanova, A.R., Polley, H.W. 2015. A CO2 concentration gradient facility for testing CO2 enrichment and soil effects on grassland ecosystem function. Journal of Visualized Experiments. 105:e53151. doi: 10.3791/53151.

Interpretive Summary: This manuscript plus an accompanying video document a technique used to create a continuous gradient in atmospheric carbon dioxide concentrations on grassland plant communities growing on soils of different texture. This approach has been successfully applied to study how grassland plant productivity may be influenced by past and future increases in atmospheric carbon dioxide concentrations, and how the productivity may be influenced differently on different soils, and therefore may vary across grasslands. This is necessary knowledge to understand how forage availability and quality may vary in grasslands grazed by livestock. Representative results from seven years of treatment with the carbon dioxide gradient, showing how increasing carbon dioxide concentration along the gradient increases plant productivity more on sandy than clay soils, primarily because of increased abundance of a productive grass species. Thus, the technique is successful at maintaining a carbon dioxide gradient and discerning how carbon dioxide effects may vary with soil type.

Technical Abstract: Continuing increases in atmospheric CO2 concentrations mandate techniques for examining impacts on terrestrial ecosystems. Most experiments examine only two or a few levels of CO2 concentration and a single soil type, but if CO2 can be varied as a gradient from subambient to superambient concentrations on multiple soils, we can discern whether past rates of ecosystem response may continue in the future and how ecosystem responses may vary across the landscape. The Lysimeter CO2 Gradient Facility was designed to apply a 250 to 500 uL L-1 CO2 gradient to Blackland prairie plant communities established on lysimeters containing clay, silty clay, and sandy soils. The facility operates on the principle that photosynthesis by vegetation enclosed in chambers can be used to progressively deplete CO2 from air flowing directionally through the chamber. During seven years of operation, the facility has maintained a linear gradient in CO2 concentration while controlling gradient-wise air temperature and dew point near ambient. The system clearly shows the shape of ecosystem responses to CO2 enrichment and differences in the rates of response to CO2 among soil types. Volumetric soil water content increased linearly on sandy loam and clay soils, but not on silty clay soil. Aboveground net primary productivity of Blackland prairie plant communities increased with CO2 to different extents on the three soils, most strongly on the sandy loam soil where the dominant grass species increased most strongly with CO2 enrichment. Thus, the facility successfully discerns the shape of ecosystem responses to CO2 enrichment from subambient to superambient concentrations and the CO2 by soil interactions affecting plant productivity that indicate how effects of atmospheric CO2 enrichment may vary across the landscape.