Title: Productivity of well-watered Panicum virgatum does not increase with CO2 enrichment Authors
Submitted to: Journal Of Plant Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 15, 2012
Publication Date: March 16, 2012
Citation: Fay, P.A., Polley, H.W., Jin, V.L., Aspinwall, M.J. 2012. Productivity of well-watered Panicum virgatum does not increase with CO2 enrichment. Journal of Plant Ecology. 5(4):366-375. Interpretive Summary: Rising atmospheric CO2 has been shown to increase aboveground net primary productivity (ANPP) in water-limited perennial grasslands, in part by reducing transpiration, thereby increasing photosynthetic water use efficiency and reducing depletion of soil moisture. However little is known about CO2 effects on monocultures of perennial C4 grasses such as Panicum virgatum, a native grass of tallgrass prairie and a potential bioenergy crop. We hypothesized that increased CO2 would not increase P. virgatum ANPP, because photosynthetic rates of this C4 grass would not increase and because reduced transpiration from reduced stomatal conductance at elevated CO2 would provide little additional benefit in increased soil moisture. The findings confirmed this hypothesis, and also revealed evidence for meristem limitation of productivity at elevated CO2 and for increased physiological coupling to CO2 concentration on the plants established.
Technical Abstract: Switchgrass is a widespread C4 tallgrass native throughout much of the U.S, is an important component of more mesic locations in grasslands, and is widely studied as a potential bioenergy crop. Much is known about switchgrass growth and productivity, but surprisingly little research has been conducted on effects of elevated atmospheric CO2 on switchgrass productivity. Although rising atmospheric CO2 is generally held to increase plant productivity, indeed, C4 grasses like switchgrass are widely viewed as experiencing little benefit from elevated CO2 unless water is limiting. This study examined CO2 effects on aboveground biomass productivity of periodically clipped, well watered and fertilized switchgrass as it established over four years in a unique experiment that imposes a continuous gradient of CO2 concentrations representing pre-industrial (250 parts per million) to mid 21st century (500 parts per million) levels. As expected, CO2 had little effect on switchgrass productivity, but caused plants to produce fewer, but larger tillers, indicating increased meristem limitation of productivity. Further, as the plants established, they became increasingly coupled physiologically to the CO2 concentration at which they were grown, reflecting the large gains in leaf area and demand for water. These results demonstrate the onset of multiple limitations to productivity in switchgrass as CO2 concentrations rise.