Carbon Dioxide and Temperature Effects on Forage Dry Matter Production

Atmospheric CO 2 and temperature may significantly modify plant production. Grasslands occupy in excess of 25% of the Earth's land area, but grassland species have received limited attention from researchers studying climate change. A 3‐yr study was conducted to determine the effects of elevated atmospheric CO 2 and temperature on dry matter (DM) harvested from the C 3 legume ‘Florigraze’ rhizoma peanut (RP, Arachis glabrata Benth.) and the C 4 grass ‘Pensacola’ bahiagrass (BG, Paspalum notatum Flügge). Both species were field grown in Millhopper fine sand (loamy siliceous Grossarenic Paleudult) in temperature‐gradient greenhouses under different CO 2 (360 and 700 μmol mol −1 ) and temperature conditions (baseline [B], B+1.5, B+3.0, and B+4.5°C, where B equaled ambient temperature). Plots (2 by 5 m) were harvested three times in 1996 and four times each in 1997 and 1998. Analyzed across years, yield increased 25% for RP ( P = 0.02) and tended to increase for BG (15%; P = 0.18) with the near doubling of CO 2 , but there was species by CO 2 interaction ( P = 0.06) as a result of the greater response to CO 2 by the C 3 legume. There was a positive effect of increasing temperature on yield of both species. Averaged across species, yield increased 11% in 1996, 12% in 1997, and 26% in 1998 as temperature increased from B to B+4.5°C. Under well‐watered conditions in this experiment, elevated CO 2 increased DM harvested of a C 3 legume and tended to increase that of a C 4 grass, while the yield response to increasing temperature was positive for both species.