CROP ECOLOGY, PRODUCTION & MANAGEMENT Carbon Dioxide and Temperature Effects on Forage Dry Matter Production

sphere represents less change in CO2 concentrations at the RuBisCO binding sites for C4, resulting in a smaller Atmospheric CO2 and temperature may significantly modify plant response for the C4 compared with the C3 plant. High production. Grasslands occupy in excess of 25% of the Earth’s land area, but grassland species have received limited attention from retemperature also generally increases accumulation of searchers studying climate change. A 3-yr study was conducted to plant DM (Deinum and Dirven, 1974), but the literature determine the effects of elevated atmospheric CO2 and temperature on on forages in this regard, and particularly tropical fordry matter (DM) harvested from the C3 legume ‘Florigraze’ rhizoma ages, is not abundant (Newton, 1991). peanut (RP, Arachis glabrata Benth.) and the C4 grass ‘Pensacola’ Dry matter production of grassland species deterbahiagrass (BG, Paspalum notatum Flügge). Both species were field mines herbivore carrying capacity and thus is a key grown in Millhopper fine sand (loamy siliceous Grossarenic Paleudult) factor affecting productivity of forage-livestock systems. in temperature-gradient greenhouses under different CO2 (360 and Additionally, in many subtropical and tropical grass700 mmol mol21) and temperature conditions (baseline [B], B11.5, lands, large fluctuation in quantity of forage produced B13.0, and B14.58C, where B equaled ambient temperature). Plots from season to season is a critical limitation to intake (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 and livestock performance (Hardy et al., 1997), resulting (P 5 0.02) and tended to increase for BG (15%; P 5 0.18) with the in up to a 6-yr period to produce a slaughter animal on near doubling of CO2, but there was species by CO2 interaction (P 5 pasture (Mott and Moore, 1977). Consequently, under0.06) as a result of the greater response to CO2 by the C3 legume. standing the impact of increasing CO2 and temperature There was a positive effect of increasing temperature on yield of both on productivity and seasonal distribution of DM of subspecies. Averaged across species, yield increased 11% in 1996, 12% tropical and tropical grassland species is particularly in 1997, and 26% in 1998 as temperature increased from B to B14.58C. important. McGinn and Wedin (1997) propose the need Under well-watered conditions in this experiment, elevated CO2 infor greater emphasis on these species when they indicate creased DM harvested of a C3 legume and tended to increase that of that most research on grassland responses to elevated a C4 grass, while the yield response to increasing temperature was CO2 and climate change has occurred in temperate repositive for both species. gions. The objectives of this experiment were to quantify effects of elevated atmospheric CO2 concentration and temperature on (i) DM production of two perennating A co2 has steadily increased from preintropical-subtropical forage species, a C3 legume (rhidustrial concentrations of 280 mmol mol21 and is zoma peanut) and a C4 grass (bahiagrass) and (ii) the predicted to double by the end of the 21st century (Barseasonal distribution of that production. nola et al., 1994; Keeling and Whorf, 1994). Increasing atmospheric temperature is expected to accompany the increase in CO2 (Jouzel et al., 1994). Jones (1997) sugMATERIALS AND METHODS gested that DM production of C3 grassland plants inSite and Species Description creases from 0.10 to 0.12% per 1 mmol mol21 increase The study was conducted in temperature-gradient greenin atmospheric CO2, while increases for C4 plants are houses (TGGs) constructed over undisturbed field soil during expected to be less. A review of effects of doubled CO2 1996, 1997, and 1998 at the Irrigation Research and Education on forage plants suggests that DM production is likely to Park, University of Florida, Gainesville (298389 N and 828229 increase 30 and 10% for C3 and C4 species, respectively W). The average annual temperature is 218C (average of years (Newton, 1991). Plants of the C4 pathway have a built1961–1990), with an average annual rainfall of 1342 mm. The in mechanism in the bundle sheath cells which allows soil was a Millhopper fine sand with a pH of 6.2 to 6.7. Soil them to maintain a higher CO2 concentration around organic matter at the site ranged from 12 to 15 g kg2. For ribulose-1,5 bisphosphate carboxylase/oxygenase (Ruthe analysis of soil P, K, Ca and Mg, the Mehlich-I extractant BisCO), enabling it to fix more CO2 at ambient levels was used. Soil Ca concentration ranged from 240 to 340 mg kg2, Mg from 98 to 115 mg kg2, P from 79 to 97 mg kg2, than does a C3 plant. Therefore, an enriched CO2 atmoand K from 6 to 11 mg kg2. Stands of RP and BG were planted on 10 Apr. 1995 (Fritschi Y.C. Newman, L.E. Sollenberger, K.J. Boote, Agronomy Dep., Univ. et al., 1999). Rhizoma peanut and BG are native to South of Florida, Gainesville, FL 32611-0300; L.H. Allen, Jr., USDA-ARS, America and are persistent perennials in North Florida. They P.O. Box 110965, Gainesville, FL 32611-0965; R.C. Littell, Statistics initiate spring growth in March in most years and are producDep., P.O. Box 110339, Gainesville, FL 32611-0339. This research was sponsored in part by National Institute for Global Environmental Change, Southeastern Region, Grant 94UOF006CR3. Florida Agric. Abbreviations: B, baseline ambient temperature; BG, bahiagrass; DM, Exp. Stn. Journal Series No. R-07168. Received 11 Oct. 1999. *Corredry matter; PAR, photosynthetically active radiation; RP, rhizoma sponding author ([email protected]). peanut; RuBisCO, ribulose-1,5-bisphosphate carboxylase/oxygenase; TGG, temperature gradient greenhouse. Published in Crop Sci. 41:399–406 (2001).