Temperature and Carbon Dioxide Effects on Nutritive Value of Rhizoma Peanut Herbage

Florigraze RP is a warm-season perennial legume used for pasture (Williams et al., 1991) or as conserved Studies assessing the impact of climate change have focused on forage (Prine et al., 1981). Capable of supporting daily plant production, but forage nutritive value, especially of legumes, has often been overlooked. The objective of this study was to deterweight gains of 1 kg in beef cattle (Bos spp.), RP is mine the effect of increasing temperature and atmospheric CO2 conpersistent under grazing and is regarded as a high quality centration on chemical composition and digestibility of rhizoma peaforage legume by livestock producers (Williams et al., nut (RP, Arachis glabrata Benth.) leaf and stem. In vitro digestible 1991). It has excellent forage quality, usually comparaorganic matter (IVDOM), neutral and acid detergent fiber (NDF and ble with that of alfalfa (Medicago sativa L.) (Romero ADF), and lignin concentrations were determined for plants grown et al., 1987). in all combinations of two CO2 (360 and 700 mol mol 1) and four There have been relatively few experiments that contemperature environments (baseline, or ambient temperature in the sidered the effects of climate change on warm-season greenhouse, B; B 1.5; B 3.0; and B 4.5 C). Forage was sampled legume nutritive value. Such data are needed because every 6 to 8 wk during two growing seasons. Neither increasing CO2 of the importance of grassland agriculture in the lower nor temperature affected leaf IVDOM, but stem IVDOM declined from 562 (B) to 552 g kg 1 (B 4.5) with increasing temperature in Southern USA and in warm climates throughout the Year 1 and from 577 to 511 g kg 1 in Year 2. Stem NDF increased world. The objectives of this experiment were (i) to with increasing temperature from 556 to 561 g kg 1 in Year 1 and quantify the effects of increasing CO2 and temperature from 519 to 526 g kg 1 in Year 2. Stem ADF (412 to 418 g kg 1) and on the nutritive value of RP leaf and stem measured lignin (80 to 93 g kg 1) increased linearly as temperature increased through IVDOM, NDF, ADF, and lignin, and (ii) to in 1 of 2 yr. Lignin as a proportion of NDF or ADF (lignin/NDF or determine the relationship between the composition of lignin/ADF) accounted for a large proportion of the variation in the fiber fraction of the stem and stem IVDOM. stem IVDOM. The RP nutritive value decreases with increasing air temperature, but it is relatively unaffected by atmospheric CO2 concentrations in the range studied. MATERIALS AND METHODS Site and Greenhouse Description I atmospheric CO2 to near a doubling of The study was conducted during 1996 and 1997 in four temcurrent concentrations and an associated increase in perature-gradient greenhouses (TGGs) constructed over undisturbed field soil at the Irrigation Research and Education Park, temperature are among changes predicted to occur in University of Florida, Gainesville (29 38 N and 82 22 W). the global environment as consequence of the burning Stands of RP were planted on 10 Apr. 1995 (Fritschi et al., of fossil fuels (Keeling et al., 1995). A major research 1999) and arranged lengthwise in one half of each TGG. A emphasis has been the impact of environmental changes TGG is a semicircular arch structure made of galvanized steel, on plant production (Idso and Idso, 2001), but effects and covered with SIXLIGHT (Taiyo Kogyo Co., Tokyo, Jaon the nutritive value of plants and plant parts consumed pan), which is a transparent polyethylene telephtalate film by herbivores has often been overlooked. The nutritive with 90% light transmission. The TGGs were 27.4-m long, value of plants, defined as the chemical composition 4.3-m wide, and 2.2-m high at the center, and were parallel and their potential digestibility, is a function of chemical, to each other in a north–south orientation with separation physical, and structural factors inherent to the plant between TGGs of 4.8 m. The first 3.6 m at the air intake end (Moore, 1994), all of which are dependent to some exand the last 1.8 m at the outlet ventilation fan end of the greenhouse were not used. Four 5by 2-m plots were laid out tent on external factors including climate. Thus, increasin the remainder of the space in each greenhouse as shown ing CO2 and temperature may affect plant chemical in Fig. 1. A more detailed description is given by Sinclair et composition and its feed value for herbivores (Wilson al. (1995) and Fritschi et al. (1999). et al., 1991; Idso and Idso, 2001). The irrigation system had 32 microjet spray heads; 16 of them were along each side of the TGG and they were spaced Y.C. Newman, L.E. Sollenberger, and K.J. Boote, Agronomy Dep., 1.8 m from each other. Irrigation was applied three times per Univ. of Florida, Gainesville, FL 32611-0300; L.H. Allen, Jr., and week using a double-overlapping microjet sprinkler pattern. J.C.V. Vu, USDA-ARS, P.O. Box 110965, Gainesville, FL 32611This method of application provided 7 to 8 mm d 1 on average 0965; and M.B. Hall, U.S. Dairy Forage Research Center, 1925 Linden during the 8to 9-mo growing season. During winter, the rate Drive-West, Madison, WI 53706-1108. This research was sponsored was reduced approximately in half. The total annual irrigation in part by the U.S. Department of Energy’s National Institute for averaged for the 2-yr period and expressed as a rainfall equivaGlobal Environmental Change through the Southeastern Region Center at the Univ. of Alabama, Contract 94UOF006CR3. Florida Agric. Exp. Stn. Journal Series No. R-10021. Received 12 Feb. 2004. *CorreAbbreviations: ADF, acid detergent fiber; B, baseline temperature; sponding author ([email protected]). DM, dry matter; IVDOM, in vitro digestible organic matter; NDF, neutral detergent fiber; OM, organic matter; PAR, photosynthetically Published in Crop Sci. 45:316–321 (2005). © Crop Science Society of America active radiation; RP, rhizoma peanut; TGG, temperature-gradient greenhouse. 677 S. Segoe Rd., Madison, WI 53711 USA