Temperature and carbon dioxide effects on nutritive value of rhizoma peanut herbage

Studies assessing the impact of climate change have focused on plant production, but forage nutritive value, especially of legumes, has often been overlooked. The objective of this study was to determine the effect of increasing temperature and atmospheric CO2 concentration on chemical composition and digestibility of rhizoma peanut (RP, Arachis glabrata Benth.) leaf and stem. In vitro digestible organic matter (IVDOM), neutral and acid detergent fiber (NDF and ADF), and lignin concentrations were determined for plants grown in all combinations of two CO2 (360 and 700 micromol mol(-1)) and four temperature environments (baseline, or ambient temperature in the greenhouse, B; B + 1.5; B + 3.0; and B + 4.5 degrees C). Forage was sampled every 6 to 8 wk during two growing seasons. Neither increasing CO2 nor temperature affected leaf IVDOM, but stem IVDOM declined from 562 (B) to 552 g kg(-1) (B + 4.5) with increasing temperature in Year 1 and from 577 to 511 g kg(-1) in Year 2. Stem NDF increased with increasing temperature from 556 to 561 g kg(-1) in Year 1 and from 519 to 526 g kg(-1) in Year 2. Stem ADF (412 to 418 g kg(-1)) and lignin (80 to 93 g kg(-1)) increased linearly as temperature increased in 1 of 2 yr. Lignin as a proportion of NDF or ADF (lignin/NDF or lignin/ADF) accounted for a large proportion of the variation in stem IVDOM. The RP nutritive value decreases with increasing air temperature, but it is relatively unaffected by atmospheric CO2 concentrations in the range studied.