Growth, pod, and seed yield, and gas exchange of hydroponically grown peanut in response to CO2 enrichment

The effects of elevated CO2 on growth, pod, and seed yield, and gas exchang e of 'Georgia Red' peanut (Arachis hypogaea L.) were evaluated under,contro lled environmental conditions. Plants were exposed to concentrations of 400 (ambient), 800, and 1200 mu mol.mol(-1) CO2 in reach-in growth chambers. F oliage fresh and dry weights increased with increased CO2 up to 800 mu mol. mol(-1), but declined at 1200 mu mol.mol(-1). The number and the fresh and dry weights of pods also increased with increasing CO2 concentration. Howev er, the yield of immature pods was not significantly influenced by increase d CO2. Total seed yield increased 33% from ambient to 800 mu mol.mol(-1) CO 2 and 4% from 800 to 1200 mu mol.mol(-1) CO2. Harvest index increased with increasing CO2, Branch length increased while specific leaf area decreased linearly as CO2 increased from ambient to 1200 mu mol.mol(-1). Net photosyn thetic rate was highest among plants grown at 800 mu mol.mol(-1). Stomatal conductance decreased with increased CO2. Carboxylation efficiency was simi lar among plants grown at 400 and 800 mu mol.mol(-1) and decreased at 1200 mu mol.mol(-1) CO2. These results suggest that CO2 enrichment from 400 to 8 00 mu mol.mol(-1) had positive effects on peanut growth and yield, but abov e 800 mu mol.mol(-1) enrichment seed yield increased only marginally.