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 exchange of 'Georgia Red' peanut (Arachis hypogaea L.) were evaluated under,controlled environmental conditions. Plants were exposed to concentrations of 400 (ambient), 800, and 1200 mu mol.mol(-1) CO2 in reach-in growth chambers. Foliage 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. However, the yield of immature pods was not significantly influenced by increased CO2. Total seed yield increased 33% from ambient to 800 mu mol.mol(-1) CO2 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 photosynthetic rate was highest among plants grown at 800 mu mol.mol(-1). Stomatal conductance decreased with increased CO2. Carboxylation efficiency was similar 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 800 mu mol.mol(-1) had positive effects on peanut growth and yield, but above 800 mu mol.mol(-1) enrichment seed yield increased only marginally.