GROWTH AND YIELD RESPONSES OF FIELD-GROWN SWEET-POTATO TO ELEVATED CARBON-DIOXIDE

Root crops are important in developing countries, where food supplies are frequently marginal. Increases in atmospheric CO2 usually lead to increases in plant growth and yield, but little is known about the res ponse of root crops to CO2 enrichment under field conditions, This exp eriment was conducted to investigate the effects of CO2 enrichment on growth and yield of field-grown sweetpotato [Ipomoea batatas (L.) Lam. ]. Plants were grown in open-top chambers in the field at four CO2 lev els ranging from 354 (ambient) to 665 mu mol mol(-1) in two growing se asons, Shoot growth was not affected significantly by elevated CO2. Yi eld of storage roots increased 46 and 75% at the highest CO2 level in the 2 yr, The yield enhancement occurred through increases in the numb er of storage roots in the first year and through increases in both th e number and size of the storage roots in the second year, Storage-roo t/shoot ratios increased 44% and leaf nitrogen concentrations decrease d by 24% at the highest CO2 level, A comparison of plants grown in the open field to plants grown in open-top chambers at ambient CO2 concen trations indicated that open-top chambers reduced shoot growth in the first year and storage-root yield in both years, These results are con sistent with the majority of CO2-enrichment studies done on pot-grown sweetpotato.