4Kimball B A, Mauney J R, Nakayama F S, et al. Effects of increasing atmospheric CO2 on vegetation. Vegetatio, 1993,104:65-67
5Allen L H Jr. Carbon dioxide increase: Direct impacts on crops and indirect effects mediated through anticipated climatic changes. In: Boote K J, Bennett J M, Sinclair T R, et al. eds. Physiology and Determi nation of Crop Yield. Madison, Wisconsin: Ameri