INTERACTION OF COTTON (GOSSYPIUM-HIRSUTUM) AND VELVETLEAF (ABUTILON-THEOPHRASTI) PLANTS FOR WATER IS AFFECTED BY THEIR INTERACTION FOR LIGHT

Transpirations of cotton and velvetleaf plants competing for water and light were estimated with heat balance stem flow gauges in a controll ed environment. Cotton and velvetleaf plants were grown together in po ts and monitored during fluctuations in soil water, irradiance, air te mperature, and humidity. Shading from other plants imposed light compe tition on velvetleaf or cotton. Velvetleaf used significantly more wat er than cotton given ample water and light. Transpiration by both spec ies was reduced in dry soit, but velvetleaf transpiration was reduced primarily by leaf abscision, while cotton leaves did not abscise. Both cotton and velvetleaf plants transpired significantly less when shade d. Leaf water potentials indicated that shaded plants experienced redu ced evaporative demand suggesting that shading reduced plant stress in dry soil. Competition for water was strongly influenced by competitio n for light.