Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 2/5/1998
Publication Date: N/A
Interpretive Summary: The effect of environmental factors on cotton photosynthesis was studied in nearly natural conditions, but where these factors could be controlled, varied independently and systematically. It was shown that doubling atmospheric carbon dioxide increased canopy photosynthesis about 50% in high light and when other conditions were not limiting. The effect of high CO2 on photosynthesis becomes progressively less as other factors (e.g. temperature, nutrients or water) become limiting. Photosynthesis of the canopy becomes progressively less soon after flowering even in uniform radiation environment because of canopy leaf aging. When the leaf aging phenomium is combined with the seasonal decline in solar radiation, it becomes apparent that photosynthesis severly limits crop growth. Boll growth normally consumes a lot of the available photosynthates and limits leaf and stem growth. This results in fewer, highly productive, new leaves being produced. In our present-day production environment, flowering occurs during late July and August, the hottest time of the year. High temperatures during that period cause fruit abscission soon after flowering. This high temperature injury is apparently due to damage to the flower parts, not to the photosynthesis process since photosynthesis proceeded at a high rate in crops that lost their young fruit.
Technical Abstract: The relation between photosynthesis and environmental factors is presented. Here, we report the results from cotton plants grown in naturally-lit plant growth chambers in which temperature, CO2, water, and nutrients were controlled and varied systematically. Photosynthesis of crop canopies was measured continuously along with other related abiotic and vegetative growth parameters. Photosynthesis is the driving process of dry matter production, but factors affecting vegetative growth and development are important aspects of cotton production. Canopy photosynthesis is not light saturated in Midsouth radiation environments. Present-day cropping practices allow the crop demand for photosynthates to occur during declining solar radiation. Current atmospheric CO2 levels are limiting cotton production, and rising CO2 will benefit cotton growth and yield. Temperature has a small effect on canopy photosynthesis and thus primary production is sustained in a wide range of temperatures. Temperature however, strongly influences vegetative growth and development and thus light capture during vegetative period, and light conversion efficiency during much of the boll-filling period. Temperature above 28 C limits both vegetative growth and more importantly boll retention or sink capacity. Water, nitrogen and potassium deficits decrease leaf growth more than photosynthesis. Thus, crop production is a function of many processes from cellular to canopy levels. Increasing production and yield requires knowledge of processes at all levels.