Physiological Responses of Three Cotton Genotypes to Irrigation Treatment and Seasonal Variation in the Water Status of the Soil-Plant-Atmosphere Continuum

Water is the most limiting factor governing agricultural productivity worldwide. Depending upon the timing and duration, drought can limit yields substantially in cotton. As competition for available groundwater increases, it is important to identify cultivars that efficiently utilize available soil moisture under water deficit conditions. The objective of this research was to quantify the physiological responses of a range of commercial cotton cultivars to contrasting irrigation treatments in southern Georgia. Classical gas exchange measurements were combined with fluorescence-based measurements of photosystem II quantum yield and electron transport rates to help identify the underlying mechanisms of drought-induced limitations to net carbon fixation under field conditions (i.e. respiration, photorespiration, and gross photosynthesis). To more adequately characterize metabolic responses to the water status of the soil-plant-atmosphere continuum, additional measurements included pre-dawn and midday leaf water potential, soil moisture status using watermark sensors, and leaf-air vapor pressure deficit.