Evaluating the Mechanisms of Photosynthetic Inhibition under Growth-Limiting, Early-Season Water Deficit Stress in Cotton

The current study evaluated the possibility that growth-limiting, early-season drought stress sufficient to decrease net photosynthesis (A(N)) would be associated with declines in stomatal conductance (g(s)) and ATP content, regardless of stress level. Studies were conducted in greenhouse facilities in Athens and Tifton, GA, and imposed different early-season drought durations to generate a range of early-season water-deficit stress conditions. The earlyseason drought durations imposed decreased A N to values ranging from 20 to 60% of the levels observed in well-watered plants. Where declines in A N were observed, g(s) and photosynthetic electron transport rate (ETR) declined substantially, indicating some level of metabolic and possibly diffusional limitation to photosynthesis. The ATP content was unaffected or actually increased in response to photosynthesis-limiting drought in both years of the study, suggesting that ATP-induced limitations to photosynthesis are minimal over a broad range of A(N) -limiting, early-season drought stress conditions in cotton (Gossypium hirsutum L.). All drought durations limited leaf, stem, reproductive, and total dry matter production. Declines in dry matter under mild stress were primarily associated decreased leaf area production, whereas decreased A(N) was likely an important contributor under more severely stressed treatments. Photosynthetic declines under growth-limiting, early-season drought do not appear to be associated with reduced ATP production, as suggested in other plant species.