Abstract

This study investigated the effects of drought during reproductive and boll development stages under elevated CO2 conditions. A pot experiment was conducted in the Soil–Plant–Atmospheric-Research (SPAR) facility using the upland cotton cultivar DP 1646 B2XF grown under control (well-watered; 0.12 m3 H2O m−3 soil) and drought (0.09 m3 H2O m−3 soil) conditions at ambient (425 ppm; aCO2) and enriched (725 ppm; eCO2) CO2 concentrations. Under drought stress, photosynthesis and stomatal conductance decreased by 35% and 63%, respectively, under aCO2, whereas reductions were less pronounced under eCO2 (20% and 36%). Under drought and aCO2, intrinsic and instantaneous water-use efficiency increased by 74% and 45%, respectively, compared to control. Biomass partitioning shifted under drought, with increased allocation to shoots (55%) and roots (9%) and reduced allocation to reproductive organs (36%), compared to control conditions. Flowers produced under drought had 21% fewer ovules under both CO2 environments, while pollen production remained unaffected. Seed cotton and lint weights were reduced by 19% and 15% under drought, respectively. However, plants grown under eCO2 attained seed cotton and lint weights that were 20% higher than those grown under aCO2, under both control and drought conditions. Drought significantly affected fiber quality, increasing micronaire by 26% and reducing fiber length by 4%, regardless of CO2 level. eCO2-driven alleviation primarily acts through carbon assimilation and yield compensation, with limited capacity to regulate developmental programming and quality formation.

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