Individual and interactive influences of elevated air temperature and soil drought at the flowering and boll-forming stage on cottonseed yield and nutritional quality

As the main byproduct of cotton production, cottonseed yields edible vegetable oil, ruminant feed, and industrial products. We evaluated the individual and interactive effects of elevated air temperature and soil drought on cottonseed yield and nutritional quality using two cotton cultivars, Sumian 15 (heat-susceptible) and PHY370WR (heat-tolerant). The experiment was conducted under three levels of soil relative water content (SRWC): (75 ± 5)%, (60 ± 5)% and (45 ± 5)% and two temperature regimes: ambient temperature (AT, 31.0/26.4 °C, mean daytime/night temperature) and elevated temperature (ET, 33.4/28.9 °C). Cottonseed yield, boll number, seed number, and single-seed weight were lower under combined ET and SRWC(45 ± 5)% than either individual stress or combined stresses in comparison with the control treatment (SRWC(75 ± 5)% under AT). Drought tended to increase oil content and reduce protein content, whereas ET showed almost the opposite effects. Under the combination of ET and soil drought, oil content was still higher than under control, although ET weakened the beneficial effects of drought. For protein, ET offset the negative impacts of mild drought on protein content, but protein content was not increased under SRWC(45 ± 5)%. Each stress or combined stress reduced oil and protein yields under all treatments, owing to declines in cottonseed yields. The combined stress reduced unsaturated fatty acid (UFA)/saturated fatty acid (SFA) and essential amino acid (EAA)/non-essential amino acid (NAA). Compared with PHY370WR, the sensitivity of Sumian 15 to the combined factors was evidenced in the following ways: (1) seed yield, yield components, oil and protein yields were decreased more for Sumian 15 than PHY370WR compared with the control treatment; (2) the combined stresses caused lower oil content, UFA, and UFA/SFA in Sumian 15 than PHY370WR; (3) interaction effects of the combined factors on protein content and EAA/NAA were detected only in Sumian 15.