Genotypic variations in photosynthetic and physiological adjustment to potassium deficiency in cotton (Gossypium hirsutum).

A hydroponic culture experiment was conducted to determine genotypic variation in photosynthetic rate and the associated physiological changes in response to potassium (K) deficiency in cotton (Gossypium hirsutum L.) seedlings with contrasting two cotton cultivars in K efficiency. The K-efficient Liaomian18 produced 66.7% more biomass than the K-inefficient NuCOTN99(B) under K deficiency, despite their similar biomass under K sufficiency. Compared with NuCOTN99(B), Liaomian18 showed 19.4% higher net photosynthetic rate (P(n), per unit leaf area) under K deficient solutions and this was associated with higher photochemical efficiency and faster export of soluble sugars from the phloem. The lower net P(n) of NuCOTN99(B) was attributed to higher capacity for nitrate assimilation and lower export of soluble sugars. Furthermore, NuCOTN99(B) showed 38.4% greater ETR/P(n) than Liaomian18 under K deficiency, indicating that more electrons were driven to other sinks. Higher superoxide dismutase (SOD) and lower catalase (CAT) and ascorbate peroxidase (APX) activities resulted in higher levels of reactive oxygen species (ROS; e.g. O(2)(-)and H(2)O(2)) in NuCOTN99(B) relative to Liaomian18. Thus, the K inefficiency of NuCOTN99(B), indicated by lower biomass and net P(n) under K deficiency, was associated with excessively high nitrogen assimilation, lower export of carbon assimilates, and greater ROS accumulation in the leaf.