Potassium ameliorates cotton (Gossypium hirsutum L.) fibre length by regulating osmotic and K + /Na + homeostasis under salt stress.

Potassium (K) application can alleviate cotton salt stress, but the regulatory mechanisms affecting cotton fibre elongation and ion homeostasis are still unclear. A two-year field experiment was conducted to explore the effects of K on the osmolyte contents (soluble sugar, K + content and malate) and related enzyme activities during the fibre elongation of two cotton cultivars with contrasting salt sensitivity (CCRI-79; salt tolerant cultivar and Simian 3; salt-sensitive cultivar). Three K application treatments (0, 150, and 300 kg K 2 O ha -1 ) were applied at three soil salinity levels (low salinity, EC=1.73 ± 0.05 dS m -1 ; medium salinity, EC=6.32 ± 0.10 dS m -1 ; high salinity, EC=10.84 ± 0.24 dS m -1 ). K application improved fibre length and alleviated salt stress by increasing the maximum velocity of fibre elongation (V max ). The increase rate of K on fibre length decreased with elevating salt stress, and the increase rate of K on V max of CCRI-79 was greater than that of Simian3. K application can increase the enzyme activities (phosphoenolpyruvate carboxylase, PEPC, E.C. 4.1.1.31; pyrophosphatase, PPase, E.C. 3.6.1.1; and plasma membrane H + -ATPase, PM H + -ATPase, E.C. 3.6.3.14) as well as the content of osmolytes associated with the enzymes mentioned above. K increased the osmolyte contents under salt stress, and the increase in the K + content of the fibres was much higher than that of soluble sugar and malate. The results of this study indicated K fertilizer application rates regulate the metabolism of osmolytes in cotton fibre development under salt stress, K + is more critical to fibre elongation. This article is protected by copyright. All rights reserved.