Potassium ameliorates cotton (Gossypium hirsutum L.) fiber 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 fiber 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 fiber 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 300kg K2O 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 fiber length and alleviated salt stress by increasing the maximum velocity of fiber elongation (V-max). The increase rate of K on fiber 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 fibers 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 fiber development under salt stress, K+ is more critical to fiber elongation.

Automated summary

Potassium (K) application can alleviate cotton salt stress and improve fiber length and the maximum velocity of fiber elongation. It also increases enzyme activities and osmolyte contents. The effect of K application on fiber elongation decreases with increasing salt stress, with CCRI-79 responding to K application better than Simian 3.