纤维长度、比强度和马克隆值是棉花三大纤维品质指标，其中纤维长度是对纺织成纱单纱强力影响最大的因素。滨海盐碱地棉田增施钾肥可使棉株克服由Na+过高导致的K+吸收障碍，极显著提高棉纤维长度。因此，本研究拟通过设置低、中、高3个盐分水平（EC=1.15、6.00、11.46 dS m-1）、3个施钾量（0、150、300kg K2O hm-2）、2个棉花品种（中棉所79，耐盐型；泗棉3号，盐敏感型）综合性试验，研究土壤不同钾钠水平对棉株K+、Na+的吸收与分配、棉叶光合产物的形成与转化的影响，研究棉株K+/Na+对调控纤维伸长的膨压物质及相关酶活性、纤维细胞壁松驰酶活性的影响，明确对棉株K+/Na+变化敏感的关键膨压物质、膨压物质代谢与纤维细胞壁松驰的关键酶及基因表达差异，揭示滨海盐碱地施钾影响棉纤维长度形成的生理机制，研究结果为生产上探索滨海盐碱地改善棉纤维长度的生理调控途径提供理论依据。

Fiber length, which together with fiber strength and micronaire is known as the "quality indexes" of cotton, is the most important factor for single yarn strength. Compared with low sodium soil, the application of potassium fertilizer can make the cotton leaves overcome K+ malabsorption due to high Na+, and significantly improve the cotton fiber length. Improving fiber length is very important for enhancing the international competitiveness of the cotton. In order to investigate the effect of K application on fiber elongation development and fiber length formation of cotton grown in saline-alkali soil, field and pot experiments will be designed with two cotton cultivars (CCRI 79, salt-tolerant；Simian 3, salt-sensitive) under three salinity levels(EC=1.15, 6.00, 11.46 dS m-1), meanwhile three potassium levels (0,150 and 300kg K2O ha-1) will be applied to each salinity level. The objectives of our research are(1) to study the effect of different potassium levels, sodium levels and K+/Na+ ratios in soil on potassium and sodium accumulation and distribution in cotton plants; (2) to explore the effect of K+/Na+ ratio in cotton plants on photosynthesis and biomass partitioning; (3) to understand the dynamic changes of matters (soluble sugar, K+, malic acid) and enzymes (plasmalemma H+-ATPase, PPase, SuSy, SPS, PEPC) involving fiber elongation, and enzymes (β-1,4-glucanase, Expansin, XET) involving cell wall loosing under different K+/Na+ ratios in cotton plants; (4) to identify the sensitive matters and enzymes to K+/Na+ ratios and compare the differences in gene expression of sensitive enzymes. These studies will be beneficial to reveal the physiological mechanism of the effect of potassium application on the growth and formation of fiber length in saline-alkali soil and it also provide theoretical basis for exploring the physiological regulation of cotton fiber elongation in saline-alkali soil.