| Salinization as an important limiting factor for land productivity, can seriously affect the food security and sustainable agricultural development. Cotton is a mainly pioneer crop in saline. Improving cotton cultivation technology in saline has become the main direction in cotton production. Studying cotton yield and quality formation in response to soil salinity,can provide a theoretical basis for the optimization of saline cotton cultivation techniques and breeding salt-tolerant varieties. The research was based on the experiments of salt tolerance evaluation and salt tolerance indexes screening among 22 main cultivars in the Yellow River and Yangtze River lower reaches. We used CCRI-79 (salt-tolerant) and Simian3 (salt-sensitive) with obvious differences in salt tolerance in the experiment, which was conducted under high (Ec 11.46 dS m-1), medium (Ec 6.00 dS m-1), low (Ec 1.15 dS m-1) soil salinity levels in 2013-2014 in Dafeng, Jiangsu Coastal Saline. The research aims to study (1) the effects of salinity stress on cotton yield and fiber quality and the sucrose metabolisms of cotton leaf and fiber; (2) the spatial - temporal changes of salt ions contents in soil and cotton plants in respond to cotton yield under different soil salinity levels. The main results were as follows:1. The analysis showed CCRI-79 was highly salt tolerant cultivar and Simian 3 was salt sensitive.The cultivars were classified on the basis of salinity tolerance by means of principal component analysis and cluster analysis considering the range of data on germination and growth traits. The correlation analysis on the relative values of most germination and growth parameters showed positive relationships among several variables. The cultivars were ranked based on the principal components analysis and five groups on salinity tolerance were sorted for the 22 cotton cultivars according to the cluster analysis. Principal component analysis results showed that radical length, coleoptiles and leaf weight and germination rate were the most significant factors and were recommended as the main indexes to identify salinity tolerance of sorghum at germination. These results showed that CCRI-79 was highly salt-tolerant and Simian 3 was salt-sensitive.2. Lint yield and fiber quality of cotton decreased with soil salinity level.Between the two cultivars with various ability of salinity tolerance,Simian 3 were influenced by salinity more significantly.The number of branches, squares, bolls and nodes decreased with salinity level, while shedding rates of squares, flowers and bolls increased. Biomass of plant and boll decreased with high salinity level, and seed cotton biomass rate decreased. Soil salinity influenced lint yield mainly by decreasing boll number per plant. Moreover, length, uniformity and strength decreased soil salinity. Between the two cultivars with various ability of salinity tolerance, Simian 3 was affected by salinity more significantly.3. Higher K+/Na+ and Ca2+ concents may be the reason of higher salt resistance in CCRI-79.Soil conductivity, contents of Na+, K+and Mg2+ in the soil increased significantly with the growth of cotton plant. Soil conductivity and cation declined with the increasing soil depth at the same growth period. Content of K+ and Ca2+ declined gradually with the increase of soil conductivity, compared with the increase trend in Na+ and Mg2+. There were no significant differences in soil salinity changes among different cultivars, which was consistent with changes of the plant ions.4. The subtending leaf was more sensitive to soil salinity stress than the functional leaf. Under soil salinity stress, boll weight was controlled by Pn,sucrocose transformation rate and SPS activity together.Chlorophyll a, Chlorophyll b and Pn of the functional leaf and subtending leaf decreased under soil salinity stress, whereas Ci firstly decreased under the medium salinity level and then increased under the high salinity level. Under soil salinity stress, the contents of soluble sugar, sucrose and starch in the functional leaf decreased significantly, whereas the contents of sucrose and starch in the subtending leaf increased as well as the activities of sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) in the functional leaf and subtending leaf. However, there was non-significant difference in inverse activity in the functional leaf and subtending leaf among the three soil salinity levels. Most of the tested indices indicated that the subtending leaf was more sensitive to soil salinity stress than the functional leaf. Throughout analyzing F values of ANOVA of the effect of years, salinity rate, cultivars, and their interaction for SPS and SuSy peak values in the subtending leaf, it was found that sucrose synthesis by SPS, is a mechanism to adapt to salinity stress, and the difference of sucrose metabolizing enzymes in the subtending leaf for the two cotton cultivars under soil salinity stress was mainly determined by SPS activity. Under soil salinity stress, reduction in Pn and sucrose transformation rate directly decrease boll weight,and higher SPS activity could efficiently synthesis sucrose to reducing cell osmotic potential in order to adapt to soil salinity stress.5. Sucrose and cellulose contents and SPS activity in fiber decreased salinity level, which were opposite to ?-1,3-glucan content. They worked together to determine the fiber length and micronaire under salinity tolerance.Fiber length was significantly positive related with maximum sucrose content and average sucrose content. Fiber strength was significantly positive correlated with maximum sucrose content, average sucrose content, cellulose content and sucrose transformation rate(Tr),while it was negative related to ?-1,3-glucan content.TSG of fiber strength had a significant positive correlation with minimum sucrose content in fiber. Fiber micronaire was significantly negatively correlated with maximum sucrose content, average sucrose content and V(Cel)max, while it was positively related to T(Cel) and ?-1,3-glucan content.The results indicated that fiber length was regulated by sucrose metabolism, while metabolisms of sucrose, ?-1,3-glucan and cellulose work together to determine the fiber length and micronaire under salinity tolerance. SPS (Sucorse phosphate synthase, E.C. 2.4.1.14)activity paralled cellulose deposition, but it was opposite to ?-1,3-glucan content. SuSy (Sucrose synthase, E.C. 2.4.1.13) activity increased with sailnity level, while invertases (E.C. 3.2.1.26)decreased. Changes of activity of ?-1,3-glucanase were the opposite to that of invertase.In summary, inorganic ions in the soil were been seltctively absorpted in cotton roots,especially for Na+ and K+ to mitigate salinity damage and Improve cotton production and fiber quality. The physiology basis were as follows: (1) to improve photosynthetic performance of leaves. (2) to improve the allocation of biomass in the reproductive organs.(3) to promote the sugar metabolism of leaf and fiber. |
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