| Flowering and boll-forming stage is the key yield determinant period of upland cotton. Short-duration waterlogging occurring during this stage significantly reduced cotton final productivity and fiber quality. Nitrogen as a mineral nutrient is required in large amounts by plants and nitrogen application could improve waterlogging resistance in plants. The study on the effects of nitrogen on physiological mechanism for cotton yield formation under waterlogging has obvious implication for improving waterlogging resistance and guiding cultural management in cotton. Pot experiments were conducted to short-term waterlogging during flowering and boll-forming stage of cotton in 2005-2006 at the research field area of Nanjing Agricultural University. Within each water treatment, three nitrogen levels (0,240 and 480kg N ha-1) were imposed. The study focused on:(1) effects of nitrogen on the accumulation and distribution of dry matter and nitrogen, yield and fiber quality under waterlogging; (2) effects of nitrogen on root growth, antioxidant enzyme activities and root vigor under waterlogging; (3) responses of photosynthesis of cotton to nitrogen under waterlogging, and the relationship between chlorophyll fluorescence characteristic, antioxidant enzyme activity, endogenous hormone content and net photosynthetic rate in cotton leaf; (4) effects of nitrogen on the cotton fiber thickening and fiber strength development under waterlogging. The main results were as follows:1. Effects of nitrogen on the accumulation and distribution of dry matter and nitrogen of cotton under waterloggingWaterlogging significantly reduced dry matter weight, nitrogen content and nitrogen accumulation amount in different organs of cotton. Waterlogging decreased the distributive indices of biomass in root and bud, flower and boll, and the distributive indices of nitrogen in leaf and bud, flower and boll; increased the distributive indices of biomass in leaf and main stem and fruit branch, and the distributive indices of nitrogen in root and main stem and fruit branch. Nitrogen could increase biomass and nitrogen in main stem and fruit branch and leaf. The accumulation amount and distributive indexes of biomass in bud, flower and boll, yield of seed cotton were all highest at 240 kg N ha-1 level under waterlogging in our experiments, deficient (0 kg N ha-1) and excessive nitrogen supply (480 kg N ha-1) are of disadvantaged to the yield and fiber quality.2. Effects of nitrogen on root physiological characteristics of cotton under waterloggingWaterlogging significantly reduced cotton root dry matter weight and the Root/Shoot ratio of plants, and the root dry matter weight reached a peak at the 240 kg N ha-1 under waterlogging, but the Root/Shoot ratio decreased with the increase of N application. Under waterlogging, soluble protein content significantly decreased in comparison with well-watered cotton, and the reduced degree increased with increasing N application. Malondialdehyde (MDA) content in cotton roots was significantly (P<0.05) increased, with the lowest at the 240 kg N ha-1 during waterlogging. Application of N increased the activities of peroxidase (POD) and catalase (CAT) of cotton root, but decreased superoxide dismutase (SOD) activity during waterlogging. Root vigor decreased by waterlogging, were the highest at the 240 kg N ha-1. At the 15 d after terminating waterlogging, N application promoted root vigor, but decreased MDA content. These results suggest that appropriate N supply (240 kg N ha-1 in this investigation) may contribute to waterlogging resistance of cotton plants through adjusting the antioxidant enzyme activities of roots, decreasing lipid peroxidation and enhancing root vigor during waterlogging (waterlogging for eight days in this investigation), excessive N supply (480 kg N ha-1) has a deleterious effect on plant waterlogging resistance, however, more N should be supplied to waterlogged cotton plants after terminating waterlogging.3. Effects of nitrogen on the photosynthesis of cotton under waterlogging, and its internal physiological mechanismWaterlogging significantly decreased the photosynthetic rate of cotton plants, the photosynthetic rate of cotton plants were highest at 240 kg N ha-1 level under waterlogging, deficient (0 kg N ha-1) and excessive nitrogen supply (480 kg N ha-1) are of disadvantaged to the photosynthesis. (1) Under waterlogging, the stomatal conductance (Gs) was reduced in compared with control and Gs were decreased with increasing N application. The minimal fluorescence (Fo) and non-photochemical quenching coefficient (qN) were increased by waterlogging, while the maximum photochemical efficiency of open photosystem (Fv/Fm), the quantum yield of electron transport (ΦpsⅡ) and the photochemical quenching (qP) were decreased. The increscent degree of Fo and qN and the reduced degree of Fv/Fm,ΦpsⅡand qP were increased with increasing N application. (2) Waterlogging significantly decreased soluble protein content, SOD activity, CAT activity, ZR content, GA content and IAA content, ZR/ABA, IAA/ABA and GA/ABA in cotton leaf, but increased POD activity, MDA content and ABA content. Under waterlogging, MDA content and ABA content of 240 kg N ha-1 cotton was smallest among the three nitrogen levels, and CAT activity, ZR content, IAA content, GA content, ZR/ABA, IAA/ABA, GA/AB A of 240 kg N ha-1 cotton was highest. At the 15th day after terminating waterlogging, there were no significant differences of antioxidant enzyme activities, MDA content and endogenous hormone contents between waterlogged cotton and control. N application promoted SOD activity, CAT activity, POD activity, ZR content, IAA content, GA content, ZR/ABA, IAA/ABA, GA/ABA and Pn, but reduced MDA content and ABA content in both waterlogged cotton and control. These results suggest that appropriate N supply (240 kg N ha-1) may contribute to development of cotton plants by adjusting the antioxidant enzyme activities and the balance of endogenous hormone, debasing lipid peroxidation under waterlogging, excessive N supply (480 kg N ha-1) are of disadvantage to cotton development.4. Effects of nitrogen on physiological characteristics of cotton fiber development under waterloggingDurig waterlogging, waterlogging significantly decreased soluble protein content, the antioxidant enzyme activities of SOD, CAT and POD, the fiber thickening related enzymes activities of sucrose synthase, sucrose phosphate synthase, invertase andβ-1,3-glucanase in cotton fiber. Under waterlogging, the antioxidant enzyme activities in cotton fiber were increased with increasing N application, and MDA content of 240 kg N ha-1 cotton was smallest among the three nitrogen levels, and the fiber thickening key enzymes activities, cellulose content, fiber strength of 240 kg N ha-1 cotton was highest. At the 15 day after terminating waterlogging, the antioxidant enzyme activities and the fiber thickening related enzymes activities of waterlogged cotton were still lower than the control, and their trends affected by N application did not change. These results suggest that appropriate N supply (240 kg N ha-1 in this investigation) may contribute to forming of high-strength fibre by adjusting the antioxidant enzyme activities, debasing lipid peroxidation, increasing the fiber thickening related enzymes activities and cellulose content under waterlogging.
|
PDF Full Text Request