Abstract
The objective of this investigation was to study the effects of nitrogen on tolerance to water-stress in cotton (Gossypium hirsutum L.) seedlings. Growth chamber studies with pots of washed sand were carried out in Fayetteville, USA, and Nanjing, Chinawith three water conditions (well-watered, drought-stressed, and waterlogging), and three nitrogen rates, low nitrogen (16 mM, approximately 224 mg N·l–1 water), medium nitrogen (24 mM, approximately 448 mg N·l–1 water) and high nitrogen (32 mM, approximately 672 mg N·l–1 water), respectively. The results showed that water-stress treatments reduced plant biomass, C/N ratio, root vigor and leaf photosynthesis (Pn). The plant response to water-stress resistance was affected by nitrogen, and was correlated with the activities of antioxidant enzymes. The changes of anti-oxidant enzymes was the highest in the low nitrogen rate in the drought-stressed and waterlogged cotton seedlings. Malondialdehyde (MDA) content increased significantly in the water-stress treatments, and was the lowest in the low nitrogen rate. There was a significant reduction of N accumulation under water stress. Low-nitrogen treatmentincreased C accumulation, while high-nitrogen treatment decreased N accumulation. Root vigor was decreased by water stress, and was highest in the low-nitrogen rate. After terminating the water stress, N application promoted root vigor, especially in waterlogged seedlings. The trends of Pn weresimilarto that of root vigor. These results suggested that low N application may contribute to cotton drought tolerance by enhancing the activity of antioxidant enzymes and conse-quently decreasing lipid peroxidation, and enhancing root vigor. However, higher N should be applied to waterlog- ging-stressed cotton seedlings after terminating waterlogging.
Highlights
Drought or waterlogging during the growing season affects various physiological and biochemical processes of upland cotton, resulting in reduction of growth, final productivity and fiber quality [1]
Waterlogging at the seedling stage has been shown to result in significant accumulation of leaf malondialdehyde and ethylene production and reduction of leaf photosynthetic rate in rape plants [16]
There are few reports on the influence of N rates on the metabolism of cotton seedlings exposed to water stress
Summary
Drought or waterlogging during the growing season affects various physiological and biochemical processes of upland cotton, resulting in reduction of growth, final productivity and fiber quality [1]. It is important to formulate effective strategies to alleviate the detrimental effects of water stress and enhance plant tolerance to drought or waterlogging in cotton plants [2]. Seedling growth is a key determinant stage of productivity in upland cotton, and short-duration water stress occurring during this stage may significantly reduce leaf expansion, photosynthesis, carbon and nitrogen metabolism, and restrain antioxidant capability [3,4], resulting in low yields and poor quality. For drought-stressed plants, Halvorson and Reule [6] found that the yield of wheat (Triticumaestivum L.), maize (Zea mays L.) and barley (Hordeum vulgare L.) increased with higher N supply.
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