Impacts of different ammonium/nitrate ratios on the growth and antioxidant defense enzyme activities in cotton seedlings exposed to low-temperature stress

ObjectivesFrequently occurred low-temperature in early spring is one of the major abiotic stresses severely restricting the growth, yield and quality of cotton (Gossypium hirsutum) in Xinjiang, China. Nitrogen supply has been proved to play significant role in regulating the resistance of crops to abiotic stress. Studying the impacts of different ratios of NH₄⁺/NO₃^– supply on the physiological process of cotton will provide a theoretical base to alleviate the negative effects induced by low-temperature stress in cotton production.

MethodsUsing cotton (Gossypium hirsutum L. cv. Xinluzao13) as the experimental material and taking a normal temperature (25℃) as control treatment, we conducted a hydroponic experiment in a growth chamber to determine the effects of different NH₄⁺-N/NO₃^–-N ratios on the electrolyte leakage rate, the concentrations of malondialdehyde (MDA), proline (Pro) and soluble protein (SP), and antioxidant enzyme activities in the leaves of cotton seedlings exposed to low-temperature (15℃).

ResultsCompared with sole supply of ammonium or nitrate-N under the normal condition (25℃), the combined supply of ammonium with nitrate significantly enhanced the biomass of all the cotton organs (P < 0.05). The dry biomass of both shoots and roots were the biggest at the ammonium/nitrate ratio of 50/50 and the smallest at the ammonium/nitrate ratio of 100/0. The biomass of all the cotton organs were significantly decreased under low temperature (15℃). The electrolyte leakage rate, MDA and Pro concentration of cotton seedlings were significantly increased under low-temperature stress (P < 0.01), and SP concentration was not significantly different (P > 0.05). The activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) decreased gradually (P < 0.01). The growth and development of cotton seedlings were restrained significantly by low-temperature stress. The electrolyte leakage rate, MDA concentration and POD activity of cotton seedlings were decreased firstly and then increased with increasing of NH₄⁺-N/NO₃^–-N ratios under both normal and low temperature. The electrolyte leakage rate, MDA concentration and POD activity of cotton seedlings were the minimum at an NH₄⁺-N/NO₃^–-N ratio of 50/50, followed by NH₄⁺-N/NO₃^–-N ratio of 0/100, and were the maximum at an NH₄⁺-N/NO₃^–-N ratio of 100/0. SP and Pro concentrations were firstly increased and then decreased, and they were the highest at an NH₄⁺-N/NO₃^–-N ratio of 25/75. Enhancing ammonium nutrition in the nutrient solution could significantly increase SOD and CAT activities (P < 0.01).

ConclusionsMixed use of ammonium with nitrate could decrease the electrolyte leakage rate and MDA concentration under low-temperature stress, increase the concentrations of osmotic adjustment substances, and improve antioxidant enzyme activities, therefore raise the resistance of cotton seedlings against low temperature. The effect of NH₄⁺-N/NO₃^–-N ratio of 50/50 has been proved to be the best.