Effects of application of N and K fertilizers on nitrogen metabolism of two genetype varieties of maize under water-stressed condition

A pot experiment was conducted under water stress and adequate water applying conditions with two genotype varieties of maize(Shaandan 9,a droughtresistant variety and Shaandan 911,a non-drought-resistant variety) to study the effects of nitrogen,potassium on NR(nitrate reductase) activity,accumulations of proline,glycine betaine and soluble protein in maize leaves at different growing stages for revealing their biological function in increase of plant resistance to drought through nitrogen metabolism.Results showed that under a water stress condition,NR activity was significantly reduced while concentrations of proline,glycine betain and soluble protein were increased.The drought resistant variety was higher in values and variation of NR activity,cncentration of soluble proline,glycinebetain and soluble protein than non-drought resistant variety.The response of the two varieties to water stress was weaker at seeding stage as shown in their lower concentrations of proline,glycine betaine and soluble protein while stronger at elongation and heading stages as shown in higher concentrations of these compounds.Of those compounds,the peak value of glycine betaine appeared later compared with proline.Application of nitrogen significantly raised NR activity and concentrations of proline,glycine betaine and soluble protein,and hence alleviated the water stress through improvement of nitrate metabolism.The effects of N application for non-drought resistant varieties were significantly different.The response of the drought-resistant variety to N addition was merely found at low rate,but there was no significant different between high and low N rates.With adequate water supply,effects of N fertilization were significantly decreased,showing that in addition to function as a nutrient,N fertilizer played a biological role in increasing drought-resistance of the crop through improving nitrogen metabolism.Potassium had stronger influence on NR activity and contents of proline,glycine betaine and soluble protein under the water stress condition comparing with N while the effect of K fertilization on metabolism was even vanished under adequate water supply condition,indicating that to markedly improve nitrogen metabolism is one of the key mechanisms of potassium to enhance drought resistance of crops.