Response of Chinese fir roots to nitrate addition under phosphorus starvation

The coordinated utilization of nitrogen and phosphorus is the key to maintaining the best plant growth and achieving maximum yield.For a long time, the research on the phosphorus nutrition efficiency of Chinese fir mainly focused on the effect of single phosphorus deficiency but ignored the possible interaction between nitrogen and phosphorus. In this study, the changes in root morphology, root secretion, protective enzyme activity, nitrogen metabolism related enzyme activity, and nitrogen and phosphorus metabolism related gene expression of Chinese fir seedlings under normal phosphorus supply and low phosphorus stress were analyzed. It was found that the root morphological response of Chinese fir family 10 was the most sensitive, and the high intensity nitrate treatment under low phosphorus stress significantly promoted root proliferation and lateral root growth. The addition of nitrate nitrogen could significantly alleviate the decrease of phosphorus content in roots of family 10 due to phosphorus deficiency stress and significantly increase the secretion of acid phosphatase and organic acids in roots. the activities of superoxide dismutase, catalase and peroxidase, and the content of malondialdehyde in roots decreased significantly. In addition, nitrate nitrogen addition could not effectively alleviate the weakening of nitrogen metabolism activity caused by low phosphorus stress. Under low phosphorus stress, nitrate reductase(NR) activity and nitrite reductase(NiR) activity decreased significantly in family 10, while NR and NiR activities in roots of nitrate nitrogen treatment were still lower than those of normal phosphorus treatment. The results of quantitative PCR analysis showed that the addition of nitrate nitrogen under normal phosphorus supply could significantly down-regulate the expression of ClNRT1.1, ClNIR1 and ClCPR2 to reduce nitrogen uptake and metabolism, while under low phosphorus stress, nitrate nitrogen addition could significantly up-regulate the expression of ClNIR1 and ClCPR2 to increase the ability of nitrate nitrogen reduction, thus improving the ability to adapt to high nitrogen and low phosphorus environment.