Effect Of Nitrogen And Phosphorus Supply On Endogenous Phytohormones Of Larch Seedlings

Larch {Larix gmelinii) is an important sylvicultural species in northeast China. However, the growth of Larch is often limited by nitrogen and phosphorus shortage for slow decomposition rate of litter resulting from low temperature and long winter in northeast area. Plant can also adjust physiological process to lessen influence of external nutritional conditions. In the present research, the nitrogen nutritional gradients were nitrogen deficiency (0 mmol/L), control (8 mmol/L) and high nitrogen (16 mmol/L). The phosphorus nutritional gradients were phosphorus deficiency (0 mmol/L), control (1 mmol/L) and high phosphorus (2 mmol/L). Endogenous phytohormones (IAA,ABA,GA₃, ZR) of seedlings under different nutritional conditions were measured on the 40th and the 80th day after treatment. The results showed as follows:1. IAA level in seedling root under nitrogen deficiency and high nitrogen supply was both higher than the control on the 40th day, and lower than the control on the 80th day. Treatments with both nitrogen deficiency and high nitrogen supply decreased GA3 concentration in root. There is a positive correlation between ZR level in root and external nitrogen supply. ZR level in the root under nitrogen deficiency and high nitrogen conditions was higher than the control.Treatment with nintrogen deficiency, IAA and GA3 concentrations in needles had no difference from the control. After 40 days of treatment with high nitrogen, IAA and GA3 concentrations in needles were higher than the control, but on the 80th day they are both went back to the control level. Both treatments with nitrogen deficiency and high nitrogen decreased ZR level in needles. Except on the 80th day of high nitrogen treatment, ABA concentrations were all lower than the control.2. IAA level in root of Seedlings under phosphorus deficiency and high phosphorus supply were both higher than the control on the 40th day, however it was negatively regulated by external phosphorus nutrition conditions. Treatments with both phosphorus deficiency and high phosphorus decreased GA3 and ZR concentritions in root. ABA level in root is always negatively related to external phosphorus nutrition.IAA and GA3 concentrations in needles were steady in different phosphorus levels. Positive relationship between ZR level in needles and phosphorus nutrition condition was found on the 40th day after treatment, and negative relationship was done on the 80th day. Treatments with both phosphorus deficiency and high phosphorus level decreased ABA concentrition in needles.We have also briefly discussed the regulational role of endogenous phytohormones on the growth of Larch seedlings under different nitrogen and phosphorus nutritional conditions, and the possible functions of endogenous phytohormones in the course of Larch seedlings adapting to the change of nitrogen and phosphorus nutritional conditions.