Effects of warming and nitrogen addition on nitrogen uptake kinetics of fine roots of Cunninghamia lanceolata seedlings in different seasons

In order to reveal the underground response of different forms of nitrogen absorption rates of Chinese fir plantations in different seasons to global warming and nitrogen deposition, a dual-factor experiment of warming and nitrogen addition was carried out at the Chenda observation point of the Sanming Forest Ecosystem and Global Change Research Station in Fujian, including The results showed that: (1) In the three seasons, the absorption rate of nitrate nitrogen at different concentrations by the fine roots of fir in the four treatments basically showed that in spring It is higher and lower in summer and autumn, while the absorption rate of ammonium nitrogen at different concentrations is opposite, which is higher in summer and autumn and lower in spring. (2) The in vitro roots of the four treatments in different seasons have different concentrations under different concentrations. The absorption of ammonium nitrogen all follows the Mie-Mann's kinetic equation, while the absorption of nitrate nitrogen does not completely follow the Mie equation, showing a two-phase kinetics. (3) In spring, compared with no nitrogen addition, Nitrogen addition increases the maximum absorption rate of NH4+ (Vmax-NH4+). In summer, compared with no temperature increase, the increase in temperature increases Vmax-NH4+. In autumn, compared with no increase in temperature, the increase in temperature reduces the half-saturation constant of NH4+ (Km-NH4+); Compared with no nitrogen addition, nitrogen addition increases Km-NH4+. Both warming and nitrogen addition have no significant effect on the nitrate nitrogen absorption rate (V100-NO3-) at 100 μmol in different seasons. Temperature and nitrogen addition have no significant interaction effects on Vmax-NH4+, Km-NH4+ and V100-NO3- in different seasons. This study shows that temperature increase will increase the NH4+ absorption capacity of Chinese fir seedlings in summer and autumn, while nitrogen addition will increase NH4+ in spring. Absorption capacity reduces the NH4+ absorption capacity in autumn, but warming and nitrogen addition will not change the NO3- absorption capacity in different seasons.