Response of photosynthetic nitrogen use efficiency in Betula utilis to altitudinal variation along Balang Mountain, Sichuan, China.

: To better understand the response and adaptation of plants to altitudinal changes, four sites at the altitude of 2200 m, 2500 m, 3100 m and 3400 m on Balang Mountain were selected to test and calculate the eco-physiological parameters in leaves of Betula utilis, including photosynthetic nitrogen use efficiency (PNUE), CO2 diffusion conductance (stomatal conductance gs and mesophyll conductance gm) and nitrogen allocation in each component (fractions of leaf nitrogen allocated to Rubisco PR, to bioenergetics PB, to light-harvesting components PL, and to cell wall PCW). Their changes with altitudinal variations and the relationships between leaf PNUE and the other parameters were analyzed. The results showed that PNUE, PR, and PB of the leaves were relatively higher at 2500 m and 3100 m. With the increases of altitude, gs and gm increased and PL decreased. The correlations between PR, PB and PNUE were significant, indicating that PR and PB were the main factors driving the changes in leaf PNUE in response to altitudinal variations. Besides, the fraction of leaf nitrogen allocated to photosynthetic apparatus (PP) was relatively higher at 2500 m and 3100 m. With increasing altitude, PCW decreased and the fraction of leaf nitrogen allocated to the other components (Pother) increased, which suggested that B. utilis leaves tended to allocate more nitrogen to the other components instead of the photosynthetic apparatus and cell wall with the increasing altitude to well adapt environmental changes.