Elevated ozone reduced leaf nitrogen allocation to photosynthesis in poplar

Abstract

We investigated the effects of elevated ozone (O3) concentration on leaf nitrogen (N), a key determinant of plant photosynthesis, with two clones of poplar grown in open-top chambers. We focus on the difference between mass-based leaf N concentration (Nmass) and area-based one (Narea) in their responses to elevated O3, and the allocation of N to different leaf components: photosynthetic apparatus, cell walls, and others under elevated O3 level. Our results showed that elevated O3 significantly increased Nmass, but reduced Narea and leaf mass per area (LMA). The two clones showed no difference in Nmass response to O3, but the more sensitive clone showed greater reduction of Narea and LMA due to O3. We also found positive relationships between Narea and photosynthetic parameters, e.g. light-saturated photosynthetic rate (Asat). Furthermore, elevated O3 significantly reduced photosynthetic N-use efficiency (PNUE) and leaf N allocation to photosynthetic components, while increasing N allocation to cell walls and other components. We concluded that plants invested more N in cell walls and other components to resist O3 damages at the expense of photosynthetic N. The change of N allocation in plant leaves in response to elevated O3 could have an impact on ecological processes, e.g. leaf litter decomposition.