Elevated ozone reduced leaf nitrogen allocation to photosynthesis in poplar

We investigated the effects of elevated ozone (O-3) 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 (N-mass) and area-based one (N-area) in their responses to elevated O-3, and the allocation of N to different leaf components: photosynthetic apparatus, cell walls, and others under elevated O-3 level. Our results showed that elevated O-3 significantly increased N-mass, but reduced N-area and leaf mass per area (LMA). The two clones showed no difference in N-mass response to O-3, but the more sensitive clone showed greater reduction of N-area and LMA due to O-3. We also found positive relationships between N-area and photosynthetic parameters, e.g. light-saturated photosynthetic rate (A(sat)). furthermore, elevated O-3 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 O-3 damages at the expense of photosynthetic N. The change of N allocation in plant leaves in response to elevated O-3 could have an impact on ecological processes, e.g. leaf litter decomposition. (C) 2018 Elsevier B.V. All rights reserved.