No significant interactions between nitrogen stimulation and ozone inhibition of isoprene emission in Cathay poplar.

Isoprene emission from plants subject to a combination of ozone (O) and nitrogen (N) has never been investigated. Cathay poplar (Populus cathayana) saplings were exposed to O (CF, charcoal-filtered air, NF, non-filtered ambient air and E-O, non-filtered air +40ppb) and N treatments (N0, 0kgNhayear, N50, 50kgNhayear and N100, 100kgNhayear) for 96days. Increasing O exposure decreased isoprene emission (11.5% in NF and 57.9% in E-O), as well as light-saturated photosynthetic rate (A) and chlorophyll content, while N load increased isoprene emission (19.6% in N50 and 33.4% in N100) as well as A and chlorophyll content. Although O and N interacted significantly in A, N did not mitigate the negative effects of O on isoprene emission, i.e. the combined effects were additive and did not interact. These results warrant more research on the combined effects of co-existing global change factors on future isoprene emission and atmospheric chemical processes.