Ozone impairs the response of isoprene emission to foliar nitrogen and phosphorus in poplar.

Tropospheric ozone (O) impairs physiological processes of plants while nitrogen (N) deposition may cause imbalances in soil N and other nutrients such as phosphorus (P) suggesting an increase of P demand for plants. However, the combined effect of O, soil N and P on isoprene emission from leaves has never been tested. We therefore examined isoprene emission in leaves of Oxford poplar clone exposed to O (ambient, AA [35.0 nmol mol as daily mean]; 1.5 × AA; 2.0 × AA), soil N (0 and 80 kg N ha) and soil P (0, 40 and 80 kg P ha) in July and September in a Free-Air Controlled Exposure (FACE) facility. We also investigated the response of isoprene emission to foliar N, P and abscisic acid (ABA) contents in September because the 2-C-methylerythritol-5-phosphate (MEP) pathway of isoprenoid biosynthesis produces ABA. We found that O increased isoprene emission in July, which was associated to increased dark respiration, suggesting an activation of metabolism against O stress as an initial response. However, O decreased isoprene emission in September which was associated to reduced net photosynthesis. In September, isoprene emission was positively correlated with leaf N content and negatively correlated with leaf P content in AA. However, no response of isoprene emission to foliar N and P was found in elevated O, suggesting that the isoprene responses to foliar N and P depended on the O exposure levels. Isoprene emission rate in 1.5 × AA and 2.0 × AA increased with increasing leaf ABA content, indicating accelerated senescence of injured leaves to favor new leaf growth when high O and nutritional availability in the soil were combined. Even though foliar N and P usually act as a proxy for isoprene emission rate, the impact of recent abiotic factors such as O should be always considered for modeling isoprene emission under climate change.