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

YTropospheric ozone (O-3) 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-3, 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-3 (ambient, AA [35.0 n mol mol(-1) as daily mean]; 1.5 x AA; 2.0 x AA), soil N (0 and 80 kg N ha(-1)) and soil P (0, 40 and 80 kg P ha(-1)) 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-3 increased isoprene emission in July, which was associated to increased dark respiration, suggesting an activation of metabolism against O-3 stress as an initial response. However, O-3 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-3, suggesting that the isoprene responses to foliar N and P depended on the O-3 exposure levels. Isoprene emission rate in 1.5 x AA and 2.0 x AA increased with increasing leaf ABA content, indicating accelerated senescence of injured leaves to favor new leaf growth when high O-3 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-3 should be always considered for modeling isoprene emission under climate change. (C) 2020 Elsevier Ltd. All rights reserved.