Response of isoprene emission from poplar saplings to ozone pollution and nitrogen deposition depends on leaf position along the vertical canopy profile. (October 2020)

• Record Type: Journal Article
• Authors: Yuan, Xiangyang; Li, Shuangjiang; Feng, Zhaozhong; Xu, Yansen; Shang, Bo; Fares, Silvano; Paoletti, Elena
• Is Part Of: Environmental pollution. Volume 265(2020)Part A
• Publication Date: 2020-10
• Subjects: Tropospheric O3 -- Nitrogen deposition -- Isoprene emission -- Poplar -- Leaf position; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2020.114909
• Languages: English
• ISSNs: 0269-7491

Abstract

Abstract: We investigated isoprene (ISO) emission and gas exchange in leaves from different positions along the vertical canopy profile of poplar saplings ( Populus euramericana cv. '74/76'). For a growing season, plants were subjected to four N treatments, control (NC, no N addition), low N (LN, 50 kg N ha −1 year −1 ), middle N (MN, 100 kg N ha −1 year −1 ), high N (HN, 200 kg N ha −1 year −1 ) and three O3 treatments (CF, charcoal-filtered ambient air; NF, non-filtered ambient air; NF + O3, NF + 40 ppb O3 ). Our results showed the effects of O3 and/or N on standardized ISO rate ( ISO rate ) and photosynthetic parameters differed along with the leaf position, with larger negative effects of O3 and positive effects of N on ISO rate and photosynthetic parameters in the older leaves. Expanded young leaves were insensitive to both treatments even at very high O3 concentration (67 ppb as 10-h average) and HN treatment. Significant O3 × N interactions were only found in middle and lower leaves, where ISO rate declined by O3 just when N was limited (NC and LN). With increasing light-saturated photosynthesis and chlorophyll content, ISO rate was reduced in the upper leaves but on the contrary increased in middle and lower leaves. The responses of ISO rate to AOT40 (accumulated exposure to hourly O3 concentrations > 40 ppb) and PODY (accumulative stomatal uptake of O3 > Y nmol O3 m −2 PLA s −1 ) were not significant in upper leaves, but ISO rate significantly decreased with increasing AOT40 or PODY under limited N supply in middle leaves but at all N levels in lower leaves. Overall, ISO rate changed along the vertical canopy profile in response to combined O3 and N exposure, a behavior that should be incorporated into multi-layer canopy models. Our results are relevant for modelling regional isoprene emissions under current and future O3 pollution and N deposition scenarios. Graphical abstract: Image 1 Highlights: The significant effects of O3 or nitrogen on isoprene were observed in lower leaves. Young expanded leaves were insensitive to all treatments. The responses of isoprene emission to different O3 metrics were similar. The O3 dose-response relationships changed with leaf position and N levels. Abstract : Isoprene emission changed along the vertical canopy profile in response to the combined effects of O3 and N. Concentration- and flux-based O3 dose–responses of isoprene emission changed with leaf position and N levels.