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Ozone (O3) pollution affects plant growth and isoprene (ISO) emission. However, the response mechanism of isoprene emission rate (ISOrate) to elevated O3 (EO3) remains poorly understood. ISOrate was investigated in two genotypes (diploid and triploid) of Chinese white poplar (Populus tomentosa Carr.) exposed to EO3 in an open top chamber system. The triploid genotype had higher photosynthetic rate (A) and stomatal conductance (g s) than the diploid one. EO3 significantly decreased A , g s, and ISOrate of middle and lower leaves in both genotypes. In the diploid genotype, the reduction of ISOrate was caused by a systematic decrease related to ISO synthesis capacity, as indicated by decreased contents of the isoprene precursor dimethylallyl diphosphate and decreased isoprene synthase protein and activity. On the other hand, the negative effect of O3 on ISOrate of the triploid genotype did not result from inhibited ISO synthesis capacity, but from increased ISO oxidative loss within the leaf. Our findings will be useful for breeding poplar genotypes with high yield and lower ISOrate, depending on local atmospheric volatile organic compound/NO x ratio, to cope with both the rising O3 concentrations and increasing biomass demand. They can also inform the incorporation of O3 effects into process-based models of isoprene emission. [ABSTRACT FROM AUTHOR]

Isoprenoid (ISOP) emissions, particularly isoprene and monoterpenes, can significantly affect local and regional air quality due to their high chemical reactivity, with hot spots over polluted megacities. We investigated ISOP emissions from 32 common woody species in Beijing (Northern China) and Nanjing (Southern China). Relationships of ISOP emissions with plant functional types (trees vs shrubs; evergreen vs deciduous), leaf textures (papery vs leathery) and leaf physiological and biochemical traits were studied. Twenty-seven species emitted ISOPs, spanning very high isoprene emissions (typical of deciduous trees with papery leaves) to minute emissions of isoprene and monoterpenes in leathery leaves. Significant positive relationships between isoprene emission and the amounts of chlorophyll content, isoprene synthase protein and leaf nitrogen were observed, while the emissions of monoterpenes were not significantly related to any leaf physiological or biochemical trait. While looking for factors driving leaf isoprene and monoterpene emissions are complicated, our study shows leaf papery texture and high chlorophyll content may indicate presence of high isoprene emitters, to be used with caution for urban greening purposes. • Emission of isoprenoids varied greatly among different urban tree species. • Isoprene emission in plants is mainly controlled by the availability of enzyme amount. • Monoterpene emissions were not related to any leaf physiological-biochemical traits. • Chlorophyll content and leaf texture can help preliminary tree species screening. [ABSTRACT FROM AUTHOR]

Isoprene and monoterpenes (MTs) are among the most abundant and reactive volatile organic compounds produced by plants (biogenic volatile organic compounds). We conducted a meta‐analysis to quantify the mean effect of environmental factors associated to climate change (warming, drought, elevated CO2, and O3) on the emission of isoprene and MTs. Results indicated that all single factors except warming inhibited isoprene emission. When subsets of data collected in experiments run under similar change of a given environmental factor were compared, isoprene and photosynthesis responded negatively to elevated O3 (−8% and −10%, respectively) and drought (−15% and −42%), and in opposite ways to elevated CO2 (−23% and +55%) and warming (+53% and −23%, respectively). Effects on MTs emission were usually not significant, with the exceptions of a significant stimulation caused by warming (+39%) and by elevated O3 (limited to O3‐insensitive plants, and evergreen species with storage organs). Our results clearly highlight individual effects of environmental factors on isoprene and MT emissions, and an overall uncoupling between these secondary metabolites produced by the same methylerythritol 4‐phosphate pathway. Future results from manipulative experiments and long‐term observations may help untangling the interactive effects of these factors and filling gaps featured in the current meta‐analysis. All single environmental changefactors (warming, drought, elevated CO2 and O3) except warming inhibited isoprene emission. On the other hand, effects on monoterpenes emission were usually not significant, with the exceptions of an overall stimulation caused by warming. [ABSTRACT FROM AUTHOR]

Isoprene emission from plants subject to a combination of ozone (O 3 ) and nitrogen (N) has never been investigated. Cathay poplar ( Populus cathayana ) saplings were exposed to O 3 (CF, charcoal-filtered air, NF, non-filtered ambient air and E-O 3 , non-filtered air + 40 ppb) and N treatments (N0, 0 kg N ha − 1 year − 1 , N50, 50 kg N ha − 1 year − 1 and N100, 100 kg N ha − 1 year − 1 ) for 96 days. Increasing O 3 exposure decreased isoprene emission (11.5% in NF and 57.9% in E-O 3 ), as well as light-saturated photosynthetic rate ( A sat ) and chlorophyll content, while N load increased isoprene emission (19.6% in N50 and 33.4% in N100) as well as A sat and chlorophyll content. Although O 3 and N interacted significantly in A sat , N did not mitigate the negative effects of O 3 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. [ABSTRACT FROM AUTHOR]

Concentration- and flux-based O3 dose-responses of isoprene emission from single leaves and whole plants were developed. Two poplar clones differing in O3 sensitivity were exposed to five O3 levels in open-top chambers for 97 d: charcoal-filtered ambient air (CF), non-filtered ambient air (NF) and NF plus 20 ppb (NF + 20), 40 ppb (NF + 40) and 60 ppb (NF + 60). At both leaf and plant level, isoprene emission was significantly decreased by NF + 40 and NF + 60 for both clones. Although intra-specific variability was found when the emissions were up-scaled to the whole plant, both leaf- and plant-level emissions decreased linearly with increasing concentration-based (AOT40, cumulative exposure to hourly O3 concentrations >40 ppb) and flux-based indices (PODY, cumulative stomatal uptake of O3 > Y nmol O3 m−2 PLA s−1). AOT40- and POD7-based dose-responses performed equally well. The two clones responded differently to AOT40 and similarly to PODY (with a slightly higher R2 for POD7) when the emission was expressed as change relative to clean air. We thus recommend POD7 as a large-scale risk assessment metric to estimate isoprene emission responses to O3 in poplar. [ABSTRACT FROM AUTHOR]

The combined effects of ozone (O3) and drought on isoprene emission were studied for the first time. Young hybrid poplars (clone 546, Populus deltoides cv. 55/56 x P. deltoides cv. Imperial) were exposed to O3 (charcoal-filtered air, CF, and non-filtered air +40 ppb, E-O3) and soil water stress (well-watered, WW, and mild drought, MD, one-third irrigation) for 96 days. Consistent with light-saturated photosynthesis ( Asat), intercellular CO2 concentration ( Ci) and chlorophyll content, isoprene emission depended on drought, O3, leaf position and sampling time. Drought stimulated emission (+38.4%), and O3 decreased it (−40.4%). Ozone increased the carbon cost per unit of isoprene emission. Ozone and drought effects were stronger in middle leaves (13th-15th from the apex) than in upper leaves (6th-8th). Only Asat showed a significant interaction between O3 and drought. When the responses were up-scaled to the entire-plant level, however, drought effects on total leaf area translated into around twice higher emission from WW plants in clean air than in E-O3. Our results suggest that direct effects on plant emission rates and changes in total leaf area may affect isoprene emission from intensively cultivated hybrid poplar under combined MD and O3 exposure, with important feedbacks for air quality. [ABSTRACT FROM AUTHOR]

Tropospheric ozone (O 3) affects isoprenoid emissions, and floral emissions in particular, which may result in potential impacts on the interactions of plants with other organisms. The effects of ozone (O 3) on isoprenoid emissions have been investigated for many years, while knowledge on O 3 effects on floral emissions is still scarce and the relevant mechanism has not been clarified so far. We investigated the effects of O 3 on floral and foliar isoprenoid emissions (mainly isoprene, monoterpenes and sesquiterpenes) and their synthase substrates from three rose varieties (CH, Rosa chinensis Jacq. var. chinensis ; SA, R. hybrida 'Saiun'; MO, R. hybrida 'Monica Bellucci') at different exposure durations. Results indicated that the O 3 -induced stimulation after short-term exposure (35 days after the beginning of O 3 exposure) was significant only for sesquiterpene emissions from flowers, while long-term O 3 exposure (90 days after the beginning of O 3 exposure) significantly decreased both foliar and floral monoterpene and sesquiterpene emissions. In addition, the observed decline of emissions under long-term O 3 exposure resulted from the limitation of synthase substrates, and the responses of emissions and substrates varied among varieties, with the greatest variation in the O 3 -sensitive variety. These findings provide important insights on plant isoprenoid emissions and species selection for landscaping, especially in areas with high O 3 concentration. Floral isoprenoid emissions were higher and more sensitive to short-term O 3 exposure relative to foliar emissions, while both foliar and floral emissions significantly decreased after long-term O 3 exposure due to the limitation of their synthase substrates. [ABSTRACT FROM AUTHOR]

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−1year−1), middle N (MN, 100 kg N ha−1year−1), high N (HN, 200 kg N ha−1year−1) and three O 3 treatments (CF, charcoal-filtered ambient air; NF, non-filtered ambient air; NF + O 3 , NF + 40 ppb O 3). Our results showed the effects of O 3 and/or N on standardized ISO rate (ISO rate) and photosynthetic parameters differed along with the leaf position, with larger negative effects of O 3 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 O 3 concentration (67 ppb as 10-h average) and HN treatment. Significant O 3 × N interactions were only found in middle and lower leaves, where ISO rate declined by O 3 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 O 3 concentrations > 40 ppb) and POD Y (accumulative stomatal uptake of O 3 > Y nmol O 3 m−2 PLA s−1) were not significant in upper leaves, but ISO rate significantly decreased with increasing AOT40 or POD Y 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 O 3 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 O 3 pollution and N deposition scenarios. Image 1 • The significant effects of O 3 or nitrogen on isoprene were observed in lower leaves. • Young expanded leaves were insensitive to all treatments. • The responses of isoprene emission to different O 3 metrics were similar. • The O 3 dose-response relationships changed with leaf position and N levels. 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. [ABSTRACT FROM AUTHOR]