• Energy Research

AbstractIsoprene 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.

AbstractThe carbon‐sink strength of temperate and boreal forests at midlatitudes of the northern hemisphere is decreased by ozone pollution, but knowledge on subtropical evergreen broadleaved forests is missing. Taking the dataset from Chinese studies covering temperate and subtropical regions, effects of elevated ozone concentration ([O3]) on growth, biomass, and functional leaf traits of different types of woody plants were quantitatively evaluated by meta‐analysis. Elevated mean [O3] of 116 ppb reduced total biomass of woody plants by 14% compared with control (mean [O3] of 21 ppb). Temperate species from China were more sensitive to O3 than those from Europe and North America in terms of photosynthesis and transpiration. Significant reductions in chlorophyll content, chlorophyll fluorescence parameters, and ascorbate peroxidase induced significant injury to photosynthesis and growth (height and diameter). Importantly, subtropical species were significantly less sensitive to O3 than temperate ones, whereas deciduous broadleaf species were significantly more sensitive than evergreen broadleaf and needle‐leaf species. These findings suggest that carbon‐sink strength of Chinese forests is reduced by present and future [O3] relative to control (20–40 ppb). Given that (sub)‐tropical evergreen broadleaved species dominate in Chinese forests, estimation of the global carbon‐sink constraints due to [O3] should be re‐evaluated.

AbstractTropospheric ozone is considered the most detrimental air pollutant for vegetation at the global scale, with negative consequences for both provisioning and climate regulating ecosystem services. In spite of recent developments in ozone exposure metrics, from a concentration‐based to a more physiologically relevant stomatal flux‐based index, large‐scale ozone risk assessment is still complicated by a large and unexplained variation in ozone sensitivity among tree species. Here, we explored whether the variation in ozone sensitivity among woody species can be linked to interspecific variation in leaf morphology. We found that ozone tolerance at the leaf level was closely linked to leaf dry mass per unit leaf area (LMA) and that whole‐tree biomass reductions were more strongly related to stomatal flux per unit leaf mass (r2 = 0.56) than to stomatal flux per unit leaf area (r2 = 0.42). Furthermore, the interspecific variation in slopes of ozone flux–response relationships was considerably lower when expressed on a leaf mass basis (coefficient of variation, CV = 36%) than when expressed on a leaf area basis (CV = 66%), and relationships for broadleaf and needle‐leaf species converged when using the mass‐based index. These results show that much of the variation in ozone sensitivity among woody plants can be explained by interspecific variation in LMA and that large‐scale ozone impact assessment could be greatly improved by considering this well‐known and easily measured leaf trait.

Nature food 4(10), 854 - 865 (2023). doi:10.1038/s43016-023-00858-y Published by Nature Research, London

An international workshop on "Adapting Agriculture to Climate Change and Air Pollution" took place at Nanjing University of Information Science and Technology, Nanjing, China, during 23-27 October, 2023. Experts working in various multi-disciplinary areas of agroecosystem and environmental research gathered for academic communication and discussions. Two discussion groups focused on "agriculture under air pollution and climate change: current challenges and priorities for the future" and "adapting agriculture to air pollution and climate change: current status and next steps." Insights derived from the discussions are summarized in this article and include opinions about current issues, knowledge gaps' identification, and potential priorities and actions that could be taken. The first discussion mainly addresses ozone impact estimates; ozone metrics for impact and risk assessments; ozone monitoring; air pollution impacts and policy; and the pivotal role of agriculture and consumer choices. The second discussion covers adaptation and mitigation; greenhouse gases and energy efficiency; concerns about the link between adaptation and mitigation; local food, planetary-health diets and carbon footprint; irrigation and climate change adaptation; scientific evidence and policy-making; air pollution and crop adaptation; machine learning and crop modeling; and challenges faced by smallholder farmers and large-scale enterprises. Hence, this report could be useful for research, educational, and policy purposes, collating opinions of experts working in diverse research areas.

Poplars are economically important tree crops and biologically important model plants, which are known to be sensitive to ozone (O3). Although surface O3 is considered as a significant global environmental issue because of its phytotoxicity and greenhouse effect, the knowledge of the dose-response (DR) relationships in poplars for the assessment of O3 risk is still limited. Hence, this study aimed at collecting data of studies with manipulative O3 exposures of poplars within FACE (Free Air Concentration Enhancement) and OTC (Open-Top Chamber) facilities. The datasets contain studies on hybrid poplar clones and a non-hybrid native poplar (Populus nigra L.) reporting both AOT40 (Accumulated exposure Over a Threshold of 40 ppb) and POD1 (Phytotoxic Ozone Dose above a threshold of 1 nmol m-2 Projected Leaf Area [PLA] s-1) to compare exposure- and flux-based indices. As a result, linear regression analysis showed that the flux-based POD1 was better than the exposure-based AOT40 to explain the biomass response of poplars to O3. From the DR relationships, a critical level (CL) of 5.7 mmol m-2 POD1 has been derived corresponding to 4% biomass growth reduction for hybrid poplar clones, which can be considered very sensitive to O3, while the non-hybrid native poplar was less sensitive to O3 (CL: 10.3 mmol m-2 POD1), although the potential risk of O3 for this taxon is still high due to very high stomatal conductance. Moreover, the different experimental settings (OTC vs. FACE) have affected the AOT40-based DR relationships but not the POD1-based DR relationships, suggesting that poplar responses to O3 were principally explained by stomatal O3 uptake regardless of the different experimental settings and exposure patterns. These results highlight the importance of the flux-based approach, especially when scaling up from experimental datasets to the O3 risk assessment for poplars at the regional or global scale.

Ground-level ozone (O3) pollution often co-occurs with anthropogenic nitrogen (N) deposition. Many studies have explored how O3 and soil N affect aboveground structure and function of trees, but it remains unclear how belowground processes change over a spectrum of N addition and O3 concentrations levels. Here, we explored the interactive impact of O3 (five levels) and soil N (four levels) on fine and coarse root biomass and biomass allocation pattern in poplar clone 107 (Populus euramericana cv. '74/76'). We then evaluated the modifying effects of N on the responses of tree root biomass to O3 via a synthesis of published literature. Elevated O3 inhibited while N addition stimulated root biomass, with more pronounced effects on fine roots than on coarse root. The root:shoot (R:S) ratio was markedly decreased by N addition but remained unaffected by O3. No interactive effects between O3 and N were observed on root biomass and R:S ratio. The slope of log-log linear relationship between shoot and root biomass (i.e. scaling exponent) was increased by N, but not significantly affected by O3. The analysis of published literature further revealed that the O3-induced reduction in tree root biomass was not modified by soil N. The results suggest that higher N addition levels enhance faster allocation of shoot biomass while shoot biomass scales isometrically with root biomass across multiple O3 levels. N addition does not markedly alter the sensitivity of root biomass of trees to O3. These findings highlight that the biomass allocation exhibits a differential response to environmentally realistic levels of O3 and N, and provide an important perspective for understanding and predicting net primary productivity and carbon dynamics in O3-polluted and N-enriched environments.