The double punch: ozone and climate stresses on vegetation

Vegetation is being hit by a double punch; air pollution and climate change. Ground level ozone is a problem reducing yield and growth of plants in natural vegetation all over the world. In Northern Norway the levels of ozone in the air is lower than in more densely populated areas. Nevertheless, the level may increase due to increased traffic of ships along the coast as larger areas are becoming free of ice in the Arctic in summer. Thus, it is important to keep track of vegetation responses near these coastal areas. Plant and climate scientists have cooperated to study the ozone concentrations of the air in Finnmark through the growth season and its effects on vegetation. In particular, effects of Arctic conditions with midnight sun have been examined, as there are indications that lack of nighttime darkness can enhance the ozone sensitivity of the plants. Further, the effect of the vegetation itself on ozone levels and climate should be taken into account, as feedback effects from vegetation to atmospheric ozone concentration and to climate may occur. The Finnmark vegetation may be stressed by ozone pollution, which may cause reduced plant sizes and a bias for less ozone sensitive species. At the same time, the vegetation is stressed by climate changes. Higher temperatures cause earlier snowmelt in spring, yielding a longer growth season. These different changes in plant growth conditions may lead to a shift in species composition and thus altered vegetation. Using climate models and models for air pollution, we have gained more information about the changes going on in these northern areas. We have experimental equipment for exposing plants to ozone under controlled environment conditions, making us able to describe and quantify the effects of ozone on the plant species of interest. With plants grown in rhizotrons, we are able to observe roots as they grow in the soil near a transparent surface, giving us the possibility of assessing aboveground as well as belowground growth responses to ozone. We also investigate whether this effect differs in conditions with and without midnight sun. In the field, we have done measurements of photosynthesis and transpiration rates for parameterization of vegetation for model work. We have chosen to place emphasis on studying diurnal variations in plant activity in the field during three different parts of the growth season. In the growth season of 2021, we had two ozone gardens established in Norway; one at Blindern in Oslo and one at Svanhovd in Pasvikdalen, Finnmark. Ozone gardens consist of plants that are known to display visible foliar injuries when they are subjected to ozone. We cultivated three cultivars of tobacco, among others, in the ozone gardens. There are two good reasons for including the three tobacco cultivars. One is that the foliar injuries due to ozone are very characterisitic, making them easily distinguishable from other injuries. In addition, the three cultivars differ in sensitivity to ozone. Thus, one can observe that the most sensitive cultivar displays injuries earlier and to a greater degree than the others do. The sensitive tobacco cultivar displayed ozone injuries from July to September. Cutleaf coneflower, an ozone garden species originating from USA, showed typical visible injuries due to ozone in the same period. One important goal for our work is to model plant responses to ozone exposure at high latitudes more precisely. We have developed a process-based method of implementing the stress caused by ozone in the model, through a reduction in the maximum photosynthesis rate. We will evaluate the model results to see if ozone effects are better predicted with the new method. We have also found that the levels of tropospheric ozone in Northern Scandinavia during the summer of 2018 were 5-8 % higher than expected from the climatology, partly because of heat and forest fires other places in Scandinavia. Our estimates show that ozone had a clear negative effect on the growth of birch forests and grassland in our study area (Pasvik, Finnmark) that year. Pine forests were, on the other hand, not that much affected. Further, we actually found this same pattern for the response of these three vegetation types to ozone exposure in 2019, which was a year with more normal climate conditions than the year before.

Double Punch har ført til et kompetansehevende tverrfaglig samarbeid. Vi har også bidratt i et større tverrfaglig miljø både nasjonalt og internt på UiO. Dette har gitt oss et nettverk av kolleger for framtidige forskningsprosjekter. Vi har også fått god kontakt med kolleger i USA som jobber med den store modellen CLM for interaksjoner mellom landområder (vegetasjon) og atmosfæren. I Europa har vi bidratt til arbeidsgruppa for estimering av effekter av ozon på landbruksprodukter og naturlig vegetasjon (ICP Vegetation) i FNs LRTAP-konvensjon (Long-Range Transboundary Air Pollution). Vi har løftet kunnskapen om de nordligste delene av Europa, og påvist at modellene ikke er godt nok tilpasset våre områder. Vi har foreslått forbedringer, og ser at de estimerte ozonskadene på vegetasjon og avling blir større enn modellene sier originalt. Det er allerede estimert at skog og landbruk mange steder i Norden taper over 5 % på grunn av ozonforurensning, men disse verdiene kan være for lave.

In the Anthropocene vegetation is hit by a double punch; air pollution and global warming. OzoNorClim investigates combined effects of ozone and climate stresses on Arctic and boreal species, with a focus on impacts of the long daylengths in this region as a novel element. Interdisciplinary research questions from the MILJØFORSK and KLIMAFORSK programmes are addressed, combining plant ecophysiology and atmosphere physics methods. OzoNorClim has a female coordinator. The work consists of plant physiological and mycological experiments to quantify the effects of ozone polluted air under the particular conditions in Northern areas, with midnight sun, and feed the new information into widely used climate and tropospheric ozone injury models. The improved models will give a better representation of the interactions between tropospheric ozone, vegetation and climate in Arctic and tundra areas, and therefore a better foundation for political decisions. The UNECE Convention on Long-range Transported Air Pollution (LRTAP) uses the Deposition of Ozone for Stomatal Exchange (DO3SE, see below) model to provide information to European policy makers. The DO3SE model will be modified according to experimental findings to make it better suited for Northern areas. Stockholm Environment Institute (York, UK, centrally placed in DO3SE development) is part of the team, and will cooperate with the Norwegian groups in this project, making our results highly available for the model users in Europe and North America. We will collaborate with Norwegian Institute for Air Research (NILU) for ozone monitoring at Svanhovd, and with Norwegian Institute of Bioeconomy Research (NIBIO) at the same place for field work. OzoNorClim is organised in five work packages, starting with field and lab work, from which results will be used to develop and apply models to estimate ozone concentrations and impacts on vegetation in combination with future climate change.