Periodic Reporting for period 3 - TUVOLU (Tundra biogenic volatile emissions in the 21st century) Reporting period: 2021-04-01 to 2022-09-30 Summary of the context and overall objectives of the project Biogenic volatile organic compounds (BVOCs) influence atmospheric oxidation causing climate feedback thought to be especially significant in remote areas with low anthropogenic emissions, such as the Arctic. Still, we do not understand the dynamics and impact of climatic and biotic BVOC emission drivers in arctic and alpine tundra, which are highly temperature-sensitive BVOC sources. This ERC consolidator project aims to redefine tundra BVOC emission estimates to account for rapid and dramatic climate warming accompanied by effects of vegetation change, permafrost thaw, insect outbreaks and herbivory. We will quantify the relationships between leaf and canopy temperatures and BVOC emissions to improve BVOC emission model predictions of emission rates in low-statured tundra vegetation, which efficiently heats up under clear skies. We will experimentally determine the contribution of induced BVOC emissions from insect herbivory in the warming Arctic by field manipulation experiments addressing basal herbivory and insect outbreaks and laboratory experiments. We will use laboratory experiments to determine if permafrost thaw leads to significant BVOC emissions from thawing and newly available soil processes, or if the released BVOCs are largely taken up by soil microbes. We will also use a global network of existing climate warming experiments in alpine tundra to assess how the BVOC emissions from tundra vegetation world-wide respond to climate change. Measurement data will help develop and parameterize BVOC emission models to produce holistic enhanced predictions for global tundra emissions. Finally, modelling will be used to estimate emission impact on tropospheric ozone concentrations and secondary organic aerosol levels, producing the first assessment of arctic BVOC-mediated feedbacks on regional air quality and climate. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far In WP1, which focuses on canopy surface temperature impacts, we have conducted field work in Abisko, Sweden (2018), Narsarsuaq, Greenland (2019) and Finse, Norway (2019). The leaf-level work with tundra shrubs has showed that evergreen and deciduous shrub species differ in temperature responses for photosynthesis and BVOC emissions (Simin et al., submitted manuscript). We have conducted plant-scale measurements on dwarf birch and grey willow on an elevation gradient to assess relationships between canopy height, plant and environmental traits as well as BVOC emissions. We have conducted ecosystem-scale measurements of BVOC fluxes in contrasting ecosystem types. Results from a Subarctic permafrost landscape on Stordalen wetland in Abisko show that during the peak growing season, a palsa area had higher BVOC emissions than a wet fen, while a lake was mainly a sink of BVOCs (Seco et al. 2020, Atmospheric Chemistry & Physics; Seco et al., manuscript in preparation). We show that the strong temperature dependency of tundra BVOC emissions is also evident at ecosystem scale (Seco et al. 2020).In the insect herbivory-focused WP2, we have conducted field work in Abisko, Sweden (2018-2020), Tromsø, Norway (2018) and Narsarsuaq, Greenland (2019). Our work on the effects of insect herbivory started with an experiment, in which we used methyl jasmonate (MeJA) to mimic insect herbivory on the dwarf birch, Betula nana. We showed that the MeJA-treatment strongly increased BVOC emissions and changed the profile of compounds released (Li et al. 2019, Nature Plants). Interestingly, climate warming strongly amplified this response. To feed on the modelling work in WP5, we have conducted three experiments to assess how the number of feeding larvae impacts BVOC emissions of the mountain birch B. pubescens var. pumila. The results indicate that there is a strong positive relationship between the number of larvae and the BVOC emissions (Rieksta et al. 2020, Frontiers in Plant Science). In WP3 with the focus on permafrost thaw emissions, we have shown that thawing permafrost releases considerable amounts of BVOCs, especially ethanol and methanol, but that the emissions to the atmosphere are lower due to active microbial uptake of BVOCs during their passage through the active layer soil (Kramshøj et al., 2018, Nature Communications). The microbial uptake may be an important, overlooked process, which functions efficiently for all kinds of BVOCs in all soils (Albers et al. 2018, Biogeosciences; Rinnan & Albers 2020, JGR Biogeosciences). The net amount and composition of BVOCs released to the atmosphere depends also on the water content of the soil, which determines the oxygen content (Kramshøj et al. 2019, Global Change Biology). The modelling work in WP5 has been proceeding in parallel with measurement activities. We wrote a review article to summarize the current understanding and to identify knowledge gaps in modelling soil BVOC-related processes (Tang et al. 2019, Reviews in Geophysics). New leaf temperature algorithms are developed in collaboration with WP1 using leaf-level data collected (Simin et al. submitted; Simin et al. in preparation) and the ecosystem level data are used for model validation (e.g. Seco et al. 2020). Herbivory (leaf area loss)-BVOC emission relationships have been assessed by experimental work in WP2 to be able to develop algorithms for model improvement. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) We have collected the first growing season long time series of BVOC exchange in arctic tundra ecosystems using the eddy covariance (EC) technique and real-time measurement of hundreds of chemical compounds simultaneously. The new understanding provided by these datasets includes seasonal variation in emissions and uptake of BVOCs, and the confirmation of a high temperature dependency of BVOC emissions from tundra vegetation, which has been earlier suggested based on small-scale enclosure data. The EC measurements have been coupled with remote sensing measurements of vegetation greenness and surface temperature. The combination provides us with strong tools to assess factors controlling BVOC exchange. We expect to improve our understanding of how tundra shrub communities respond to the warming climate in terms of BVOC emissions.Our pioneering finding about BVOC release from permafrost thaw has been complemented with process understanding related to separation of BVOC production/release versus uptake in soil. We showed that while thawing of permafrost soil can release a high amount of certain BVOCs and a high diversity of compounds in general (Kramshøj et al. 2018, Nature Communications), the actual emission to the atmosphere is dependent on the balance between the release and microbial uptake processes that appear to be ubiquitous (Rinnan & Albers 2020, JGR Biogeosciences) and affected by environmental conditions (Kramshøj et al. 2019, Global Change Biology). The work related to soil processes in ecosystem BVOC exchange is still at its infancy and will likely lead to important new understanding in the future.We have provided novel understanding on the importance of insect herbivory in affecting BVOC emissions in the Arctic. Our work shows that while increasing temperatures have very strong effects on BVOC emissions from arctic ecosystems, the effect of herbivory is even more drastic for certain compounds during active insect feeding periods. Surprisingly, the responses to insect herbivory also appear to be strongly amplified by temperature, highlighting the importance of ecosystem-atmosphere interactions in the changing Arctic (Li et al. 2019, Nature Plants). Transporting measurement instrumentation for ecosystem measurements of tundra volatiles in Abisko
