Phenological stage of tundra vegetation controls bidirectional exchange of BVOCs in a climate change experiment on a subarctic heath

Abstract

Traditionally, biogenic volatile organic compound (BVOC) emissions are often considered a unidirectional flux, from the ecosystem to the atmosphere, but recent studies clearly show the potential for bidirectional exchange. Here we aimed to investigate how warming and leaf litter addition affect the bidirectional exchange (flux) of BVOCs in a long-term field experiment in the Subarctic. We also assessed changes in net BVOC fluxes in relation to the time of day and the influence of different plant phenological stages. The study was conducted in a full factorial experiment with open top chamber warming and annual litter addition treatments in a tundra heath in Abisko, Northern Sweden. After 18 years of treatments, ecosystem-level net BVOC fluxes were measured in the experimental plots using proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS). The warming treatment increased monoterpene and isoprene emissions by ≈50%. Increasing temperature, due to diurnal variations, can both increase BVOC emission and simultaneously, increase ecosystem uptake. For any given treatment, monoterpene, isoprene, and acetone emissions also increased with increasing ambient air temperatures caused by diurnal variability. Acetaldehyde, methanol, and sesquiterpenes decreased likely due to a deposition flux. For litter addition, only a significant indirect effect on isoprene and monoterpene fluxes (decrease by ~50%-75%) was observed. Litter addition may change soil moisture conditions, leading to changes in plant species composition and biomass, which could subsequently result in changes to BVOC emission compositions. Phenological stages significantly affected fluxes of methanol, isoprene and monoterpenes. We suggest that plant phenological stages differ in impacts on BVOC net emissions, but ambient air temperature and photosynthetically active radiation (PAR) also interact and influence BVOC net emissions differently.Our results may also suggest that BVOC fluxes are not only a response to changes in temperature and light intensity, as the circadian clock also affects emission rates.

Bidirectional Exchange of Biogenic Volatile Organic Compounds in Subarctic Heath Mesocosms During Autumn Climate Scenarios

“…Vegetation in the area is mixed, low (canopy height 5-15 cm) tundra heath vegetation composed of evergreen and deciduous dwarf shrubs, graminoids, and a few herb species, as well as mosses. For further site description, see Baggesen et al (2021). Mesocosm collection was performed by cutting and digging out an 18 × 18 × 11 cm (length × width × height) square of soil including the above and below ground organic material and intact vegetation and transferring those samples into polypropylene containers (Ghirardo et al, 2020).…”

“…Most arctic field research into biogenic volatile organic compounds (BVOCs) ends in late summer, before the first snow, and is first initiated again after snowmelt, in early summer (Baggesen et al., 2021 ; Faubert et al., 2010 ; Tiiva et al., 2008 ; Valolahti et al., 2015 ). BVOC dynamics during the long autumn and winter periods are largely unexplored because biological productivity is relatively low and plants are inactive and unproductive.…”

“…BVOCs are mainly emitted from green plants and flowers (Peñuelas et al., 2014 ), plant litter (Greenberg et al., 2012 ; Svendsen et al., 2018 ), and soils (Aaltonen et al., 2011 ; Tang et al., 2019 ), whereas uptake is highest in soils (Albers et al., 2018 ; Rinnan & Albers, 2020 ). Thus, the highest BVOC emissions occur during peak summer, when leaf biomass has its maximum (Baggesen et al., 2021 ; Tang et al., 2018 ), and the highest BVOC uptake by the ecosystem, relative to emissions, is presumed to occur outside the growing season (Seco et al., 2020 ).…”

“…Climate warming in the Arctic increases the fluxes of temperature‐sensitive BVOCs from the ecosystem during the growing season (Baggesen et al., 2021 ; Faubert et al., 2010 ; Lindwall et al., 2016 ; Tiiva et al., 2008 ; Valolahti et al., 2015 ), whereas autumnal warming could be hypothesized to only have a minor effect on BVOC emissions, due to the natural decrease in green biomass during the autumn (Anderson et al., 2016 ) and hence, decrease in vegetation‐derived BVOC production. Although vegetation is less active at the onset of autumn, there may still be a clear vegetation‐dominated emission (Rinnan et al., 2013 ).…”

“…soils (Albers et al, 2018;Rinnan & Albers, 2020). Thus, the highest BVOC emissions occur during peak summer, when leaf biomass has its maximum (Baggesen et al, 2021;Tang et al, 2018), and the highest BVOC uptake by the ecosystem, relative to emissions, is presumed to occur outside the growing season (Seco et al, 2020).…”