Tihomir Simin:
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Volatile organic compounds (VOCs) have a strong impact on atmospheric chemistry, but their emission from tundra vegetation has not been investigated in detail, until recently. The aim of this thesis was to assess the influence of leaf surface temperature and plant traits on VOC emission from tundra vegetation on branch and ecosystem scales. At the branch scale, a portable photosynthesis system was used to measure the plant ecophysiological traits and to collect the VOCs using adsorbent cartridges. Air temperature and vapor pressure deficit, measured from a nearby weather station, were the main abiotic regulators of leaf surface temperature and VOC emission in northern Sweden. Evergreen tundra shrubs had a higher leaf surface-to-air temperature difference (5.5- 6.5 ºC) compared to the deciduous shrubs (3.7- 4 ºC). Temperature optima for photosynthesis were higher than expected in deciduous species (24-31 ºC), while the increase of photosynthesis at temperatures over 30 ºC suggests high thermal tolerance of evergreen tundra shrubs.
In an experiment in Greenland, Salix shrubs growing in a low elevation valley were 45% taller, but emitted 63% less isoprene compared to the ones from a high elevation mountain slope. Leaf surface temperature decreased with height of Salix shrubs roughly 4 ºC m-1. At the ecosystem scale, eddy covariance method was applied and coupled with supporting meteorological measurements. One of the studies compared periods in July and September for fluxes of six VOCs in northern Sweden, while the other compared two growing season-long isoprene emission data series from northern Sweden and central Norway. The studies showed that tundra ecosystems are a significant source of isoprene in summer and that that isoprene emission has a strong relationship with temperature. A popular VOC emission model, MEGAN, was used in studies on both scales and performed well overall, but did not capture the strong relationship between temperature and VOC emission. The results of this thesis indicate strong VOC emission from tundra vegetation, especially at high surface temperatures. With the ongoing climate change, air temperatures will likely increase, while light and soil moisture availability will differ locally, affecting the surface temperature and VOC emission from tundra vegetation. Altered VOC emission patterns suggest changes to the local climates of future tundra ecosystems.