Seasonal variation in biogenic volatile organic compound (BVOC) emissions from Norway spruce in a Swedish boreal forest

Terpene emissions from the top-canopy layer (at 20 m) of one 118-year-old Norway spruce tree were measured between June and September 2013 using a branch chamber. Total terpene emissions varied from 0.05 to 332.5 μg g_dw ^-1 h^-1 with a peak in August. Monoterpenes dominated throughout the summer and on average accounted for 65% of the total terpene mass, followed by sesquiterpenes (29%) and isoprene (6%). The values obtained with an optimized hybrid model, assuming the partitioning of monoterpene emissions from both de novo synthesis and storage structures, were in good agreement with the observed emissions (Pearson’s r = 0.94) at the branch level. De novo monoterpene emissions were found to dominate in all campaigns (> 50%) with almost 100% in June. The highest standardized (30 °C, 1000 μmol photons m^-2 s^-1) monoterpene emission rate was 210.3 μg g_dw ^-1 h^-1 in August, followed by that in June (68.8 μg g_dw ^-1 h^-1). Therefore, both de-novo-synthesis and long-term observations that include seasonal variations are needed for accurately upscaling terpene emissions.