The shift in plant species composition in a subarctic mountain birch forest floor due to climate change would modify the biogenic volatile organic compound emission profile

Abstract

Background and aims Mountain birch forests dominate in the Subarctic but little is known of their nonmethane biogenic volatile organic compound (BVOC) emissions. The dwarf shrubs Empetrum hermaphroditum, Vaccinium myrtillus and Vaccinium uliginosum co-dominate in the forest floors of these forests. The abundance of these three dwarf shrubs relative to each other could be affected by climate warming expected to increase nutrient availability by accelerating litter decomposition and nutrient mineralization. We 1) compared the BVOC emission profiles of vegetation covers dominated by E. hermaphroditum and V. myrtillus plus V. uliginosum in a subarctic mountain birch forest floor, 2) distinguished the BVOCs emitted from plants and soil and 3) measured how the BVOC emissions from the different vegetation covers differed under darkness. Methods BVOCs were sampled during two growing seasons using a conventional ecosystem chamberbased method, collected on adsorbent and analyzed with gas chromatography-mass spectrometry.Results High abundance of E. hermaphroditum increased the sesquiterpene emissions. Soil released fewer different BVOCs than controls (i.e. natural vegetation) but the total emission rates were similar. Darkness did not affect the emissions. Carbon emitted as BVOCs was less than 0.2% of the CO 2 exchange. Conclusions Our results suggest that sesquiterpene emissions from subarctic mountain birch forest floors would be reduced following an increased abundance of V. myrtillus and V. uliginosum with climate change because these species respond rapidly to increased nutrient availability.

Off-season biogenic volatile organic compound emissions from heath mesocosms: responses to vegetation cutting

“…This finding is in line with the results of Faubert et al (2012) who found that E. hermaphroditum was an important sesquiterpene source for the mountain birch forest floor emissions measured during the growing season. The total BVOC emission rate of the mixed heath mesocosms, 10.33 μg m −2 h −1 , was in the same range as the emission rates during the growing season from in situ measurements in Abisko: 10.9–14.61 μg m −2 h −1 for a mixed wet heath (Tiiva et al, 2008; Faubert et al, 2010) and 3.5–45 μg m −2 h −1 for an E. hermaphroditum -dominated forest floor (Faubert et al, 2012), depending on the year. The emission rates of the present experiment may be somewhat understated due to the light intensity in the growth chambers being lower than for open ecosystems under field conditions in full sunlight.…”

“…VOCs were sampled by a push-pull system described by Faubert et al (2010, 2012) for 30 min. A transparent polycarbonate chamber (23 × 23 cm, height 25 cm), equipped with a fan to mix the headspace air, was placed on top of a water-filled groove in the aluminum frame holding each mesocosm.…”

“…The emission rates were calculated following the procedure outlined in Faubert et al (2012) taking into account the different soil surface microtopographies in each mesocosm and the additional air volume due to the slightly higher flow rate into than out from the chamber.…”

“…The contribution of BVOCs to the carbon loss from soil is minimal relative to the respiratory CO 2 effluxes (Aaltonen et al, 2011; Faubert et al, 2012). However, BVOCs are important as reactive atmospheric trace gases, and BVOC oxidation products contribute to secondary organic aerosol formation and may even be involved in new particle formation (see e.g., Fuentes et al, 2000; Jimenez et al, 2009; Riipinen et al, 2012).…”

“…Most of the forest floor emissions were reported to stem from needle litter and roots rather than from bulk soil (Hayward et al, 2001), although the potential soil emissions could not be separated from those of belowground plant material with the applied experimental strategy (removing soil layers). A field study conducted in a mountain birch forest in Abisko, northern Sweden compared emissions from vegetated forest floor plots to emissions from plots where aboveground vegetation had been removed by cutting (Faubert et al, 2012). The removal of the aboveground vegetation reduced the number of different BVOCs emitted whilst having no significant effects on the total quantity emitted, but again, it was not possible to separate emissions from soil and belowground plant parts.…”