Monoterpene emissions from Scots pine and Norwegian spruce

Abstract

Rates of monoterpene emissions from Scots pine (Pinus sylvestris) and Norwegian spruce (Picea abies) have been measured at four sites in Sweden with a dynamic flow chamber technique. Forest floor emissions have been made in the pine forest with the static chamber technique. Sampling was done with Tenax TA and analysis and detection by GC and ion trap detection. The compounds A 3-carene and a-pinene were the predominant terpenes emitted from the crown and floor of the Scots pine forest. Alpha-pinene was the main terpene emitted from Norwegian spruce at the sites in southern and central Sweden, while A 3-carene was predominant at the northern site. The relative composition of the emission of both species underwent changes in early spring and fall. Emission rates, normalized to temperature, were seen to vary diurnally with a maximum at midday, and seasonally with maxima in early May and October, and a summer maximum in June-July. The possible dependence of the emission rate on needle growth rate and other plant-physiological processes is discussed. A higher emission rate and different relative composition of the emission was seen to occur when the vegetation was wet, as compared to dry vegetation. The emission from the pine forest floor was seen to have a composition different from that of the crown and a seasonality of the rate similar to that of the crown. The ground emission could not be explained by sources in the litter or ground vegetation alone, and it is suggested that the root system of the trees is also an emission source. The emission rate from the pine forest floor was of the order of 30% of the crown emission. The July rate of emission from the crown of Scots pine, normalized to 20øC and averaged over four sites in Sweden, was 0.8 _+ 0.4 (gdw (grams dry weight) h) -1 , and for Norwegian spruce, 0.5 _ 0.7/xg(gdw h) -1 . It would seem that previous regional and global estimates of hydrocarbon fluxes to the atmosphere have used emission factors which are too high for boreal coniferous forests. 1. 1991]. All model studies are, however, in part thwarted by the gaps in our knowledge concerning the size and variation of natural hydrocarbon fluxes as well as their oxidation pathways and products. This is especially the case for the monoterpenes (hereafter referred to as the terpenes). The terpenes are acyclic, monocyclic, and bicyclic isomers of the formula C10H16, biosynthesized by many plant species, especially coniferous trees. Their flux to the atmosphere is estimated to be the largest, globally, of the natural nonmethane hydrocarbons (NMHCs) [Zimmerman et al., 1978; Altshuller, 1983]. As first reported by Tingey et al. [1978], the rate of their emission from conifers to the atmosphere varies exponentially with leaf temperature, similar to the temperature dependence of the terpene vapor pressures. Using the temperature dependencies reported in the literature for various coniferous species in different parts of the world, 20øC emission rates are seen to vary by 2 orders of magnitude, from 0.1 to about 10 •g ...

Isoprene and monoterpene fluxes measured above Amazonian rainforest and their dependence on light and temperature

“…Emissions from ecosystems in these regions are often observed to be largely based on temperature-controlled evaporation from storage pools and independent of light [ Lerdau et al, 1997] with monoterpenes often observed accumulating within the forest atmosphere at night [Janson, 1993;Rinne et al, 2000;Bouvier-Brown et al, 2009]. However, monoterpene emissions from tropical ecosystems are generally assumed as emitted from de novo production in a light-dependent manner, analogous to isoprene .…”

Are monoterpene emissions influenced by humidity?

“…Some researches have claimed that relative humidity influences monoterpene emissions [e.g. Dement et al, 1975], whereas others have disputed it [Juuti et al, 1990;Janson, 1993]. The current monoterpene emission model does not include such dependencies [Guenther et al, 1995].…”

Exchange of volatile organic compounds in the boreal forest floor

“…However, the maximum flux (373 μg m -2 h -1 ) measured by Hellén et al (2006) with adsorbent tubes was notably higher than that quantified with the same technique in this study. Hellén et al (2006) assumed that needle litter and fine roots in topsoil were the main sources of the terpenoids, which were also suggested by the studies of Janson (1993) and Hayward et al (2001). The forest floor remained a source of terpenoids not only during the growing season, but also during winter, however, the flux level was clearly lowered, approximately by a factor of ten.…”

“…Some field studies indicate that the majority of them may originate from decomposing organic matter and living plant roots (Janson 1993, Hayward et al 2001, Asensio et al 2008a, Leff and Fierer 2008, Gray et al 2010, Greenberg et al 2012. Soil microbial activity is correlated with net rates of VOC emissions over a range of different forest soils (Asensio et al 2007a, 2008b, Leff and Fierer 2008, which stresses the importance of microbes and microbial processes as sources of soil VOCs.…”

“…However, complex processes and high spatial heterogeneity occurring belowground complicate the study of VOC sources. Several studies indicate that living plant roots and decomposing organic matter are the likely sources of forest floor VOCs (Janson 1993, Hayward et al 2001, Asensio et al 2008a, Leff and Fierer 2008, Gray et al 2010). The VOC emissions from above-and belowground litter are perhaps the best example of the diversity of processes taking part in the release of VOCs to the atmosphere.…”