New foliage growth is a significant, unaccounted source for volatiles in boreal evergreen forests

Abstract

Abstract. Estimates of volatile organic compound (VOC)emissions from forests are based on the assumption that foliage has a steady emission potential over its lifetime, and that emissions are mainly modified by short-term variations in light and temperature. However, in many field studies this has been challenged, and high emissions and atmospheric concentrations have been measured during periods of low biological activity, such as in springtime. We conducted measurements during three years, using an online gas-exchange monitoring system to observe volatile organic emissions from a mature (1 year-old) and a growing Scots pine shoot. The emission rates of organic vapors from vegetative buds of Scots pine during the dehardening and rapid shoot growth stages were one to two orders of magnitude higher than those from mature foliage; this difference decreased and finally disappeared when the new shoot was maturing in late summer. On average, the springtime monoterpene emission rate of the bud was about 500 times higher than that of the mature needles; during the most intensive needle elongation period, the monoterpene emission rate of the growing needles was 3.5 higher than that of the mature needles, and in September the monoterpene emission rate of the same years' needles was even lower (50 %) than that of the previous years' needles. For other measured compounds (methanol, acetone and methylbutenol) the values were of the same order of magnitude, except before bud break in spring, when the emission rates of buds for those compounds were on average about 20-30 times higher than that of mature needles. During spring and early summer the buds and growing shoots are a strong source of several VOCs, and if they are not accounted for in emission modeling a significant proportion of the emissions -from a few percent to even half of the annual cumulative emissions -will remain concealed. The diurnal emission pattern of growing shoots differed from the diurnal cycle in temperature as well as from the diurnal emission pattern of mature shoots, which may be related to processes involved in shoot or needle elongation. Our findings imply that global estimations of monoterpene emission rates from forests are in need of revision, and that the physiological state of the plants should be taken into account when emissions of the reactive gases such as monoterpenes are estimated.

Methanol emissions from maize: Ontogenetic dependence to varying light conditions and guttation as an additional factor constraining the flux

“…A reduction in methanol emission rates along with the maturity of the leaf is a well-known phenomenon which is related to the decrease in leaf growth with time and which has been reported by several other researchers (MacDonald and Fall, 1993;NemecekMarshall et al, 1995;Galbally and Kirstine, 2002;Hüve et al, 2007;Aalto et al, 2014). Reduction levels found in our study are in line with previous measurements on other crop, broadleaf and needleleaf species, which have been recently compiled by Wells et al (2012).…”

From emissions to ambient mixing ratios: online seasonal field measurements of volatile organic compounds over a Norway spruce-dominated forest in central Germany

“…length measurements) induced emissions that were up to 2 orders of magnitude stronger, compared with the ones prior to the event. Persistent and exceptionally strong emissions of methanol were observed during the growing period (May-June) as well as on some days before the new twigs started to grow, similar to the observations of Aalto et al (2014). The strongest emission rates for the majority of oxVOC and isoprenoids occurred after a storm event in which strong winds damaged the bark of the enclosed branch (DOY 167).…”

Field measurements of biogenic volatile organic compounds in the atmosphere using solid-phase microextraction Arrow

“…Indeed, some anti-correlation was found between the measured monoterpenes and these parameters. This result is likely to reflect the increased photooxidation during periods of the day when PAR is high, since the effects of temperature and/or light on monoterpene emissions have been described previously (Aalto et al, 2014). Nonetheless, on-fiber oxidation might occur during SPME collection.…”

“…They also have an important biological role, for example as allelopathic and defense compounds against pathogens and herbivores (Kesselmeier and Staudt, 1999). Measurement of monoterpenes is usually performed by online proton transfer reaction-mass spectrometry (PTR-MS; e.g., Aalto et al, 2014;Rantala et al, 2015). This technique offers fast detection of VOCs, high sensitivity, good time resolution, and low detection limits (Graus et al, 2010).…”