Leaf level emissions of volatile organic compounds (VOC) from some Amazonian and Mediterranean plants

Abstract

Abstract. Emission inventories defining regional and global biogenic volatile organic compounds (VOC) emission strengths are needed to determine the impact of VOC on atmospheric chemistry (oxidative capacity) and physics (secondary organic aerosol formation and effects). The aim of this work was to contribute with measurements of tree species from the poorly described tropical vegetation in direct comparison with the quite well-investigated, highly heterogeneous emissions from Mediterranean vegetation. VOC emission from sixteen plant species from the Mediterranean area were compared with twelve plant species from different environments of the Amazon basin by an emission screening at leaf level using branch enclosures. Analysis of the volatile organics was performed online by a proton-transfer-reaction mass spectrometer (PTR-MS) and offline by collection on adsorbent tubes and subsequent gas chromatographic analysis. Isoprene was the most dominant compound emitted followed by monoterpenes, methanol and acetone. The average loss rates of VOC carbon in relation to the net CO2 assimilation were found below 4% and indicating normal unstressed plant behavior. Most of the Mediterranean species emitted a large variety of monoterpenes, whereas only five tropical species were identified as monoterpene emitters exhibiting a quite conservative emission pattern (α-pinene < limonene < sabinene < ß-pinene). Mediterranean plants showed additional emissions of sesquiterpenes. In the case of Amazonian plants no sesquiterpenes were detected. However, missing of sesquiterpenes may also be due to a lack of sensitivity of the measuring systems. Furthermore, our screening activities cover only 1% of tree species of such tropical areas as estimated based on recent biodiversity reports. Methanol emissions, an indicator of growth, were found to be common in most of the tropical and Mediterranean species. A few species from both ecosystems showed acetone emissions. The observed heterogeneous emissions, including reactive VOC species which are not easily detected by flux measurements, give reason to perform more screening at leaf level and, whenever possible, within the forests under ambient conditions.

Diel and seasonal changes of biogenic volatile organic compounds within and above an Amazonian rainforest

“…If rain events cause such an anoxia, this would explain the observed mixing ratios below the LOD (LOD acetaldehyde 0.28 ppb) in the understorey, a considerable increase at the crown, and a quick decrease towards the atmosphere during the wet season. A similar pattern, indicating plant production, was found for acetone and MEK, which is supported by other studies (Isidorov et al, 1985;Kirstine et al, 1998;Bracho-Nunez et al, 2013). However, for the vertical profile of acetone during the dry season, the peak was observed above the canopy, possibly due to a dominance of photochemistry just above the canopy (Seco et al, 2007).…”

“…Similarly, MEK mixing ratios changed to comparable mixing ratios in and above the canopy during the dry season. Despite the 4-fold increase from the wet to the dry season at the 79 m level, mixing ratios within the canopy remained similar (∼400 ppt) as compared to the wet season, suggesting that the MEK within the canopy does not originate from isoprene oxidation (Bracho-Nunez et al, 2013). In addition, the vertical distribution of these oxygenated compounds during the dry season compared very well to the calculated isoprene oxidation product-to-isoprene ratio.…”

“…Although few observations exist, MEK has been shown to be emitted from vegetation (Isidorov et al, 1985;Kirstine et al, 1998;Jardine et al, 2010;Bourtsoukidis et al, 2014). However, it is also an oxidation product butane Bracho-Nunez et al, 2013).…”

“…Despite the high variability, a maximum of oxidative capacity was generally observed at 53 m. The vertical profiles of acetone, MEK and acetaldehyde during the wet season showed a maximum inside the canopy at midday. Acetaldehyde is reported to be emitted by the forest crown as a by-product of fermentation processes within roots due to water flooding and root anoxia (Kesselmeier et al, 2009;Bracho-Nunez et al, 2013). If rain events cause such an anoxia, this would explain the observed mixing ratios below the LOD (LOD acetaldehyde 0.28 ppb) in the understorey, a considerable increase at the crown, and a quick decrease towards the atmosphere during the wet season.…”

Seasonality of isoprenoid emissions from a primary rainforest in central Amazonia

“…2a, b, c) and total monoterpenes (Fig. 2d, e, f) had higher mixing ratios during daytime (10:00-16:00, LT) than during nighttime (22:00-04:00, LT) for all seasons, supporting the findings that emissions of isoprene Harley et al, 2004) and monoterpenes (Bracho-Nunez et al, 2013;Kuhn et al, 2002Kuhn et al, , 2004aJardine et al, 2015) from Amazonian plant species, at least at this site, are primarily light-dependent and stimulated by increasing temperature. During daytime, isoprene had a maximum mixing ratio within the canopy.…”