Seasonality of Isoprenoid Vertical Gradient Within a Primary Rainforest in Central Amazonia

Tuesday, 16 December 2014
Eliane Gomes Alves1, Kolby Jardine2, Julio Tota3, Angela B Jardine1, Ana Maria Yanez-Serrano1,4, Thomas Karl5, Alex B Guenther6, Julia V Tavares7 and Bruce W Nelson8, (1)INPA National Institute of Amazonian Research, Climate and Environment Department, Manaus, Brazil, (2)Lawrence Berkeley National Laboratory, Berkeley, CA, United States, (3)Federal University of West Para, Institute of Engineering and Geoscience, Santarem, PA, Brazil, (4)Max Planck Institute for Chemistry, Mainz, Germany, (5)University of Innsbruck, Institute for Meteorology and Geophysics, Innsbruck, Austria, (6)Pacific Northwest National Laboratory, Richland, WA, United States, (7)INPA National Institute of Amazonian Research, Ecology Department, Manaus, Brazil, (8)INPA National Institute of Amazonian Research, Manaus, Brazil
Vertical mixing ratio gradients of isoprene, total monoterpenes (TMt) and total sesquiterpenes (TSt) were quantified, within and above the canopy, in a primary rainforest in central Amazonia , using a Proton Transfer Reaction – Mass Spectrometer (PTR-MS). We also estimated the fluxes of these compounds from the canopy into the atmosphere. Measurements were carried out from the dry season (Sept/2010) to the wet season (Jan/2011), continuously. All compound mixing ratios were higher during the dry season than during the wet season; the same behavior was observed for ambient air temperature and photosynthetically active radiation (PAR). Isoprene and TMt mixing ratios were higher within the canopy as compared to near the ground and above the canopy. Daytime TSt mixing ratios were higher near the ground than within and above the canopy. Isoprene and TMt had a diurnal cycle similar to diurnal cycles of air temperature and PAR suggesting that the emission of these compounds are light dependent and stimulated by increasing temperature. However, this same behavior was not observed for TSt. This is probably due to the fact that sesquiterpene emissions are not strongly light dependent; the ozonolysis of sesquiterpenes during daytime could reduce ambient sesquiterpene concentrations; and a less turbulent atmospheric boundary layer during nighttime could make the mixing ratio of sesquiterpenes higher near the surface at nighttime. Daytime flux estimations also presented seasonal variation for the fluxes of all compounds, such that fluxes of: isoprene ranged from 0.4 to 1.5 mg m-2 h-1, TMt ranged from 0.2 to 0.8 mg m-2 h-1, and TSt ranged from 0.1 to 0.25 mg m-2 h-1, being the highest end during the dry season. These flux estimations suggested that the canopy could be the main source of those compounds for the atmosphere for all seasons. Our results provide the first in situ observations of seasonal mixing ratio gradients of isoprenoids in central Amazonia, and suggest that some of the isoprenoid seasonal variations could be driven by changes in light, temperature and leaf phenology.