Mudanças sazonais na emissão de isoprenóides em uma floresta primária na Amazônia central

Abstract

Tropical forest are the largest source of isoprenoids to the global atmosphere. Accounting for the representativeness of the Amazonian rainforest in relation to the all tropical forests in the globe, it is possible to highlight the need of isoprenoid measurements in this ecosystem. Yet, a few studies of seasonal variation with in situ measurements are just starting to investigate isoprenoid and other Volatile Organic Compound (VOC) emissions in the Amazonian rainforest. In this study, vertical mixing ratio profiles 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 (PTRMS). Fluxes of these compounds from the canopy into the atmosphere were estimated by the inverse Lagrangian transport model, and measurements were carried out from the dry season (September/2010) to the wet season (January/2011), continuously . Also, measurements of isoprene fluxes using a Relaxed Eddy Accumulation system (REA) were carried out in intensive campaigns from June/2013 to December/2013, characterizing four seasons: the wet-to-dry transition season, the dry season, the dry-to-wet transition season and the beginning of the wet season. Results showed a seasonal trend for the isoprenoid emissions, being maximum isoprenoid emissions found during the dry season and the dry-to-wet transition season. For isoprene, low emissions were observed during the wet-to-dry transition season, suggesting that this low emission could be related to variations in leaf demography and estimates of leaf phenology. A comparison of satellite-derived isoprene emission and ground-based isoprene emission have shown that both presented the same trend of seasonality. MEGAN 2.1 did not show good agreement with isoprenoid emission measurements, however this could be related to the fact that only seasonal changes in light and temperature were considered to run this model, which may not reproduce simultaneous effects of other environmental and biological factors, as leaf phenology. Results here shown suggest thta, besides seasonal changes in light and temperarure, the seasonal variation in isoprenoid emissions could also be driven by seasonal changes in leaf demography and leaf ontogeny.