Volume 15, issue 13 | Copyright
Biogeosciences, 15, 4019-4032, 2018
https://doi.org/10.5194/bg-15-4019-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 03 Jul 2018

Research article | 03 Jul 2018

Leaf phenology as one important driver of seasonal changes in isoprene emissions in central Amazonia

Eliane G. Alves1, Julio Tóta2, Andrew Turnipseed3, Alex B. Guenther4, José Oscar W. Vega Bustillos5, Raoni A. Santana2, Glauber G. Cirino6, Julia V. Tavares1, Aline P. Lopes1, Bruce W. Nelson1, Rodrigo A. de Souza7, Dasa Gu4, Trissevgeni Stavrakou8, David K. Adams9, Jin Wu10, Scott Saleska11, and Antonio O. Manzi12 Eliane G. Alves et al.
  • 1Department of Environmental Dynamics, National Institute for Amazonian Research (INPA), Av. André Araújo 2936, CEP 69067-375, Manaus-AM, Brazil
  • 2Institute of Engineering and Geoscience, Federal University of West Para (UFOPA), Rua Vera Paz s/n, CEP 68035-110, Santarem-PA, Brazil
  • 32B Technologies, Inc., 2100 Central Ave., Boulder, CO 80301, USA
  • 4Department of Earth System Science, University of California, Irvine, CA 92697, USA
  • 5Chemistry and Environment Center, National Institute for Energy and Nuclear Research (IPEN), Av. Lineu Prestes 2242, CEP 05508-000, São Paulo-SP, Brazil
  • 6Department of Meteorology, Geosciences Institute, Federal University of Para, Belém, PA 66075-110, Brazil
  • 7Meteorology Department, State University of Amazonas (UEA), Av. Darcy Vargas 1200, CEP 69050-020, Manaus-AM, Brazil
  • 8Royal Belgian Institute for Space Aeronomy, Avenue Circulaire 3, 1180 Brussels, Belgium
  • 9Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, Av. Universidad 3000, 04510, Mexico city, Federal District, Mexico
  • 10Department of Environmental and Climate Sciences, Brookhaven National Laboratory, Upton, NY 11973, USA
  • 11Ecology and Evolutionary Biology Department, University of Arizona, Cherry Avenue and University Boulevard, Tucson, AZ 85721, USA
  • 12National Institute for Spatial Research, Center of Weather Forecasting and Climate Studies, Rod. Presidente Dutra, km 40, Cachoeira Paulista-SP, Brazil

Abstract. Isoprene fluxes vary seasonally with changes in environmental factors (e.g., solar radiation and temperature) and biological factors (e.g., leaf phenology). However, our understanding of the seasonal patterns of isoprene fluxes and the associated mechanistic controls is still limited, especially in Amazonian evergreen forests. In this paper, we aim to connect intensive, field-based measurements of canopy isoprene flux over a central Amazonian evergreen forest site with meteorological observations and with tower-mounted camera leaf phenology to improve our understanding of patterns and causes of isoprene flux seasonality. Our results demonstrate that the highest isoprene emissions are observed during the dry and dry-to-wet transition seasons, whereas the lowest emissions were found during the wet-to-dry transition season. Our results also indicate that light and temperature cannot totally explain isoprene flux seasonality. Instead, the camera-derived leaf area index (LAI) of recently mature leaf age class (e.g., leaf ages of 3–5 months) exhibits the highest correlation with observed isoprene flux seasonality (R2 = 0.59, p < 0.05). Attempting to better represent leaf phenology in the Model of Emissions of Gases and Aerosols from Nature (MEGAN 2.1), we improved the leaf age algorithm by utilizing results from the camera-derived leaf phenology that provided LAI categorized into three different leaf ages. The model results show that the observations of age-dependent isoprene emission capacity, in conjunction with camera-derived leaf age demography, significantly improved simulations in terms of seasonal variations in isoprene fluxes (R2 = 0.52, p < 0.05). This study highlights the importance of accounting for differences in isoprene emission capacity across canopy leaf age classes and identifying forest adaptive mechanisms that underlie seasonal variation in isoprene emissions in Amazonia.

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This study shows that leaf quantity and leaf age have an important effect on seasonal changes in isoprene emissions and that these could play an even more important role in regulating ecosystem isoprene fluxes than light and temperature at seasonal timescales in tropical forests. These results bring novelty and new insight for future research because in the past leaf phenology was not considered as an important factor that controls biological processes in the tropics.
This study shows that leaf quantity and leaf age have an important effect on seasonal changes in...
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