Fluxos superficiais de CO2 e de energia em um plantio de palma de óleo durante e após o El-Niño 2015-2016 no Leste da Amazônia

Abstract

The 2015-2016 El Niño-Southern Oscillation (ENSO), after the 1950s, was one of the most extreme weather events ever recorded. In the Amazon, ENSO is the cause of reduced rainfall, increased solar radiation and air temperature, consequently, soil moisture is reduced, and the vapor pressure deficit is high, as variables that influence the development and production of oil palm. In this context, the objective of the thesis was to quantify the surface fluxes of CO2 and energy, defining the physical variables that control these processes seasonally and interannually in an oil palm plantation with interspecific hybrid (HIE) (Elaeis guineensis Jacq x Elaeis oleifera (Kunth) Cortés) in eastern Amazonia during the ENSO period (2015 and 2016) and in normal years (2017 and 2018). The CO2 and H2O flux data were calculated using the eddy covariance (EC) method. Photosynthetic parameters were estimated by adjusting the light response curve (LCR) using a non-rectangular hyperbole model. The averages of the Net Ecosystem CO2 Exchange (NEE) and the maximum CO2 assimilation rate (Amax) were higher during the years with ENOS, especially in the wet season. In the normal year of 2017, the greatest assimilation occurred in the dry season. The energy fluxes were higher in the years 2015 and 2016, showing high values of sensible heat flux (H) and latent heat flux (LE). Most of the net radiation (Rn) was used for evapotranspiration processes (52 to 74%). Biophysical controls such as aerodynamic conductance (Ca), surface conductance (Cs) and decoupling factor (Ω) were also calculated to better understand the behavior of the oil palm. Cs showed higher values in 2015 and 2016, indicating greater stomatal opening. Results that corroborated with the same period of the maximum found for NEE and LE. Ca was higher in the dry season, especially in 2015, favoring gas exchange. In 2015 (ENSO), Ω (in both seasonal periods) demonstrated that evapotranspiration was more influenced by vegetation. The physical variables showed weak to strong correlations with NEE, H, LE and Cs, depending on seasonality and year. The most significant were incident photosynthetically active radiation, vapor pressure deficit and soil moisture. Therefore, the interspecific hybrid was shown to be resilient to severe ENSO, with an increase in the CO2 assimilation and LE. As well, it was observed that HIE showed similar behaviors with the equatorial Amazonian forests and different to the plantations located in Southeast Asia in normal year.