CO2 gas exchange in oil palm plantation under 2015 ENSO conditions in eastern Amazonia

The 2015/2016 El Niño Southern Oscillation (ENSO) was one of the most severe, as strong as in 1997/1998, and reached mainly the eastern Amazon. ENSO in the Amazon causes a decrease in precipitation and increase in temperature. Oil palm in dry conditions, low humidity, high temperatures and soil water deficit has its photosynthesis inhibited, decreased evapotranspiration and stomatal conductance and inflorescence abortion, for example. The objective of this study was to estimate the CO2 gas exchange in interspecific hybrid oil palm plantation (Elaeis guineensis Jacq x Elaeis oleifera (Kunth) Cortés), relating to the effects of the meteorological variables in the 2015 ENOS in the eastern Amazon. The study area was a 12-year-old oil palm plantation (01°51'43.2"S, 048°36'52.2"W) in the municipality of Moju, Pará, Brazil, where a micrometeorological observation tower was installed. Were quantified the meteorological variables such as photosynthetically active radiation (PAR), vapor pressure deficit (VPD) and soil moisture. And the fluxes of CO2 and H2O for application of the eddy covariance method. Photosynthetic parameters were estimated using the light response curve (LCR) in the non-rectangular hyperbole model. The results were shown seasonally, the months of the wet season (December to June) presented precipitation greater than 150 mm/month and the dry season (July to November) with monthly precipitation less than 150 mm, being a threshold that influences the water deficit for the oil palm. The dry season presented a reduction of more than 57% in the precipitation, when compared to the climatological normal data of Belém. The daily average of net CO2 exchange was higher in the wet season of -22.50 (± 0.40) µmol m-² s-¹ at 11:00 am and -22.14 (± 0.68) µmol m-² s-¹ at 10:30 am (local hour) in the dry season. In the wet season the parameters of LCR were lower quantum efficiency (0.0479 ± 0.0039 μmol CO2 μmol-¹ photon absorbed), higher CO2 assimilation rate (35.82 ± 1.92 µmol m-² s-¹) and lower ecosystem respiration (6.11 ± 0.39 μmol m-² s-¹). The dry season exhibited a quantum efficiency of 0,0494 (± 0,0063) μmol CO2 μmol-¹ photon absorbed, CO2 assimilation rate of 31,02 (± 1,93) µmol m-² s-¹ and higher ecosystem respiration (6.61 ± 0.65 μmol m-² s-¹). PAR and VPD preconditioned to net CO2 exchange with a correlation coefficient of 0.75 and 0.72 and of determination of 0.56 and 0.52, in the wet and dry seasons, respectively. These results are important for a better understanding of oil palm behavior in the face of a severe weather event in eastern Amazonia.