Improving NEE estimates using stability criteria to obtain subcanopy respiration

Improved carbon estimates are crucial for understanding the role of terrestrial ecosystems as sinks or sources of carbon. The exchange of carbon between the Amazon forest and the atmosphere is complex due to the high density canopies, which attenuate winds and inhibit intracanopy turbulence. In this study, Net Ecosystem Exchange (NEE) rates were estimated by adapting the traditional method to include respiration of ecosystem (Reco) when the flow inside the canopy is decoupled from the flow above it. Turbulence measurements, CO2 and water vapor data were collected at different heights at the ATTO experimental site, located in the central Amazon in the year of 2022. These data set was used to indentify the signal of Reco with root respiration, litter and microbial respiration using parameters such as friction velocity (u*), horizontal wind speed (U), standard deviation of the vertical wind velocity (σw). The preliminary results show that the most suitable heights for demonstrating the decoupled sub-canopy regime at ATTO are 5 and 50m. According to the method proposed by Thomas et al. (2013), the scenarios for ATTO are as follows: (i) Fully coupled canopy, where above-canopy EC fluxes represent the entire ecosystem, accounted for 49%; (ii) Decoupled sub-canopy, where EC fluxes observed within the sub-canopy are decoupled from those of the sub and above-canopy layers, accounted for 23%; and (iii) Decoupled ground layer, where EC fluxes are disregarded for NEE and the sub-canopy system is not coupled to the soil, accounted for 15%. The next steps will determine the NEE for each of these scenarios and will include a higher Reco than the current one. A decrease in NEE is expected.