This paper presents the conceptualization, methodological adjustment and experimental application of the micrometeorological technique eddy covariance - EC, to measure energy, water vapor and CO2 fluxes in two coffee agroecosystems: the first under full sunlight, and the second under shade, both with equatorial Andean hillslope conditions. With a footprint and fetch calculation, the required distance from the edge of the field in the prevailing wind direction to the EC tower is three times higher under shade than full sun. The shaded agroecosystem reached maximum average carbon fixation rates of 21.26 ± 2.469 μmolCO2.m-2s-1 ( = 0.05) (61% higher than under 100% sunlight) which gives a high carbon sink capacity to the association of coffee plants with shading Pigeon peas (Cajanus cajan L). The average evapotranspiration rate was 2.33 ± 0.0102 mm.d-1 ( = 0.05) and 2.08 ± 0.00732 mm.d-1 under shade and 100% sunlight, respectively. The proportion of net radiation that reached the soil was 2% under shade and 4% under 100% sunlight. Likewise, the soil energy loss during the night was lower under shade, indicating less day-night temperature range in the latter agroecosystem. The methodological adjustment and the results of this first work using EC in Colombian coffee plantations, contribute to the development of reliable research regarding gas and energy exchanges between the atmosphere and ecosystems in conditions of the equatorial Andean hillslope.

We studied the link between carbon and water fluxes to understand the response of net ecosystem carbon exchange (NEE) to water availability conditions of three different potato water regimes cropping systems [full irrigation (FI), deficit irrigation (DI) and rainfed (RF)]. Through the eddy covariance technique, we measured CO2 and water vapor exchanges and determined surface resistances, omega factor, and inherent water use efficiency (IWUE). Additionally, continuous plant growth determinations of leaf area index (LAI) and specific leaf area (SLA) were made over the three cropping systems. The RF potato was a net carbon source (NEE = 187.21 ± 3.84 g C m−2), while both, FI (NEE= −311.96 ± 12.82 g C m−2) and DI (−17.3 ± 4.6 g C m−2) were a net carbon sink. Greater sink activity is due to high fluxes of gross primary productivity (GPP) [where the GPP > ecosystem respiration (Reco)] and evapotranspiration (ET), and the high efficiency in the exchange of carbon and water. Without water limitations, the larger canopy, with greater photosynthetic activity (GPP/Reco > 2) as well as with low internal resistance offers a greater area for water and carbon exchange, and the highly coupled and synchronized ET – GPP fluxes are primarily controlled by the radiative environment. The lower sink capacity of the DI potato crop and the carbon source activity from the RF, are consequences of a smaller area for water and carbon exchange due to the smaller canopy, and a low IWUE from decoupled and desynchronized carbon and water exchange caused by unbalanced restrictions on ET and GPP fluxes. Specifically, at DI potato, ET remained at a high rate, while GPP was reduced by means of non-stomatal limitations. In the rainfed potato, vapor pressure deficit (VPD) played a significant role increasing midday canopy resistance (Rc) up to 13 times compared to irrigated sites, when VPD was around 0.8 kPa. In consequence, ET and GPP fluxes decreased together, but GPP decreased more than ET because of stomatal and non-stomatal limitations.