Carbon and water vapor exchanges coupling in irrigated and rainfed Andean potato (Solanum tuberosum subsp. andigenum) agroecosystems

Abstract

We studied the response of net ecosystem carbon exchange (NEE) to water availability conditions by detailing the dynamics of H2O and CO2 exchanges between the canopy and atmosphere of three different potato water regimes cropping systems [full irrigation (FI), deficit irrigation (DI) and rainfed (RF)]. Through the eddy covariance method, we measured carbon and water fluxes and determined the inherent water use efficiency (IWUE) as a conceptual frame for comparing diurnal cycles of carbon and water and quantifying their coupling/decoupling degree. Surface resistances and the omega (Ω) factor were computed to know the degree of canopy control over carbon and water fluxes. Additionally, leaf area index (LAI) and specific leaf area (SLA) were measured over the cropping systems. The highest sink activity at the FI site (NEE= −311.96 ± 12.82 g C m−2) was due to the larger canopy, with high autotrophic activity and low internal resistance which supported a highly coupled and synchronized ET – GPP exchange represented in the higher IWUE (4.7 mg C kPa s-1 kg-1 H2O). The lower sink capacity at the DI site (NEE= −17.3 ± 4.6 g C m−2) and the net carbon source activity from the RF (NEE = 187.21 ± 3.84 g C m−2) are consequences of a smaller area for water and carbon exchange, and a low IWUE (2.3 and 1.01 mg C kPa s-1 kg-1 H2O, respectively) from decoupled and desynchronized carbon and water exchange caused by unbalanced restrictions on ET and GPP fluxes.