Upscaling gross primary production from leaf to canopy for potato crop (Solanum tuberosum L.)
Estimating gross primary production (GPP) is important to understand the land-atmosphere CO2 exchange for major agroecosystems. Eddy covariance (EC) measurements provide accurate and reliable information about GPP, but flux measurements are often not available. Upscaling strategies gain importance as an alternative to the limitations of the use of the EC. Although potato is an important agroecosystem for worldwide carbon balances, there are currently no studies on potato GPP upscaling processes. This study reports two GPP scaling-up approaches from the detailed leaf-level characterization of gas exchange of potato. Multilayer and big leaf approaches were applied for extrapolating chamber and biometric measurements from leaf to canopy. Measurements of leaf area index and photosynthesis were performed from planting to the end of the canopy life cycle with a LP-80 ceptometer and a IRGA Li-Cor 6800, respectively. The results were compared to concurrent measurements of surface-atmosphere GPP from the EC technique. Big-leaf models were able to simulate the general trend of GPP during the growth cycle, but they overestimated the GPP during the maximum LAI phase. Multilayer models correctly reproduced the behavior of potato GPP and closely predicted both the daily magnitude and half-hourly variation in GPP when compared to EC measurements. Upscaling is a reliable alternative, but the good treatment of LAI and net photosynthetic light-response curve are decisive factors to get better GPP estimates. The results improved the knowledge of the biophysical control in the carbon fluxes of the potato crop.
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