Eddy covariance captures four-phase crassulacean acid metabolism (CAM) gas exchange signature in Agave

Mass and energy fluxes were measured over a field of Agave tequilana in Mexico using eddy covariance (EC) methodology. Data were gathered over 252 d, including the transition from wet to dry periods. Net ecosystem exchanges (F-N,F-EC) displayed a crassulacean acid metabolism (CAM) rhythm that alternated from CO2 sink at night to CO2 source during the day, and partitioned canopy fluxes (F-A,F-EC) showed a characteristic four-phase CO2 exchange pattern. Results were cross-validated against diel changes in titratable acidity, leaf-unfurling rates, energy exchange fluxes and reported biomass yields. Projected carbon balance (gCm(-2) year(-1), mean +/- 95% confidence interval) indicated the site was a net sink of -333 +/- 24, of which contributions from soil respiration were +692 +/- 7, and F-A,F-EC was -1025 +/- 25. EC estimated biomass yield was 20.1 Mg(dry) ha(-1) year(-1). Average integrated daily F-A,F-EC was -234 +/- 5 mmol CO2 m(-2) d(-1) and persisted almost unchanged after 70 d of drought conditions. Regression analyses were performed on the EC data to identify the best environmental predictors of F-A. Results suggest that the carbon acquisition strategy of Agave offers productivity and drought resilience advantages over conventional semi-arid C3 and C4 bioenergy candidates.