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

Abstract

Mass and energy fluxes were measured over a field of Agave tequilana in Mexico using eddy covariance (EC) methodology. Data were gathered over 252d, including the transition from wet to dry periods. Net ecosystem exchanges (FN,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 (FA,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-2year-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 FA,EC was -1025±25. EC estimated biomass yield was 20.1Mg(dry)ha-1year-1. Average integrated daily FA,EC was -234±5mmolCO2m-2d-1 and persisted almost unchanged after 70d of drought conditions. Regression analyses were performed on the EC data to identify the best environmental predictors of FA. Results suggest that the carbon acquisition strategy of Agave offers productivity and drought resilience advantages over conventional semi-arid C3 and C4 bioenergy candidates.