Water quality changes seasonal variations in root respiration, xylem CO2, and sap pH in citrus orchards

•Seasonal and diurnal courses of inorganic carbon transport in sap, and efflux are quantified.•Inclusion of xylem transported CO2 changed estimates of Q10 and carbon balance.•Reduced root growth for TWW irrigation may be due to high summer respiration.•The magnitude of respiratory losses may explain reduced yields for TWW irrigation.