FIGURE 3.1. Carbon balance models that are coupled to water and nutrient cycling operate by predicting
carbon uptake and losses through a series of processes, starting with photosynthesis and the absorption of solar
radiation by leaves. Gross primary production (GPP) is further limited by other environmental variables affecting
canopy stomatal conductance. Deducting foliar maintenance respiration during the daylight hours provides an
estimate of net assimilation (A). Including canopy respiration at night yields an estimate of daily net canopy
exchange (NCE) for a 24-hr period. Net primary production (NPP) is calculated by accounting for additional
autotrophic losses associated with synthesis (Rs) and maintenance (Rm) throughout each day.