### 2.18.2.1. Available Carbon[¶](#available-carbon "Permalink to this headline")

The carbon available for FUN, \\(C\_{avail}\\) (gC m\-2) is the total canopy photosynthetic uptake (GPP), minus the maintenance respiration fluxes (\\(m\_r\\)) and multiplied by the time step in seconds (\\(\\delta t\\)). Thus, the remainder of this chapter considers fluxes per timestep, and integrates these fluxes as they are calculated.

> \\\[C\_{avail} = (GPP - m\_r) \\delta t\\\]

Growth respiration is thus only calculated on the part of the carbon uptake that remains after expenditure of C by the FUN module.

