Figure 1 Schematics of a radiation index (RI) based on the
radiation balance and its relationship with gross primary productivity
(GPP). Rn is the net radiation which indicates the net energy
balance of an ecosystem; DSR, DLR, USR and ULR are the downwelling
short- and long-wave radiations and upwelling short- and long-wave
radiations, respectively; and I is the effective radiation which
reflects the net heat transmissions within a system through long-wave
radiations.