PHOTOINHIBITION IN TROPICAL FOREST UNDERSTOREY SPECIES WITH SHORT-LIVED AND LONG-LIVED LEAVES

1. Shade-tolerant species that inhabit the understorey have a range of leaf lifetimes (from 1 to 8 years), which may indicate a variety of s trategies for dealing with increases in light associated with tree-fal l gaps. We hypothesized that species with long-lived leaves should be more tolerant of an increase in light levels than species with short-l ived leaves. 2, In understorey plants of 12 shade-tolerant rain-forest species, photoinhibition, measured as a reduction in the chlorophyll fluorescence parameter F-v/F-m when leaf discs were exposed to 1 h at 1000 mu mol m(-2)s(-1), was greater in species with short-lived leaves than species with long-lived leaves. 3, Less photoinhibition in speci es with long-lived leaves was not associated with higher levels of non -photochemical dissipation (NPQ) of absorbed light, but may be the res ult of a higher yield of photosystem II compared with short-lived leav es. 4, Thus, species with long-lived leaves are more tolerant of abrup t increases in light that occur when tree-fall gaps are formed than sp ecies with short-lived leaves. 5, Discs from leaves of all species gro wing in tree-fall gaps had higher levels of NPQ, yield of photosystem II and more rapid recovery from photoinhibition than leaves developed in the understorey; however, there were no differences among species w ith short- and long-lived leaves.