Habitat segregation of C-3 and CAM Nidularium (Bromeliaceae) in response to different light regimes in the understory of a swamp forest in southeastern Brazil

The facultative epiphytic bromeliads Nidularium procerum and N. innocentii grow terrestrially in distinct but neighbouring patches of a swamp forest u nderstory in southeastern Brazil. N. innocentii (C-3) is restricted to a sh aded, periodically flooded patch, and N. procerum (CAM) to a semi-exposed, permanently flooded patch. Semi-exposed and shaded leaves of both species w ere used to evaluate the efficiency of photochemical energy conversion in p hotosystem II and the extent of non radiative energy dissipation of these t wo contrasting photosynthetic pathways. By late afternoon, both semi-expose d C-3 and CAM plants were still unable to fully recover from photoinhibitio n suffered earlier at the peak of irradiance, although this effect was more marked in the C-3-species. Light response curves of fluorescence parameter s obtained on a cloudy and a sunny day also suggested that semi-exposed con ditions are more favourable to the CAM than to the C-3 species. Both the C- 3 and the CAM Nidularium are shade-adapted, but CAM allows colonization by N. procerum of patches eventually exposed to higher irradiance. This partia lly explains the habitat segregation of these species in this swamp forest. It remains to be seen how rhizome flood-tolerance relates to this pattern.