PARENT SESSION
Oral Session #13: Plant Ecology: Light Relationships. Presiding: J. Rebbeck.
Monday, August 6, 2001. 1:00 PM to 4:30 PM. Hall of Ideas P&Q.
Adaptation to different light regimes in the Hawaiian lobeliads: dynamic photosynthetic light responses and the outcome of in silico transplants.
Montgomery, Rebecca1,2, Givnish, Thomas1,2, 1 2
ABSTRACT- Hawaiian lobeliads have radiated into habitats from open alpine bogs to densely shaded rain-forest interiors. Shaded environments are not uniformly dark, but punctuated by frequent sunflecks that carry much of the photosynthetically active light that strikes plants. We asked whether lobeliads in habitats characterized by infrequent, short sunflecks were capable of rapid photosynthetic induction - which is critical for efficient carbon uptake during sunflecks. We characterized the light regimes experienced by field populations of 11 species representing each Hawaiian sublineage, based on direct datalogging and computer analysis of canopy photographs. Total PAR varied from 3.0 to 24.2 mol day-1, with the average length and total duration of sunflecks less in more densely shaded sites. As expected, photosynthetic induction was significantly more rapid in species occupying more shaded sites. Induction after 60 s in high light ranged from 28.4% in cliff-dwelling Lobelia yuccoides to 59.4% in rain-forest understory Cyanea pilosa. Rates of photosynthetic induction showed little relationship to static photosynthetic parameters. In silico transplants - in which each species' photosynthetic light response is run in its own and other species' dynamic light regimes - demonstrated the adaptive nature of observed species differences. For example, Cyanea pilosa in its understory light regime outperforms Trematolobelia kauaiensis, while Trematolobelia in its open-ridge light regime outperforms Cyanea.
KEY WORDS: adaptive radiation, photosynthetic light responses, Hawaii, sunflecks