Shade adaptation of the Hawaiian tree-fern (Cibotium glaucum (Sm.) H. & A.)

Abstract

Shade adaptation of both gametophytes and sporophytes of a Hawaiian tree-fern, (Cibotium glaucum (Sm.) H. & A.) was measured by growing plants under a range of light intensities and at 2 daylengths, at 20 or 25°C. Three ecophysiological parameters of shade adaptation and adjustment, initial slope of the photosynthesis curve in response to increasing light intensity (α), rate of light saturated photosynthesis (PN max), and rate of photosynthesis at the intensity given during growth (PN growth), were determined by infra•red gas analysis. Both sporophytes and gametophytes showed shade adaptation by a decline in α with increasing irradiation during growth and shade adjustment by a light saturation value for shade-grown plants that was well above the level of light at which the plants were grown. Sporophytes exhibited one feature of sun plants; PN max increased with increasing irradiation during growth. Morphological adaptations to low light intensity included a narrowing of the gametophyte, higher chlorophyll contents on a fresh weight basis of both gametophytes and sporophytes, and reduced thickness of sporophyte fronds. A greater total frond area of shade•grown sporophytes was brought about by a greater area of individual fronds and a longer retention time of fronds. Rates of frond production and expansion were little affected by light intensity.