Morphological and Physiological Responses to Irradiance in the CAM Epiphyte Tillandsia usneoides L. (Bromeliaceae)

Abstract

Spanish moss (Tillandsia usneoides L.) was collected in situ in South Carolina from sunny and shady locations and grown in a greenhouse under high and low irradiance. Morphological characteristics, including leaf size, internode length, trichome size and density, and stomatal size and density, were similar among plants at the different irradiance levels. Chlorophyll (Chl) a/b ratios did not change with irradiance, but total Chl concentrations were higher in plants exposed to lower irradiances. In spite of these changes in pigment composition, similar levels of nocturnal acidification were found in field, but not greenhouse, plants at all irradiance levels. Thus, Spanish moss can respond physiologically, but not morphologically, to changes in environmental irradiance levels. This ability should prove beneficial to an epiphyte growing in microsites of widely varying irradiance.