Crassulacean Acid Metabolism in the Epiphyte Tillandsia usneoides L. (Spanish Moss)

Abstract

Patterns of C02 exchange in Spanish moss under various experimental conditions were measured using an infrared gas analysis system. Plants were collected from a study site In North Carolina and placed in a gas exchange chamber for several days of continuous measurements. No substantial seasonal effects on COj exchange were observed. High rates of nocturnal CO, uptake were observed under day/night temperature regimes of 25/10, 25/15, 25/20, 30/20, and 35/20 C; however, daytime temperatures of 40 C eliminated nighttime COi uptake and a nighttime temperature of 5 C eliminated nocturnal C02 uptake, regardless of day temperature. Constant chamber conditions also inhibited nocturnal COi uptake. Constant high relative humidity (RH) slightly stimulated COi uptake while low nighttime RH reduced nocturnal COj uptake. Reductions in daytime irradiance to approximately 25% full sunlight had no effect on C02 exchange. Continuous darkness resulted in continuous COi loss by the plants, but a CO] exchange pattern similar to normal day/ night conditions was observed under constant illumination. High tissue water content inhibited CO* uptake. Wetting of the tissue at any time of day or night resulted in net CO» loss. Abrupt increases in temperature or decreases in RH resulted in sharp decreases in net CO* uptake. The results indicate that Spanish moss is tolerant of a wide range of temperatures, irradiances, and water contents. They also indicate that high nighttime RH is a prerequisite for high rates of CO> uptake.