Seasonal patterns of growth, tissue acid fluctuations, and 14CO2 uptake in the crassulacean acid metabolism epiphyte Tjllandsia usneoides L. (Spanish moss).

Seasonal patterns of growth, 14CO2 uptake, and fluctuations in tissue titratable acidity were studied over the course of a year at a study site in the coastal plain of North Carolina.Elongation rates of Spanish moss strands were maximal in the summer and minimal in the winter. Summer maximal biomass addition rates were calculated to be 3.4 mg·month-1. Mortality of the strands was greatest in the winter months. Rates of 14CO2 uptake and fluctuations in tissue acidity were greatest in the summer over a fairly broad spectrum of environmental conditions (day and night temperatures, irradiance, length of drought). Maximal 14CO2 uptake rates (1.2 mg CO2·mg Chl-1 ·h01) were measured in May 1978. Rates of 14CO2 uptake and fluctuations in titratable acidity were inhibited below 5°C and eliminated at 0°C air temperatures.Isothermal diurnal conditions resulted in low rates of 14CO2 uptake. Tissue water content did not appear to be a major factor controlling 14CO2 uptake rates. However, tissue wetting by rain severely reduced nighttime uptake yet stimulated low rates of daytime 14CO2 uptake. This was the only condition in which daytime 14CO2 uptake occurred, excluding the early morning and late afternoon 14CO2 uptake typical of many Crassulacean Acid Metabolism (CAM) plants.The results suggest that tissue water content is not the major factor controlling CO2 uptake as has been found in many other CAM species; and that low temperatures limit the growth of Spanish moss in North Carolina.