Dew deposition on epiphytic bromeliad leaves: an important event in a Mexican tropical dry deciduous forest

Dew deposition was calculated for leaves of the epiphytic bromeliads Tillandsia brachycaulos and T. elongata in a tropical dry deciduous forest in Yucatan, Mexico, over one year. Plant characteristics and water relations were also measured. Estimations were made by using energy balance analysis and the Penman-Monteith equation. Dew accumulation was also quantified using a cloth-plate method and by change in mass of whole plants. Tissue water content and total leaf area were similar in the two species, but maximum tank water content was three-fold greater for T. elongata than for T. brachycaulos, which had a lower degree of tissue desiccation tolerance than T. elongata. Succulence for T. brachycaulos changed little during most of the year, decreasing significantly only during one month in the dry season. Leaf water potential and osmotic pressure did not change significantly after a dew-deposition event. Theoretical dew per night on leaves was greatest during the early dry season (about 0.72 mm) compared with 0.34 mm in the rainy season and 0.008 mm in the late dry season. Dew amounts alone are not adequate to support growth but may maintain a favourable water balance for epiphytic bromeliads during the driest months of the year.