How Much Water is in the Tank? Model Calculations for Two Epiphytic Bromeliads

How Much Water is in the Tank? Model Calculations for Two Epiphytic Bromeliads

Water-impounding foliage (=tank) characterizes many bromeliadspecies but, to date, a quantitative evaluation of the effectivenessof these structures to bridge rainless periods is not available.We present a model that analyses the capacity of these phytotelmatato supply moisture to the bromeliad as a function of plant size,and parameterize it for two epiphyte species,Tillandsia fasciculataandGuzmaniamonostachya. All parameters related to the recharging of a tank(e.g. catchment area, or tank capacity) and those related towater loss from the tank (e.g. tank water surface, or waterabsorption from the tank by the plant) changed with plant size.For both species a similar qualitative size-related patternemerged: smaller individuals dried out much faster than largerconspecifics. Modelling the changes in tank water content foran entire year revealed that in the seasonal climate of BarroColorado Island, Panama, tanks of smaller plants (1 g d. wt)are expected to lack water for up to 110 d (inT. fasciculata).Regardless of plant size, individuals ofG. monostachyawere consistentlymore efficient thanT. fasciculatain maintaining moisture intheir tanks. Our results provide insight into the limitationsof water-impounding tanks as an adaptation to cope with an intermittentwater supply typical for epiphytic habitats. These limitationsare particularly pronounced for smaller individuals.Copyright1999 Annals of Botany Company. Epiphytes, water relations, Barro Colorado Island, bromeliads, water tanks, phytotelmata.