Various field studies in tropical forests have indirectly demonstrated
the efficiency of nutrient uptake mechanisms by epiphytic and epiphyllic
organisms. An investigation conducted by Jordan and Herrera (1981)
included measuring concentrations of Calcium, Potassium, Phosphorous, Magnesium,
Sulfur, and Ammonium at the forest floor and in nearby openings in
the Venezuelan Amazon for one year. The purpose of the study was to determine
whether nutrient concentrations differ between throughfall (rainwater passing
through the canopy) and pure rainfall. As indicated below, several
nutrients, most notably Calcium and Phosphorous, are consistently higher
in rainfall throughout the year sampled, suggesting that these nutrients
are absorbed within the canopy community before reaching the ground.
Another study, which measured the concentrations of phosphate (PO4
) and ammonium (NH4 ) in rainfall, throughfall and throughfall
as it was coming off of pinnae from epiphyll-laden pinnae of Welfia
georgii indicated that ammonium, more so than phosphate, is efficiently
absorbed and retained on leaf surfaces (Bentley 1987). The
question remaining to be answered is: Which component of the epiphyll community
contributes most to the contribution of nutrients?
What other factors influence nitrogen fixation rates in epiphylls?