Short-term 15N uptake kinetics and nitrogen nutrition of bryophytes in a lowland rainforest, Costa Rica.

Abstract

Though bryophytes can markedly affect the hydrological and biogeochemical cycles of tropical rainforests, virtually nothing is known on their nutritional requirements. Here, short-term 15N uptake kinetics of NO3-, NH4+ and glycine were studied in nine species of bryophytes in a lowland wet tropical forest, Costa Rica. Net uptake of all three N forms obeyed to saturation (Michaelis-Menten) kinetics between 1 and 500 µmol L-1. Mean Km (Vmax) values ranged between 21 µm (6.6 µmol g-1 DW h-1, nitrate), 94 µm (43.5 µmol g-1 DW h-1, ammonium) and 126 µm (37.6 µmol g-1 DW h-1, glycine). No significant differences were evident between epiphyllous and epiphytic bryophytes. Concentrations of nitrogenous solutes of external sources ranged between 1.7 and 35.9 µm. External nitrogen concentrations and kinetic constants of the bryophyte species allowed estimation of net uptake rates in the field. The mean uptake rates were 1.8 µmol g-1 DW h-1 for nitrate, 3.6 µmol g-1 DW h-1 for ammonium, and 3.4 µmol g-1 DW h-1 for glycine, indicating that amino acids significantly contribute to bryophyte nutrition.