Which abiotic factors limit vegetative growth in a vascular epiphyte?

Abstract

1. Vegetative growth in vascular epiphytes is assumed to be severely limited by intermittent supply of water and nutrients, but experimental evidence for this notion is meagre. The effects of water, nutrient supply and light on growth were studied in an epiphytic bromeliad, Vriesea sanguinolenta Cogn. & Marchal (syn. Werauhia sanguinolenta) in a large forest gap in a lowland forest of Panama, in a full-factorial design. To investigate ontogenetic drift, three plant-size classes (≈5, 15 and 35 cm leaf length) were included in the experiment. 2. Water supply had the strongest influence on growth, but the magnitude of this effect differed considerably among size classes. Nutrient supply affected growth only in small and intermediate-sized plants. More light (60% of direct irradiation) tended to decrease growth rates compared to 30% irradiation. 3. Small plants showed by far the highest potential to adjust their relative growth rate (RGR) in response to favourable growing conditions. 4. Despite these size-related differences, absolute RGRs were extremely low compared to studies with other plant groups, confirming the notion that vascular epiphytes are inherently slow-growing plants.