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Aims: Tropical tree and lianas in the understory are limited by soil nutrients despite growing in extremely low light. It is not known if nomadic vines are also limited by nutrients in low light conditions.Methods: We measured differences in root architecture and mycorrhizal colonization, and leaf nutrients of a nomadic vine, Philodendron fragrantissimum (Araceae), in nitrogen (N) and phosphorus (P) fertilization plots in a lowland tropical moist forest in central Panama to measure potential nutrient limitation.Results: Relative to plants in control plots, leaf P concentration was 54% higher and leaf N concentration was 10% higher for plants in the P- and N-addition treatments, respectively. The N:P of leaves suggested P-limitation in the N-addition treatment and the control but not in the P-addition treatment. Root branching was highest in the P-addition treatment, and P-addition reduced mycorrhizal colonization.Conclusions: The large effect of P fertilization suggests that, like many tropical plants, P. fragrantissimum has the potential to be P-limited. Although further study is needed, we suggest that nomadic vines be added to the growth forms that respond to nutrient addition in the forest understory and conclude that nutrient-limitation seems like the rule rather than the exception in the light-limited understory. [ABSTRACT FROM AUTHOR]

The effects of irrigation on fine root biomass, root production and litterfall were measured at the community level, in a semideciduous lowland forest in Panama. Biomass of roots less than 2 mm in dia. in the first 10 cm of the soil (measured with soil cores), was higher in irrigated (1.80 Mg ha-1) than in non-irrigated plots (1.24Mg ha-1). During the dry season, productivity of roots (measured with ingrowth cylinders filled with root-free soil), was higher in irrigated (1.6 g m-2 day-1) than in control plots (0.3 g m-2 day-1). In control plots, root productivity was highly seasonal. Maximum root growth into the root-free soil, occurred during the transitions from dry to wet, and from wet to dry season, possibly as a response to water and/or nutrientpulses. Litterfall was not significantly different between irrigated(3.8 g m-2 day-1) and control plots (3.7 g m-2 day-1). The results of this study show that root-productivity is limited by the water supply during the dry season,and that water by itself, is not a limiting factor for community-level litter production. [ABSTRACT FROM AUTHOR]