Longevity, lignin content and construction cost of the assimilatory organs of Nepenthes species.

Abstract

This study examined level of causal relationships amongst functional traits in leaves and conjoint pitcher cups of the carnivorous Nepenthes species. Physico-chemical properties, especially lignin content, construction costs, and longevity of the assimilatory organs (leaf and pitcher) of a guild of lowland Nepenthes species inhabiting heath and/or peat swamp forests of Brunei, northern Borneo were determined. Longevity of these assimilatory organs was linked significantly to construction cost, lignin content and structural trait of tissue density, but these effects are non-additive. Nitrogen and phosphorus contents (indicators of Rubisco and other photosynthetic proteins), were poor predictors of organ longevity and construction cost, suggesting that a substantial allocation of biomass of the assimilatory organs in Nepenthes is to structural material optimized for prey capture, rigidity and escape from biotic and abiotic stresses rather than to light interception. Leaf payback time - a measure of net carbon revenue - was estimated to be 48-60 d. This is in line with the onset of substantial mortality by 2-3 months of tagged leaves in many of the Nepenthes species examined. However, this is a high ratio (i.e. a longer minimum payback time) compared with what is known for terrestrial, non-carnivorous plants in general (5-30 d). It is concluded that the leaf trait bivariate relationships within the Nepenthes genus, as in other carnivorous species (e.g. Sarraceniaceae), is substantially different from the global relationship documented in the Global Plant Trait Network.