Nitrogen cycling dynamics in the carnivorous northern pitcher plant, Sarracenia purpurea

1. In nutrient-poor environments, plants employ many strategies to acquire and recycle scarce nutrients. Predictable relationships among a variety of leaf traits, including leaf nitrogen (N) suggest that how plants obtain, use, store and re-use N is a major component of plant fitness. The northern pitcher plant, Sarracenia purpurea , receives nitrogen from multiple sources: NH 4 and NO 3 dissolved in precipitation; N mineralized from captured prey; the scant N in saturated peat; and N remobilized from storage. In two greenhouse experiments, we examined N cycling in S. purpurea and consider how these dynamics relate to prior observations that this carnivorous plant has an unusually low photosynthetic rate for its tissue N content. 2. In the first experiment we assessed assimilation, translocation, storage and remobilization of 15 N supplied to pitchers and roots. In the second experiment, we examined how 15 N assimilated by the first pitcher produced at the start of the growing season contributed to the production and maintenance of subsequent pitchers, roots and rhizomes. 3. Patterns of N cycling were similar at the individual-leaf and whole-plant level. Pitchers assimilated 55%–69% of available 15 N and served as both the largest sink for newly assimilated N (> 90% of the 15 N assimilated during 2004) and the largest source of N remobilization the following spring. In contrast, N assimilated by roots was low and accounted for < 2·5% of the overall S. purpurea N budget. Sarracenia purpurea used both stored N and newly-acquired N throughout the growing season. The importance of stored N decreased throughout the growing season as newly assimilated N contributed more to later pitcher production. 4. Our detailed mechanistic analysis of nitrogen cycling dynamics of S. purpurea suggests why this plant has a low photosynthetic rate for its tissue N content. Excess nitrogen is stored for future use, and production of new pitchers is primarily aimed at enhancing prey capture rather than increasing photosynthetic tissue. Key-words : 15 N, carnivorous plants, nitrogen cycling, Sarracenia , universal spectrum of leaf traits