Nitrogen Cycling Dynamics in Sarracenia Purpurea at Harvard Forest 2004-2005

In nutrient poor systems, plants employ many strategies in order to acquire and recycle scarce nutrients, including nitrogen. Low leaf N content is associated with low photosynthetic rates, but carnivorous plants have unusually low photosynthetic rates given their N content. The northern pitcher plant Sarracenia purpurea readily uses any available nitrogen: NH4 and NO3 dissolved in precipitation; N mineralized from captured prey; the scant N in saturated peat; and N remobilized from storage. However, the dynamics of N cycling within S. purpurea are poorly understood. We conducted two greenhouse experiments to examine N-cycling dynamics of S. purpurea at the whole-plant and individual-leaf levels. In the first experiment we assessed assimilation, translocation, storage, and remobilization of 15N supplied to pitchers and roots. In the second experiment, we examined how 15N 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. Patterns of N cycling were similar at the individual-leaf and whole-plant level. Pitchers assimilated 55 - 69% of available 15N and served both as the largest sink for newly assimilated N (more than 90% of the 15N assimilated during 2004) and the largest source of N remobilization the following spring. In contrast, N assimilated by roots was low and accounted for less than 2.5% of the overall S. purpurea N budget. S. purpurea uses both stored N and newly-acquired N throughout the growing season. The importance of stored N decreases throughout the growing season as newly assimilated N contributes more to later pitcher production.