Organic and Inorganic Nitrogen Uptake by Sarracenia Purpurea

The nitrogen-limited carnivorous pitcher plant Sarracenia purpurea and its associated detritus-based food web is a model system for studying plant nutrient dynamics. We tested if S. purpurea can directly take up intact amino acids and compared uptake of organic and inorganic forms of nitrogen (N) across a gradient of N deposition. At sites in Canada and the United States, individual pitchers with complete or incomplete food webs were fed U-13C-15N-glycine, U-13C-15N-phenylalanine and 15NH415NO3 individually and in mixture. Plants took up intact amino acids. Acquisition of each N form provided in isolation exceeded uptake of the same form in mixture. At the high deposition site, uptake of 15N from amino acids was higher than uptake of 15N from inorganic nitrogen. At the low deposition site, uptake of 15N from all three forms of N were similar. Completeness of the associated food web had no effect on 15N uptake. By taking up intact amino acids, Sarracenia purpurea can short-circuit the inorganic N cycle, thus minimizing potential bottlenecks in N availability that result from the plant’s reliance for nitrogen mineralization on a seasonally reconstructed food web operating on infrequent and irregular prey capture