Organic and Inorganic Nitrogen Uptake by Sarracenia Purpurea at Harvard Forest and Fort Albany ON 2007

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.氮限制型食肉食虫植物紫瓶子草（Sarracenia purpurea）及其关联的腐食食物网，是研究植物养分动态的经典模式系统。本研究旨在验证紫瓶子草能否直接摄取完整氨基酸，并沿氮沉降梯度对比了有机与无机氮（N）的吸收效率。在加拿大与美国的多个研究点位，我们分别或混合投喂13C-15N全标记甘氨酸、13C-15N全标记苯丙氨酸以及15NH415NO3给具有完整或残缺食物网的单个捕虫瓶。实验结果表明，紫瓶子草可直接摄取完整氨基酸；单一氮源的吸收量均高于混合氮源中对应氮形式的吸收量。在高氮沉降点位，氨基酸来源的15N吸收量显著高于无机氮来源的15N吸收量；而在低氮沉降点位，三种氮形式的15N吸收量无显著差异。关联食物网的完整与否对15N吸收量无显著影响。紫瓶子草通过直接摄取完整氨基酸，可绕过无机氮循环，从而缓解因依赖以偶发且不规则的猎物捕获为运作基础的季节性重建食物网进行氮矿化所带来的氮有效性潜在瓶颈。