Tracking uptake of submerged macrophytes (Ceratophyllum demersum)-Derived nitrogen by cattail (Typha angustifolia) using nitrogen stable isotope enrichments

External inputs and internal cycling are two pathways of nutrients to the aquatic macrophytes in the wetland ecosystem. Internal sources of nutrients include plant die-off and the decomposition of organic matter. In this study, we used a stable nitrogen isotope (15N) enrichment experiment to track the timing and magnitude of cattail (Typha angustifolia) use of coontail (Ceratophyllum demersum) - derived nitrogen (CDN) in a freshwater wetland. Dry coontail powder enriched in 15N (δ15N = 1259 ± 15‰) was buried in the soil close to the roots of cattail plants in field mesocosms at the Yeyahu National Preserve, Beijing, China, from July 22 to September 30, 2014. Different parts (roots, rhizomes, stems, leaves and leaf apexes) of the cattail plants were collected at day 0, 14, 28, 42, 49, 56, 63 and 70 for stable isotope analysis. Results reveal uptake of the nitrogenous nutrient from coontail detritus by cattail four weeks after being exposed to CDN. The maximum uptake rate for excess 15N in roots, leaves, stems, rhizomes and leaf apexes were 1.55 ± 0.84, 0.69 ± 0.11, 0.33 ± 0.08, 0.14 ± 0.11, 0.06 ± 0.02 mg 15N m−2. The root system is the largest pool of nitrogen in cattails, which serves as the source of nitrogen for other plant parts. The uptake rate per unit biomass was highest in the leaf apexes.