AME 80:93-99 (2017)  -  DOI: https://doi.org/10.3354/ame01844

ABSTRACT: We performed a tracer experiment using the stable isotope ¹⁵N to investigate nitrogen incorporation by epiphytic algae via its host plant, Vallisneria natans, from the sediment with increasing nutrients in the water column. ¹⁵N was added as ¹⁵NH₄Cl to the sediment, and its fate was traced with increasing nutrient availability in the water column and sediment. Samples of epiphytic algae and V. natans were examined for δ¹⁵N. The results indicated that with increased nitrogen and phosphorus availability in the water column, the ability of epiphytic algae and the leaves of V. natans to utilize nitrogen originating from sediment was significantly decreased (p < 0.05), while the ability of the roots of V. natans to utilize nitrogen from sediment changed very little (p > 0.05). Under the same nutrient levels in the water column, the ability of the roots and leaves of V. natans to utilize nitrogen originating from sediment was higher in high-nutrient sediment than that in low-nutrient sediment (p < 0.05), while the ability of epiphytic algae to utilize nitrogen from sediment changed very little (p > 0.05). Thus, epiphytic algae and the tissues of V. natans can be arranged with respect to their accumulated ¹⁵N as follows: epiphytic algae < leaves < roots; nitrogen incorporation by epiphytic algae originating from sediment was negligible compared to the tissues of V. natans in this experiment. This suggested that when concentrations of nitrogen and phosphorus are >1.0 and 0.1 mg l^-1 in the water column, respectively, sediment as a nitrogen source is negligible for the growth of epiphytic algae.

KEY WORDS: Nitrogen incorporation · Epiphytic algae · Vallisneria natans · ¹⁵N labeling · Sediment