Carbon and nitrogen dynamics in shallow photic systems: Interactions between macroalgae, microalgae, and bacteria

• Published in: Limnology and oceanography 2011-07, Vol.56 (4), p.1489-1503
• Main Authors: Hardison, A. K., Anderson, I. C., Canuel, E. A., Tobias, C. R., Veuger, B.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; General aspects; Marine; Synecology
• ISSN: 0024-3590; 1939-5590
• DOI: 10.4319/lo.2011.56.4.1489

We tracked carbon (C) and nitrogen (N) uptake into sediments in the presence and absence of benthic macroalgae using dual stable isotope tracers in combination with compound-specific isotope analyses of hydrolyzable amino acids and phospholipid-linked fatty acids to quantify the uptake and retention of C and N within bulk sediments, benthic microalgae (BMA), and heterotrophic bacteria. Stable isotope tracers (as 15 NH 4 + and H 13 CO 3 − ) were added to mesocosms either via the surface water or pore water for the first 14 d of the 42-d experiment. Macroalgae and sediments exposed to ambient light and dark cycles rapidly took up label from both sources and retained label for at least 4 weeks after isotope additions ended. BMA dominated sediment uptake of 13C and 15N, initially accounting for 100% of total uptake. Over time, heterotrophic bacterial uptake became relatively more important, increasing from 0% on day 1 to 20–50% on day 42, indicating a close coupling between BMA and bacterial production. In treatments with macroalgae, sediment 13C and 15N uptake was ∼ 40% lower than treatments without macroalgae, likely because of shading of the sediment surface by macroalgae, which decreased BMA production, which in turn decreased bacterial production. Overall, sediments served as a sink for C and N through uptake and retention by the microbial community, but retention was lower in the presence of macroalgae.