Temporal and spatial variability of in situ nitrogen fixation activities associated with the Mediterranean seagrass Posidonia oceanica meadows. (6th June 2017)

• Record Type: Journal Article
• Authors: Agawin, Nona S. R.; Ferriol, Pere; Sintes, Eva; Moyà, Gabriel
• Is Part Of: Limnology and oceanography. Volume 62:Number 6(2017)
• Page Start: 2575
• Page End: 2592
• Publication Date: 2017-06-06
• Subjects: Limnology -- Periodicals; Oceanography -- Periodicals; Océanographie; Limnologie; Limnology; Oceanography; Computer network resources; Périodique électronique (Descripteur de forme); Ressource Internet (Descripteur de forme); Periodicals; 551.4805
• DOI: 10.1002/lno.10591
• Languages: English
• ISSNs: 0024-3590

Abstract

Abstract: This study provides the first extensive data on in situ rates of N2 fixation in minimally disturbed Posidonia oceanica meadows and their temporal and spatial variability along the Mallorcan coasts in the Mediterranean Sea. Benthic bell‐jar chambers were deployed underwater enclosing (1) natural P. oceanica shoots, (2) matted sediment of P. oceanica with the leaves carefully removed by clipping to assess the contribution of N2 fixation associated with leaves, and (3) adjacent unvegetated sediment to assess the contribution of N2 fixation by the sediment. In all of the chambers, N2 fixation varied seasonally, with highest rates during summer and lowest in winter. Average N2 fixation rates in chambers enclosing natural P. oceanica shoots ranged from 0.06 mg N m −2 d −1 to 1.51 mg N m −2 d −1 (0.004–0.107 mmol N m −2 d −1 ) in summer. Careful removal of leaves generally reduced N2 fixation rates by 16–89%. The N2 fixation rates in unvegetated sediments ranging from 0.01 mg N m −2 d −1 to 1.99 to mg N m −2 d −1 (7.1 × 10 −4 –0.14 mmol N m −2 d −1 ) have similar magnitudes in sediments with P. oceanica . This suggests that these sediments are "hot spots" for N2 fixation. Exploratory analyses of environmental factors that may influence N2 fixation rates highlight temperature and pore water total phosphorus concentrations as important factors.