Black mangrove (Avicennia germinans) stands in south Texas grow in association with other autotrophic organisms including herbaceous halophytes and cyanobacterial mats. Despite the relevant ecosystem services provided by this coastal plant community, limited information exists on its functioning, in particular as it pertains to nutrient dynamics, namely nitrogen (N). Nitrogen stable isotopes were used to assess potential N sources for plant growth in this community. Plant tissue (leaves), cyanobacteria, and sediment were sampled once every season for one year. Total N in A. germinans (2.6 %) and associated saltwort (Batis maritima) (2.1 %) was higher than in cyanobacteria (0.6 %), and sediment (0.1 %). Isotopic signatures (δ15N) in A. germinans (5.85 ‰) and B. maritima (4.75 ‰) were more similar to sediment (5.21 ‰) than to cyanobacteria (1.98 ‰), suggesting mangroves and saltwort obtain N mostly from the sediment; no evidence of N transfer from cyanobacteria was found
