Diversity and Activity of Diazotrophs in Great Barrier Reef Surface Waters

摘要: Discrepancies between bioavailable nitrogen (N) concentrations and phytoplankton growth rates in the oligotrophic waters of Great Barrier Reef (GBR) suggest that undetermined N sources must play a significant role supporting primary productivity. One such source could be biological dinitrogen (N2) fixation through activity “diazotrophic” bacterioplankton. Here, we investigated N2 diazotroph community composition over 10° S latitude within GBR surface waters. Qualitative were found to variable across but relatively high coastal, inner outer waters, reaching 51 nmol L-1 d-1. Diazotroph assemblages, identified by amplicon sequencing nifH gene, dominated cyanobacterium Trichodesmium erythraeum, proteobacteria from Gamma A clade, -proteobacterial phylotypes related sulfate-reducing genera. However, communities exhibited spatial heterogeneity, correlated with shifts dissolved inorganic nutrient concentrations. Specifically, heterotrophic diazotrophs generally increased relative abundance increasing phosphate N, while was proportionally more abundant when these nutrients low. This study provides first in-depth characterisation dynamics oligotrophic, N-limited GBR. Our observations highlight need re-evaluate cycling coral reef systems, include diverse fixing assemblages as potentially water column.