title: Spatial patterns and links between microbial community composition and function in cyanobacterial mats.
abstract: We imaged reflectance and variable fluorescence in 25 cyanobacterial mats from four distant sites around the globe to assess, at different scales of resolution, spatial variabilities in the physiological parameters characterizing their photosynthetic capacity, including the absorptivity by chlorophyll a (A chl), maximum quantum yield of photosynthesis (Y max), and light acclimation irradiance (I k). Generally, these parameters significantly varied within individual mats on a sub-millimeter scale, with about 2-fold higher variability in the vertical than in the horizontal direction. The average vertical profiles of Ymax and I k decreased with depth in the mat, while A chl exhibited a sub-surface maximum. The within-mat variability was comparable to, but often larger than, the between-sites variability, whereas the within-site variabilities (i.e., between samples from the same site) were generally lowest. When compared based on averaged values of their photosynthetic parameters, mats clustered according to their site of origin. Similar clustering was found when the community composition of the mats' cyanobacterial layers were compared by automated ribosomal intergenic spacer analysis (ARISA), indicating a significant link between the microbial community composition and function. Although this link is likely the result of community adaptation to the prevailing site-specific environmental conditions, our present data is insufficient to identify the main factors determining these patterns. Nevertheless, this study demonstrates that the spatial variability in the photosynthetic capacity and light acclimation of benthic phototrophic microbial communities is at least as large on a sub-millimeter scale as it is on a global scale, and suggests that this pattern of variability scaling is similar for the microbial community composition.
authors.affiliation: Microsensor Group, Max-Planck Institute for Marine Microbiology Bremen, Germany ; Marine Microbial Ecology Group, Red Sea Research Center, KAUST Thuwal, Saudi Arabia.
authors.forename: Mohammad A A
authors.initials: MA
authors.lastname: Al-Najjar
authors.affiliation: Microbial Habitat Group, Max-Planck Institute for Marine Microbiology Bremen, Germany.
authors.forename: Alban
authors.initials: A
authors.lastname: Ramette
authors.affiliation: Marine Biological Section, Department of Biology, University of Copenhagen Helsingør, Denmark ; Plant Functional Biology and Climate Change Cluster, University of Technology Sydney Sydney, NSW, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Kühl
authors.affiliation: Biology Department, UAE University Al-Ain, UAE.
authors.forename: Waleed
authors.initials: W
authors.lastname: Hamza
authors.affiliation: Microsensor Group, Max-Planck Institute for Marine Microbiology Bremen, Germany.
authors.forename: Judith M
authors.initials: JM
authors.lastname: Klatt
authors.affiliation: Microsensor Group, Max-Planck Institute for Marine Microbiology Bremen, Germany ; Department of Earth Sciences - Geochemistry, Utrecht University Utrecht, Netherlands.
authors.forename: Lubos
authors.initials: L
authors.lastname: Polerecky
keywords: biogeography; hyperspectral imaging; imaging PAM; microbial community structure; photosynthetic microbial mats; spatial link between structure and function