Oxygen dynamics in Trichodesmium spp. aggregates

Abstract

Oxygen concetrations measured within, and surrounding aggregates of the planktonic diazotrophic cyanobacterium Trichodesmium spp. are the product of balance of the relative rates of photosynthetic O2 production and a number of O2 consuming mechanisms. These O2 consuming mechanisms may be grouped into those operating at: 1) the physiological level of the Trichodesmium trichomes themselves (physiological mechanisms), 2) the level of the hydrodynamical and diffusive effects of aggregate size and shape (physical mechanisms), and 3) the level of the O2 budget of the entire community of organisms (including microheterotrophs) that occur within these aggregated (community mechanisms). Changes in the balance of production of O2 from photosynthesis and removal of oxygen from these mechanisms result in aggregate internal oxygen concentrations (under conditions of saturating irradiance) which range from anaerobic to >500μM O2. Net oxygen evolution by aggregates is possible throughout the diel cycle, and some diel changes in the net oxygen flux from the aggregates are seen. Large differences are observed in the O2 flux from aggregates of T. thiebautii and T. erythraeum at the same time of day, the former being a greater net producer of O2. Photosynthetic performance, and O2 consumption vary appreciably among aggregates on population and community levels. The observed difference in O2 dynamics may be related to the relative diazotrophic capability of individual aggregates. -from Authors