PHOTOSYNTHESIS-IRRADIANCE PATTERNS IN BENTHIC MICROALGAE: VARIATIONS AS A FUNCTION OF ASSEMBLAGE THICKNESS AND COMMUNITY STRUCTURE

摘要: Photosynthesis-irradiance (P-I) characteristics of periphyton (microphytobenthos) have been considered primarily for entire assemblages. How P-I responses vary with mat thickness and community composition has not in detail. We used a combined approach modeling, microscale determinations photosynthetic rate light attenuation, whole-assemblage O 2 flux measurements to explore relationships. The modeling suggested that the onset saturation photoinhibition will occur at higher irradiance whole-mat (decreased photosynthesis very high irradiance), biomass-specific maximum rate, initial slope function (a) should decrease as assemblage increases or attenuation increases. Spherical microsensor profiles variety stream algae indicated strongly compressed photic zone coefficients 70‐1791 m21 scalar photon fluence density. O2 microelectrode showed little if any 4 mm depths one filamentous green algal (Ulothrix) assemblage, relatively low coefficient, no second Ulothrix community. An dominated by unicellular cyanobacterium exhibited mm, dense cyanobacterial (Phormidium)/xanthophyte (Vaucheria) all. data revealed over several millimeters depth (photoacclimation). These supported model predictions regard effects optical on values photoinhibition. Whole-community from 15 intact assemblages positive relationships between chlorophyll density expressed per unit area; were negative when rates a. None whole Thus, communities consistent predictions.