Light attenuation and photosynthesis of aquatic plant communities

We compiled 414 studies from the literature to test if general relationships exist between chlorophyll concentra-tion, light attenuation, and gross photosynthesis across phytoplankton communities, macrophyte stands, and attached microalgal mats. We also evaluated the upper limit to photosynthesis in the various communities. Along with increasing chlorophyll concentration, the photic zone diminishes from> 100 m in sparse phytoplankton communities to centimeters-meters in macrophyte stands to <l mm in dense microalgal mats. This compression of the photic zone is paralleled by a marked increase in volumetric photosynthesis (mmol O? m mX h I). In contrast, integral photosynthesis (mmol O2 mm ’ h-l) remains relatively constant, depending on both the photic zone and volumetric photosynthesis. A similar upper limit (-60 mmol 0, m-2 h--l) is attained in dense macrophyte and phytoplankton communities when most of the irradiance is captured by plants. Integral photosynthesis, however, is often far below this upper limit because background light attenuation by particles and dissolved organic matter restrict photosyn-thesis in many aquatic plant communities. Moreover, limitation of CO, and 0, exchange may constrain integral photosynthesis in dense plant communities, which are often subject to severe CO? depletion and O2 supersaturation. Photosynthetic organisms in phytoplankton, macrophyte, and benthic microalgal communities have several functiona