Light attenuation and photosynthesis of aquatic plant communities

Abstract

We compiled 414 studies from the literature to test if general relationships exist between chlorophyll concentration, 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 photosynthesis 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.

Hydrochemical processes in lowland rivers: insights from in situ, high-resolution monitoring

“…The suggestion that algae, rather than macrophytes, control photosynthesis contrasts with the finding of Palmer-Felgate et al (2008), who suggest aquatic plants control photosynthesis in the upper reaches of the River Kennet. There is no obvious link between the rate of photosynthesis and chlorophyll concentrations in The Cut; the rates of photosynthetic oxygen production are also higher than expected, given the present concentrations of chlorophyll (Krause-Jensen and Sand-Jensen, 1998). This result is due to the importance of periphyton and that the chlorophyll probe measures suspended algae only (Flynn et al, 2002).…”

Importance of structure and density of macroalgae communities (Fucus serratus) for photosynthetic production and light utilisation

“…However, measurements of photosynthetic production in aquatic macrophyte communities are surprisingly few (e.g. Van der Bijl et al 1989, Krause-Jensen & Sand-Jensen 1998, and studies of the environmental and plant structural features determining community ABSTRACT: Determination of photosynthetic production in plant communities is essential for evaluating plant growth rates and carbon fluxes in ecosystems, but it cannot easily be derived from the photosynthetic response of individual leaves or thalli, which has been the focus of virtually all previous aquatic studies. To evaluate the regulation of aquatic community production, we measured the photosynthetic production of thallus parts and entire communities of Fucus serratus (L.) of different density and spatial structure exposed to varying photon flux density and dissolved CO 2 concentration.…”

Temporal dynamics and regulation of lake metabolism

“…Nutrient enrichment, for example, has been found to push lakes from net heterotrophy to net autotrophy by stimulating GPP more than R (del Giorgio and Peters 1994;Schindler et al 1997;del Giorgio et al 1999). Greater inputs of dissolved organic matter stimulate R and may even reduce photosynthesis because of greater background light attenuation in the water column and, thereby, lead to net heterotrophy (del Giorgio and Peters 1994;Krause-Jensen and Sand-Jensen 1998). Ecosystem metabolism is also sensitive to changes in food web structure influencing algal biomass and GPP (Schindler et al 1997;Pace and Cole 2000).…”