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and their effect on photosynthesis of aquatic plant communities.
In phytoplankton communities, a high diversity of photosynthetic pigments is associated with elevated light capture and biomass , , , . In contrast to terrestrial vascular plants, phytoplankton and macroalgae can contain a variety of photosynthetic pigments, resulting in a diverse array of colour variations within the photosynthetic thalli of rhodophyta, chlorophyta and phaeophyta. Thus, algal species may show large differences in their resource-use abilities which reflect the physiological traits underpinning any diversity–productivity relationship in assemblages. Further, within macroalgal assemblages, where light delivery to the lower portions of the canopy and sub-canopy is limited , , there are large differences in photosynthetic properties between canopy and sub-canopy species (e.g., ratio of structural to photosynthetic tissues; ) and the thallus morphology of sub-canopy species can vary considerably from size and shapes of blades, filaments, or crusts, all with unique photosynthetic traits and patterns of self-shading. Combined with high concentrations of photosynthetic pigments in shaded portions of algal thalli , sub-canopy species are often efficient light harvesters, capable of driving total assemblage NPP above that of the canopy alone , .
The absorption of light by autotrophic communities and fixation of carbon crucially underpins energy transfer in almost all ecosystems. Yet, despite a rich history of photosynthetic research dealing with the spectral regions of photosynthetically active radiation (PAR) used by photosynthetic organisms –, there have been few attempts to integrate measurements of spectral light attenuation and spectral light use by diverse assemblages of macroalgae. Biodiversity-ecosystem-function studies have usually found a positive relationship between plant diversity and primary productivity –, but the ecophysiological mechanisms of complementary resource use have been poorly explored . Although others have found that species identity and total biomass – are important in accounting for variation in NPP, the high diversity and turnover in macroalgal assemblages inhabiting the sub-canopy beneath larger canopy forming macroalgae suggests high niche differentiation. Pigment complementarity may, therefore, be capable of enhancing resource use efficiency within canopies, as has been demonstrated in phytoplankton assemblages , –.
Trophic state index - Wikipedia
Phototrophs underpin most ecosystem processes, but to do this they need sufficient light. This critical resource, however, is compromised along many marine shores by increased loads of sediments and nutrients from degraded inland habitats. Increased attenuation of total irradiance within coastal water columns due to turbidity is known to reduce species' depth limits and affect the taxonomic structure and architecture of algal-dominated assemblages, but virtually no attention has been paid to the potential for changes in spectral quality of light energy to impact production dynamics. Pioneering studies over 70 years ago showed how different pigmentation of red, green and brown algae affected absorption spectra, action spectra, and photosynthetic efficiency across the PAR (photosynthetically active radiation) spectrum. Little of this, however, has found its way into ecological syntheses of the impacts of optically active contaminants on coastal macroalgal communities. Here we test the ability of macroalgal assemblages composed of multiple functional groups (including representatives from the chlorophyta, rhodophyta and phaeophyta) to use the total light resource, including different light wavelengths and examine the effects of suspended sediments on the penetration and spectral quality of light in coastal waters. We show that assemblages composed of multiple functional groups are better able to use light throughout the PAR spectrum. Macroalgal assemblages with four sub-canopy species were between 50–75% more productive than assemblages with only one or two sub-canopy species. Furthermore, attenuation of the PAR spectrum showed both a loss of quanta and a shift in spectral distribution with depth across coastal waters of different clarity, with consequences to productivity dynamics of diverse layered assemblages. The processes of light complementarity may help provide a mechanistic understanding of how altered turbidity affects macroalgal assemblages in coastal waters, which are increasingly threatened by diminishing light quantity and altered spectral distributions through sedimentation and eutrophication.
Research | Yale School of Forestry & Environmental …
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