Autumnal Production by Bacteria and Autotrophs Attached toTypha latifoliaL. Detritus

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Abstract
From Typha latifolia detrital samples incubated in a natural wetland, both bacterial production and photosynthetic production, as well as chlorophyll mass, autotroph biovolume and rate of detritus decay, were determined under shaded and unshaded (full-sun) conditions over a 60-day interval during autumn. Bacterial biomass productivity (BBP) and algal/cyanobacterial photosynthesis on the field-incubated detritus were measured in the laboratory over a gradient of photon flux density (PFD: 0—500 μmol m−2 s−1) by use of a light pipetting apparatus. Estimates of chlorophyll regimes and carbon fixation indicated a pattern of physiological adjustment by algae and cyanobacteria to the prevailing light intensity in the field treatments. Under shaded conditions, chlorophyll mass was as much as three times greater than the mass under unshaded conditions, yet there were no apparent differences in autotroph biovolume; additionally, total chlorophyll-derived pigments (chlorophyll a + phaeophytin) were consistently higher under shaded conditions. Photosynthetic rates in the detrital periphyton also indicated shade adaptation, e.g., at PFDs of 20—100 μmol m−2 s−1, photosynthetic rates from the shaded regime were generally equivalent to or exceeded rates in periphyton from the unshaded treatment. In contrast, at higher intensities (250 and 500 μmol m−2 s−1), photosynthetic output of periphyton incubated under unshaded regimes surpassed those of shaded samples. BBP was not stimulated by higher light regimes, yet the rate of T. latifolia decay was statistically higher (+4—6%) under unshaded conditions as compared to shaded conditions.

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