AUTUMNAL PRODUCTION BY BACTERIA AND AUTOTROPHS ATTACHED TO TYPHA-LATIFOLIA L DETRITUS

From Typha latifolia detrital samples incubated in a natural wetland, both bacterial production and photosynthetic production, as well as ch lorophyll mass, autotroph biovolume and rate of detritus decay, were d etermined under shaded and unshaded (full-sun) conditions over a 60-da y interval during autumn. Bacterial biomass productivity (BBP) and alg a/cyanobacterial photosynthesis on the field-incubated detritus were m easured in the laboratory over a gradient of photon flux density (PFD: 0 - 500 mu mol m(-2) s(-1)) by use of a light pipetting apparatus. Es timates of chlorophyl regimes and carbon fixation indicated a pattern of physiological adjustment by algae and cyanobacteria to the prevaili ng light intensity in the field treatments. Under shaded conditions, c hlorophyll mass was as much as three times greater than the mass under unshaded conditions, yet there were no apparent differences in autotr oph biovolume; additionally, total chlorophyll-derived pigments (chlor ophyll a + phaeophytin) were consistently higher under shaded conditio ns. Photosynthetic rates in the detrital periphyton also indicated sha de adaptation, e.g., at PFDs of 20 - 100 mu mol m(-2) s(-1), photosynt hetic rates from the shaded regime were generally equivalent to or exc eeded rates in periphyton from the unshaded treatment. In contrast, at higher intensities (250 and 500 mu mol m(-2) s(-1)), photosynthetic o utput of periphyton incubated under unshaded regimes surpassed those o f shaded samples. BBP was not stimulated by higher light regimes, yet the rate of T. latifolia decay was statistically higher (+4 - 6%) unde r unshaded conditions as compared to shaded conditions.