Bacterioplankton dynamics in a large mesotrophic lake: II. concentrations and turnover of dissolved amino acids
published: Dec 22, 1998
ArtNo. ESP141014401001, Price: 29.00 €
Seasonal and vertical dynamics of concentrations and turnover of dissolved free (DFAA) and combined amino acids (DCAA) by bacterioplankton were studied in 1990 and 1991 in mesotrophic Lake Constance, Germany, on the basis of weekly to biweekly samplings at 7 depths between 1 and 50 or 120 m. Concentrations of DFAA ranged between < 20 and 480 nm with highest values at the end of the phytoplankton spring bloom when daphnid grazing was very high. concentrations of dcaa ranged between 610 and 3755 nm amino acid equivalents. in contrast to dfaa, however, highest concentrations of dcaa occurred in summer. the average c n ratios of dfaa and dcaa ranged from 2.6 to 3.7 with most values between 2.8 and 3.3. dfaa incorporation (dfaainc) fluctuated largely and accounted for < 5 to ca. 100 % of the c demand for bacterioplankton biomass production (bp). the mean ratio of dfaainc/BP, however, ranged only between 0.2 and 0.4 indicating that other substrates were utilized as well. The turnover time of DFAA also fluctuated largely and ranged between 2.6 and > 50 d with shortest times during the phytoplankton spring bloom. The interannual variability was most pronounced in summer. In 1991 the turnover of DFAA was significantly enhanced as compared to the previous summer as shown by higher rates of DFAAinc, ratios of DFAAinc/BP, concentrations of DCAA and shorter turnover times of DFAA. The regression analysis of the seasonal dynamics of concentrations and utilization of DFAA and DCAA by bacterioplankton and phytoplankton and zooplankton parameters showed annual differences and between the periods in May/June (spring) and later in the season. Concentrations of DFAA and DCAA and DFAAinc were not significantly correlated to chlorophyll-a or primary production except in spring 1990. The former parameters, however, exhibited significant, though different, correlations to daphnids, ciliates and heterotrophic nanoflagellates in both years. Vertical dynamics of concentrations and bacterial utilization of dissolved amino acids often exhibited close correlations, in particular between concentrations of DCAA and bacterial abundance and production suggesting that DCAA, besides DFAA, were important substrates for bacterioplankton growth.