Temporal and Vertical Difference in Factors Limiting Growth Rate of Heterotrophic Bacteria in Lake Biwa |
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Authors: | TB Gurung J Urabe |
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Institution: | (1) Center for Ecological Research, Kyoto University, Kamitanakami, Hirano-Cho 509-3, Otsu, 520-2113, Japan, JP |
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Abstract: | Abstract
Dilution bioassays were performed to examine the seasonal and vertical difference in the relative importance of factors limiting
growth of heterotrophic bacteria in Lake Biwa. The lake water diluted by 0.2 μm lake filtrate (1:6.6) was enriched either
with glucose (C), inorganic phosphorus (P), ammonium nitrogen (N), amino acids (AA), or a combination of these, and incubated
for 2 days at the depths where lake water was collected (2.5, 20 and 30 m depths). Experiments showed that at 2.5 m, P was
the most deficient resource for bacterial growth, but the magnitude of P limitation depended on water temperature. Among others,
amino acids showed a slight but significant stimulation of bacterial growth rates during the fall. At 20 and 30 m, however,
growth stimulation by resource addition was rarely detected. Vertically reciprocal translocation experiments revealed that
the growth rate was limited by low temperature rather than resource supply at the greater depths. The results support a simple
view that bacterial growth rate is basically regulated by water temperature, but high growth rate is not realized in summer
because of resource depletion. The present study suggests that both temperature and P supply play a crucial role in biogeochemical
cycling of organic matter in Lake Biwa through the bacterial growth rate.
Received: 10 March 1999; Accepted: 14 May 1999 |
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