1994 Fiscal Year Final Research Report Summary
ROLE OF MICROBIAL LOOP IN AQUATIC CARBON AND NITROGEN CYCLES
| Project/Area Number |
05454603
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Environmental dynamic analysis
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| Research Institution | NAGOYA UNIVERSITY |
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Principal Investigator |
YOSHIOKA Takahito NAGOYA UNIV., INST.HYDROSPHERIC-ATMOSPHERIC SCI., ASSISTANT., 大気水圏科学研究所, 助手 (50202396)
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| Co-Investigator(Kenkyū-buntansha) |
HAGA Hiroki LAKE BIWA MUSEUM PROJECT OFFICE SHIGA PREFECTURE,CURATOR, 学芸技師
NAGATA Toshi NAGOYA UNIV., INST.HYDROSPHERIC-ATMOSPHERIC SCI., ASSISTANT., 大気水圏科学研究所, 助手 (40183892)
SAKAMOTO Mitsuru NAGOYA UNIV., INST.HYDROSPHERIC-ATMOSPHERIC SCI., PROFESSOR. (30022536)
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| Project Period (FY) |
1993 – 1994
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| Keywords | HYDEOSPHER / MICROBIAL LOOP / C,N CYCLES / PICOPLANKTON / BACTERIA / DOM / REGENERATION / STABLE ISOTOPE |
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| Research Abstract |
The purpose of this study was to examine the role of microbial food webs in the carbon and nitrogen cycling within pelagic environments of freshwater lakes. Studies were categorized in three categories. (1) Mechanism of ammonia regeneration and its controlling factor, (2) Mechanism of bacterial decomposition and utilization of dissolved organic nitrogen, and (3) Food web analysis using stable isotope ratios. We, thus, analyzed the role of microbial loo p on C and N cycles with interdisciprinary approaches (microbiological and geochemical ones). We particularly focused on mechanisms of ammonium regeneration and bacterial utilization of dissolved organic matter (DOM). Measurements of size-fractionated NH4 regeneration in mesotrophic Lakes Kizaki and Biwa revealed that bacteria and bacterivores contribute substantially to total NH4 regeneration ; up to 80% of NH4 regeneration was attributable to heterotrophs in the <20mum fraction. Bacteria appeared to be a source rather than a sink of NH4 in the study area. To further examine the regulation of carbon and nitrogen metabolism by freshwater bacteria, we measured concentrations and bacterial utilization of dissolved free (DFAA) and combined amino acids (DCAA) in Lake Biwa.
Preliminary results suggested that DCAA rather than DFAA were the major source of organic nitrogen for bacteria. Our results demonstrate that carbon and nitrogen fluxes driven by the microbial loop play the key role in ecosystem functioning and community dynamics in freshwater environments.
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