부산대학교 도서관

BACKGROUND : It is generally accepted that recalcitrant dissolved organic carbon ( RDOC) concentrations in the ocean are in the region of 42 p,mol/L. However, the concentrations of RDOC in the karst river systems remain unidentified and there is little evidence about these compounds unavailable to microbial degradation. OBJECTIVES: To reveal the existence of RDOC and its concentrations in the karst river systems, by collecting water samples at different depths (0 m, 5 m and 10 m) from three typical sites (city-river section, reservoir area and outflow area) in the dammed Liu River in 2006. METHODS: Water samples (3 L) were pre-filtered in-situ using 3 pan filter membranes, and then filtered through 0. 22 pan pore-size filter membranes. The 0. 22 filters were used for DNA extraction following the manufacturer’s instructions of the Power Water DNA Isolation Kit ( Mobio laboratories, Inc. , Carlsbad, CA, USA). The real-time PCR assay of the 16S rRNA gene, as a marker of phytoplankton - bacteria, was carried out in a volume of 25 μL. The assay mixture contained 12.5 μL Green - 2 - Go qPCR Mastermix (Sangon Biotech Co. , Ltd, China) , 1 μL of primer (10 μmol/μL) , 9. 5 μL of distilled water, and 1 μL of template DNA (at 5 ng/ μL). Thermal cycling conditions for 16S rRNA gene were as follows; an initial cycle of 95Ti for 3 min, 39 cycles of 95 T for 60 s. 56Ti for 60 s. 72CC for 60 s, and 72T for 5 min. The primers for 16S rRNA gene were designed as 338f ( 5' - CCTACGGGAGGCAGCAG - 3') and 518r ( 5' - ATTACCGCGGCTGCTGG - 3'). Thermal cycling, fluorescent data collection, and data analysis were carried out with CFX96 Touch11" Real-time PCR Detection System ( Bio-Rad, USA) according to instruction manual. The filtrates after through 3 p.m filter membranes were transferred to sterile glass bottles. The bottles were incubated in the dark room at 30Ti for 180 days. Dissolved organic carbon ( DOC) concentrations of all water samples were determined at 30 days interval on a total organic carbon analyzer ( Multi N/C 3100) at the Institute of Karst Geology, CAGS. The obtained data were performed for correlation analyses using the Pearson correlation method (one-tailed t test) with significance defined as P <0.05 by using SPSS 13.0 software for Windows XP (IBM. Armonk, NY. USA). RESULTS: The relationship between Ct and log starting concentration is linear (R2 >0.99). The amplification efficiencies are 90% - 105%. 24.63 μmol/L RDOC is stored in the dammed Liu River systems, supporting the hypothesis that they are resistant to microbial degradation and the dilution limits dissolved organic carbon utilization. CONCLUSIONS: These findings demonstrate the mechanism for the long-term storage of RDOC in karst hydrosphere, which has hitherto been largely ignored. The advanced techniques ( Fourier-transform ion cyclotron resonance mass spectrometry) provide new evidence to test the initial hypotheses for existence of RDOC in the deep karst reservoir waters. [ABSTRACT FROM AUTHOR]