碩士 / 國立中山大學 / 海洋生物研究所 / 101 / This study investigated the spatial and temporal distribution of unicellular nitrogen-fixing organisms (diazotrophs) in the northern South China Sea (SCS). The diazotrophs contain nitrogenase that can be detected by whole-cell immunocytochemical method using the antibody of nitrogenase, and distinguished and counted readily under a microscope. From present study, the unicellular diazotrophs were classified to four categories according to their sizes and shapes, coccoid cells with diameters of 1-2 μm (1-2 μm C), coccoid with diameters of &;gt;2 μm (&;gt;2 μm C), rod shape with diameters of 1-2 μm (1-2 μm R), and rod shape with diameters of &;gt;2 μm (&;gt;2 μm R). All of the field work were conducted between May and December of 2010 during three cruises, including CR1455 (spring), CR1487 (summer) and CR950 (winter). The summer cruise was carried out one week after the passage of a typhoon, which could be different from summer cruise without typhoon event. Sampling stations were located between 21°-22°N and 116.5°-122.5°E covering the shelf, slope and basin of the northern South China Sea. One station was in the upstream Kuroshio. In addition to the field data, some nutrient enrichment experiments were conducted on board the ship, including one on the shelf and one on the basin stations during the summer cruise, and one on the slope station during the winter cruise. Surface water from each station were enriched with including phosphate, iron, phosphate and iron simultaneously, respectively and were compared with unamended control. All trearments were incubated on deck for 48 hours.
The cell densities of the unicellular diazotrophs on surface water (20.4-23.8×104 cells L-1) were somewhat higher in spring and summer than in winter. Water column (0-100 m) integrated abundances (14.8-16.7×109 cells m-2) were slightly higher in summer and winter than spring. However, their seasonal differences were not significant after statistical tests. Among the four categories, 1-2 μm C was the most abundant group, occupying 47% and 49% of total unicellular diazotrophs in the surface water and the whole water column, respectively. The second abundant group was &;gt;2 μm C (39% and 33%), and the least abundant groups were 1-2 μm R (6% and 8%) and &;gt;2 μm R (8% and 9%). The surface cell density of 1-2 μm C (9.7-11.5×104 cells L-1), 1-2 μm R (0.8-1.8×104 cells L-1) and &;gt;2 μm R (1.3-2.4×104 cells L-1) were all highest in summer. The surface density of &;gt;2 μm C (7.0-11.1×104 cells L-1) was however highest in spring. Statistical test, however, showed an unsignificant seasonal differences, except that 1-2 μm R which was significantly (p&;lt;0.05) higher in summer than winter and spring. The cell density of &;gt;2 μm C was negatively correlated to both surface nitrate concentration and the N/P ratio, and pasitively correlated to stratification of water column. Cell densities of two coccoid diazotrophs (1-2 μm C and &;gt;2 μm C) both were positively correlated to the dust influx. This suggested that high abundance of &;gt;2 μm C occurred at low nitrate concentration and/or high phosphate/iron concentratio. The results of the nutrient enrichment experiments farther support these biological features. As contrast to unamended control, the abundances of &;gt;2 μm C and &;gt;2 μm R were enriched when phosphate and iron were added simultaneously in summer. Similarly, iron enrichment also stimulated the growth of 1-2 μm R. Vertical distribution of the four diazotrophic groups were relatively different.
The cell density of the coccoid diazotrophs (1-2 μm C and &;gt;2 μm C) decreased with depth, with ratios of their densities in the surface (0-50 m): middle (50-100 m): bottom layers (100-150 or 200 m) vertical density profile being 1.4:1:0.7 and 1.6:1:0.7, respectively. High densities in the surface water column might associate with the low nitrate concentration. By contrast, the vertical distribution of 1-2 μm R was relatively homogenous with a vertical cell density profile of 1.2:1:0.9. Among the diazotrophs, &;gt;2 μm R showed a highest ratio in the bottom layer, as their vertical cell density profile being of 1.4:1:1.0. The phenomenon implicated that &;gt;2 μm R, compared with other diazotrophic groups, probably requires lower illumination and/or higher abundances of phosphate and iron.
| Identifer | oai:union.ndltd.org:TW/101NSYS5270016 |
| Date | January 2013 |
| Creators | Liang-fen Jian, 簡良芬 |
| Contributors | Yuh-Ling Lee Chen, Houng-Yung Chen, 李玉玲, 陳宏遠 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 157 |
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