Supply of available iron in the Kuroshio and South China Sea as studied by the expressions of iron deficiency induced protein A in Trichodesmium spp.

• Main Authors: Bo-Ruei Huang, 黃柏瑞
• Other Authors: Houng-Yung Chen
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/87685256079280036964

碩士 === 國立中山大學 === 海洋生物研究所 === 99 === This research studied the iron deficient condition of the nitrogen-fixing filamentous cyanobacteria Trichodesmium in neighboring oligotrophic northern South China Sea and upstream Kuroshio. The iron deficiency was detected by the immunocytochemical analysis of the expression of iron deficiency induced protein A (IdiA), a protein translated by Trichodesmium cells under iron deficiency. IdiA expression rate (percentage of cells stained by IdiA antiserum in total cells) was used to represent the iron deficiency status. Trichodesmium samples were collected in four cruises by net-towing or bottle-sampling in the Kuroshio and the shelf, slope and basin of the South China Sea between December 2008 and May 2010, representing three seasons: Spring (CR899 and CR1455), Summer (CR910) and Winter (CR886). The results showed that the IdiA expression rates vaied greatly among the stations in the South China Sea. Iron supplies from various sources decreased the IdiA expressions rates (i.e., less iron deficient). These sources include: (1) Mixing from deep layer, such as in the continental shelf of the South China Sea in which internal wave occured, and upwelling occurred in the continental slope; (2) Mixing at some stations in the South China Sea basin from the input of river dischange, especially in the events after typhoon. During these events, stations with lower surface water salinities usually implied lower IdiA expression rates. In contrast, the basin station that were high in salinities showed high IdiA expression rates, higher than the rates in the Kuroshio. These stations generally had strongly stratified water coulumn, and therefore might limit the ward mixing of deep water. The incubation experiment conducted showed that 24 hours after adding iron, Trichodesmium IdiA expression rates were significantly decreased. The Kuroshio, with its water column stratification weaker than South China Sea, the IdiA expression rates were lower than the basin stations in South China Sea, and positively relatied with the stratification index, indicating that deep advection may be the main source of iron. In the incubation experiments in Kuroshio, the expression rates did not significantly differ with iron or without iron addition. The IdiA expression rates in both regions were not related to flux of atmospheric dust, indicating the input from the dust was not key point to decrease iron deficiency of Tricodesmium in this two region. This study shows that iron deficient condition of diazotrophic Trichodesmium in South China Sea and upstream Kuroshio were related to vertical mixing and horizontal discharge, but not dust flux. This study is first time to apply immunocytochemical analysis on field experiments to explain iron deficiency in the ocean.