造礁石珊瑚共附生固氮微生物的固氮活性

Nitrogen-fixation activity of the hermatypic corals associated diazotrophs

造礁石珊瑚是珊瑚礁生态系统的主要建造者,其共附生微生物参与的生物固氮过程可以缓解寡营养海域的氮素限制,从而维持珊瑚礁生态系统较高的初级生产力。本研究以位于海南三亚鹿回头和西沙南沙洲两地的造礁石珊瑚为对象,采用乙炔还原法测定了不同季节及不同物种的珊瑚共附生固氮微生物的固氮活性;同时测定了海水营养盐含量,分析了珊瑚固氮活性与环境因子之间的关系。结果表明:三亚鹿回头海域的鹿角杯形珊瑚(Pocillopora damicornis)、澄黄滨珊瑚(Porites lutea)和芽枝鹿角珊瑚(Acropora gemmifera)的固氮活性无季节性差异;但相同季节3种珊瑚的固氮活性具有显著的物种间差异,其中鹿角杯形珊瑚的固氮活性最高(P<0.05),夏季为5.925×10^(-11)mol C_2H_4·g^(-1)·h^(-1),冬季为6.471×10^(-11)mol C_2H_4·g^(-1)·h^(-1);西沙寡营养条件下的澄黄滨珊瑚的固氮活性在夏季为5.401×10^(-11)mol C_2H_4·g^(-1)·h^(-1),显著高于同一季节三亚鹿回头的澄黄滨珊瑚的固氮活性(1.971×10^(-11)mol C_2H_4·g^(-1)·h^(-1))(P<0.01)。研究表明,在营养盐浓度较高的背景下,珊瑚的固氮活性受环境因子和季节变化的影响较小。西沙南沙州海水中溶解性营养盐浓度的升高可能会减弱珊瑚共附生固氮微生物的固氮能力。

Hermatypic corals are the main constructor of coral reef ecosystems. The nitrogen（ N）fixation by hermatypic corals associated microbes can relieve N limitation in oligotrophic tropical waters,and consequently sustain high primary productivity of the coral reef ecosystems. In this study,the acetylene reduction assay（ ARA） method was applied to detect the N fixation rate of diazotrophs associated with the corals inhabited in Luhuitou Peninsula,Sanya,Hainan and Nanshazhou,Xisha Island. The concentrations of dissolved inorganic nutrients were measured to explore the relationship between N fixation rate and environmental factors. The N fixation rate of all investigated corals in Luhuitou Peninsula showed no significant seasonal change. There were significant differences in the N fixation rates among Pocillopora damicornis,Porites lutea,and Acropora gemmifera. The highest N fixation rate was detected in Pocillopora damicomis（ P〈0. 05）,being 5.925×10^-11 mol C2H4·g^-1·h^-1and 6. 471 × 10^-11 mol C2H4·g^-1·h^-1in summer and winter,respectively. The N fixation rate of Porites lutea（ 5. 401 × 10^-11 mol C2H4·g^-1·h^-1from oligotrophic Xisha was significantly higher than that from Lunhuitou（ 1.971×10^-11 mol C2H4·g^-1·h^-1（ P〈0.01）. Our results revealed no seasonal variation of N fixing rate in coral reef ecosystems with high concentration of nutrients. In addition,the high concentration of soluble nutrients in seawater may reduce the N fixation activity in corals.