Seasonal variation in dinitrogen fixation and oxygen fluxes associated with two dominant zooxanthellate soft corals from the northern Red Sea
Seasonal variation in dinitrogen fixation and oxygen fluxes associated with two dominant zooxanthellate soft corals from the northern Red Sea
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DOI：
10.3354/meps11091
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发表时间：
2015-01-20
影响因子：
2.5
通讯作者：
Wild, Christian
中科院分区：
文献类型：
--
作者：
Bednarz, Vanessa N.;Cardini, Ulisse;Wild, Christian
由特殊的原核生物（重氮营养体）固定二氮（N-2）是海洋中生物可利用氮(N)的重要来源。在珊瑚礁中，几种底物和生物与重氮营养体有关，但动物黄嘌呤类软珊瑚的潜在N-2固定活性尚未研究。这些软珊瑚可能对向珊瑚礁生态系统输入新氮作出重要贡献，因为它们可以覆盖今天珊瑚礁的大量底栖区。因此，本研究调查了红海北部边缘珊瑚礁中2个优势虫黄藻软珊瑚群（Sarcophyton p.和Xeniidae）在1年的4个季节中对N-2的固定作用，并辅以呼吸测量孵育和关键环境参数的现场监测。研究结果显示，两种软珊瑚在所有季节都有可检测的N-2固定。石藻类对N-2的年固定比Xeniidae高3倍，但两种软珊瑚表现出相似的季节规律。夏季水温和光强最高，无机养分有效性最低，氮-2固结显著增加。珊瑚呼吸在夏季达到峰值，并与N-2固定呈正相关，而光合作用在营养丰富的春季表现出最大速率。考虑到N对繁殖和生长的重要性，氮-2固定可能是夏季软珊瑚营养的关键组成部分，此时水体中的无机养分利用率最低，可能不足以维持软珊瑚的高代谢需求。
Dinitrogen (N-2) fixation by specialized prokaryotes (diazotrophs) represents an important source of bioavailable nitrogen (N) in the ocean. In coral reefs, several substrates and organisms are associated with diazotrophs, but potential N-2 fixation activity by zooxanthellate soft corals has not yet been investigated. Such soft corals may contribute importantly to the input of new N into the reef ecosystem, as they can cover substantial benthic areas in today's coral reefs. Therefore, this study investigated N-2 fixation of 2 dominant zooxanthellate soft coral groups (Sarcophyton sp. and Xeniidae) in a northern Red Sea fringing reef during all 4 seasons of 1 yr. This was supplemented by respirometry incubations and in situ monitoring of key environmental parameters. Findings revealed detectable N-2 fixation for both soft corals during all seasons. Annual N-2 fixation by Sarcophyton sp. was 3 times higher than that by Xeniidae, but both soft corals exhibited similar seasonal patterns. N-2 fixation significantly increased during summer, when water temperature and light intensity were highest and inorganic nutrient availability was lowest. Coral respiration also peaked during summer and was positively correlated to N-2 fixation, while photosynthesis revealed maximum rates during the nutrient-enriched spring season. Given the importance of N for reproduction and growth, N-2 fixation may be a key component of soft coral nutrition during summer, when inorganic nutrient availability in the water column is lowest and likely not sufficient to sustain the high metabolic demand of soft corals.