Nitrogen Identity Drives Differential Impacts of Nutrients on Coral Bleaching and Mortality
Nitrogen Identity Drives Differential Impacts of Nutrients on Coral Bleaching and Mortality
复制标题
DOI：
10.1007/s10021-019-00433-2
复制
发表时间：
2020-06-01
期刊：
影响因子：
3.7
通讯作者：
Holbrook, Sally J.
中科院分区：
文献类型：
--
作者：
Burkepile, Deron E.;Shantz, Andrew A.;Holbrook, Sally J.
氮污染增加了珊瑚对热致漂白的敏感性。然而，不同形式的氮（硝酸盐与铵/尿素）可能对珊瑚的耐热性产生不同的影响。我们使用了18个月的现场实验，法属波利尼西亚的莫雷阿的贫营养前礁，测试不同形式的氮（硝酸盐与尿素）如何影响珊瑚漂白。该实验跨越了2016年和2017年的两次中度热应力事件。硝酸盐增加漂白患病率在鹿角珊瑚高达100%和Pocillopora高达60%相比，控制珊瑚。尿素暴露往往有中间的影响漂白（没有不同的控制或硝酸盐暴露的珊瑚）在这两个类群。重要的是，硝酸盐延长了Acropora和Pocillopora的漂白，因为即使在热应力结束后，硝酸盐暴露的珊瑚仍然漂白，而对照和尿素暴露的珊瑚大部分已经恢复。硝酸盐暴露也增加了Pocillopora殖民地的部分死亡率的患病率和超过三倍的殖民地，完全死亡的数量。我们的数据是第一个显示不同形式的氮对珊瑚漂白和死亡率在天然珊瑚礁环境中的对比效应，连接以前的模式从大规模的相关研究结果从更多的机械实验室实验。最重要的是，我们发现，暴露于硝酸盐的珊瑚表现出更频繁的漂白，漂白时间更长，并且比低氮条件下的珊瑚更容易死亡。暴露于过量的氮，特别是人为的氮，可能会降低珊瑚漂白的温度阈值，即使没有超过典型的热应力阈值，也会引发受污染珊瑚礁的漂白事件。
Nitrogen pollution increases the susceptibility of corals to heat-induced bleaching. However, different forms of nitrogen (nitrate vs. ammonium/urea) may have different impacts on thermal tolerance of corals. We used an 18-month field experiment on the oligotrophic fore reef of Moorea, French Polynesia, to test how different forms of nitrogen (nitrate vs. urea) impacted coral bleaching. The experiment spanned two moderate thermal stress events in 2016 and 2017. Nitrate increased bleaching prevalence in Acropora by up to 100% and in Pocillopora by up to 60% compared to control corals. Urea exposure often had intermediate effects on bleaching (not different from either control or nitrate-exposed corals) in both taxa. Importantly, nitrate prolonged bleaching in both Acropora and Pocillopora as nitrate-exposed corals remained bleached even after thermal stress ended, while control and urea-exposed corals had mostly recovered. Nitrate exposure also increased the prevalence of partial mortality in Pocillopora colonies and more than tripled the number of colonies that completely died. Our data are the first to show contrasting effects of different forms of nitrogen on coral bleaching and mortality in a natural reef environment, linking previous patterns from large-scale correlative studies with results from more mechanistic laboratory experiments. Most importantly, we showed that corals exposed to nitrate exhibited more frequent bleaching, bleached for longer duration, and were more likely to die than corals in low nitrogen conditions. Exposure to excess nitrogen, particularly anthropogenic nitrogen, may lower the temperature threshold at which corals bleach, triggering bleaching events on polluted reefs even when typical thermal stress thresholds have not been crossed.