Collaborative Research: Diel dynamics of dissolved organic matter production and remineralization as a driver of coral reef nutrient recycling

该项目发展了对珊瑚礁生态系统中昼夜微生物生态学和生物地球化学的核心理解。它的背景下如何关键的营养循环过程不同梯度的珊瑚覆盖和营养物质的可用性，两个因素强调作为珊瑚礁下降的主要驱动力在人类世，使管理人员寻求加强基于生态系统的方法来恢复珊瑚礁有用的结果。调查人员正在长期生态研究站（MCR-LTER）收集莫雷阿周围珊瑚礁微生物和生物地球化学过程的昼夜测量结果。 它们正在利用从珊瑚到大型藻类占优势的海底覆盖的既定空间梯度和养分投入。总的来说，这项研究提高了我们对这些关键环境因素如何影响昼夜微生物-DOM相互作用和营养循环的理解。在Mo'orea观察到的正在进行的大型藻类相变被假设为与营养污染有关，这项工作直接告知了解这些变化如何影响Mo'orea珊瑚礁的营养循环。两所少数民族高等教育机构共同培训了几名本科生和两名研究生，一名生物学研究生和一名海洋学研究生。该项目还支持与海洋探索研究所的积极外展计划，重点是让代表性不足的高中生参与圣地亚哥的海洋职业，与UH学院海洋赠款计划，以支持珊瑚礁恢复能力的倡议，在夏威夷当地。珊瑚礁表现出一些最高的初级生产率和任何生态系统类型的分解，但坚持在一些最贫营养的沃茨上，这意味着大量营养素通过有机物质的紧密循环。在过去的世纪里，对珊瑚礁生物地球化学的研究强调，细菌分解有机物可能是维持营养物质和珊瑚礁生产力的一种机制。该项目应用现代宏基因组学和非靶向代谢组学来测试昼夜微生物-DOM相互作用如何驱动珊瑚礁中的营养循环和保留的明确定义的假设。调查人员首先解决耦合在原位昼夜动态的有机和无机C，N和P（使用散装元素和光谱方法），微生物丰度和人口结构（使用DNA测序和流式细胞术）和DOM的化学成分（使用非目标串联质谱）在多个珊瑚礁栖息地的梯度底栖覆盖和营养物质的可用性。这些模式为第二次原位昼夜采样活动提供了信息，解决了代谢途径（使用宏基因组学），酶外活性（使用转录组学和酶测定）和特定代谢物转化（通过分子网络跟踪）的动态耦合，以提取在营养循环中发挥作用的微生物有机物分解的常见机制。该项目是在莫雷阿珊瑚礁长期生态研究计划内进行的，利用了大量关于多个珊瑚礁栖息地的时间序列数据，并将我们的原位采样与正在进行的物理，地球化学和生物监测计划结合起来。通过将尖端的分子方法与野外生态学和微生物海洋学中成熟的技术相结合，该研究计划确定了营养物分解和再矿化过程中的关键微生物和分子，长期以来，人们一直认为营养物分解和再矿化过程是维持珊瑚礁健康的核心。该奖项反映了NSF的法定使命，并通过利用基金会的知识价值和更广泛的影响进行评估，被认为值得支持审查标准。

This project develops a core understanding of diel microbial ecology and biogeochemistry in coral reef ecosystems. It contextualizes how crucial nutrient recycling processes vary across gradients of coral cover and nutrient availability, two factors highlighted as the main drivers of reef decline in the Anthropocene, making the results useful to managers seeking to enhance ecosystem-based approaches to reef restoration. The investigators are collecting diel measurements of microbial and biogeochemical processes at coral reefs around Mo’orea at the Long Term Ecological Research site there (MCR-LTER). They are using established spatial gradients of benthic cover, from coral to macroalgal dominance, and nutrient inputs. Overall the research improves our understanding of how these key environmental factors influence diel microbe-DOM interactions and nutrient recycling. The ongoing macroalgal phase shifts observed at Mo’orea are hypothesized to be related to nutrient pollution, and this work directly informs understanding of how these changes are impacting nutrient cycling in the reefs of Mo’orea. The training of several undergraduate students and two graduate students, one in Biology and one in Oceanography is shared between two minority serving institutions of higher education. The project also supports active outreach programs with the Ocean Discovery Institute focused on engaging underrepresented high school students in ocean-oriented careers in San Diego, and with the UH College Sea Grant Program to support coral reef resilience initiatives locally in Hawai‘i.Coral reefs exhibit some of the highest rates of primary production and decomposition of any ecosystem type yet persist in some of the most oligotrophic waters on the planet, implying tight recycling of macronutrients through organic matter. The last half century of work on the biogeochemistry of reefs have highlighted this bacterial decomposition of organic matter as a likely mechanism for maintaining nutrient retention and reef productivity. This project applies modern metagenomics and untargeted metabolomics to test clearly defined hypotheses of how diel microbe-DOM interactions drive nutrient recycling and retention in reefs. The investigators are first resolving coupled in situ diel dynamics of organic and inorganic C, N and P (using bulk elemental and spectroscopic methods), microbial abundances and population structures (using DNA sequencing and flow cytometry) and the chemical composition of DOM (using untargeted tandem mass spectrometry) in multiple reef habitats across a gradient of benthic cover and nutrient availability. These patterns inform the second in situ diel sampling campaign resolving the dynamic coupling of metabolic pathways (using metagenomics), exoenzymatic activity (using transcriptomics and enzyme assays) and transformations of specific metabolites (tracked via molecular networking) to distill common mechanisms of microbial organic matter decomposition that play a role in nutrient cycling. This project is being conducted within the Moorea Coral Reef Long Term Ecological Research program, leveraging a wealth of time series data on multiple reef habitats as well as contextualizing our in situ sampling with ongoing physical, geochemical and biological monitoring programs. By integrating cutting edge molecular approaches with well-established techniques in field ecology and microbial oceanography, this research program identifies key microbial and molecular players in the nutrient decomposition and remineralization processes long hypothesized to be central to maintaining healthy reefs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.