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

本项目发展了对珊瑚礁生态系统中微生物生态学和生物地球化学的核心理解。它阐述了关键的养分循环过程如何在珊瑚覆盖和养分可用性的梯度中变化，这两个因素被强调为人类世珊瑚礁下降的主要驱动因素，使结果对寻求加强基于生态系统的珊瑚礁恢复方法的管理人员有用。研究人员正在那里的长期生态研究站（MCR-LTER）收集Mo 'orea附近珊瑚礁的微生物和生物地球化学过程的实时测量数据。他们正在利用已确定的底栖生物覆盖的空间梯度，从珊瑚到大型藻类的优势，以及营养投入。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微生物- dom相互作用和营养循环的理解。在Mo 'orea观察到的持续的大藻相移被假设与营养污染有关，这项工作直接帮助理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养了几名本科生和两名研究生，其中一名是生物学，一名是海洋学。该项目还支持积极的外展项目，包括海洋发现研究所（Ocean Discovery Institute），专注于吸引圣地亚哥代表性不足的高中生从事与海洋有关的职业，以及犹他大学海洋资助项目（UH College Sea Grant Program），支持夏威夷当地的珊瑚礁恢复倡议。珊瑚礁是所有生态系统类型中初级生产和分解速度最高的，但在地球上一些最富营养的水域中仍然存在，这意味着大量营养物质通过有机物进行紧密的再循环。过去半个世纪对珊瑚礁生物地球化学的研究表明，细菌对有机物的分解可能是维持营养物质保留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关于微生物- dom相互作用如何驱动珊瑚礁中营养物质循环和保留的明确假设。研究人员首先解决了有机和无机C、N和P的耦合原位动力学（使用大量元素和光谱方法），微生物丰度和种群结构（使用DNA测序和流式细胞术）以及DOM的化学组成（使用非靶向串联质谱）在多个珊瑚礁栖息地中跨越底栖生物覆盖和营养可用性的梯度。这些模式为第二次原位取样活动提供了信息，该活动解决了代谢途径（使用宏基因组学）、外酶活性（使用转录组学和酶分析）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起作用的微生物有机物分解的共同机制。该项目是在Moorea珊瑚礁长期生态研究计划中进行的，利用了多个珊瑚礁栖息地的丰富时间序列数据，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。通过将前沿分子方法与野外生态学和微生物海洋学的成熟技术相结合，本研究项目确定了长期以来被假设为维持健康珊瑚礁的核心的营养分解和再矿化过程中的关键微生物和分子参与者。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.