N2 Fixation in Marine Sponges: A New Nitrogen Source for Coastal Ecosystems

微生物对氮(N)的转化强烈影响海洋群落和生态系统的动态和多样性。来自N2固定的新N的输入是特别有趣的。众所周知，许多种类丰富的海洋海绵都拥有被认为可以固定N2的大型多样微生物群落，尽管很少有数据支持这一假设。近年来，在对佛罗里达群岛多个海绵物种的稳定同位素研究中，根据它们的d15N值确定并区分了两个基本的海绵类群。除了低d15N值（表明N2固定）外，一组进行了15N2掺入试验。在这项研究中，北卡罗来纳大学教堂山分校的研究人员将专注于量化低氮和高氮海绵中微生物固氮以及光合作用和呼吸作用的速率。对低氮和高氮海绵的进一步比较研究将使用分子生物学技术（例如16S、nifH、DGGE、FISH分析）来检查它们的微生物群落，并在测试海绵中识别活性的固定氮微生物。科学家团队还将研究整个海绵生命周期中固氮共生体-海绵相互作用的动态，并估计海绵新氮输出的水平。在探索了佛罗里达群岛的自然环境梯度后，该研究将扩展到巴哈马圣萨尔瓦多岛附近的贫营养水域，以调查其他环境参数（如光照水平）如何影响海绵的d15N值和N2固定速率。这项研究不仅将解决长期以来关于海绵中N2固定和海绵作为珊瑚-藻类和其他沿海生态系统新N来源的重要性的问题，而且还将扩大我们对海洋微生物-无脊椎动物关联的生物地球化学意义的基本理解，以及环境因素如何控制这些系统中发生的生物地球化学过程的速率。

ABSTRACTOCE- 0351893 Microbial transformations of nitrogen (N) strongly influence the dynamics and diversity of marine communities and ecosystems. Inputs of new N from N2 fixation are of particular interest. Many species of abundant marine sponges are known to host large and diverse microbial communities thought to fix N2, although few data support this assumption. In recent studies of stable isotopes of multiple sponge species in the FL Keys two basic groups of sponges were identified and differentiated by their d15N values. In addition to low d15N values, which are indicative of N2 fixation, one group had a 15N2 incorporation assay. In this study, researchers from the University of North Carolina at Chapel Hill will focus on quantifying rates of microbial N2 fixation together with photosynthesis and respiration in low and high d15N sponges. Further comparative studies with low and high d15N sponges will use molecular biology techniques (e.g., 16S, nifH, DGGE, FISH analyses) to examine their microbial communities and to identify active N2-fixing microbes within test sponges. The team of scientists will also examine the dynamics of N2-fixing symbiont-sponge interactions throughout the sponge life cycle and estimate levels of new N export from sponges. After exploring a natural environmental gradient in the Florida Keys the study will be expanded to oligotrophic waters off San Salvador Island, Bahamas, in order to investigate how other environmental parameters, such as light levels, affect d15N values of sponges and rates of N2 fixation. This research will not only address the longstanding questions regarding N2 fixation in sponges and importance of sponges as a source of new N for coral-algal reefs and other coastal ecosystems but also broaden our basic understanding of the biogeochemical significance of marine microbial-invertebrate associations and how environmental factors control the rates of biogeochemical processes occurring within these systems.