BIOCOMPLEXITY: Collaborative Research: Factors Affecting, and Impact of, Diazotrophic Microorganisms in the Western Equatorial Atlantic Ocean

生物复杂性：合作研究：影响西赤道大西洋重氮营养微生物的因素和影响这项生物复杂性研究侧重于西赤道大西洋（WEQAT）的浮游生物动态。这是一个复杂且研究不足的生态系统，对该地区以及加勒比海等下游地区的海洋资源产生重大影响。该研究以重氮营养（固氮）微生物为重点物种。地质、物理、生物、化学甚至社会因素都对WEQAT重氮营养菌的种群生物学和活性有重要影响。重氮营养体反过来又通过输入固定氮(N)对其他浮游植物和营养水平产生重大影响。亚马逊河通过改变盐度和水柱分层对该地区产生物理影响，并通过引入铁和硅酸盐对该地区产生地球化学影响，这些铁和硅酸盐可以在生物上刺激硅藻的生长，硅藻含有固定氮的内共生菌胞内黎切菌。此外，该地区从非洲萨赫勒地区的沙尘中获得了大量的季节性大气铁输入，这可以促进重要的固氮蓝藻Trichodesmium的生长。这种大气铁源直接沉积在生物活性最大的地表水上。对于木霉而言，物理环境（如高风速）也会抑制其活性和华花的形成。在亚马逊盆地和非洲萨赫勒地区，重氮营养体可能受到土地利用方式的影响，海洋浮游生物固定的氮可以通过刺激初级生产力和渔业产量来影响人类。利用遥感和船上测量，科学家们将研究构成这些重氮营养浮游生物种群的复杂过程，影响它们在二氧化碳和氮气固定中的重要性，而二氧化碳和氮气固定反过来又影响其他浮游生物过程。将直接参考铁和硅的主要输入途径以及物理环境来研究trichodesium和Hemiaulus / Richelia组合的季节和空间关系。合作科学家小组将研究与每个重氮营养群落相关的营养结构，包括过程的垂直分布以及相关的自养和异养浮游生物种群。这些数据将用于开发和验证生物地球化学和滋养动力学模型，这些模型包含了WEQAT地区特征的复杂物理、化学和生物相互作用。反过来，这些模型将被用来检验这样一种假设，即物理强迫通过其对重氮营养种群和食物网结构的影响，影响氮的固定，并在一定程度上决定了WEQAT的高生产率。这项工作结合了观察和模型来解决生物复杂性中的三个基本问题：1)非线性和高维系统中生态系统结构和功能之间的关系；2)非线性生态系统对环境强迫的响应；3)相关的细节水平，包括物理空间的分辨率，必须纳入非线性系统以捕捉全球生态系统属性的动态（这里是高生产力）。该研究将极大地促进我们对世界海洋重要地区物理和生物地球化学过程之间相互作用的理解，并确定这些相互作用如何调节海洋生态系统生产力的变化。

BIOCOMPLEXITY: Collaborative Research: Factors affecting, and impact of, diazotrophic microorganisms in the western Equatorial Atlantic Ocean This biocomplexity research focuses on plankton dynamics in the western Equatorial Atlantic Ocean (WEQAT). This is a complex and understudied ecosystem that has significant impacts on marine resources in the region as well as in downstream areas such as the Caribbean Sea. The study centers on diazotrophic (nitrogen fixing) microorganisms as keystone species. Geological, physical, biological, chemical and even social factors all have a major influence on population biology and activity of diazotrophs in the WEQAT. Diazotrophs in turn have a major impact on other phytoplankton and trophic levels through input of fixed nitrogen (N). The Amazon River affects the region physically by changing salinity and thereby water column stratification, and geochemically by introducing iron and silicate which can then biologically stimulate the growth of diatoms that contain the N2 fixing endosymbiont Richelia intracellularis. Furthermore, the area receives significant seasonal atmospheric inputs of iron in dust from the Sahel region of Africa, which can promote the growth of the important N2 fixing cyanobacterium Trichodesmium. This atmospheric iron source is directly deposited on the surface waters where biological activity is greatest. For Trichodesmium, the physical environment (e.g. high wind speed) can also inhibit activity and the formation of blooms. Diazotrophs may be affected by land use practices in the Amazon Basin and the African Sahel, and N2 fixed by marine plankton can affect humans by stimulating primary productivity and fishery yields. Using both remote sensing and shipboard measurements, scientists will examine the complex processes which structure these planktonic diazotroph populations, influence their importance in CO2 and N2 fixation, which, in turn, affect other planktonic processes. The seasonal and spatial relationships of Trichodesmium and Hemiaulus / Richelia associations will be examined with direct reference to the major routes of inputs of Fe and Si, and with regard to the physical environment. The group of collaborating scientists will examine the trophic structures associated with each diazotrophic community, including the vertical distribution of processes and associated autotrophic and heterotrophic plankton populations. These data will be used to develop and verify biogeochemical and trophodynamic models that incorporate the complex physical, chemical and biological interactions that characterize the WEQAT region. The models will, in turn, be used to examine the hypothesis that physical forcing, through its effect on the diazotrophic populations and the structure of the food web, influences N2 fixation and, in part, determines the high productivity of the WEQAT. The work uses a combination of both observations and models to address three fundamental issues in biocomplexity: 1) the relationship between ecosystem structure and function in a system that is both nonlinear and high-dimensional; 2) the response of a nonlinear ecosystem to environmental forcing; and 3) the relevant level of detail, including the resolution of physical space, that must be incorporated in nonlinear systems to capture the dynamics of a global ecosystem property (here, high productivity). The research will significantly advance our understanding of the interaction between physical and biogeochemical processes in an important area the world's oceans, and identify how these interactions regulate variability in marine ecosystem productivity.