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：西赤道大西洋固氮微生物的影响因素和影响这一生物复杂性研究的重点是西赤道大西洋（WEQAT）的浮游生物动态。 这是一个复杂和研究不足的生态系统，对该区域以及加勒比海等下游地区的海洋资源产生重大影响。研究的中心是固氮微生物作为关键物种。地质、物理、生物、化学甚至社会因素都对WEQAT中固氮生物的种群生物学和活性产生重大影响。固氮生物反过来又通过输入固定氮（N）对其他浮游植物和营养级产生重大影响。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在地球化学上对该地区产生影响，这些铁和硅酸盐可以在生物学上刺激含有N2固定内共生体Richelia intracellularis的硅藻的生长。此外，该地区还从非洲萨赫勒地区的灰尘中获得了大量的季节性大气铁输入，这可以促进重要的N2固定蓝细菌Trichodesmium的生长。这种大气铁源直接沉积在生物活动最大的表面沃茨上。对于束毛藻，物理环境（例如高风速）也可以抑制其活动和水华的形成。亚马逊盆地和非洲萨赫勒地区的土地使用做法可能会影响固氮生物，海洋浮游生物固定的N2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，科学家们将研究这些固氮生物种群结构的复杂过程，影响它们在CO2和N2固定中的重要性，而CO2和N2固定反过来又影响其他固氮过程。Trichodesmium和Hemiaulus / Richelia协会的季节和空间关系将直接参考铁和硅的输入的主要途径，并与物理环境进行检查。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和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态地球化学和营养动力学模型，这些模型将WEQAT区域特有的复杂的物理、化学和生物相互作用结合起来。该模型将，反过来，被用来检查的假设，物理强迫，通过其对重氮营养种群和食物网的结构的影响，影响N2固定，并在一定程度上，决定了高生产力的WEQAT。这项工作使用观测和模型相结合的方法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;以及3）相关的细节水平，包括物理空间的分辨率，必须将其纳入非线性系统，以捕捉全球生态系统的动态特性（这里是高生产力）。 这项研究将大大促进我们对世界海洋这一重要领域的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.