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：影响赤道大西洋西部重氮微生物的因素这项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。这是一个复杂而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有重大影响。本研究以重氮(固氮)微生物为核心物种。地质、物理、生物、化学甚至社会因素都对WEQAT的种群生物学和重氮菌的活性有重要影响。固氮菌通过输入固定氮(N)进而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从而改变水柱分层在物理上影响该地区，并通过引入铁和硅酸盐在地球化学上影响该地区，然后可以在生物上刺激硅藻的生长，这些硅藻含有固定内共生菌Richelia in ellularis的氮气。此外，该地区从非洲萨赫勒地区的尘埃中获得了大量的季节性大气铁输入，这可以促进重要的固定氮气的蓝藻Trichodesum的生长。这种大气铁源直接沉积在生物活性最强的地表水中。对于木霉来说，物理环境(如高风速)也会抑制活动和水华的形成。亚马逊盆地和非洲萨赫勒地区的土地利用做法可能会影响固氮菌，海洋浮游生物固定的氮气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浮游重固氮微生物种群的复杂过程，影响它们在固定二氧化碳和氮气方面的重要性，进而影响其他浮游过程。将直接参照铁和硅的主要输入途径以及物理环境来研究毛霉菌和半毛菌/黎氏菌群落的季节和空间关系。这组合作的科学家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。这些数据将被用来开发和验证生物地球化学和营养动力学模型，其中包含了WEQAT地区特有的复杂的物理、化学和生物相互作用。这些模型将被用来检验这一假设，即物理强迫通过对重氮营养种群和食物网结构的影响，影响氮气固定，并在一定程度上决定WEQAT的高生产率。这项工作使用观测和模型的组合来解决生物复杂性中的三个基本问题：1)生态系统结构和功能之间的关系，在一个既是非线性又是高维的系统中；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，必须纳入非线性系统以捕捉全球生态系统属性的动态(在这里，高生产力)。这项研究将极大地促进我们对世界海洋这一重要区域的物理和生物地球化学过程之间的相互作用的理解，并确定这些相互作用如何调节海洋生态系统生产力的变异性。

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.