DISSERTATION RESEARCH: Effects of urbanization and climate change on denitrifier community structure and function

人类的福利在很大程度上依赖于水净化和养分循环等生态系统服务。这些自然服务中的许多反过来又依赖于地球上最丰富和最多样化的有机体群体所进行的反应？微生物。值得注意的是，人们对人类驱动力如何影响微生物群落的结构和功能知之甚少。为了帮助解决这一研究差距，该项目将涉及一系列实验，以探索城市化和气候变化可能如何影响溪流中的反硝化细菌(反硝化菌)群落。反硝化细菌是唯一可以从生态系统中永久去除活性氮(N)的生物。水体中过多的活性氮会导致严重的水质问题，如有害的藻华和区域缺氧。因此，河流中的反硝化细菌提供了一种重要的生态系统服务。S项目的目标是通过实验确定通常与流域城市化和气候变化相关的多种应激源是否以及如何影响河流反硝化细菌的群落结构和功能。这些应激源包括污染物和营养物质浓度的增加，以及更高的温度。为了实现这一目标，来自八个不同研究流的微生物群落将受到化学处理(重金属、盐和营养物质)的组合，并在三种温度(28、38和48摄氏度)之一下培养。利用分子指纹技术对培养前后的反硝化菌群落组成进行表征，并对培养前后的脱氮量进行测定。项目结果将被用来解决以下问题：1)城市化和气候变化可能改变反硝化菌群落结构，2)反硝化菌群落结构变化可能增加或降低反硝化细菌的速率，3)应激源之间的相互作用是相加的还是协同的。此外，通过从不同流域城市化程度的研究溪流中提取群落，实验结果将被用来推断城市溪流和森林溪流中的反硝化群落和反硝化率对进一步的环境退化是更敏感还是更不敏感。大多数关于溪流的知识来自对未受干扰的溪流的研究，但美国的大多数溪流都受到人类活动的严重影响。最近，针对城市河流中N循环的研究呈爆炸式增长，但这项工作在很大程度上忽略了参与N转化的微生物群落。通过探索城市化和气候变化对河流反硝化菌群落的影响，拟议项目的结果将导致对反硝化的新见解，反硝化是N循环的重要组成部分。该项目可提供与河流管理和恢复工作有关的信息。更广泛的影响还将包括指导学生。这位博士生的论文研究正在被纳入与当地一名高中教师共同开发的关于人类对水生态系统的影响的高中环境科学课程。项目成果还将通过在同行评议的期刊上发表书面出版物和在国家会议上作口头陈述的方式向更广泛的科学界传播。

Human welfare depends heavily on ecosystem services like water purification and nutrient cycling. Many of these natural services, in turn, rely on reactions performed by the most abundant and diverse group of organisms on Earth ? microbes. Remarkably little is known about how human drivers affect the structure and function of microbial communities. To help address this research gap, this project will involve a series of experiments to explore how urbanization and climate change may affect denitrifying bacteria (denitrifier) communities in streams. Denitrifiers are the only organisms that can permanently remove reactive nitrogen (N) from ecosystems. Too much reactive N in water bodies leads to serious water quality problems like harmful algal blooms and regional hypoxia. Denitrifiers in streams, therefore, provide an important ecosystem service. The project?s objective is to experimentally determine if and how multiple stressors commonly associated with watershed urbanization and climate change affect stream denitrifier community structure and function. These stressors include increased pollutant and nutrient concentrations, as well as higher temperatures. To meet this objective, microbial communities from eight different study streams will be subjected to combinations of chemical treatments (heavy metals, salt, and nutrients), and incubated at one of three temperatures (28, 38, and 48ºC). The amount of N removed will be measured over the incubation period and denitrifier community composition before and after incubation will be characterized by using molecular fingerprinting methods. Project results will be used to address whether 1) urbanization and climate change are likely to change denitrifier community structure, 2) changes to denitrifier community structure are likely to increase or decrease denitrification rates, and 3) interactions among stressors are additive or synergistic. Furthermore, by taking communities from study streams with various degrees of watershed urbanization, experiment results will be used to draw inferences on whether denitrifier communities and denitrification rates in urban versus forested streams are more or less sensitive to further environmental degradation. Most knowledge of streams comes from studying undisturbed streams, but the majority of U.S. streams are heavily impacted by human activity. Recently, there has been an explosion of research targeting N cycling in urban streams, but this work has largely ignored the microbial communities mediating N transformations. Findings from the proposed project will lead to new insights on denitrification, an important component of the N cycle, by exploring effects of urbanization and climate change on stream denitrifier communities. The project may provide information relevant to stream management and restoration efforts. Broader impacts will also include mentoring students. The doctoral student's dissertation research is being incorporated into the high school environmental science curriculum on human impacts on aquatic ecosystems being developed with a local high school teacher. Project findings will also be disseminated to the broader scientific community by written publications in peer reviewed journals and oral presentations at national conferences.