The Spatial Distribution of Isotopic Tracers in Urban Organic Matter: Understanding Multiple and Confounding Effects of Human Activities on Urban Vegetation

植物与环境的相互作用在自然生态系统中得到了广泛的研究，但在城市生态系统中研究甚少。在城市环境中，二氧化碳浓度、臭氧浓度、氮沉降和温度都升高，它们可能影响植物的生理过程，并提供环境效益。该项目的总体目标是提高我们对城市植物-环境相互作用和生态系统服务的理解。具体而言，本项目旨在：1)确定影响洛杉矶盆地植物过程及其空间分布的主要环境和地理因素；2)量化植物生理与城市生态系统服务之间的联系；3)利用植物有机物质作为大气污染物空间分布的代表，即作为“生物监测仪”。这些问题将通过在整个研究区域取样植物生物量和用同位素示踪剂估计植物气体交换和污染参数来解决。通过分析禾草样品中稳定碳、放射性碳、稳定氮和稳定氧同位素丰度的空间分布，可以估算植物气体交换、植物能量平衡、植物物质中污染源碳和氮的吸收比例以及这些污染物在大气中的相对含量。之所以选择洛杉矶盆地作为研究区域，是因为那里有大量关于土地覆盖、气象变量和大气污染物分布的数据集。通过建立这些参数的栅格数据库，并评估与土地利用、气候和污染物变量之间的空间相关性，可以确定变化的城市环境、植物过程和生态系统服务之间的联系。目前，关于城市和其他高度变化环境中的植物如何对多种干扰作出反应，科学上存在很大的不确定性。这种数据差距限制了有效管理城市植被以最大化其环境效益的能力。本研究的几个方面对解决环境问题和自然资源管理具有高度的适用性。生态系统服务将通过计算植物从大气中去除化石燃料燃烧产生的碳和氮的数量，并通过评估影响城市热岛效应的植物能量平衡来直接估算。拟议的方法还提供了利用城市生物量的同位素组成绘制与人类健康有关的大气污染物分布图的潜力。这可能是估算长期综合大气污染物浓度的一种非常具有成本效益的方法。拟议的数据收集是在加州大学欧文分校的当地进行的，因此提供了很好的机会来吸引学生，并将研究地点和结果整合到课程和教育活动中。

Interactions between plants and the environment have been widely studied in natural ecosystems, but very poorly studied in urban ecosystems. Carbon dioxide concentrations, ozone concentrations, nitrogen deposition, and temperature are all elevated in urban environments, where they may affect physiological processes in plants as well as provide environmental benefits. The overall goal of this project is to improve our understanding of urban plant-environment interactions and ecosystem services. Specifically, this project seeks to: 1) identify the major environmental and geographical factors that affect plant processes and their spatial distribution in the Los Angeles basin; 2) quantify the linkage between plant physiology and urban ecosystem services; and 3) use plant organic material as a proxy for the spatial distribution of atmospheric pollutants, i.e. as a "biomonitor." These issues will be addressed by sampling plant biomass across the study region and estimating plant gas exchange and pollution parameters with isotopic tracers. By analyzing the spatial distribution of stable carbon, radiocarbon, stable nitrogen, and stable oxygen isotope abundance in grass samples, it is possible to estimate plant gas exchange, plant energy balance, the proportion of pollution-derived carbon and nitrogen incorporated into plant material, and the relative amounts of these pollutants in the atmosphere. The Los Angeles Basin was chosen as a study region because extensive datasets of the distribution of land cover, meteorological variables, and atmospheric pollutants are available there. By creating a raster database of these parameters and evaluating spatial correlations with land use, climatic and pollutant variables, linkages between the modified urban environment, plant processes, and ecosystem services can be determined. There is currently a great deal of scientific uncertainty as to how plants in urban and other highly modified environments respond to multiple disturbances. This data gap has limited capabilities for effectively managing urban vegetation in order to maximize its environmental benefits. Several aspects of this study are highly applicable to environmental problem solving and natural resource management. Ecosystem services will be directly estimated by calculating the amount of fossil fuel combustion-derived carbon and nitrogen removed from the atmosphere by plants and by evaluating plant energy balance, which influences the urban heat island effect. The proposed methodology also offers potential for utilizing the isotopic composition of urban biomass to map distributions of atmospheric pollutants that are of concern to human health. This may be a very cost-effective method of estimating atmospheric pollutant concentrations integrated over long time periods. The proposed data collection is local to the University of Califonria-Irvine campus and therefore provides excellent opportunities to engage students and integrate research sites and results into courses and educational activities.