Department of Natural Sciences, Faculty of Science and Engineering, Manchester Metropolitan University, Manchester, M1 5GD, UK.
Environ Sci Process Impacts. 2021 Dec 15;23(12):2021-2036. doi: 10.1039/d1em00274k.
Nitrogen speciation, distinguishing nitrate (NO) and ammonium (NH), is commonly undertaken in soil studies, but has not been conducted extensively for lichens. Lichen total nitrogen contents (N wt%) reflect airborne atmospheric nitrogen loadings, originating from anthropogenic sources ( vehicular and agricultural/livestock emissions). Albeit nitrogen being an essential lichen nutrient, nitrogen compound ( NO and NH) concentrations in the atmosphere can have deleterious effects on lichens. Moreover, N wt% do not provide information on individual nitrogen compounds, NO and NH which are major constituents of atmospheric particulate matter ( PM and PM). This study presents a novel method to separate and quantify NO and NH extracted from lichen material. An optimal approach was identified by testing different strengths and volumes of potassium chloride (KCl) solutions and variable extraction times, the use of 3% KCl for 6 hours can achieve a same-day extraction and subsequent ion chromatography (IC) analysis for reproducible lichen nitrate and ammonium concentration determinations. Application of the method was undertaken by comparing urban and rural samples to investigate the relative importance of the two nitrogen compounds in contrasting environments. Findings presented showed that lichen nitrogen compound concentrations varied in rural and urban samples, suggesting different atmospheric nitrogen loadings from potentially different sources ( agricultural and traffic) and varied deposition patterns ( urban layout impacts). Despite potential impacts of nitrogen compounds on lichen metabolism, the approach presented here can be used for quantification of two different nitrogen compounds in lichen biomonitoring studies that will provide specific information on spatial and temporal variability of airborne NO and NH concentrations that act as precursors of particulate matter, affecting air quality and subsequently human health.
氮形态分析，即区分硝酸盐（NO）和铵（NH），常用于土壤研究，但在地衣研究中尚未广泛开展。地衣总氮含量（Nwt%）反映了空气传播的大气氮负荷，源自人为源（车辆和农业/牲畜排放）。尽管氮是地衣的必需营养物质，但大气中氮化合物（NO 和 NH）的浓度会对地衣产生有害影响。此外，Nwt% 并不能提供关于单个氮化合物的信息，NO 和 NH 是大气颗粒物（PM 和 PM）的主要成分。本研究提出了一种从地衣材料中分离和定量提取 NO 和 NH 的新方法。通过测试不同浓度和体积的氯化钾（KCl）溶液以及不同的提取时间，确定了最佳方法，使用 3%KCl 提取 6 小时可以实现当天提取和随后的离子色谱（IC）分析，从而可重复测定地衣硝酸盐和铵盐的浓度。通过比较城市和农村样本，应用该方法研究了两种氮化合物在不同环境中的相对重要性。研究结果表明，地衣氮化合物浓度在农村和城市样本中存在差异，表明来自潜在不同源（农业和交通）的大气氮负荷不同，沉积模式也不同（城市布局的影响）。尽管氮化合物对地衣代谢有潜在影响，但本文提出的方法可用于地衣生物监测研究中两种不同氮化合物的定量，从而提供有关空气传播的 NO 和 NH 浓度的时空变异性的具体信息，这些浓度作为颗粒物的前体，影响空气质量，进而影响人类健康。
