Isotopic Composition (δ15N and δ18O) of Urban Forests in Different Climate Types Indicates the Potential Influences of Traffic Exhaust and Relative Humidity

Previous studies have shown that climatic and anthropogenic factors influence the variations in stable isotope signature of tree materials an urban ecosystem. However, responses trees to various precipitation interventions are unclear. To fill research gap, isotopic composition (δ15N δ18O) total nitrogen content soil-plant system forests were measured, focusing on typical species (Populus tomentosa Ficus virens). The was done under land uses China’s Beijing Shenzhen megacities (with different humidity conditions). linear mixed-effect model revealed δ15N values leaves roadside virens significantly higher than those park sites, away from road difference = 7.2‰). In contrast, Populus exhibited a non-significant −1.8‰). Further regression analysis could be attributed proximity highways, suggesting vehicle exhaust trees. also δ18O leaves. assess conditions leaves, ratio atmospheric intercellular vapor pressures (ea/ei) canopies estimated. result ea/ei for tomentosa, ascribed variation two megacities. These results highlight can potentially serve as bioindicators pollution humidity. Our findings ecophysiological related N O they vary according traffic relative Consequently, valuable indicators contamination, forming nature-based solution citizen welfare improvement.