The stoichiometry of carbon,nitrogen and phos-phorous in plants can reflect the interactions between plants and their environment.The interplay between plant nutri-ents,climatic factors,and soil properties and the underlying regulatory mechanisms are pillars of ecology but remain underexplored.In this study of plant C-N-P stoichiometry and nutrient resorption in Castanopsis hystrix groves in three cities(Guangzhou,Zhongshan,and Lechang)that repre-sent an urban-rural gradient in Guangdong Province,South China,we explored potential relationships among NO2 con-centrations,diameter at breast height(DBH),and resident human population.Mean annual temperature,mean annual precipitation,insolation duration per year,and the human resident population differed significantly among the three cities.Soil C-N-P was always highest in suburban Lechang,and the concentration of NO2 was highest in urban Guang-hzou(55.33±0.67 μg m-3)and positively correlated with the resident population and leaf N:P.Our findings suggest that C-N-P stoichiometry of C.hystrix was better explained by NO2 than by soil C-N-P stoichiometry and that nutrient resorption was better explained by leaf nutrients and DBH than by NO2 and soil stoichiometry.Our study supports the hypothesis that rapid urbanization influences NO2 concen-trations and microclimate,which may jointly change the stoichiometry of plant nutrients in the forest ecosystems.