Nitrogen availability and iWUE have modulated the radial growth of temperate evergreen and deciduous trees near expanding city over past 100 years

Understanding the dynamic growth response of trees to climate and environment changes near to expanding city is crucial for appropriate management in maintain forest structure,functionality,and ecological service.The northern Qinling Mountains in China,identified as a climate-sensitive region with a rising trend in NOx and PM2.5 emissions,particularly in areas near to the expanding city such as Xi'an city,receiving the strong nitrogen deposition in recent decades.Used tree-ring width measurements(basal areal increment,BAI),carbon(δ13C)and nitrogen(δ15N)isotope,as well as C/N,we explore the effects of climates,intrinsic water-use efficiency(iWUE)and nitrogen availability on tree species,including chestnut(Castanea mollissima),oak(Quercus aliena)and pine(Pinus tabulaeformis),closing to expanding Xi'an city.Our findings indicate that in northern Qinling region,radial growth of two deciduous tree species accelerated during past two decades compare to evergreen pine.Tree radical growth of oak and pine trees has been primarily influenced by intrinsic water-use efficiency(iWUE)and δ15N over the past century,and seems to have been affected by the CO2 fertilization effect.Tree-ring δ15N of pine declined continuously over past 100 years,comparing to differing staring year around 1980s of two deciduous tree species.From 1970 to 2018,broadleaf and deciduous trees exhibited significant responses to iWUE and δ15N(p＜0.05),whereas in coniferous pine trees,the individual effects of iWUE and δ15N were weaker(p＞0.05).When considering enhanced nitrogen deposition,NOx significantly promoted the growth of all three tree species,and the individual effects of NOx on BAI of three tree species were all significant(p＜0.05).Our results contribute to a better understanding of the radial growth response of broadleaf and coniferous trees to urban expansion,providing valuable insights for evaluating the interactions between forest carbon and nitrogen under the influence of climate and environmental changes.