城市化进程引发了一系列环境问题，导致气象条件、空气质量及土壤属性在城郊梯度上产生空间差异，进而影响城郊梯度上植物的生长与功能性状。叶片是植物进行光合作用、物质生产以及水气交换的主要器官，其属性可以有效反映植物为适应环境变化而采取的生态策略，具有重要的生态学意义。此外，木本植物能够从大气和土壤中汲取养分，从而气象因子、大气污染物和土壤属性的变化能够对叶片属性产生影响。研究城郊梯度上气象因子、大气污染物、土壤属性和木本植物叶片属性的变化规律及其影响因素，有助于揭示城市化进程对生态环境与生态系统的影响。

北京市是中国典型的超大规模城市之一。本研究以北京市为例，在四个方向上沿城区-郊区梯度各设置5个采样点（共20个采样点），采集土壤和木本植物叶片样品，并测定土壤和叶片属性。结合气象因子、大气污染物以及量化后的人为影响因子，分析了北京市城郊梯度上气象因子、大气污染物、土壤属性和叶片属性的变化规律，探究了影响气象因子、大气污染物、土壤属性和叶片属性变化的关键因素。本研究的主要结论如下：

（1）气象因子和大气污染物在城郊梯度上的变化规律：年均温和6月份均温沿城郊梯度降低，而年降水量和6月份降水量在城郊梯度上没有显著规律；6月份平均大气污染物浓度有显著的空间变化规律，其中平均O₃浓度沿城郊梯度升高，平均NO₂和SO₂浓度沿城郊梯度降低。地形和人为因子对城市气象因子和大气污染物的变化有一定影响，随着海拔降低和人口密度增加，年均温和6月份均温升高；随着主干路路网密度增加，6月份平均O₃浓度减小，而平均NO₂、SO₂浓度增大。北京市城郊梯度上气象因子和大气污染物的变化证明了北京市存在明显的城市热岛效应和城市大气污染，体现了城市化进程中强烈的人为活动对城市气象因子和大气污染物产生了深刻的影响。

（2）土壤属性在城郊梯度上的变化规律：土壤pH值在城郊梯度上的变化规律不显著；土壤全C含量、全N含量、有效N含量和δ¹⁵N在城郊梯度上呈先下降后上升的趋势；土壤有效P含量在城郊梯度上呈下降趋势。气象因子对土壤属性变化有一定的影响，随着温度升高，土壤pH值和有效P含量减小，土壤全N和有效N含量增大；随着降水增加，土壤全N和有效N含量减小。相比之下，人为因子对土壤属性变化的影响较大。随着绿地年龄增大，土壤pH值减小，土壤全C、全N和有效N含量增大；随着人口密度增大，土壤全C含量增大；随着主干路路网密度增大，土壤全N、有效N和有效P含量增大；随着农田占比增大，土壤δ¹⁵N减小。城市中的气象因子与人为因子共同调控了土壤属性在北京市城郊梯度上的变化，体现了城市化对城市土壤的化学属性产生了较为明显的影响。

（3）木本植物叶片属性在在城郊梯度上的变化规律：叶片比叶面积、叶片N含量、叶片δ¹⁵N和△δ¹⁵N_leaf-soil在城郊梯度上有显著降低的趋势；叶片C含量和叶片C:N在城郊梯度上有显著上升的趋势；叶绿素含量、叶片P含量和叶片N:P在城郊梯度上无显著变化。在影响北京市城郊梯度上木本植物叶片属性变化的因素中，植物类型的贡献量最高，不同植物类型间的叶片属性存在显著差异。同时，环境因子和人为因子也会影响叶片属性的变化，随着土壤有效P含量增大，叶片比叶面积、叶片N含量和叶片P含量增大，叶片C含量和叶片C:N减小；随着降水量增加，叶片比叶面积和叶片N含量减小，叶片C:N增大；随着采样点附近农田占比增大，叶片δ¹⁵N和△δ¹⁵N_leaf-soil减小；相反，随着采样点附近主干路路网密度增大，叶片δ¹⁵N和△δ¹⁵N_leaf-soil增大。北京市木本植物叶片属性在城郊梯度上的变化一方面体现了环境因子和人为因子对植物生长发育产生的一定影响，另一方面体现了不同植物类型之间的巨大差异。

综上，人为因子对北京市城市气象因子、大气污染物和土壤属性有较强影响；而城郊梯度上木本植物叶片属性受人类活动的直接和间接影响较小，差异主要由于植物类型不同所致。

Urbanization process have caused a series environmental issues, which resulted in the spatial differences of meteorological conditions, air quality, and soil properties along the urban-suburban gradient, and further influenced the growth and functional traits of plants. Leaves are the main organs of plants for photosynthesis, material production and water and gas exchange. Leaf traits can effectively reflect the ecological strategies adopted by plants to adapt to environmental changes, thus have important ecological significance. In addition, woody plants absorb nutrients from atmosphere and soil, so meteorological factors, air pollutants, and soil properties have impacts on the leaf traits. Therefore, the study of changes of meteorological factors, air pollutants, soil properties and woody plant leaf traits along the urban-suburban gradient is helpful to reveal the impacts of urbanization on ecological environment and ecosystem.

Beijing is one of China's typical megacities. In this study, taking Beijing as an example, five sampling points were set up along the urban-suburban gradient in four directions (totally 20 sampling points). Soil and woody plant leaf samples were collected to measure the properties of them. By combining meteorological factors, air pollutants and quantified human factors, we analyzed the changes of meteorological factors, air pollutants, soil properties and leaf traits along the urban-suburban gradient of Beijing, and explored the key driver factors. The main conclusions of this study are as follows:

(1) Along the urban-suburban gradient, annual mean temperature and June mean temperature decreased, while annual precipitation and June precipitation had no significant trends. June mean atmospheric pollutant concentrations had significant spatial patterns, in which mean O₃ concentration increased, while mean NO₂ and SO₂ concentrations decreased. Topographic and human factors had certain impacts on urban meteorological factors and air pollutants. With the decrease of evelation and increase of population density, annual mean and June mean temperature increased. With the increase of trunk road network density, June mean O₃ concentration decreased, while mean NO₂ and SO₂ concentrations increased. The changes of meteorological factors and air pollutants along the urban-suburban gradient proved that Beijing had obvious urban heat island effect and urban air pollution, and reflected that urbanization have had profound impacts on the urban atmospheric environment.

(2) Along the urban-suburban gradient, soil pH value had no significant trend; soil total C concentration, total N concentration, available N concentration and δ¹⁵N first decreased and then increased; while soil available P concentration decreased significantly. Meteorological factors had certain impacts on soil properties. With the increase of temperature, soil pH value and available P concentrations decreased, while soil total N and available N concentrations increased. With the increase of precipitation, soil total N and available N concentrations decreased. In contrast, human factors had relatively great impacts on soil properties. With the increase of green space age, soil pH value decreased, while soil total C, total N and available N concentrations increased. With the increase of population density, soil total C concentration increased. With the increase of trunk road network density, soil total N, available N and available P increased. With the increase of cropland share, soil δ¹⁵N decreased. Therefore, changes of soil properties along the urban-suburban gradient of Beijing were jointly affected by meteorological factors and human factors, which reflected that urbanization had obvious impacts on the chemical properties of urban soils

(3) Along the urban-suburban gradient, SLA, leaf N concentration, leaf δ¹⁵N and △δ¹⁵N_leaf-soil decreased significantly; leaf C concentration and leaf C:N increased significantly; while leaf P concentration and leaf N:P had no significant trends. Leaf traits varied greatly among different plant types, which explained a large extent to the changes of woody plant leaf traits along the urban-suburban gradient. In addition, environmental factors and human factors also have impacts on leaf traits. With the increase of soil available P concentration, SLA, leaf N concentration and leaf P concentration increased, while leaf C concentration and leaf C:N decreased. With the increase of mean annual precipitation, SLA and leaf N concentration decreased, while leaf C:N increased. With the increase of the cropland share and decrease of the trunk road network density near sampling point, leaf δ¹⁵N and △δ¹⁵N_leaf-soil decreased. The changes of woody plant leaf traits along the urban-suburban gradient of Beijing reflected not only the impacts of environmental factors and human factor on plant growth and development, but also the significant difference between different plant types.

In summary, human factors strongly influenced Beijing meteorological factors, air pollutants, and soil properties, but less directly or indirectly affected the woody plant leaf traits along the urban-suburban gradient, which the variations were mainly explained by plant types.