基于同位素技术的城市绿地植物碳吸存动态差异及溯源研究

In this project，three urban green space systems, including Beijing Institute of Landscape Architecture, Beijing Olympic Forest Park and Mentougou urban forest ecosystem research station, will be deliberately selected as experimental sites. The off-axis integrated cavity output spectroscopy technique will be used to measure air CO2 concentration as well as δ13C and δ18O value in air CO2.The 13C and 18O fingerprints of automobile, coal-fired , gas-fired exhaust gas, landscape plant respiration and soil respiration will be set up with the data from the above measurments. Keeling plot method and isotope linear mixing model will be used to quantify the proportion of fossil fuels fired CO2 accounting for the total CO2 emission or landscape plant respiration CO2 accounting for the total CO2 emission by measuring the CO2 concentration, δ13C and δ18O in air CO2 of the three green space systems in different seasons. Sophora japonica, Ginkgo biloba, Euonymus japonicas, Carex giraldiana are common plant species in the three urban green space systems. The phloem or stem of the four plants will be sampled regularly at different distances from the fourth, fifth and sixth Ring Road of Beijing. The difference of the carbon and oxygen isotope compisition in leaf and phloem sap organic matter of S. japonica, G. biloba, E. japonicas, C. giraldiana as well as carbon and oxygen isotope compisition in different green space systems will be compared and analyzed. All the works are expected to determine the dynamic difference and traceability of carbon sequestration of landscape plant in urban green space system. The proposed work will provide scientific basis for the selection of landscape plants with good sequestration capacity and the optimization of plant allocation in urban green space system.

以四环路旁北京市园林科研院绿地、五环路旁奥林匹克森林公园绿地、六环旁北京门头沟城郊森林生态系统定位站绿地为试验对象,采用立轴积分腔输出光谱技术测定CO2中13C和18O稳定同位素,构建机动车尾气、燃煤废气、天然气废气、绿地植物和土壤呼吸产生CO2的碳氧同位素指纹图谱。以不同季节3块绿地空气的δ13C和δ18O变化为突破点,利用Keeling曲线方法结合线性模型分割化石燃料燃烧和绿地系统的碳排放并确定相对贡献率。定期选取3块绿地共有的国槐、银杏、大叶黄杨和苔草的韧皮部或茎部,离心后测定可溶性糖的δ13C和δ18O,叶片烘干磨碎后测定碳含量、δ13C和δ18O,分析3块绿地中4种植物碳含量、δ13C和δ18O差异,结合采样地点CO2的δ13C和δ18O进行分析,确定不同植物光合气体交换对化石燃料燃烧产生的CO2吸存动态变化和差异,为遴选良好碳吸存能力绿地植物和城市绿地植物优化配置提供科学依据。

城市生态系统是由自然、经济和社会所组成的复杂系统，化石燃料消费集中，是大气新增CO2的主要碳源。城市绿地植物对减缓城市环境压力具有极其重要作用。本研究构建了机动车尾气、燃煤废气、天然气废气和绿地系统呼吸产生CO2气体的稳定碳氧同位素指纹图谱。城市主干道空气中CO2主要来源于机动车尾气排放，平均车速和车道占有率是影响CO2浓度的主要因子。早晚高峰来源于汽车尾气CO2的比例超过全天约6%以上，交通拥堵明显增加了CO2的排放。北京市区CO2浓度和δ13C值存在较大的时空差异，城区CO2浓度最高，近郊次之，远郊最低，CO2存在明显的穹顶式分布，但δ13C值变化分布恰好相反。在生长季节中，城区绿地内外的ΔCO2和Δδ13C值显著高于郊区和远郊。4块绿地内外的ΔCO2浓度值均与LAI呈显著负相关，Δδ13C值均与LAI成极显著的对数函数关系。生长季节中太阳辐射、温度和LAI对市区和近郊绿地内外ΔCO2浓度产生显著影响，温度和太阳辐射是影响Δδ13C值的主要因子。城市绿地系统CO2浓度和CO2增量中机动车尾气贡献率随远离道路呈明显下降趋势，“乔-灌-草”结构比单一乔木结构对CO2的削减作用更明显，且最大削减率的位置更靠近绿地边缘。水分胁迫会对叶片、树干韧皮部中δ13C和δ18O值的负面影响，δ13C和δ18O存在时滞现象，与太阳辐射、相对湿度和VPD关系密切。市区、近郊和远郊等不同位置国槐的δ13C和δ18O值差异不显著，国槐并未表现出对化石燃料CO2的特异性吸存。因此，本研究确定在生长季节中，绿地生态系统降低城市空气中CO2浓度，改变了空气中碳氧同位素组成，乔灌草复层结构的城市绿地对化石燃料CO2削减作用明显，水分条件较好绿地植物通过光合作用比水分胁迫植物更好地进行碳吸存。