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北京城市草地土壤CO2排放和CH4吸收通量的变化特征及其影响因素

Characteristics and controlling factors of annual soil CO2 emissions and CH4 uptakes from urban turfgrasses in Beijing

  • 摘要: 随着城市人口密度的不断增长和城市化进程的加快,城市生态系统已成为影响全球气候变化的热点区域。但是,城市草地作为城市生态系统的重要组成部分,其对土壤—大气CO2和CH4交换过程的影响尚不明确。为此,本文依托北京城市绿地生态系统定位观测研究站,采用静态暗箱-气相色谱方法对三种典型城市草地类型(即以C4草种为主的暖季草地和以C3草种为主的冷季草地与林下地被)的土壤CO2排放和CH4吸收通量及其辅助环境因子进行了一个完整周年的田间原位观测研究。结果表明,三种城市草地类型的土壤CO2排放和CH4吸收通量在整个观测期内具有相似的季节变化动态,这说明不同城市草地类型对土壤呼吸和CH4吸收通量的季节变化特征无明显影响。城市草地土壤CO2排放的季节变化主要受土壤温度和土壤水分含量变化的影响,二者的协同作用可以解释土壤CO2排放变化的77%~87%;而城市草地土壤CH4吸收通量的变化主要受土壤水分含量的影响,且两者之间呈显著负相关关系。在全年尺度上,三种城市草地类型的土壤CO2年排放量在12.1~15.2 t C ha-1 yr-1之间,其土壤CH4年吸收量范围为3.71~4.27 kg C ha-1 yr-1。尽管城市草地非生长季的低温通常会抑制微生物活性而降低土壤呼吸和CH4吸收强度,但结果显示非生长季土壤CO2排放和CH4吸收量分别占全年总量的10%~18%和39%~51%,突出了开展完整周年观测研究的重要性。对比三种城市草地类型,以C4草种为主的暖季草地相较于冷季草地和林下地被(二者均以C3草种为主)具有明显较高的土壤CO2年排放量,但却显著降低了土壤CH4年吸收量,这与其土壤性质以及植被特性的差异有关。综上,该研究结果表明种植C3草种有利于城市草地土壤—大气CO2和CH4交换过程的减排增汇,这将有助于合理规划和利用城市草地,以缓解快速城市化对气候变化所带来的影响。

     

    Abstract: With accelerating urban expansion and increasingly growing city population density, urban ecosystems are becoming the hotspots of global climate change. Urban turfgrasses can themselves be a vitally important part of cities, however, its effects on soil-atmosphere exchanges of carbon dioxide (CO2) and methane (CH4) remains unclear. In this study, we performed year-round field measurements of soil respiration (CO2) and CH4 fluxes and associated with environment factors from three typical urban turfgrass turfgrasses (i.e., warm-season turfgrass (WT) dominated by C4 plants species, cool-season turfgrass (CT) and shade-enduring turfgrass (ST), both dominated by C3 plant species) at the Urban Ecosystem National Observation and Research Station, Beijing, using a static opaque chamber method combined with gas chromatography analysis. Our results showed that across the experimental period, soil CO2 emissions or soil CH4 uptakes from all urban turfgrasses exhibited a comparable seasonal pattern, indicating that the seasonality of soil CO2 and CH4 fluxes was significantly affected by different urban turfgrass type. Soil CO2 emissions from urban turfgrasses were positively correlated with soil temperature and soil water content, and their combined effects could explain about 77%-87% of the variations in soil CO2 emissions, In contrast, the variations of soil CH4 uptake were mainly regulated by soil water content, and soil CH4 uptake was negatively correlated with soil water content. Over the annual scale, the cumulative soil CO2 emissions for all urban turfgrasses ranged from 12.1 to 15.2 t C ha-1 yr-1, and annual CH4 uptakes were between 3.71 and 4.27 kg C ha-1 yr-1. Although low temperatures during the non-growing season usually reduce soil CO2 emissions and CH4 uptakes by inhibiting the related microbial activities, our results revealed that total soil CO2 emissions and CH4 uptakes across the non-growing season contributed to 10%-18% and 39%-51% of the annual budgets, respectively, highlighting the importance of measurements spanning the full year. Among the three urban turfgrasses, the WT dominated by C4 plant species showed significantly higher annual soil CO2 emissions but lower annual soil CH4 uptakes as compared to the CT and ST (both of which were dominated by C3 plants species). This was mainly in connection with differences in soil properties and vegetation characteristics between the urban turfgrasses. Overall, our fundings suggest that in the context of various urban turfgrasses being expanding substantially along with rapid urbanization, the efforts of conscious planning and design of C3 related urban turfgrasses may benefit the reduction of soil-atmosphere exchanges of CO2 and CH4, making contribution to mitigating climate change.

     

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