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.