Abstract:
With accelerating urban expansion and increasingly growing city population density, urban ecosystems are becoming the hotspots of global climate change. Although urban turfgrasses are a vital part of cities, their effects on soil–atmosphere exchanges of carbon dioxide (CO
2) and methane (CH
4) remain unclear. In this study, we performed year-round field measurements of soil respiration (CO
2 fluxes) and CH
4 fluxes, associated with environmental factors, from three typical urban turfgrasses (i.e., warm-season turfgrass (WT) dominated by C
4 plant species(in photosynthesis, CO
2 is fixed as three-carbon compounds and four-carbon compounds) and cool-season turfgrass (CT) and shade-enduring turfgrass (ST), both dominated by C
3 plant species (in photosynthesis, CO
2 is fixed as three-carbon compounds)) at the Urban Ecosystem National Observation and Research Station, Beijing. The measurements were performed by a static opaque chamber method combined with gas chromatography analysis. Our results showed that across the experimental period, soil CO
2 emissions and soil CH
4 uptakes from all urban turfgrasses exhibited comparable seasonal patterns. Soil CO
2 emissions from urban turfgrasses were positively correlated with soil temperature and soil water content, and their combined effects could explain approximately 77%–87% of the variations in soil CO
2 emissions. In contrast, the variations of soil CH
4 uptake were mainly regulated by soil water content. The soil CH
4 uptake was negatively correlated with soil water content. Over the annual scale, the cumulative soil CO
2 emissions for all urban turfgrasses were 12.1–15.2 t C ha
−1 a
−1, and annual CH
4 uptakes were 3.71–4.27 kg C ha
−1 a
−1. Generally, low temperatures during the nongrowing season usually reduce soil CO
2 emissions and CH
4 uptakes by inhibiting the related microbial activities. However, our results revealed that total soil CO
2 emissions and CH
4 uptakes across the nongrowing 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, WT exhibited significantly higher annual soil CO
2 emissions but lower annual soil CH
4 uptakes compared with CT and ST. This difference was mainly related to the differences in vegetation characteristics and soil properties among the turfgrasses. Overall, our findings suggest that in the context of substantially increasing use of various urban turfgrasses accompanying rapid urbanization, the conscious planning and design of C
3-related urban turfgrasses may help reduce the soil–atmosphere exchanges of CO
2 and CH
4, thereby contributing to mitigating climate change.