Dynamic Characteristics of Soil Respiration in Park Green Spaces in Qingdao City

Urban green spaces play an essential role in maintaining the carbon cycle and mitigating climate change in urban ecosystems. In order to gain more carbon sinks from urban green ecosystems, it is essential to determine the carbon sequestration statuses and soil respiration rates of dominant green spaces, especially park green spaces. However, in comparison to natural ecosystems, the dynamic characteristics of soil respiration in artificial park green spaces remain unclear. This study investigated the soil respiration rates for three forest communities (dominated by Prunus serrulata var. lannesiana, Cedrus deodara, Ginkgo biloba, respectively), a shrub community (dominated by Aucuba japonica var. variegata) and a lawn community (dominated by Poa pratensis) in the Qingdao Olympic Sculpture and Culture Park. We used the CRIAS-3 portable photosynthesis system in combination with the SRC-1 soil respiration chamber to measure the soil respiration rate from July 2022 to June 2023 and analyzed the dynamic variations in the soil respiration rate for these specific plant communities. Our results showed that the diurnal variation in soil respiration presented a unimodal curve for the five plant communities, and it peaked at midday or in the early afternoon. They also exhibited a significant seasonal difference in the soil respiration rate, which was characterized by higher rates in summer and lower rates in winter. The lawn community exhibited significantly higher soil respiration rates compared to the woody plant community. The mean annual soil respiration rate (RS) was, respectively, 2.88 ± 0.49 µmol·m−2·s−1, 1.94 ± 0.31 µmol·m−2·s−1, 1.43 ± 0.21 µmol·m−2·s−1, 1.24 ± 0.14 µmol·m−2·s−1 and 1.05 ± 0.11 µmol·m−2·s−1 for the lawn community, Ginkgo biloba community, Prunus serrulata var. lannesiana community, shrub community and Cedrus deodara community. The soil temperature at a 10 cm depth (T10) accounted for 67.39–86.76% of the variation in the soil respiration rate, while the soil volumetric water content at a 5 cm depth (W5) accounted for 9.29–44.01% of the variation for the five plant communities. The explained variance for both T10 and W5 ranged from 67.8% to 87.6% for the five plant communities. The Q10 values for the five different communities ranged from 1.97 to 2.75. Based on these findings, this paper concludes that the factors influencing the soil respiration process in urban green spaces are more complicated in comparison to natural ecosystems, and it is essential to comprehensively analyze these driving factors and key controlling factors of soil respiration across urban green spaces in future studies.