CO 2 Flux Characteristics of Different Plant Communities in a Subtropical Urban Ecosystem

Shanghai, China, is a city that is relatively representative of various cities in China due to its geographical location and socio-economic dynamics. The role of urban vegetation in the carbon cycle of urban developments in these types of cities is now being studied. We focus on identifying which urban plant community types have a greater influence on CO 2 flux in cities, thus providing a scientific basis for low-carbon urban greening. Based on the eddy covariance (EC) observation system, ART Footprint Tool, plant inventory, and ecological community classification, we show that the CO 2 flux characteristics of different plant communities vary temporally. The carbon sink duration during summer was the longest (up to 10 h) and the carbon sink duration was the shortest during winter (7.5 h). In addition, we discovered that the CO 2 flux contribution rates of different plant community types are distinct. The annual average CO 2 contribution rates of the Cinnamomum camphora - Trachycarpus fortunei community and the Metasequoia glyptostroboides + Sabina chinensis community are 11.88% and 0.93%, respectively. The CO 2 flux contribution rate of the same plant community differs according to season. The CO 2 contribution rate of the Cinnamomum camphora - Trachycarpus fortunei community exhibits local maxima during winter and summer, with a maximum difference of 11.16%. In contrast, the Metasequoia glyptostroboides + Sabina chinensis community has a CO 2 contribution rate of 0.35% during the same period. In general, summer is the season with the lowest CO 2 flux contribution rate of plant communities, and winter is the season with the highest CO 2 flux contribution rate. However, the Cinnamomum camphora + Salix babylonica community and the Cinnamomum camphora + Sabina chinensis community present the opposite pattern. Finally, the diurnal variation characteristics of CO 2 flux in different communities have the same trend, but the peak values differ significantly. Overall, daily CO 2 flux peak value of the Metasequoia glyptostroboides community and the Cinnamomum camphora - Trachycarpus fortunei community indicate that these two plant communities exhibit a strong capacity for CO 2 absorption in the study area. According to these research results, urban greening efforts in subtropical climates can increase the green space covered by the Cinnamomum camphora - Trachycarpus fortunei and the Metasequoia glyptostroboides community types when urban greening, so as to appropriately reduce the CO 2 emitted into the atmosphere.