Analysis on the temporal variation of soil CO2 flux and its response to the environmental factors in Haikou urban lawn—A case study of the south campus of Hainan Normal University

To explore the change characteristics of soil CO2 flux and its response to air temperatures, soil temperatures, soil moistures and other environmental factors, the soil respiration rates of tropical urban lawn ecosystems were measured by using the LI-8100A Soil CO2 Flux System, and meanwhile air temperatures, soil temperatures at 5 cm and soil moisture 0-10 cm in depth were monitored from November of 2013 to October of 2014. The results showed that: 1) Daily variation of soil respiration was single peak curve. The peaks usually occurred at 09:00-16:00, and the time when peak values generally appeared were different in different months and weather conditions. Yearly variation of soil respiration was also a single peak curve. The mean daily soil respiration rate was 0.86 to 4.27 μmol·(m2·s)-1, with the maximum in June, and the minimum in December. 2) There was a significant positive correlation between soil respiration rate and air temperature and soil temperature. However, the relationship between the CO2 flux and soil volumetric water content was more complex, and the correlation was not significant. 3) Rainfalls had complicated effects on soil respiration. A light rain didn’t significantly change soil respiration, but a heavy rainfall could have an obvious extrusion effect on soil CO2 flux. At the early stage of a heavy rainfall process, soil respiration rate increased with the increase of rainfall, however, continuous rainfall could increase the soil moisture, and rainfall became an important factor limiting soil respiration.