Short-term impacts of Ocnerodrilus occidentalis and Evodia lepta on soil CO2 fluxes in an Acacia auriculaeformis plantation in Guangdong Province, China.
Aims: The exotic earthworm Ocnerodrilus occidentalis is widespread in plantation and abandoned areas in Guangdong, China. Its distribution is gradually expanding due to insensitivity to temperature, moisture, soil pH and soil organic matter. Study of the processes of soil carbon dynamics affected by O. occidentalis can provide new insights for the reduction of soil carbon emissions. Our objective was to investigate the short-term impacts of this exotic earthworm and native plants on soil CO2 fluxes. Methods: A field experiment was conducted in an Acacia auriculaeformis plantation at the Heshan Hilly Land Interdisciplinary Experimental Station. CO2 fluxes were measured for 15 days in situ using the static chamber technique and analyzed with a gas chromatogram. Important findings: Both O. occidentalis and Evodia lepta had no significant effects on soil CO2 fluxes. The effects of plant physical processes (such as shading), plant biological processes (such as secretion of root exudates) and overall processes on soil CO2 fluxes were -32.1%, 40.9% and 8.8%, respectively, in treatments without earthworm addition, and were -7.2%, 30.7% and 23.5%, respectively, in treatments with earthworm addition. Plant physical processes inhibited soil CO2 emissions, but enhanced the effects of the earthworm on soil CO2 emissions (increased by 39.3%). Plant biological processes enhanced soil CO2 emissions, but inhibited the effects of earthworms on soil CO2 emissions (decreased by 23.5%). Earthworm addition showed almost no significant impacts on most soil physical and chemical properties, but enhanced the activity of soil bacteria and led to a closer correlation between soil CO2 fluxes and soil physical and chemical properties. Meanwhile, earthworm activities changed the relationships between soil CO2 fluxes and soil hydrothermal factors. Hence, soil CO2 fluxes were not only influenced by hydrothermal factors, but also regulated by above- and below-ground biological processes. Therefore, it was difficult to determine an effective way to reduce forest soil CO2 emissions if only the amount of soil CO2 is considered and the impact of plant biological processes on soil CO2 fluxes is ignored. In order to reduce soil carbon efflux, it will be useful to note the potential of the independent and interactive effects of plant physical processes, plant biological processes and earthworm activity on soil CO2 flux.