蚯蚓和三叉苦对亚热带人工林土壤N2O和CH4通量的短期效应

在广东鹤山大叶相思(Acacia auriculaeformis)人工林内设置外来蚯蚓西土寒宪蚓(Ocnerodrilus occidentalis)和乡土植物三叉苦(Evodia lepta)野外控制实验，用静态箱-气相色谱法对土壤N2O和CH4通量进行15 d的原位测定，研究蚯蚓和三叉苦对土壤N2O和CH4通量的影响。结果表明，三叉苦并未明显增加土壤N2O和CH4的通量，而假植物(模拟三叉苦的物理效应)则显著促进了土壤N2O的释放通量。整个实验阶段，蚯蚓效应分别使无植物对照和三叉苦处理土壤N2O通量增加了26.7%和66.3%，而在种假植物条件下，添加蚯蚓使土壤N2O通量降低了39.7%；同时，蚯蚓效应使对照处理土壤CH4吸收通量增加了10.3%，使假植物处理土壤CH4吸收通量降低了90.6%，而使三叉苦处理土壤CH4释放通量增加了301.8%。可见，蚯蚓能够促进人工林土壤N2O释放；同时促进人工林土壤从CH4“汇”向“源”转变。三叉苦的物理过程促进土壤N2O的释放，而三叉苦的生物过程抑制土壤N2O的排放。如何减缓人工林中土壤N2O和CH4的排放，必须综合考虑植物物理过程、生物过程以及蚯蚓对土壤N2O和CH4排放过程影响的独立效应和交互效应。

Short-term Effects of Earthworm and Evodia lepta on Soil N2O and CH4 Fluxes in a Subtropical Plantation

A field experiment was conducted in Acacia auriculaeformis plantation at the Heshan Hilly Land Interdisciplinary Experimental Station to investigate the short-term effects of earthworm (Ocnerodrilus occidentalis) and plant (Evodia lepta) on soil N2O and CH4 fluxes. The N2O and CH4 fluxes were measured in situ using the static chamber technique and analyzed with gas chromatogram for 15 days. The results showed that E. lepta did not significantly enhance soil N2O and CH4 fluxes, but fake plant (to simulate the physical effects of E. lepta) significantly increased soil N2O emissions (P<0.05). Earthworm promoted soil N2O fluxes in both control (without plant or fake plant) and the treatment with E. lepta by 26.7% and 66.3%, respectively. Contrary to our hypothesis, the effects of additional earthworm on soil N2O fluxes were not always positive. In the treatment with fake plant, the earthworm effects decreased the N2O fluxes by 39.7%. Meanwhile, the earthworm increased the CH4 uptake by 10.3% in control, but decreased the CH4 uptake by 90.6% in the treatment with fake plant and decreased CH4 uptake by 301.8% in the treatment with E. lepta. Earthworm addition shifted the soil CH4 from uptake to emission in the treatment with E. lepta and significantly decreased soil CH4 uptake in the treatment with fake plant (P<0.05). The results indicated that earthworm could accelerate soil N2O emission and might even convert CH4 sinks into sources in the A. auriculaeformis plantation. The physical effect of E. lepta facilitated soil N2O emission, while the biological processes of E. lepta might suppress soil N2O efflux. No significant correlations between N2O as well as CH4 fluxes and hydrothermal factors were found in the present study. In order to reduce the soil greenhouse gas emission, it will be useful to consider both the independent and interactive effects of plant physical processes, plant biological processes and earthworm activity on the efflux and influx of soil greenhouse gases.