季节性冻融对亚高山冷杉林土壤微生物数量的影响

Effects of Seasonal Freeze-Thaw Cycles on Quantity of Soil Microbes in the Subalpine Fir Forest

以川西亚高山地区分布范围最广和面积最大的冷杉林为研究对象,采用对照处理试验和动态采样分析相结合的研究方法,研究冻融事件对高寒森林土壤微生物数量的影响。结果表明:经过一个季节性冻融后,土壤细菌和放线菌数量显著降低,真菌数量明显增加。在自然环境梯度下,土壤细菌和真菌数量随海拔降低基本呈持续升高的变化趋势,放线菌数量则随海拔的降低而降低。腐殖质层(AL)、淀积层(BL)和母质层(CL)的微生物数量呈现不同的变化规律,海拔3298m的AL,CL土层细菌数量分别比3582m的AL,CL增加4.2%和7.0%,BL土层细菌数量降低了0.6%;海拔3023mAL,BL和CL土层细菌数量分别比3298m的相应土层增加11.5%,3.5%和2.1%。真菌数量在海拔3298m的AL,BL和CL分别比3582m的AL,BL和CL土层增加10.5%,10.3%和16.4%;3023m的AL,BL和CL分别比3298m的相应土层增加2.4%,1.7%和3.5%。放线菌数量在海拔3298m的AL土层比3582m的增加0.7%,BL和CL土层分别降低5.9%和13.9%;3023m的AL和BL土层分别比3298m增加5.2%和5.2%,CL土层降低12.4%。上述结果和室内模拟试验基本一致。同时,季节性冻融作用循环后,土壤真菌与细菌比值有所升高,这说明不同的微生物类群对季节性冻融循环的响应存在很大的差异,这种差异可能是季节性冻土区生态系统维持的重要生态学机制。

Fir（Abies faxoniana） distributes widely in the alpine and subalpine region of western Sichuan. To understand effects of freeze-thaw events on soil microbial community, microbial number was investigated monthly in a fir forest, employing the method of lab freeze/thaw cycles in combination with field soil sampling. Bacterial and actinomycete number in soil decreased and fungal count increased after a seasonal freeze-thaw season cycle. Bacterial and fungal counts increased with the decreased altitude, while actinomycete count decreased with the decreased altitude. Different microbes had various change pattern in numbers with altitude in humus layer（AL）, illuvial laYer（BL） and parent material layer（CL）. Compared with the 3 582 m altitude, bacterial count in the AL and CL at the 3 298 m altitude increased 4.2% and 7.0%, respectively, but that in the BL decreased 0.6%. Meanwhile, bacterial count increased 11.5% , 3.5% and 2. 1% in the AL, BL and CL at the 3 023 m altitude in comparison with the 3 298 m altitude, respectively. Fungi count in the AL, BL and CL increased by 10. 5% , 10. 3% and 16.4% at the 3 298 m altitude in comparison with 3 582 m altitude, respectively, while it increased by 2. 4% , 1.7% and 3.5% at the 3 023 m altitude in comparison with 3 298 m altitude, respectively. Actinomycete count in the AL at the 3 298 m altitude increased by 0. 7% than that at the 3 582 m altitude, but decreased 5.9% and 13.9% in the BL and CL. In the AL and BL, it increased 5.2% and 5.2% respectively at the 3 023 m altitude than that at the 3 298 m altitude, while in the CL it decreased 12. 4%. These results were in agreement with the simulation freeze/thaw cycle experiment in lab. The results also revealed that the seasonal freeze-thaw cycle increased the ratio of soil fungi to bacteria. These results demonstrated that different microbial groups responded differentially to the seasonal freeze- thaw cycle, which may be an important ecological mechanism for maintaining the seasonal frozen ecosystem.