【目的】研究可溶性有机物( DOM)输入对森林土壤 CO2排放及微生物群落的影响，为探讨 DOM 在森林生态系统碳循环中的作用提供依据。【方法】设置添加米槠凋落叶DOM、杉木凋落叶DOM、米槠枯死根DOM、杉木枯死根 DOM 及添加去离子水(对照)处理，通过36 h短期室内培养，研究添加米槠及杉木凋落叶和枯死根 DOM 后土壤 CO2排放速率最大值出现的时间及对土壤微生物群落的影响。【结果】无论米槠还是杉木，其凋落叶 DOC 含量均显著高于枯死根 DOC含量，而凋落叶 DOM 的腐殖化指数( HIX)则显著低于枯死根 DOM 的 HIX，添加米槠枯死根 DOM 和杉木枯死根 DOM 的土壤 CO2排放速率在第2 h达到最大值，分别是对照的7.3和8.3倍，在24 h 时则降低至最大值的78.9%和66.3%；而添加米槠凋落叶 DOM 和杉木凋落叶 DOM 的土壤 CO2排放速率在12 h时达到最大值，分别是对照的20.6和13.2倍，在24 h 时则分别降低至最大值的84.0%和53.1%；磷脂脂肪酸( PLFA)分析结果显示，土壤添加米槠凋落叶 DOM 后革兰氏阳性细菌、革兰氏阴性细菌、放线菌和真菌的 PLFAs含量显著低于土壤添加杉木凋落叶 DOM 的27%，38%，46%和41%(P＜0.05)；土壤添加米槠枯死根 DOM 后革兰氏阳性细菌、革兰氏阴性细菌和真菌 PLFAs 含量显著低于添加杉木枯死根 DOM 的21%，21%和22%( P ＜0.05)；培养36 h时，添加米槠凋落叶 DOM 的土壤和对照土壤中 G+∶G－(革兰氏阳性细菌∶革兰氏阴性细菌)高于培养前，但添加米槠凋落叶 DOM 的土壤中真菌∶细菌低于培养前，这与其他处理的结果相反，表明添加不同来源 DOM 对土壤微生物群落的影响不一致。【结论】外源添加 DOM 后土壤 CO2排放速率最大值的出现时间由外源添加 DOM 的组成和化学性质决定，而且外源添加 DOM 显著影响土壤微生物的群落组成。%Objective]DOM ( dissolved organic matter) is an important labile carbon source in soil,and can be an important factor regulating CO2 emission of forest soil. This study will improve understanding of the role of DOM on forest C cycle.[Method]We added DOM from leaf litter and dead roots of Cunninghamia lanceolata and Castanopsis carlesii to soil to examine the effects of carbon inputs on soil CO2 efflux and microbial community composition by phospholipid fatty acid ( PLFA) analysis through laboratory incubations for 36 hours. The treatments were as follows:soil with DOM from C. carlesii leaf litter,soil with DOM from C. lanceolata leaf litter,soil with DOM from C. carlesii dead root,soil with DOM from C. lanceolata dead root,and a control ( soil with deionized water) . Mineral soil (0 -10 cm) was from an 11-year-old C. lanceolata plantation in Sanming of Fujian Province,China. Carbon mineralization was determined using CO2 respiration method.[Result]The contents of dissolved organic carbon ( DOC) from leaf litter were much higher than those from dead roots, and the humification index ( HIX ) values of the DOM were opposite. The maximum rates of C mineralization occurred in 2 hours following addition of DOM from dead roots of C. lanceolata and C. carlesii,and were 7. 3 and 8. 3 times higher than that of control respectively,then decreased to 78. 9% and 66. 3% of the maximum values by 24 hours. In contrast,the maximum rates of C mineralization were in 12 hours following addition of DOM from leaf litter of C. lanceolata and C. carlesii,and the magnitudes were 20. 6 and 13. 2 times that of control respectively,then decreased to 84. 0% and 53. 1% of the maximum by 24 hours. PLFA analysis showed that the contents of gram-positive bacteria, gram-negative bacteria,actinomycetes and fungi in soils added with DOM from C. carlesii leaf litter were 27%,38%, 46% and 41% lower than those of soils added with DOM from C. lanceolata leaf litter,respectively (P < 0. 05). Compared to soils added with DOM from dead roots of C. lanceolata,the contents of gram-positive bacteria,gram-negative bacteria and fungi were 21%,21% and 22% lower in soils added with DOM from dead roots of C. carlesii,respectively (P<0. 05). After 36 h incubation,the ratios of gram-positive bacteria to gram-negative bacteria in soils added with DOM from C. carlesii leaf litter and the control were higher than those in untreated soil,while compared to untreated soil,the ratio of fungi to bacteria was lower following additions of DOM from leaf litter of C. carlesii. [Conclusion]There was significant difference in the microbial community composition following additions of DOM from various sources,and the maximum rates of C mineralization following addition of DOM depended on the quantity and quality of DOM.
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