DOM对米槠次生林不同土层土壤微生物呼吸及其熵值的影响

可溶性有机质(Dissolved organic matter,DOM)作为土壤可溶性有机碳的重要来源,进入土壤之后通过改变土壤微生物数量和活性影响土壤矿化。DOM输入对土壤微生物呼吸和熵值的研究多集中在表层土壤,但对深层土壤微生物呼吸和熵值的影响关注较少。通过室内培养实验(120 d)研究米槠(Castanopsis carlesii)鲜叶DOM添加对表层土壤(0—10 cm)和深层土壤(40—60 cm)微生物呼吸及其土壤代谢熵和微生物熵的影响,为揭示DOM输入对亚热带森林土壤碳过程的影响提供理论依据。结果表明,在培养第1天,添加DOM的表层和深层土壤CO_2瞬时排放速率均显著高于对照(P0.001),分别是对照(不添加DOM)的3.58倍和6.93倍,之后显著下降。就累积排放量而言,无论是DOM添加处理还是对照,表层土壤显著大于深层土壤;在米槠鲜叶DOM添加后,表层土壤累积排放量显著大于对照的表层土壤(P0.001),但DOM添加处理深层土壤累积排放量与对照的深层土壤无明显差异。就微生物生物量碳而言,表层土壤微生物生物量碳含量在培养期间显著大于深层土壤。在整个添加DOM培养期间,表层土壤微生物生物量碳含量显著大于表层对照土壤,深层土壤微生物生物量碳含量显著大于深层对照土壤(第3天除外)。培养结束时(120 d),米槠鲜叶DOM添加处理下,表层土壤和深层土壤有机碳含量与第3天相比分别减少26%和19%。米槠鲜叶DOM添加处理后的深层土壤代谢熵(qCO_2)显著低于对照的深层土壤和DOM添加处理的表层土壤qCO_2(P0.001),说明外源DOM进入深层土壤后提高了土壤微生物对碳的利用效率。米槠鲜叶DOM添加处理后的深层土壤微生物熵是培养第3天的1.58倍,显著大于培养初期(P0.05),而DOM添加处理的表层土壤、对照的表层土壤与深层土壤的微生物熵分别是培养第3天的68%、79%和21%,说明DOM添加提高了深层土壤质量。

Effects of dissolved organic matter addition on soil microbial respiration and quotient values in a secondary Castanopsis carlesii forest

Dissolved organic matter (DOM) as an important source of soil dissolved organic carbon, it affects soil mineralization through changes of soil microbial quantity and activity. However, many reports about the DOM impact on soil microbial respiration and quotient focused on surface soil, its effect on deep soil is less paid attention. A 120-day incubation experiment was done to reveal the effects of DOM from Castanopsis carlesii fresh leaf on soil microbial respiration and quotient values of surface soil (0-10 cm) and deep soil (40-60 cm) in a secondary Castanopsis carlesii forest. It will provide some knowledge about the role of DOM input on soil C process in subtropical forests. The results showed that on the first day, instantaneous CO₂ emission rates of surface and deep soils after DOM addition were significantly higher than those in control treatments (P < 0.001), being 3.58 and 6.93 times of the control, respectively, but after that CO₂ emission rates reduced significantly. In DOM added treatment or control, the cumulative CO₂ emission in surface soil was significantly greater than that in the deep soil. After adding DOM, the cumulative CO₂ emissions from surface soil was significantly higher than from the control (P < 0.001). However, no obvious difference for the cumulative CO₂ emission from deep soil between DOM addition and control treatments was found. Microbial biomass C (MBC) content of surface soil during the incubation period was significantly greater than that in deep soil. The MBC content in surface soil under DOM addition treatment was higher than that in control treatment during the incubation period. The same trend was for the deep soil except for the third day. Under DOM addition treatment, soil organic C contents in surface and deep soils on the 120th day were 26% and 19% less than those on the third day, respectively. At the end of incubation, the soil metabolic quotient (qCO₂) in DOM added deep soil was significantly lower than those in deep soil of the control and DOM added surface soil (P < 0.001), indicating the increase of carbon use efficiency after DOM addition into deep soil. After incubation for 120 days, microbial quotient of DOM added deep soil was 1.58 times than that of the initial period (the 3rd day). In contrast, soil microbial quotients of surface soil under DOM added treatment and surface and deep soils of control treatment were 68%, 79% and 21% on the 3rd day, respectively. This showed that DOM addition was beneficial for the improvement of the quality of deep soil.