杉木和米槠凋落叶DOM对土壤碳矿化的影响

DOM(Dissolved organic matter)是土壤微生物呼吸的重要底物,凋落物淋溶的DOM对土壤碳矿化具有重要影响。选择中亚热带地区具有代表性的杉木(Cunninghamia lanceolata)和米槠(Castanopsis carlesii)凋落叶作为研究对象,通过两个月的短期室内培养,把不同凋落叶浸提出的DOM添加到培养瓶中,定期测定土壤碳矿化速率,计算土壤碳累积矿化量,探讨两种等浓度等量DOM添加对土壤碳矿化的影响,并分析DOM化学性质在土壤碳矿化过程中的重要性。结果表明:米槠凋落叶浸提得到的DOC(Dissolved organic carbon)和DON(Dissolved organic nitrogen)浓度均显著高于杉木凋落叶的(P0.05),而杉木凋落叶浸提得到的DOM的UV吸收值(SUVA_(254))和HIX(Humification index)均显著低于米槠凋落叶的(P0.01)。添加等浓度等量杉木和米槠凋落叶DOM到土壤中均显著增加了土壤碳矿化速率,在第1天内分别比对照高198%和168%,3d后下降到61.8%和44.1%,14d后基本处于平稳状态,表明外源有机物添加对土壤碳矿化的前期影响较大。培养过程中,添加杉木和米槠凋落叶DOM的土壤碳矿化累积量均能采用双因素指数模型进行拟合(r~2=0.99),但添加两者凋落叶DOM后土壤碳矿化累积量没有显著差异。

Effects of dissolved organic matter from Cunninghamia lanceolata and Castanopsis carlesii leaf litter on soil C mineralization

The leaching of dissolved organic matter (DOM) from leaf litter, and the subsequent supply of an available carbon pool for microbial growth, can be important factors regulating forest C mineralization. Field studies have shown that with increasing DOM, soil respiration rates increase observably. Numerous studies have assessed the difference of dissolved organic C (DOC) and the C chemistry of solubility during leaching of DOM from different litters. The chemical structure of DOM and the complexity of its molecules were found to correlate with C mineralization. Our objectives were to investigate how differences in chemistry of DOM from Cunninghamia lanceolata and Castanopsis carlesii leaf litter affected soil CO₂ fluxes in laboratory incubations. Mineral soils from a depth of 0-10 cm from a 39-year-old C. carlesii plantation forest in Sanming, Fujian, China were incubated for 2 months after adding the same concentrations and amounts of DOM from C. lanceolata and C. carlesii leaf litter. CO₂ production was continuously measured during 59 days of laboratory incubation, and soil CO₂ evolution patterns were determined by fitting the double exponential model (r²=0.99). Results showed that: (1) C chemistry varied significantly between DOM from C. lanceolata and C. carlesii leaf litter (P < 0.05). UV and fluorescence spectra of DOM from C. lanceolata leaf litter were lower than those of C. carlesii leaf litter, which suggested that DOM from C. lanceolata leaf litter has a lower content of aromatic C. (2) Following additions of DOM from C. lanceolata and C. carlesii leaf litter to soils, rates of C mineralization increased by 198% and 168%, respectively, decreased to 61.8% and 44.1%, respectively, by day 3 and then decreased progressively. This indicated that an increase in soil C mineralization induced by the addition of external DOM to soil was short-term. (3) There was no significant difference in the cumulative mineralized C between the addition of DOM from C. lanceolata and C. carlesii leaf litter. Further research should be done to investigate the reasons for this lack of a significance difference.