杉木和米槠凋落叶DOM对土壤碳矿化的影响

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

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(P<0.05),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(P<0.01)。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。

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 CO2evolution 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.