| As one part of carbon and nutrient cycling in forest ecosystems, the importance of dissolved organic matter released from soil and forest floor, had been recognized. Dissolved organic carbon is a key fraction of active carbon pool in forest soils and its dynamics (including release and adsorption) will affect function of soils as "source" or "sink" of organic carbon. Also, flux of DOM plays an important role in the recycling of carbon, nitrogen and phosphorus, and in the transport of pollutants. Despite intensive research on dynamics of DOM and its controls in the last decade, there is few information on DOM originated from soils and forest floors in China. In the context, seasonal dynamics and release of DOM through leaching were studied in a natural forest of Castanopsis kawakamii and adjacent monoculture plantations of C. kawakamii and Chinese fir (Cunninghamia lanceolate) in Sanming, Fujian. In addition, impact of hydrological process on the dynamics of DOM was studied in plantations of Schima superba and Chinese fir in Minbei experimental site of water conservation located in Jianou, Fujian. The results showed that:(1) Absorption values of dissolved organic matter (DOM), which released from soils and forest floors invarious forest stands, declined with wavelength in ultraviolet-visible region. UV/VIS absorption spectra of DOM from forest floor showed a peak at around 200 nm, but it is not true for DOM from forest soil. Concentrations of DOC was highly correlated linearly with E200 for the same DOM source, suggesting that the concentrations of DOC can be estimated by E200 of DOM.(2) In 0~100 cm soil layer, the average DOC concentrations of soils from natural forest of C. kawakamii andplantations of C. kawakamii and Chinese fir were 559.8 mg-kg-1, 593.2 mg-kg-1 and 458.9 mg-kg-1 respectively, and occupied 5.33%, 6.81% and 6.16% of those of soil organic carbon. DOC concentrations declined with depth in 0-40 cm soils and increase lightly in depth of 40~100 cm. There was most significant difference in DOC concentration in surface 10cm soils among three forests. The corresponding value in natural C. kawakamii forest was 1310.3 mg'kg-1, being 1.5 and 2.4 times as much as those in plantations of C. kawakamii and Chinese fir.(3) Seasonal trends of DOC concentrations in soils of 0- 10cm and 10-20cm were similar with maximal valuein autumn, while concentrations of DON and DOP peaked in winter. Maximal DOC concentrations in forest floors of different stands all occurred in winter, the values of DON concentration in the L (litter) and F (fragmented) layers was highest in autumn and in summer for H (Humus) layer. For change of concentrations of DOP in forest floors, their maximal values were in winter.(4) Besides volume of leachates, the most significant effect of pH value on releases of DOC, DON and DOPwas found through orthogonal experiment about leaching of DOM. While impacts of water temperature and flow velocity were non-significant In addition, there were significant effects of these factors on DOP release from forest floors, whereas it was not found for released DOC in forest floors. For controls on DON release, the effect of acidity was dominated.(5) Acid rain simulation experiments showed that acidity, soil type and cultivated time affected DOC concentrations of leachates from soils and forest floors highly significantly. High acidity (pH=2.0) accelerated leaching of DOC in soils, while its restraint effect was for DOC in forest floors. Also, there were non-significant impacts of pH values of 3.5 and 5.0 on DOC leaching from soils and forest floors.(6) Exponential function was adapted to concentration changes of DOC from soils and forest floors during processes of static and dynamics leaching. Continuous adsorption experiment using soil (20-40cm) core in series showed that half of DOC concentration declined during leaching through the first soil core except for the samples of C. kawakamii. Further, leaching with original soil cores reflected that DOC was...
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