| Dissolved organic matter(DOM)is considered as a sensitive indicator of SOM change and an important component of terrestrial biogeochemical cycling.It is closely related to carbon accumulation in soils and nutrient availability to microorganisms and plants.The sorptive interaction of DOM in soil is a relatively reactive and dynamic process,influencing the carbon cycle and the fate of organic and other inorganic species in the forest ecosystem.DOM is sensitive to the changes of la(?)use,and plant species can affect soil carbon dynamic.Also different tree species can lead to changes in litter quality inputs.To get some insight into the dynamic turnover of DOM in ecosystem,we studied the adsorption characteristics and changes in chemical structures of DOM from litters of castanopsis kawakamiiand pinus taiwanensis in soils of coniferous forest and broad leaved forest such as castanopsis kawakamii natural forest and pinus taiwanensis natural secondary forest.The research results showed that:(1)IM adsorption equation was the best fit to the adsorption characteristics of DOM from these two plants in soils among various adsorption models.And DOM adsorption was effected by the initial concentration of DOM.(2)The adsorption did not react easily in all treatments.In addition,the enthalpy changes were negative indicated that all adsorption reactions were exothermic.As the increase of temperature,the adsorption quantity of DOM decreased.Furthermore,the adsorption data could be satisfactorily described with the pseudo-second-order kinetic model.And some physical forces involved during the process of adsorption and intermolecular interaction existed in the adsorbed groups.At the initial stages,the adsorption reactions were fairly quick,and then slowed down.As the consequence of this,the adsorption of DOM in soils could reach equilibrium in 360 min.Besides,the adsorption rate could be affected by intra-particle diffusion,but it was not the only dominant factor.And the adsorption kinetics of different DOM in two types of soils conformed with Elovich model.(3)The chemical structures of dissolved organic matter were analyzed by ultraviolet-visible spectra,fluorescence spectra and fourier infrared spectra,the results showed that the chemical structures of DOM from pinus taiwanensis were more condensed and humified.All soil samples adsorbed the aromatic compounds with high degree of condensation,phenols and carboxy groups.However,aliphatics,alcohols and alkanes with lower adsorption activity tended to release to the solution from soils.Moreover,soils adsorbed more components of DOM derived from castanopsis kawakamii,including aromatics,condensed compounds and other labile and low molecular weight compounds.But soils had strong selecting adsorption character for DOM from pinus taiwanensis.(4)Fe and Al oxides in soils could provided available adsorption sites that aromatics and carboxyl groups of DOM could be adsorbed by complexation between these metals and organic ligands.Clay composition improved adsorption of DOM by Van der Wals and cation bridge.The content of soil organic matter inhibited DOM adsorption and the value of SOC/?(Feo+Alo)affected the affinity between soils with DOM too.If the saturation of adsorption site was high,DOM could desorb from soils.In conclusion,DOM from different plants had weak adsorption in two types of forest soils in subtropical China.Besides,DOM was susceptible to lose due to high temperature in the area.The composition of soil DOM from castanopsis kawakamii natural forest was relatively simple compared to pinus taiwanensis secondary natural forest and its soil carbon pool was more liable.While soil DOM of pinus taiwanensis secondary natural forest was refractory and the turnover of carbon pool was comparatively slow. |
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