Characterization Of Soil Organic Matters Replacement And Adsorption By Molecular Markers

In the last twenty years,researchers have reported a series of non-idea interactions between soil organic matter?SOM?and organic contaminants such as nonlinear adsorption behavior and competitive adsorption.However,because of inadequate understanding of the heterogeneity of SOM,how to describe and predict the non-idea interaction is still a challenge at present,which makes it a bottleneck for studying behavior and remediation of organic contaminants.Molecular biomarker methods have been widely used and play an important role in understanding the source,composition,maturity and degradation of SOM.This kind of methods would provide new clues for studying the non-idea interactions between SOM and organic contaminants.In this study,the distribution and degradation information of molecular biomarkers including extractable-organic solvent lipids?free lipid??alkanoic acids,alkanes,alkanols and steroids?,lignin derived phenols?vanillyl phenols?V?,syringyl phenols?S?and cinnamyl phenols?C??,and benzene-polycarboxylic acids?BPCAs?were obtained by using the methods of continuous extraction of organic solvents,copper oxide?CuO?oxidation of lignin,and nitric acid oxidation,respectively.We first used molecular markers to investigate the protection effects of organic matter?OM?degradation of different plant sources and reactive minerals on OM components?take pine needles?Pinus yunnanensis?and Castanea henryi leaves?Skan?Rehd.et Wils.as an example?.The replacement behavior of SOM in the typical area of human disturbance of Yunnan province was then described based on the modified molecular markers?take Xishuangbanna economic rubber forest and Yuanyang terrace as an example?.In the end,the relationship between SOM heterogeneity and the nonideal interaction of organic contaminants was described using multiterminal molecular markers.The main results of this study are as follows:?1?Molecular markers were used to analyze the effects of different plant origins and mineral on the degradation of OM.The degradation experiments of plants and soils showed that the contents of lignin?VSC?and alkanoic acids in plant tissues all decreased with the degradation.Lignin in the leaves of chestnut is more easily degraded than that of pine needles.In the soil degradation experiments,the contents of lignin and free lipids increased with the occurrence of degradation.In the degradation experiments of vegetation samples with the addition of kaolinite,we found that the degradation of lignin and free lipid were inhibited because of the added kaolinite.This indicates that the interaction between soil particles and OM can be a reason for explaining the stability of the above components.Therefore,the degradation of OM depends not only on plant types but also on soil minerals.?2?The protective effects of active minerals on OM were explored by using molecular markers.In the study of economic rubber plantation and Yuanyang terrace,the content of free lipids?especially alkanoic acids?increased significantly after removal of active minerals.The degradation parameters also changed obviously according to the removal of active minerals,such as the carbon dominance index of alkanes,CPI;the ratio of long chain carbon alkanoic acids?C>20?to short chain carbon alkanoic acids,RLS_AF;the carbon dominance index of alkanoic acids,CPI_AF.Meanwhile,VSC was also observed to be largely released and dissolved especially in Yuanyang terrace with frequent human activities?reduced by 80%?.The lignin degradation parameters showed that the ratio of acid to aldehyde?Ad/Al?_V in V monomer increased,indicating that highly oxidized lignin molecules were released after the removal of active minerals.The stability of these lignin components may be more dependent on active minerals.This phenomenon was further confirmed in the upper and lower layers of Yuanyang terrace after washing(the upper layer rich in organic matter,L_OM;the lower layer rich in inactive minerals,L_NR).In addition,the formation of organic-inorganic complexes was not obviously influenced by the interference of human activities.It was found that the increase of free lipids in the dry land of Yuanyang terrace?TD?was similar to or even slightly higher than that in the soil without human disturbance?NS?.This was mainly due to the introduction of a large number of OM?such as long term application of farmyard manure?and the enrichment of active minerals?such as amorphous ferrite?,which promoted the formation of organic and inorganic complexes.?3?The source and degradation of SOM?Yuanyang terrace and economic rubber forest?under human disturbance were traced by free lipid markers after demineralization.Results showed that alkanoic acids may be derived from the original plants?such as bamboo leaves?and newly planted rubber trees?such as rubber leaves?in the 0,10,60 years old rubber plantation soils,while alkanols and alkanes were mainly derived from the original plants.As the rubber plantation was replaced,the degradation parameters of free lipid markers such as CPI_ALK decreased,indicating that the degradation of OM was accelerated after the rubber plantation replaced the tropical rain forest.In Yuanyang terrace,the high degradation parameters such as RLS_AF and the averaged carbon length ACL values in cultivated soils also indicated that the long-term human disturbance accelerated the degradation of OM.The cultivation in paddy field is more conducive to the preservation of free lipid than that in dry land.Although the source of lignin cannot be changed after demineralization,lots of lignin was washed away.Thereupon,the lignin molecular markers before demineralization were conservatively selected in this study to trace the degradation of lignin under different human interferences.It was found that the values of S/V and C/V in rubber forest soil were far below the corresponding values of local plants,and the lignin degradation parameters?Ad/Al?_V???Ad/Al?_S?were much higher than those of the corresponding plants.This implied that the lignin in the soil underwent significant degradation during decay processes,which may be closely related to the local climate in Xishuangbanna.The S/V value of lignin in TD and TP was significantly greater than 0.6 in the samples from Yuanyang terrace,indicating that the source of lignin in cultivated soil was mainly from angiosperm.The lower S/V value of lignin in NS?about 0.2?was consistent with the local pine species,and the lignin phenol vegetation index?LPVI?further confirmed this result.In addition,the contents of lignin and free lipid decreased with the increasing soil depth.Studies have shown that the degradation degree of lignin and free lipid increased with the increasing soil depth.However,the degradation parameters of this study showed that lignin and free lipid were not degraded obviously.The sources of deep soil and surface soil were similar,indicating that deep soil was beneficial to the preservation of OM.Therefore,the reduction of lignin and free lipid in deep soil was due to fewer sources rather than degradations.?4?Based on traditional chemical characterization methods,molecular markers will be an important supplement to study the adsorption behavior of organic contaminants in soil.Lipids,lignin and black carbon?BC?have important contributions to the adsorption of organic contaminants,especially hydrophobic organic contaminants.The information of molecular markers indicated that a large number of highly oxidized lignin molecules and sugars were released after the removal of active minerals,while BC and free lipid were significantly enriched.The adsorption coefficient K_d of PHE increased two times after acid washing,whereas the K_d value of OFL decreased by three times.Based on the standardization of organic carbon,the K_OC values of PHE were much higher in soil adsorbent after acid treatment,indicating stronger interactions between PHE and SOM.The removal of active minerals led to the decrease of the intercept and slope of the linear relationship between K_d and f _OC of OFL,suggesting a reduced dependence of OFL on minerals and SOM components.These results may be attributed to the release of polar components of SOM?high?Ad/Al?_V ratio?such as sugars and highly oxidized lignin after the removal of active minerals.The dissolution of active minerals may lead to the enhanced migration risks of the ionic organic contaminants,and the migration risks of the hydrophobic organic contaminants can be weakened based on the point of view of the migration of organic contaminants.Nevertheless,more evidences are still needed for further explaination.In conclusion,our study is a coupling of the dynamics changes of SOM and the environmental behavior of organic contaminants.Molecular markers provide useful technical means for recognizing composition and adsorption characteristics of SOM.Future research can be focused on studying the dynamic changes of SOM by using the multimolecular markers in combination with traditional chemical characterization methods,such as the interaction of degradation process with organic contaminants,to provide more basic data for establishing the non-ideal interaction model between SOM heterogeneity and organic contaminants.