Organic Matter Source And Degradation As Revealed By Molecular Biomarkers

In recent years,frequent disturbances in human activities such as overgrazing,farming,deforestation,and afforestation have significantly changed the carbon balance between soil and atmosphere,thereby slowing or accelerating global climate change.Soil is the most important and most active carbon stock in terrestrial ecosystems.Therefore,the global carbon cycle has a close relationship with the turnover cycle of SOM.The study of the soil carbon cycle will be the most important part of the global carbon cycle.It plays an important role in the regulation of global climate change and is also a key link that directly or indirectly affects the recycling of other elements.In this study,two soil samples?BJ and YS?with different tillage activities were collected and compared for their SOM composition,distribution characteristics and degradation status by biomarker method to analyze the effects of human tillage activities on SOM.The total carbon content of BJ decreased from 1.75%?YS?to 1.58%?BJ?,indicating that the content of SOM in BJ decreased significantly.The content of aliphatic acids increased from 127.22 mg g^-1 C?YS?to345.09 mg g^-1 C?BJ?,the long chain alkanes C29 and C31,and the undetected alkanes in the plantain leaves and stems appeared in BJ,suggesting that a large quantity input of plantain fractions.The ratio of C/N decreased from 14.94?YS?to 11.47?BJ?,as well as the ACL_FA value of alkanes and the ratio of 3,5-DHBA/V increased from 23.87?YS?to 24.97?BJ?and from 0.52?YS?to 0.64?BJ?,indicating that the degradation status of BJ was higher than that of YS.Short-chain alkanes and the V class of lignin might derive from the organic-mineral complexes in the original soil.The lipids extractable by organic solvent are important components in soil organic matter?SOM?,and were used to trace the sources and degradation of SOM.Previous studies have suggested soil mineral protection of lipids,which might decrease the extraction efficiency of some lipid compounds by organic solvents.This study therefore applied a mild acid treatment to remove most of the reactive mineral particles without altering SOM chemical structures in 10%HF/1M HCl?1:4 w:v?.Based on lipid biomarker information obtained through before and after acid treatment,we can observe that,after removal of active minerals,organic solvents on the lipid extraction efficiency increased significantly.This study collected and tested solutions generated during the acid treatment and increased the scientificity to quantitative the amount of lipids.The minerals showed significant differences in the selective protection to different components of lipids.In this study,the amount of protected n-alkanoic acids in the range of 73⁸5%,the amount of protected n-alkanol in the range of 41⁶2%,the amount of protected n-alkanes in the range of26⁴6%.After the vegetation was replaced,The increased alkanoate and alkane in soil input by the plant tissues of plantain directly,and the alkanols probably input by the hydrolysis of wax esters.Under the interference of man-made tillage activities,the C content in 0-20cm decreased.The results showed that cultivated activities may enhance SOM degradation and accelerate SOM turnover.Understanding SOM behavior in this area will definitely provide important information for soil management and to evaluate carbon cycling in human-affected ecological systems.