Screening Of Eroded Soil Organic Carbon Source Tracers And Their Influence On Source Identification Accuracy

Organic carbon source analysis is an effective way to identify land use types and measure soil erosion effects.However,there are uncertainties in the transport-deposition process of soil organic carbon source signals,which in turn affects the accuracy of the analysis.Therefore,identifying important erosion sources and screening stable and effective organic carbon source signals are key scientific issues to be solved urgently.For this reason,this study takes soil under typical land use types in the red soil hilly area of southern China as the research object,adopts the methods of field sampling and indoor controlled cultivation analysis,based on variance analysis,linear regression analysis,correlation analysis,PARAFAC（Parallel factor analysis）model,Mix SIAR（Mixed Stable isotope analysis in R）analytical model Equal quantitative means to explore the variation characteristics of source signals（source heterogeneity,conservation characteristics）during the mixing process of organic carbon sources,quantitatively calculate the contribution rate of soil organic carbon sources from different sources in mixed end-member of different sources,and clarify the source of organic carbon.The influence mechanism of signal changes on source analysis,explore the identification ability of soil organic carbon source signals under mixed end-member of different sources,and screen effective organic carbon source signals,in order to provide theoretical support for improving the high-resolution analysis method of soil organic carbon sources,and provide theoretical support for the improvement of high-resolution analysis methods of soil organic carbon sources.Provide a scientific basis for optimizing the spatial distribution of regional land use under the influence of erosion-deposition.The main conclusions of the study include:（1）Under ideal conditions,the fluorescence index is not suitable for the source analysis of soil organic carbon,and stable isotopes are relatively stable in the source analysis.Through source heterogeneity analysis,there was no significant difference in the fluorescence index among the source endmembers,but there was a significant difference in the content ofδ¹³C（P=0.0249）.Combined with the mixture conservative analysis,the linear fit of the fluorescence index with the mixture ratio is not high,and the Sm/SD is generally low（Sm/SD<0.1）.Among them,the tryptophan-like component（C2）,the ratio of fluorescent components（C3/C2）,and the fluorescence index（FI,BIX）did not change linearly with the mixing ratio of the source（P>0.05）;It showed a linear change（P<0.05）,and the linear fit was high（R²>0.85）.By comparing the analytical contribution deviation of the source signal,the contribution deviation of the fluorescence index under different source mixed endmembers is higher,and the contribution deviation of the fluorescence index FI is as high as34.43%;while the contribution deviation ofδ¹³C between different source mixed endmembers is low.（<10%）,indicating that its analysis accuracy is high and it is relatively stable in source analysis.（2）Under light conditions,stable isotope abundance changes are small,but have a great impact on the accuracy of analysis.Theδ¹⁵N value showed a trend of first enrichment and then depletion with the light culture time,and the decline range was large（0.07%-1.48%）.The fluctuation ofδ¹³C value under light conditions is not significant.The accuracy of source analysis usingδ15N is greatly affected by lighting conditions.For the mixed end-member of A-G,G-W,and A-W sources,with the increase of culture time,the results of source analysis usingδ¹³C alone are more stable.The addition ofδ¹⁵N increases the degree of curve fluctuation and reduces the accuracy of source analysis results.For the S-A mixed end-member,the results obtained byδ¹³C andδ¹⁵N analysis seriously deviate from the normal contribution range,and the results obtained byδ¹³C analysis overestimate the contribution of sugarcane field sources,whileδ¹⁵N underestimates the contribution of sugarcane field sources.（3）Under flooding conditions,the abundance ofδ¹³C changed little,while the abundance ofδ¹⁵N fluctuated significantly.The accuracy of source analysis of bothδ¹³C andδ¹⁵N was affected by flooding conditions.The abundance ofδ¹³C in the mixed endmembers of A-W source and G-W source basically did not change,while the abundance ofδ¹³C in the mixed end-member of A-G and S-A became lower.In contrast,theδ¹⁵N value fluctuates greatly under the influence of flooding conditions,with a decrease range of 13.93%-82.01%.The results of accurate analysis ofδ¹³C sources under mixed endmembers of different sources are affected to different degrees by flooding conditions.Under the mixed endmembers of A-W（tillage-forest）sources and A-G（tillage-grass）sources,the accuracy of the source analysis ofδ¹³C is more accurate.The influence of flooding conditions is small（the contribution deviation is less than 10%）,while the mixed end-member of G-W（grass-forest）source and S-A（gan-tillage）source are greatly affected by flooding conditions.The accuracy of source analysis usingδ¹⁵N is greatly affected by flooding conditions,and the contribution deviation under mixed endmembers of all sources is greater than 20%.To sum up,based on the analysis of the heterogeneity,conservation,and contribution bias of organic carbon sources,the fluorescence index is not suitable for the source analysis of soil organic carbon,and stable isotopes are more accurate in the source analysis of soil organic carbon,but The accuracy of source analysis is affected by lighting and flooding conditions.Compared withδ¹⁵N,δ¹³C is more suitable for the source analysis of soil organic carbon.