| Litter is an important"link"connecting vegetation–soil complex,and its decomposition is an important link of ecosystem energy and material cycle,which plays an important role in soil carbon and nitrogen cycle and soil biological environment in returned farm Land.To explore the impact of litter decomposition on the dynamic changes of soil carbon and nitrogen in abandoned farm Land and the mechanism of enzyme activity during the decomposition process,the R.pseudoacacia(RP)forest at different recovery stages in the Loess Hilly–gully region was taken as the research object in this study.Combined the field sampling and indoor analysis,we studied the characteristics of litter decomposition,the changes in soil carbon,nitrogen components and soil enzyme activities during the process of litter decomposition.This study is expected to provide a scientific basis for understanding the interaction mechanism between the litter decomposition and the soil of the abandoned farm Land in the Loess Hilly–gully region.The main results are as follows:(1)The decomposition rate of RP litter was high in growing period and low in non–growing period.The release patterns of carbon and nitrogen from litter is different.The decomposition rate of RP litter was the highest(10.40–11.76gy-1)during the middle decomposition period(180–360 days,from April to October),and the lowest(1.48–2.41gy-1)during the late decomposition period(360–540 days,from October to January).The decomposition rate of litter presented the characteristics of rapid decomposition in the growing season,slow decomposition in the non–growing season,rapid decomposition in the early stage of decomposition,and slow decomposition in the later stage.The C content of litter varied from 406.46gkg-1 to 274.65gkg-1,which continues to decrease significantly during the decomposition process;the N content of litter significantly decreased during 0–90 days,increases significantly during 90–180 days,and continued to decrease during 180–540 days.The litter carbon content of RP was continuously released and the litter nitrogen showed the law of leaching–enrichment–release during the decomposition process.(2)During the decomposition process of RP litter,the content of soil carbon and nitrogen components changed significantly,and the litter carbon and nitrogen were significantly correlated with soil carbon and nitrogen components.With the advancement of the decomposition process of litter,STC and SOC content presented a fluctuating characteristic of rising–decreasing–rising–declining.The SIC content of the soil presented an opposite trend with SOC.LOC,DOC and MBC presented a downward–rising–falling trend,and both continue to rise significantly during the peak decomposition period.STN presented a rising–falling–rising–stable change characteristics,SNN,DON and MBN continued to rise significantly during 90–360 days of decomposition,while SAN declined during the peak of decomposition,and increased significantly during270–540 days.During the decomposition process of litter,the decomposition rate of litter and the rate of change of litter C and N all had a strong and significant correlation with the rate of change of soil C and N components,indicating that the decomposition characteristics of litter during the decomposition process of litter can significantly affected the soil carbon and nitrogen components change dynamically.(3)Litter–soil C and N were significantly correlated with microbial biomass C and N contents,and the enzyme activities related to microbial C and N metabolism were significantly correlated with soil C and N components.During the process of litter decomposition,the enzyme activities of?–1,4–glucosidase(BG),?–1,4–N–acetylglucosaminosidase(NAG),leucine arylamidase(LAP)and cellobiohydrolase(CBH)all decreased significantly during the decomposition period of 0–90days,increased significantly during the period of 90–270 days,and then decreased;the activities of peroxidase(PER)and polyphenol oxidase(PPO)continued to increase during the period of 90–360 days.The decomposition rate of litter was significantly correlated with enzyme activity.The C change rate of litter was significantly positively correlated with soil PER and PPO enzyme activities;during the decomposition process,soil temperature and SWC were significantly positively correlated with soil enzyme activity,and p H was a significant negative correlation with enzyme activity.In the process of litter decomposition,STC was significantly positively correlated with CBH and PPO enzyme activities,and soil active organic carbon components were significantly correlated with enzyme activities;STN and organic nitrogen components were significantly correlated with NAG and LAP enzyme activities.Litter–soil C and N were significantly correlated with microbial biomass C and N contents,and the enzyme activities related to microbial C and N metabolism were significantly correlated with soil C and N components.In summary,the decomposition rate and the release characteristics of carbon and nitrogen during the decomposition process of the RP plantation litter were significantly related to the dynamic changes of soil carbon and nitrogen components;the litter–soil carbon and nitrogen were significantly related to the microbial carbon and nitrogen content.The activity of carbon and nitrogen metabolizing enzymes was significantly related to the soil carbon and nitrogen components;soil temperature and moisture significantly affected the activity of soil microbial carbon and nitrogen metabolizing enzymes.In other words,the accumulation of soil carbon and nitrogen in the process of litter decomposition affected the metabolism of microbial carbon and nitrogen,thereby mediating the effect of enzyme activity on soil carbon and nitrogen components,and soil temperature and water regulated the effect of soil enzyme activity on soil carbon and nitrogen components. |
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