Seasonal Variation Characteristics Of Soil Enzyme Activities And Active Carbon,Nitrogen Components Under Different Land-use Types

Changes in land uses and land cover patterns play an important role in global regional and local climate change.Land-use types can be achieved through changes in land cover or agricultural activities,which have significant and lasting effects on soil physical,chemical and biological properties.Soil enzymes are important biological activity indexes of soil quality and remediation status.Soil active carbon and nitrogen have high sensitivity to soil homeostasis.And soil enzyme activities and active carbon,nitrogen are sensitive to the changes of environmental factors.Therefore,soil enzyme activities and active carbon,nitrogen can be used as important biological indicators reflecting ecosystem function changes to guide the management of soil ecosystems.Five typical land-use types in the rocky mountainous areas of North China,including farmland,abandoned land and artificial forest(Platycladus orientalis,Robinia pseudoacacia and Quercus variabilis)were selected as research objects.Soil samples of 0～10,10～20 and 20～30 cm depth were taken in 4 times(March,June,September and December).Soil enzyme activities(β-glucoside catalase protease and urease)and active carbon,nitrogen components(Dissolved organic carbon:DOC,Dissolved organic nitrogen:DON,Microbial biomass carbon:MBC,Microbial biomass nitrogen:MBN,Ammonium nitrogen:NH4+-N,Nitrate nitrogen:NO3--N,DOC/DON and MBC/MBN)were compared and analyzed in dynamic changes,response to seasonal changes and their correlations with other soil physical and chemical properties under different land-use types.The main results were as follows:(1)Soil enzyme activities and active carbon,nitrogen components were different with the change of land-use types,and the soil β-glucoside enzyme,catalase,protease,urease activities and soil DOC,DON,MBC,NH4+-N,NO3--N contents and DOC/DON ratio reached significant levels(P<0.05),The soil four enzyme activities and active carbon,nitrogen contents in farmland and Platycladus orientalis artificial forest were significantly higher than those of other land-use types,especially Platycladus orientalis artificial forest.But Those in Quercus variabilis artificial forest were significantly lower than those of other land-use types.In terms of ecological stoichiometry,the soil DOC/DON ratio of Platycladus orientalis artificial forest was the highest,indicating that its roots might be more inclined to absorb and use the soil DON.The soil MBC/MBN ratios of Platycladus orientalis artificial forest and farmland were between 8 and 12,indicating that the dominant of soil microorganisms in Platycladus orientalis artificial forest and farmland might be fungus.However,the soil MBC/MBN ratios of Robinia pseudoacacia,Quercus variabilis artificial forest and abandoned land were between 4 and 6,indicating that the dominant of soil microorganisms in Robinia pseudoacacia,Quercus variabilis artificial forest and abandoned land might be bacteria.The results were also revealed that farming of planting of Plarycladus orientalis artificial forest could improve soil physical,chemical and biological properties,and enhance soil fertility in the rocky mountainous areas of North China.(2)Soil enzyme activities and active carbon,nitrogen components showed significant seasonal variations under the five land-use types,but soil NO3--N content and MBC/MBN ratio did not reach the significant level(P<0.05).The soil βglucosidase,protease and urease activities were higher in June and lower in December,and soil catalase activity was slightly lower in June.The soil DOC,DON,MBC and MBN contents were both the highest in March,but the time period when they reached the lowest value was different.The soil DOC content was the lowest in September and December,the soil DON content was the lowest in June,and the soil MBC and MBN contents were both low in June and December.However,soil NH4+-N and NO3--N contents had no obvious seasonal variation.Soil DOC/DON and MBC/MBN ratios were higher in June.With the deepening of soil depth,soil enzyme activities and soil active carbon,nitrogen contents decreased,but the soil DOC/DON and MBC/MBN ratios did not change significantly.(3)Correlation analysis showed that the soil β-glucosidase catalase,protease activities and the DOC content were significantly positively or negatively correlated with other soil factors(P<0.01).Except for soil total nitrogen(TN)and pH,soil urease activity was significantly positively or negatively correlated with other soil factors(P<0.05).Soil DON content was positively correlated with soil organic carbon(SOC),TN,available nitrogen(AN),available phosphorus(AP)contents and water content(P<0.05).Except for soil available potassium(AK)content,soil MBC content was significantly positively or negatively correlated with other soil factors(P<0.05).Soil NH4+-N content was significantly correlated with soil particle size volume fraction(P<0.01).Except for soil AN content,soil NO3--N content was significantly positively or negatively correlated with other soil factors(P<0.05).Soil DOC/DON and MBC/MBN ratios were significantly negatively correlated with soil TN content and water content(P<0.05).Soil enzyme activities and soil active carbon,nitrogen contents were also significantly positively or negatively correlated(P<0.05).Stepwise Unear regression analysis showed that soil SOC and TN ontents were important factors affecting soil enzyme activities and active carbon,nitrogen contents,implying the changes of soil enzyme activities and active carbon,nitrogen contents under different land-use types may be the result of the comprehensive effects of temperature,humidity,soil substrate content and plant types,which can also provide theoretical basis for the improvement of soil quality and the sustainable utilization of ecosystem in this region.