Effects Of Simulated Nitrogen Deposition On Soil Enzyme Activities In Temperate Typical Forests And Steppes In Northeast China

The increase in nitrogen deposition caused by the continuous increase of global nitrogen deposition has become an important environmental factor affecting the material cycle in forest ecosystems and grassland ecosystems.Under the condition of increasing nitrogen deposition year by year,studying the effect of nitrogen deposition on soil enzyme activity can provide an important theoretical basis for a more accurate and direct understanding of the material cycle characteristics of terrestrial ecosystems in Northeast China and their response to increased nitrogen deposition.The northeast region has a vast territory,the forest ecosystem and grassland ecosystem are vast.In order to investigate the effects of increased nitrogen deposition on soil enzymes in key processes of biomass cycling and grassland ecosystems in Northeast China,this study selected Larix gmelini plantation and primary broad-leaved Pinus koraiensis forest to represent forest ecosystems in Northeast China.The Erguna Meadow Steppe and the Xilinhot typical grassland represent the grassland ecosystem in Northeast China,and the soil enzyme activities of inorganic nitrogen(NH4NO3)and inorganic nitrogen without added inorganic nitrogen were compared and analyzed.The experiment was divided into two treatments:control treatment(CK:0kg N hm-2·a-1)and inorganic nitrogen treatment(Larix gmelini plantation IN:10 kg N hm-2·a-1;primary broad-leaved Pinus koraiensis forest IN:20 kg N hm-2·a-1;meadow steppe,typical steppe:IN:10 g N m-2·a-1),Larix gmelini plantation and primary broad-leaved Pinus koraiensis forest contain 3 replicates per treatment,and meadows and typical grasslands contain 6 replicates per treatment.The results showed that ?-1,4-glycosidase(BG),acid phosphatase(AP)and peroxidase(PER)activities increased by 71.2%,7.9%and 28.8,respectively,in the forest ecosystem after adding inorganic nitrogen;cellobiohydrolase(CBH),leucine aminopeptidase(LAP)and polyphenol oxidase(POX)activities decreased by 27.1%,22.5%and 4.6%,respectively.The corresponding soil carbon,nitrogen and phosphorus increased by 31.0%,93.9%and 23.6%,respectively.Soil cellobiohydrolase(CBH),acid phosphatase(AP)and peroxidase(PER)activities in grassland ecosystems increased by 71.5%,20.6%and 42.9%,respectively;the activities of P-1,4-glucosidase(BG),leucine aminopeptidase(LAP)and polyphenol oxidase(POX)decreased by 19.5%,42.1%and 28.4%,respectively.Correspondingly,the soil carbon,nitrogen and phosphorus also changed.The organic carbon decreased by 3.0%,the total nitrogen increased by 16.0%,and the total phosphorus increased by 53.7%.The above results indicate that the increase in nitrogen deposition promotes the activity of ?-1,4-glucosidase,acid phosphatase and peroxidase in forest ecosystems,inhibiting cellobiohydrolase,leucine aminopeptidase and polyphenol oxidase activity.It also promoted the accumulation of soil organic carbon,total nitrogen and total phosphorus in forest ecosystems.The increase of nitrogen deposition promotes the activity of cellulose disaccharide hydrolase,acid phosphatase and peroxidase in grassland ecosystem,inhibiting ?-1,4-glucosidase,leucine aminopeptidase and polyphenol oxidase activity.It also promoted the accumulation of total nitrogen and total phosphorus in the grassland ecosystem and inhibited the accumulation of soil organic carbon.It can be seen that nitrogen deposition has different effects on the same soil enzymes in different ecosystems,and the soil element content also changes with the change of soil enzyme activity,that is,nitrogen deposition has potential different effects on the nutrient cycling of different ecosystems.