| Soil is a dynamic system with rich organic matter content.Soil microorganisms play an important role in the decomposition of soil organic matter,and promote the material cycle of soil ecosystem.Saprophytic fungi and ectomycorrhizal fungi(EMF)are the main decomposer of soil organic matter in soil,which could participate in nutrient cycle by regulating the enzyme activity.With the use of fossil fuels and fertilizers,a large amount of carbon and nitrogen is introduced into the soil,which destroys the balance of soil nutrients.In this paper,the effects of exogenous nitrogen and biochar,exogenous nitrogen and litter on soil biological activity and the role of EMF on the transformation of nitrogen in oak forest soil were studied.The results provide a theoretical basis for the establishment and improvement of carbon and nitrogen cycling model of forest ecosystem.The main results are as follows:(1)The activity of alkaline phosphatase was significantly promoted by the addition of biochar in alkaline soil(P<0.05),and reach the highest activity 1500 μg/g C6H5NO3 g-1 d-1 on 7th day,which increased by 152.25% compared with the control group.Biochar greatly increased the invertase activity(P<0.05)in acid soil,on 14 th day,the activity of invertase was enhanced significantly,and increased from 2.88 mg g-1 to 21.26 mg g-1 d-1,which was increased by up to 202.6%.Biochar inhibited the activity of soil urease.Biochar significantly enhanced acid soil respiration(P<0.05)at 0th,3rd and 7th days,and had little effect on soil respiration in alkaline soil.The effect of nitrogen addition on acid phosphatase was weak in acid soil;nitrogen addition promoted the activity of invertase,100 μg/g and 200 μg/g nitrogen increased the invertase activity stronger than 500 μg/g nitrogen.The effect of nitrogen addition on urease increased with the increase nitrogen concentration.In alkaline soil,nitrogen addition had little effect on enzyme activity.The effect of nitrogen addition on soil respiration was weaker in both acid and alkaline soils.(2)Nitrogen addition has little effect on nitrite reductase activity,litter significantly promoted the activity of nitrite reductase(P<0.05).On 3rd day,with 1/2 litter addition,nitrite reductase activity in soil was 2.622±0.206 mg NO2-N g-1 24h-1,which increased by 39.5% compared with the control group.During 0~3 days,both 500 μg/g nitrogen and litter inhibited protease activity and then both of which promoted protease activity.Among them,1/2 litter had the strongest effect on protease,protease activity increased from 0.082±0.009 μg g-1 to 0.206±0.01 μg g-1,increased by up to 60.2%.Nitrogen addition promoted urease activity,and 500 μg/g nitrogen had a stronger effect on urease.On 3rd day,500 μg/g nitrogen increased urease activity by 50%.During 0~3 days,the urease activity was promoted by litter,and then the urease activity was inhibited.On 3rd day,the promoting effect of litter on urease was the strongest,which increased by 43%.Nitrogen addition promoted soil respiration.During 0~3 days,promoting effect of 200 μg/g nitrogen on soil respiration was stronger than 500 μg/g nitrogen.During 7~28 days,The promoting effect of 200 μg/g nitrogen on soil respiration was increased gradually with the concentration of nitrogen.The effect of litter on soil respiration is weak.The effect of combined application of litter and nitrogen on soil enzyme activity and soil respiration were similar to that of litter added alone.(3)The experiment detected 1052 different fungal taxa.Among all fungal taxa,698 genera of fungi were Ascomycota,286 species of fungi were Basidiomycetes.There was a small amount of other fungi,including Chytridiomycota,Glomeromycota and Zygomycota.The highest abundance ectomycorrhizal fungi is Russula.In summer,the maximum abundance of EMF in humus,humus with sand barrier and humus without sand barrier are Lactarius,Cenococcum and Scleroderma respectively.In autumn,the maximum abundance of EMF in humus,humus with sand barrier and humus without sand barrier are Russula,Scleroderma and Scleroderma respectively.(4)The activities of β-1,4-N-acetyl glucosidase(NAG),leucine aminopeptidase(LAP),protease(PRO),nitrite reductase(NIR)and urease(URE)were measured in summer and autumn.In addition to NIR in the soil,other enzymes in soil are higher than in the humus.In humus,the activity of PRO and LAP in autumn was significantly higher than that in summer(P<0.05),and the activity of PRO increased from 217.26±6.04 IU/L in the summer to 287.51±11.49 IU/L in autumn,improved 32.4%.The LAP activity in the root tip was the lowest in all samples.The activities of NIR,PRO and LAP in the humus with sand barrier were lower than that in the sand free humus.In humus with sand barrier,the activity of NAG in autumn was significantly higher than that in summer,the activity of URE was significantly lower than that in summer;the activity of PRO,NAG and LAP in humus without sand barrier were significantly increased in autumn(P<0.05),the activity of URE decreased significantly in autumn(P<0.05).(5)The activity of β-1,4-N-acetyl glucosidase,leucine aminopeptidase,protease,nitrite reductase and urease were significantly correlated with the fungal diversity index.The activities of nitrogen conversion related enzymes were also closely related to the changes of fungal community structure.Compared with summer,the abundance and diversity of EMF fungi were increased in humus with sand barrier and humus without sand barrier in autumn.The percentage of Scleroderma increased from 0.1% to 5.83% from summer to autumn in humus with sand barrier.The percentage of Scleroderma increased from 1.6% to 5.03% from summer to autumn in humus without sand barrier.All kinds of EMF ratio were improved.Correspondingly,the activities of nitrogen conversion also enhanced.Correlation enzymes correlation analysis and PCA showed that there was a significant positive correlation between Scleroderma and enzyme activity.The results showed that EMF played an important role in the regulation of nitrogen cycling related enzyme activities in soil nitrogen transformation. |
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