| Long-term acid input into forest ecosystem will significantly affect the energy flow and nutrient cycling process of forest ecosystem.At present,in addition to environmental protection to reduce acid deposition,the method of adding lime is usually used to neutralize the acid deposited into the soil.This study is based on a long-term acid-alkali substances addition control experiment established in natural Pinus tabuliformis forest in Taiyue Mountain,Shanxi Province.To study the response characteristics of soil microbial nutrient utilization strategies to acid-alkali substances addition,for purpose to provide a theoretical basis for the effects of acid-alkali substances addition on the energy and nutrient requirements of soil microorganisms in boreal forest ecosystems in China.This study started in 2015 and carried out an experiment of adding acid-alkali substances to Pinus tabuliformis forest soil every May.Ammonium nitrate and lime were used as the sources of acid-alkali substances.Set up control treatment group(CK),acid treatment group(N1,N2,N3 and N4)and alkali treatment group(L1,L2,L3,L4)respectively,each treatment has 4 replicates.And the soil of 0-10 cm and 10-20 cm soil layer of the sample plot was collected at the end of August 2019 to determine soil p H,nutrients,microbial biomass and extracellular enzyme activities.We also studied the nutrient utilization strategy of soil microorganisms using enzyme stoichiometry and vector analysis.The results were as follows:The ammonium nitrate addition significantly affected the soil p H value,nutrient content,microbial biomass,soil enzyme activities and enzyme stoichiometric characteristics in 0-10 cm soil layer.Specifically,with the increase of ammonium nitrate addition,soil p H,organic carbon,dissolved organic carbon,microbial biomass carbon and phosphorus content gradually decreased,and the dissolved organic nitrogen content increased significantly;High concentration ammonium nitrate addition(N4)significantly increased the activities of soil C-acquiring enzyme and P-acquiring enzyme,while significantly decreased the N-acquisition enzyme activity;The results showed that ammonium nitrate addition promoted the carbon and phosphorus limitation of soil microorganisms,and the promotion effect was significantly related to the concentration of ammonium nitrate.In the 10-20 cm soil layer,except for soil dissolved organic nitrogen,the other soil factors showed no significant difference in response to ammonium nitrate addition.Correlation analysis and structural equation mode showed that ammonium nitrate significantly affected soil microbial nutrient utilization strategy by affecting surface soil p H,nutrient content and microbial biomass.With the lime addition,in the 0-10 cm soil layer,soil p H value increased significantly,but the variation characteristics of soil nutrient content,microbial biomass and enzyme activity depended on the lime addition concentration,and the response of soil microbial nutrient utilization strategy to lime addition showed no significant difference.The content of soil dissolved organic carbon was significantly decreased by high concentration lime addition(L4),while dissolved organic nitrogen increased significantly by low concentration lime addition(L1,L2 and L3).Lime addition significantly decreased the soil microbial biomass carbon content,and had no significant influence on the soil microbial biomass phosphorus content,and the low concentration lime increased the soil microbial biomass nitrogen content significantly.With the increase of lime addition,soil C/N/P-acquiring enzyme activities increased at first and then decreased,and reached the maximum value in L1 treatment,which was significantly higher than that in the control treatment.The vector length and vector angle had no significant change under lime addition,but the vector angle decreased with the increase of lime addition,which showed that soil microorganisms tended to reduce phosphorus limitation with the increase of lime addition.Except for total phosphorus,the soil nutrient content and microbial biomass in 0-10 cm soil layer were higher than those in 10-20 cm soil layer.The acid-alkali substances addition did not change the vertical distribution of soil nutrients.In conclusion,the effects of acid-alkali substances addition on soil p H,nutrient content,microbial biomass,extracellular enzyme activity and microbial nutrient utilization strategy were mainly concentrated in 0-10 cm soil layer.Ammonium nitrate addition significantly affected the nutrient utilization strategy of surface soil microorganisms,while lime addition had no significant effect on the nutrient utilization strategy of soil microorganisms. |
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