Effects Of Increased Carbon And Nitrogen Input On Inorganic Phosphorus Conversion In Soil Of Pinus Sylvestris Var.mongolia Sand Fixation Forest

In the current economic situation,the environmental problems are more serious.The excessive use of fossil fuels has injected much NOx into the atmosphere,which eventually enters the ecosystem through atmospheric deposition.With the increase of atmospheric N deposition,P in forest ecosystem has been greatly affected.Phosphorus is an essential nutrient element for plant growth,it is second only to nitrogen in importance,and its availability is mainly sustained by phosphorus cycling.However,with the influence of atmospheric nitrogen deposition,part of the P in the soil is easily fixed,the P cycle is affected,and the availability of P is significantly reduced,thus restricting the healthy development of the entire ecosystem.In this paper,the 13-year-old Pinus sylvestris sand-fixing forest in Horqin Sandy Land of Inner Mongolia was taken as the experimental object.Through long-term nitrogen addition and double treatment of litter in the field,the control experiment was conducted to analyze the soil physical and chemical properties,microbial properties and the response of phosphorus composition to the experimental treatment.The main conclusions are as follows:(1)The soil p H and base cation content of Pinus sylvestris decreased significantly with the addition of nitrogen,and the decrease of base cation content was mainly caused by the decrease of Ca²⁺content.Lower base cations resulted from acidic of soil caused by adding N,and the loss of cations will further cause soil acidification.The soil acidification induced by nitrogen addition was alleviated by litter doubling treatment.(2)Nitrogen addition could lead to soil acidification and inhibit microbial activity,which resulted in the decrease of microbial biomass carbon(C_mic),microbial biomass phosphorus(P_mic)and acid phosphatase activity(APA)of soil in Pinus sylvestris plantation.Nitrogen addition and litter double handling of mongolica plantation have significant interaction effect on APA,their interaction can increase the APA.On the one hand,it may be that APA is enhanced by P limitation caused by N addition,on the other hand,it may be that the carbon is the main limiting nutrient elements of microbes,and the increase of litter increased mongolia soil carbon input,for microbial growth and the synthesis of APA provides nutrients,thus to increase the activity of APA.(3)Under the conditions of N addition,tthe ability to adsorb P of soil of Pinus sylvestris plantation was significantly higher than that of the other three treatments,but the effect of N addition would only show up after the P concentration of the soil solution reached about 23 mg L^-1.The soil P concentration of Pinus sylvestris in the experiment could not reach this standard,therefore,P adsorption had little effect on the P conversion in this experiment.(4)Nitrogen addition and doubling of litter had significant interaction effects on the content of unstable organic phosphorus(Na HCO₃-Po),their interaction can reduce the content of Na HCO₃-Po.And the interaction effect of increasing carbon and nitrogen input on unstable organic phosphorus mainly came from the interaction effect on acid phosphatase activity(APA).Carbon and nitrogen input to increase the influence of soil phosphorus transformation of mongolia projects mainly through to the instability of organic phosphorus(Na HCO₃-Po),the influence of the correlation analysis results show that the lower soil phosphatase activity is easy to cause unstable soil organic phosphorus(Na HCO₃-Po)to the instability of inorganic phosphorus(Na HCO₃-Pi)mineralization is reduced,so that the effectiveness of soil phosphorus,into plants to absorb the advantage of phosphorus components.