Exploration Of Contents And Variation Mechanisms Of Soil Carbon,Nitrogen,Phosphorous In Forests Of Beijing-Tianjin-Hebei Region

Beijing-Tianjin-Hebei(BTH)region is one of the high N pollution hotspots,but whether the contents and spatial variations of soil carbon(C),nitrogen(N),phosphorus(P)have been influenced by elevated N inputs remain poorly understood.Here we reported soil C,N and P for 27 forests along a N deposition gradient as 22.4–112.9kg N·ha^-1·yr^-1 in the BTH region of northern China.We considered the effects of soil physical characters,plant leaf and climatic factors on the contents and stoichiometry of soil C,N and P.(1)Mean C and N contents of forests in the BTH region was lower than those reported for forests in the global scale and in China,which suggested the low organic material level of the study region.Mean Total P(TP)contents of forests in the BTH region was higher than those of global scale while lower than those in China.The mean soil C/N was lower than those of the globe and China,mean soil N/P was lower than those in global but higher than the averaged in China.(2)Multi-regression analyses showed that the soil types and soil pH were the main factor influencing the soil inorganic C(SIC).Soil types,microbial biomass C(MBC),nitrate contents and vegetation types affected the spatial variations of SOC contents.Soil microbial biomass N(MBN)and pH were the main factors regulating the spatial variations of soil TN.Soil NH₄⁺-N and NO₃^--N were mainly influenced by the soil moisture,MBN and soil TN,respectively.Soil TP was significantly influenced by soil types and soil moisture.The soil stoichiometry was significantly influenced by soil physical characters and nutrient status,which soil nutrient status were the main factors.As MBC and MBN were significantly affected by soil moisture and pH values which increased with mean annual precipitation(MAP)and temperature(MAT),respectively.(3)While levels of soil TN in forests of the BTH region have been elevated compared with investigations in past decades.The soil TN of south and middle parts of the BTH region have increased faster than the north part with lower N deposition rates,which revealed an effect of continuously high atmospheric N inputs on soil N enrichment.But the N deposition didn't affect the spatial variation of soil TN.In conclusion,N deposition in the BTH region increased the soil TN in time scale,instead of spatial scale.The soil C,N,and P status soil C,N and P status in forests of the BTH region would be more responsive to climate change than N deposition.This study provides a theoretical basis for the development of forest ecosystem function management measures in high nitrogen deposition areas.