Effects Of Ammonium Nitrate And Alkali Lime Addition On Fine Root Biomass And Morphological Characteristics Of Pinus Tabulaeformis In Taiyue Mountain

In this study,natural Pinus tabulaeformis forest in Taiyue Mountain of Shanxi Province was selected as the research object.In order to explore the response of root biomass,root morphology(root length,specific root length,mass density,surface area),nutrient stoichiometry and soil microenvironment to exogenous addition,four ammonium nitrate addition gradients(N5=5g/m~2,N10=10g/m~2,N20=20g/m~2,N40=40 g/m~2)were set up.And four alkali lime addition gradients(lime50=50g/m~2,lime100=100g/m~2,lime200=200g/m~2,lime400=400g/m~2)were used.Plots without any substance were used as control(CK).The relationship between root system and additives of Pinus tabulaeformis was discussed.The main conclusions are as follows:(1)Fine root biomass decreased with soil depth,and increased with the increase of diameter class in the same soil layer.Ammonium nitrate and alkali lime had no significant effect on fine root biomass(P>0.05),but the appropriate addition of ammonium nitrate and alkali lime improved soil nutrient conditions,and then promoted the increase of fine root biomass.The promotion effect of ammonium nitrate on fine root biomass increased with the increase of diameter class;the effect of alkali lime on fine root biomass fluctuated greatly.(2)The root length,specific root length,mass density and surface area of fine roots in the surface layer(0-10cm soil layer)were higher than those in the subsurface layer(10-20cm soil layer).The root length,specific root length and surface area decreased with the increase of diameter class,and the mass density increased with the diameter class.The results showed that the effects of exogenous substances on the surface fine roots were quite different.The appropriate concentration of exogenous substances promoted the morphological indexes of subsurface fine roots,and the 0-1 mm diameter class fine roots were more sensitive to the environment.(3)The contents of organic carbon and total nitrogen in fine roots ranged from 510-580 g/kg and 4.2-5.6 g/kg,respectively.After the addition of exogenous substances,the C/N of surface fine roots showed a decreasing trend.The addition of ammonium nitrate increased the C/N of subsurface fine roots first and then decreased.The addition of alkali lime only promoted C/N at low concentration.On the whole,the effect of ammonium nitrate on fine root C/N was more obvious than that of alkali lime.(4)Soil p H had no significant effect on soil p H,only the surface soil p H was negatively correlated with ammonium nitrate addition gradient,positively correlated with alkali lime addition gradient,soil p H was not significantly correlated with fine roots,soil p H was not the main reason for fine root performance differences.