Effects Of Nitrogen And Carbon Additions On Soil Phosphorus Composition And Phosphorus Cycle Enzyme Activities In Grassland

Phosphorus(P)is an essential element for plant growth,Therefore maintain and supply of P play important role in keeping grassland ecosystem stability.With the global nitrogen(N)deposition increased,soil P composition and P cycle enzyme activities changed in grassland ecosystem.At the same time,the impact of simultaneous carbon(C)additions on these changes needs to be further explored.This thesis is based on N and C additions experiment set in the Inner Mongolia Erguna Forest Steppe Ecosystem Research Station of the Institue of Appleid Ecology,Chinese Academy of Sciences.Through five years of nitrogen and carbon addition.The amount of N added was five level as N0(control),N25(25 kg N ha-1 yr-1),N50(50 kg N ha-1 yr-1),N100(100 kg N ha-1 yr-1),N200(200 kg N ha-1 yr-1).And three level C additions were C0(control),C250(250 kg N ha-1 yr-1),and C500(500 kg N ha-1 yr-1).Soil enzymology,and 31P-NMR techniques were used to study the effects of N and C additions on soil P composition and P cycle enzyme activities.RDA analysis and structural equation models(SEM)were used to study the correlations between soil P composition and P cycle enzyme activities.The main contents showed as:(1)N additions significantly reduced soil p H,water moisture,and available phosphorus(AP),significantly increased total carbon(TC),total nitrogen TN),total phosphorus(TP),total organic phosphorus(TOP),and had no significant effect on C/N.C additions alleviated the decrease in soil p H caused by high N addition(N200);(2)31P-NMR analysis showed that,total inorganic phosphorus(TIP)in grassland soil mainly existed in the form of orthophosphate,and the TOP is mainly composed of phosphate monoester and phosphate diester.N additions significantly reduced soil pyrophosphate and phosphate diester contents,and increased soil polyphosphate and phosphonate contents.C additions significantly increased soil pyrophosphate content.N and C additions had no significant effected on soil orthophosphate and phosphate monoester.SEM analysis,showed that orthophosphate is an important component affecting AP,phosphate diester is an important source of phosphate monoester;(3)N additions significantly reduced soil acid phosphatase(Ac P),phosphodiesterase(PD),pyrophosphatase(IPP),and dehydrogenase activities(DHA).C additions significantly increased soil Ac P,PD,and DHA activities.The additions of C with high N addition significantly increased soil phosphatase activities,and conducive to the sustainable supply of soil P;(4)RDA analysis of soil parameters and P cycle enzyme and DHA activities showed that,soil p H was the best explained in soil enzyme activities variations,and the it was significantly correlated with DHA.SEM analysis indicated that N additions directly affected soil AP,also indirectly affected soil AP through Ac P,PD,and IPP activities.C additions indirectly affected soil AP through IPP activities.