Effects Of Cenchrus Spinifex Invasion On The Soil Nitrogen Transform Characteristics

Cenchrus spinifex,an invasive plant species found in agriculture and pasture areas of northern China,spread fast in Horqin sandy land,with the characteristics of strong resistance to drought and barrenness.C.spinifex invasion results in single dominant community,following the changes of structre and function of ecosystems.Find out the effects of C.spinifex invasion on the soil nitrogen transform characteristics,would provide a theoretical basis for revealing the ecological mechanism of C.spinifex and developing scientific and effective prevention and control measures.In this study,we focused on analysis of the effects of C.spinifex on soil nitrogen and plant nitrogen pools in Horqin sandy grassland.In addition,a laboratory incubation experiment was conducted with two exogenous N forms?NO₃^--N and NH₄⁺-N?and three plant types?C.spinifex,Roegneria kamoji and no plants?to investigate these interactive effects on soil net N mineralization rate,net nitrification rate and net amination rate.Furthermore,a pot experiment with ¹⁵N tracing techniques was designed to study the biological nitrogen fixation ability of C.spinifex,compared with two native grasses,Elymus dahuricus and Agropyron cristatum.The results showed as followed:1.The total soil nitrogen pool in C.spinifex invaded-area increased significantly by 47.5%and 20.8%?P<0.05?,soil ammonium nitrogen pool decreased significantly by 25.6%and 25.2%?P<0.05?,nitrate nitrogen pool increased by 19.8%and 11.0%?P>0.05?,inorganic nitrogen pool decreased by2.4%and 6.9%?P>0.05?,nitrate nitrogen/inorganic nitrogen increased significantly by 23.0%?P<0.05?,compared with those in bare and native plant R.kamoji areas,respectively.The plant shoot nitrogen decreased significantly by 18.7%in C.spinifex compared with native plant R.kamoji?P<0.05?.2.Soil net N mineralization rate of C.spinifex invaded-soil was increased,net nitrification rate was increased?June to July?and decreased?August to October?,net amination rate was decreased before tillering stage and increased after tillering stage,compared with those of bare and native plant R.kamoji soil.With the addition of NH₄⁺-N or NO₃^--N,net N mineralization rate of C.spinifex invaded-soil was decreased after tillering stage.The order of correlation with net nitrification rate and net amination rate was exogenous N>plant type>interaction effect.The order of correlation with net mineralization rate was exogenous N>interaction effect>plant type.3.Atom%¹⁵N,atom%¹⁵N excess and atom%¹⁵N weighting excess of C.spinifex were all significantly lower than those of E.dahuricus and A.cristatum?P<0.05?.The nitrogen utilization of C.spinifex and E.dahuricus were 48.5%and 47.0%?P>0.05?,respectively,and no significant difference was observed.Ndfa in C.spinifex accounted for 60.2%,compared with E.dahuricus.These results suggested that the characteristics on the high efficient use for nitrogen of this invasive weed might an ecological adapation mechnisim,leading to successful colonization and spread in Horqin Steppe.