Preferential Utilization For Inorganic In The Invasive Plant Xanthium Strumarium And The Native Xanthium Sibiricum

The main purposes of this dissertation are to explore the differences between the invasive plant Xanthium strumarium and its native congener X.sibiricum in differential uptakes of different forms of inorganic nitrogen?selective absorption and utilization characteristics?,promoting understanding invasion mechanisms of invasive plants in terms of nutritional utilization.The paper carried out experiments on the experimental materials of X.strumarium and X.sibiricum seedlings,and studied the absorption and growth characteristics of the invasive and native Xanthium plants at different ratios of ammonium nitrate.We measured their absorption kinetics parameters of nitrate-nitrogen and ammonium-nitrogen in nutrient solutions with different nitrate to ammonium ratios?1:0,3:1,1:1,1:3 and 0:1?by ion depletion method,and then we analyzed the differences between the invasive and native Xanthium plants in the absorption potential for two nitrogen forms.We grew the invasive and native Xanthium plants in soil with 30%sand with five nitrate to ammonium ratios?1:0,3:1,1:1,1:3 and 0:1?,and studied their responses to inorganic forms in terms of root isozymes activities,biomass,morphological characteristics and photosynthetic characteristics,Ion depletion test results show that Vmax,affinity and a of NO₃^--N of the invasive plant X.strumarium was significantly higher than that of NH₄⁺-N under a single nitrogen form.For the native plant X.sibiricum,however,Vmax and a of NH₄⁺-N was higher than that of NO₃^--N.Under mixed nitrogen sources,X.strumarium seedlings showed higher Vmax,affinity and a to NO₃^--N in any nitrate to ammonium ratios,while X.sibiricum seedlings had higher Vmax,affinity and a to NH₄⁺-N.The addition of ammonium or nitrate nitrogen affected the absorption of two inorganic nitrogens by X.sibiricum and X.strumarium seedlings.It is indicated that the addition of little amount of ammonium nitrogen into solution with nitrate as only nitrogen source?such as NO₃^--N:NH₄⁺-N=3:1 or 1:1?increased Vmax,and a but decreased affinity to NO₃^--N for X.sibiricum seedlings;addition of large amount of ammonium nitrogen into the solution?such as NO₃^--N:NH₄⁺-N=1:3?decreased Vmax,a and affinity to NO₃^--N by X.sibiricum seedling.Adding nitrate nitrogen to solution with ammonium as only nitrogen source?such as N03--N:NH₄⁺-N=1:3?increased Vmax,affinity and a of NH₄⁺-N for X.sibiricum seedlings.Addition of little amount of ammonium nitrogen into solution with nitrate as only nitrogen source?such as NO₃^--N:NH₄⁺-N=3:1 or 1:1?decreased affinity and a of NO₃^--N for X.strumarium seedlings;adding nitrate nitrogen to solution with ammonium as only nitrogen source increased Vmax rate and decreased affinity and a of NH₄⁺-N for X.strumarium seedlings.The results of species comparison showed that the uptake of nitrogen by X.sibiricum and X.strumarium seedlings was opposite.Compared with X.strumarium seedlings,X.sibiricum seedlings had higher Vmax,affinity and a of NH₄⁺-N.Compared with X.sibiricum seedlings,X.strumarium seedlings generally had higher Vmax,affinity and a of NO₃^--N.When the concentration of total nitrogen was constant,the absorption rate of NH₄⁺-N by X.sibiricum was higher than that of NO₃^--N,and that of NH₄⁺-N by X.strumarium seedlings was lower than that of NO₃^--N.The results of growth test show that nitrate reductase activity of X.strumarium seedlings was significantly higher but glutamine synthetase activity was significantly lower compared with those of X.sibiricum seedlings.Under single ammonium nitrogen treatment,the maximum net photosynthetic rate and total biomass of X.strumarium seedlings were significantly lower than those of other treatments with different amounts of nitrate nitrogen.In contrast,X.sibiricum seedlings had the lowest total biomass under high nitrate to ammonium ratio.With the increase of nitrate to ammonium ratio,photosynthetic rate and total biomass increased significantly for X.strumarium,and the advantages of the invader over X.sibiricum also increased.The overall performance is that ammonium nitrogen promoted the growth of X.sibiricum seedlings,and nitrate nitrogen promoted the growth of X.strumarium seedlings.In conclusion,X.strumarium seedlings preferred to utilize nitrate nitrogen and X.sibiricum seedlings preferred to utilize ammonium nitrogen.