Effect Of Elevation CO₂ On Nitrogen Uptake Characteristic And Growth Of Larix Gmelinii And Pinus Sylvestris Var. Mongolica

Pinus sylvestris and Larix gmelinii are main forestation trees in northeast forest of China. In this paper,the effects of absorbing character and growth to two types nitrogen of Pinus sylvestris and Larix gmeliniii when CO₂ level set up 350μmol·mol^-1and 700μmol·mol^-1,at the same nitrogen levels(8mmol·L^-1),NH₄⁺-N/NO₃^--N separately set 25/75,50/50,75/25,in artificial climate box utilized two years old seedling of this two tress.The results were summarizes as follows:(1)By contrast with the normal CO₂ concentration,when CO₂ concentration increased and supplied more NH₄⁺-N but less NO₃^--N(NH₄⁺-N:NO₃^--N=75:25),Pinus sylvestris for the absorption of NO₃^--N had little change,but the absorption of NH₄⁺-N was increased earlier and latter decreased;when the concentration of NH₄⁺-N andNO₃^--N were equal(NH₄⁺-N:NO₃^--N =50:50),the tree increased the absorption of NO₃^--N,the absorption of NH₄⁺-N had no change;when supplied more NO₃^--N but less NH₄⁺-N(NH₄⁺-N:NO₃^--N=25:75),the absorption of NH₄⁺-N and NNO₃^--N had no obvious change either.All of these showed that, Pinus sylvestriswas fond of NO₃^--N,when the concentration of CO₂ increased and NO₃^--N was lacked,the tree may increase absorption of NH₄⁺-N.(2)By contrast with the normal CO₂ concentration,when CO₂ concentration increased and supplied more NH₄⁺-N but less NO₃^--N(NH₄⁺-N:NO₃^--N=75:25),Larix gmelinii for the absorption of NO₃^--N had obvious increased,but the absorption of NH₄⁺-N had no change; when the concentration of NH₄⁺-N and NO₃^-N were equal(NH₄⁺-N:NO₃^--N=50:50),the absorption of NO₃^--N had little increased,and the absorption of NH₄⁺-N had no change;when supplied more NO₃^--N but less NH₄⁺-N(NH₄⁺-N:NO₃^--N=25:75),the absorption of NH₄⁺-N and NO₃^--N had no obvious change either.All of these showed that,Larix gmelinii absorb NH₄⁺-N mainly,and absorb some NO₃^--N also,when the concentration of CO₂ increased and NH₄⁺-N was lacked,the tree may increased absorption of NO₃^--N.(3)Be contrasted with the normal concentration,the increased concentration of CO₂ Lowered the concentration but increased the contains of N in the two seedlings,when the NH₄⁺-N/NO₃^--N which contains of N in Pinus sylvestris overall is 75/25,50/50å’Œ25/75.it increased 14.5%,23%å’Œ37%respectively;and the NH₄⁺-N/NO₃^--N which contains of N in Larix gmelinii overall is 75/25,50/50å’Œ25/75,it increased 65%,22%å’Œ52%respectively.When the NH₄⁺-N/NO₃^--Nis 25/75,the N 'contains in Pinus sylvestris is highest,and when the NH₄⁺-N /NO₃^--N is 75/25,the N'contains in Larix gmelinii is highest.It proved that in the foster period,the increased concentration of CO₂ promote the absorption of N both in Pinus sylvestris and Larix gmelinii seedlings. (4)The doubled concentration of CO₂ promote the bottom growth of Pinus sylvestris and Larix gmelinii,furthermore,it increased the biomass of two kinds seedlings.when NH₄⁺-N /NO₃^--N is 25/75 in Pinus sylvestris and NH₄⁺-N/NO₃^--N is 75/25 in Larix gmelinii,the bottom growth increased most,it roused 112%å’Œ110%。The increased concentration of CO₂ promotes the two tree's biomass.(5)the doubled concentration of CO₂ increased Pinus sylvestris'contains of chlorophyll in leafs and soluble sugar,but it affects the contains in leaf's soluble starch unobvious.compared to the normal concentration of CO₂,the doubled concentration of CO₂ increased the contains of chlorophyll in the leafs of Larix gmeliniiand when the NH/-N/NO₃^--N is 25/75,the contains of chlorophyll is highest.When the concentration of CO₂ is doubled and NH₄⁺-N/ NO₃^--N is 50/50,the contains of chlorophyll in Larix gmelinii' leafs reached most.