NH₄⁺/NO₃^-Adaptability Of Main Conifers In Cold-temperate

Larix gmelinii,Pinus sylvestris var.Mongolica and Picea koraiensis are not only the dominant macrophanerophytes species,but also the extremely economic value of the timber species in the cold-temperate forests,China.For a long time,owing to savage development and natural disasters such as forest fire,the original forest habitats has been seriously disturbed.During the secondary succession,the soil nitrogen nutrition habitat have changed.Plants frequently well adapt to their nutrition habitat during a long evolution process,and these adaptations may contribute to the unique spatial and temporal distributions of these species.During the secondary succession,it may be an important feature for restore native plant that dominant tree species to adapt the change in soil nitrogen nutrition habitat.In the current study,Larix gmelinii,Pinus sylvestris var.mongolica and Picea koraiensis seedlings of the cold-temperate were cultivated by nutrient solution.Conifers were cultivated with hydroponics and sand culture.The experiment was carried out to investigate N adaptability of different nitrogen forms in N uptake,N assimilation,photosynthetic characteristicsand growth condition.The main results and conclusions were as follows:(1)The mineral nitrogen absorption of Larix gmelinii,Pinus sylvestris var.mongolica and Picea koraiensis seedlings are large in NH4+ dominant nutrient habitat.(2)NR activity of conifer seedlings in roots and needles under NH4+ dominant nutrient habitat was lower than that under NO3-dominant nutrient habitat(except for NH4+ dominant mixed nitrogen of Picea koraiensis needles).GS activity of Larix gmelinii seedlings in roots and needles were not significant in nitrogen forms,GS activity of Pinus sylvestris var.mongolica seedlings in roots and needles under NO3-dominant nutrient habitat was high,GS activity of Picea koraiensis seedlings in roots and needles under NH4+ dominant nutrient habitat was high;GDH activity of conifer seedlings in needles under NH4+ dominant nutrient habitat(except for single NH4+ of Larix gmelinii)was significantly higher than that under NO3-dominant nutrient habitat;Soluble protein contents of Larix gmelinii and Pinus sylvestris var.mongolica seedlings in needles under NH4+ dominant nutrient habitat was significantly higher than that under NO3-dominant nutrient habitat;Soluble protein contents of Picea koraiensis seedlings in roots(except for uniform mixed nitrogen)and needles was not significant in nitrogen forms.(3)No obvious difference was found among the treatments of photosynthetic pigments of Larix gmelinii seedlings;Photosynthetic pigments of Pinus sylvestris var.mongolica seedlings under NH4+ dominant nutrient habitat was significantly higher than that under NO3-dominant nutrient habitat;No obvious difference was found among the treatments of photosynthetic pigments of Picea koraiensis seedlings(except for NH4+ dominant mixed nitrogen).Net photosynthetic rate and transpiration rate of Larix gmelinii seedlings was not significant in nitrogen forms;Net photosynthetic rate of Pinus sylvestris var.Mongolica seedlings under NH4+-N dominant nutrient habitat was significantly higher than that NO3-dominant nutrient habitat,transpiration rate of Pinus sylvestris var.Mongolica seedlings under single NH4+ was significantly higher than that under other treatments;Transpiration rate of Picea koraiensis seedlings under NH4+ dominant nutrient habitat was significantly higher than that NO3-dominant nutrient habitat and transpiration rate under mixed nitrogen was high.(4)Dry weight of Larix gmelinii seedlings in roots,needles and plantlet under single NH4+and NH4+ dominant nutrient habitat were high,but that hadn't significant difference;Dry weight of Pinus sylvestris var.Mongolica seedlings in roots,stems,needles and plantlet under single NH4+ and NH4+ dominant nutrient habitat was high;Dry weight of Picea koraiensis seedlings in roots was not significant in nitrogen forms and dry weight of Picea koraiensis seedlings in stems,needles and plantlet under single NH4+ and NH4+ dominant nutrient habitat were high.