Growth And Physiological Responses Of Seedlings Of Four Species To Different Nitrogen Forms

In recent years, plenty of researches have been carried out on plant nitrogen uptake, utilization of amino acids, but most of them focus on the study of the crops whose life cycle is short and easy to cultivate. Studies about the effects of amino acids on the growth and physiology of trees have just received attention in forestry. At present, it has been reported that organic nitrogen of amino acids in conifer seedlings have good effects on promoting growth, and the promoting effects are not less than and even more than inorganic nitrogen, but there are also some studies suggesting that the promoting effects of amino acids are not as good as inorganic nitrogen. So whether organic nitrogen of amino acids can promote the growth of trees universally? Whether there are differences on the promoting effects due to various tree species? Whether different tree species have different growth responses to various kinds of amino acid fertilizers? To answer these questions, we need to carry out more studies on more tree species, then analyze and verify them. Therefore, we choose four kinds of common tree species in northeast area which are biological nitrogen fixing shrub-Lespedeza (Lespedeza bicolor), hybridization broad-leaved tree species-black poplar (Populus simoniix P. nigara), broad-leaved tree species-birch (Betula Platyphylla) and coniferous tree species-Changbai Larch (Larix olgensis) seedlings. Through the application of different nitrogen forms and different nitrogen application amount, the growth and physiological responses will be explored, aiming at providing reference for the evaluation of amino acids’promoting effects on growth of different kinds of trees. Research results show that:(1) Effects of different nitrogen application amounts on seedlings’ growth and physiology of four kinds of tree species are different. Among them, nitrogen application significantly improves Lespedeza’s seedling height, root-collar diameter and crown root ratio and promotes its biomass accumulation. All growth indicators of Lespedeza seedlings have reached the maximum among all the treatments after medium nitrogen level treatment. Lespedeza’s root nitrogen concentration shows the same varying pattern with its above-ground biomass and root biomass (medium nitrogen level treatment>high nitrogen level treatment>low nitrogen level treatment). The maximum value of Lespedeza’s net photosynthetic rate occurs in the medium organic nitrogen level treatment. Different from the varying pattern of Lespedeza, high nitrogen level treatment is more advantageous to black poplar and birch and Changbai Larch seedlings’ growth whose seedling height, root-collar diameter and above-ground biomass reach the maximum among all their treatments.(2) The effects of different nitrogen forms on the four kinds of seedlings’ growth and physiology are also different. Among them, organic nitrogen (arginine) processing is relatively more conducive to the growth of Lespedeza and birch seedlings than inorganic nitrogen (ammonium nitrate) treatment. Organic nitrogen treatment significantly increases the Lespedeza seedlings’ height, root-collar diameter, crown root ratio and biomass. These growth index differences of birch seedlings are not significant, but seedlings under organic nitrogen treatment grow better than inorganic nitrogen processing; on the contrary, black poplar and Changbai Larch seedlings under inorganic nitrogen (ammonium nitrate) treatment grow better whose height, root-collar diameter and biomass under the treatment of inorganic nitrogen are slightly higher than organic nitrogen treatment. Black poplar’s root, stem and leaf nitrogen concentrations under low nitrogen level treatment are higher than those under medium nitrogen and high nitrogen level treatments, and its leaf nitrogen concentration under inorganic nitrogen treatment is higher, correspondingly black poplar’s net photosynthetic rate is the highest under low and inorganic nitrogen treatment.(3) Effects of different amino acids and their combinations on four kinds of seedlings’ growth and physiology are not the same. Among them, Lespedeza seedlings under arginine and glycine acid (Arg*Gly) treatment, black poplar under arginine and glutamic acid (Arg*Glu) treatment, birch under glycine and glutamic acid (Gly*Glu) treatment and Changbai Larch under arginine and glutamic (Arg*Glu) processing grow better. Glutamic acid (Glu) treatment of Lespedeza and black poplar seedlings’ leaf nitrogen concentration is higher than other treatments. Black poplar’s net photosynthetic rate under glutamic acid (Glu) treatment reaches the biggest among all the treatments. The net photosynthetic rate of Lespedeza seedlings under three kinds of amino acids combination (Arg*Glu*Gly) treatment is the highest.