| With the intensification of global climate and environmental change, rise of earth’s average surface temperature, shortage of water resources, available soil water content decreased and atmospheric nitrogen deposition has become an important global environmental problem. Soil nitrogen and moisture are many terrestrial ecosystems in the main factor limiting plant growth, significant influence on the distribution and growth of plants. Drought caused by global climate sing-an north larch forest in our country, combined with China’s increasing atmospheric nitrogen deposition, cause forest soil available nitrogen content increasing. Therefore, to explore the growth of larch seedlings under drought and nitrogen combination properties, physiological characteristics and adaptive mechanism, to improve the system vegetation drought conditions, understand the boreal forest ecosystem function and the change of the pattern is of great significance, as well as reasonable adjustment sewage sludge in the process of Larix gmelinii breeding management, optimizing cultivation measures to provide theoretical reference. A pot controlled experiment with two factors were subjected to a completely random design with three water gradient (normal water stress supply condition70%-80%、 medium water stress condition50%-60%、 severe water stress condition35%-45%field water capacity)and four N supply (N0:0, Nl:5, Nm:10and Nh:15g NH4NO3-N·m-2·a-1) regimes. The aim of this study is to investigate the effect of water stress and nitrogen fertilization on growth and physiological characteristics of one year-old Larch seedlings. The result showed that:(1) With the increase of the degree of drought stress, under different nitrogen treatment larch seedlings’plant height, basal diameter growth has a downward trend, and for larch seedling biomass accumulation and biomass allocation pattern having a significant impact. The more serious the drought stress, the less leaf area, total biomass accumulation, the ground biomass, The more serious the drought stress, the less leaf area, total biomass accumulation, the ground biomass, and have a significant impact. Under the interaction of drought stress and nitrogen, nitrogen treatment can promote growth to a certain extent, but under the condition of different moisture there is a different nitrogen effect. Under the condition of normal water supply, the increase in nitrogen level seedling growth index and biomass accumulation. And drought stress condition, after excessive nitrogen seedling growth, biomass accumulation have fallen down. The plant reducing leaf area, to reduce the blade allocation proportion, to reduce their water consumption status, and increase the stem and root distribution proportion, to distribute the limited resources more biomass to underground part and stem biomass.(2) Under different drought stress treatment, larch seedlings photosynthesis significantly suppressed. With the increase of drought degree in the same light intensity when seedlings Pn gradually reduce, light saturation point was gradually reduced. And the right amount of nitrogen under the conditions of different drought stress can to a certain extent, improve the photosynthetic ability of larch seedlings. Under low nitrogen treatment in severe drought has obvious promoting effect to the plant photosynthetic capacity, and the promoting effect weakened under high nitrogen treatment and to suppress. Severe drought conditions, seedling Pmax in HN levels showed low, under LN levels showed a maximum value. At this time nitrogen treatment of Pn and Ci have showed the same change trend, Pn decline is caused by the stomatal factors.Under different drought stress treatment, larch seedlings stem respiration also significantly suppressed. Under high nitrogen treatment in severe drought has obvious reduce stem respiration. Level of HN under the condition of normal water supply, and level of MN under the condition of middle water supply, seedlings stem respiration is significantly higher than other nitrogen levesl under the same conditions of water supply.Drought stress rised the content of larch seedlings leaf chla, chlb, total chl and chla/b. But the same water treatment under different nitrogen levels between the different change trends, the amount of nitrogen level can significantly improve the larch seedlings chla, chlb, total chl content. Under MS and HS conditions, level of HN inhibits the accumulation of photosynthetic pigment. But under the condition of MS, MN levels showed a higher level of photosynthetic pigment. And under the condition of the HS, LN levels showed a higher level of photosynthetic pigment.(3) Larch seedlings leaf relative water content (LRWC) decreased with increasing the degree of drought stress, under the same water treatment under different nitrogen levels LRWC change also each are not identical. LRWC under moderate drought stress, with the increasing of N application levels showed a trend of after rising first down, LRWC under the MN level showed the highest, significantly higher than other nitrogen levels. Under severe drought stress, LRWC showed the same change trend with the moderate drought stress, but LRWC under LN levels showed high.(4) Seedling total SS content decreased with the increase of the degree of drought stress, and the same water treatment under different nitrogen levels between the changing trend also shows as a consistent trend, only change in different. Under the condition of the HS, content of leaf, stem and root SS increases with the increase of N application show the first after reduce the trend, and LN treatment showed the highest content of SS, HN processing showed leaf content is the lowest. As the aggravate that the drought stress. Compared with the control, plants under various nitrogen levels had more Pro, MDA content. Under moderate drought stress, compared with controls the seedling Pro content, MDA content under different n application levels showed a small upward trend, but under the MN level the content up minimum amplitude; Under severe drought stress, compared with controls the seedling Pro content, MDA content under different n application levels showed a bigger upward trend, and with the highest content of HN levels, the lowest content of LN level. |
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