Morphological And Physiological Responses Of Fraxinus Mandshurica Seedling Roots To Nitrogen Stress

Nitrogen is indispensable to plant growth and development, but it is usually confine resource in the soil, the plant roots can be made morphology, structure and physiological adaptive response through self-regulation at nitrogen stress, by which root can increase the chances of survival in the stress condition. Fine root absorb nutrients and water from soil, which is vital organs of plant, how the root morphology, structure and physiological of Ash response to the different N availability does is ambiguous? Therefore, in this study, one-year-old seedlings of Ash were studied by sand-cultured in pots with three nitrogen (N) level treatments (1,8,16 mmol/L ) in greenhouse. We measured the parameters of morphology of total roots and the first three order roots, anatomical properties, the N, C contents and roots physiological, then analyzed the mechanism of seedlings response to the nitrogen level treatments, these results may improve the technology of forestry management and production of seedlings. The main results were below:Morphology of total seedling roots was significant changed under different N treatment. The total surface area and total length increased significantly with increasing N concentrations supplied at July, August and September; which increased significantly along with the extension of time at every N level. The mean diameter was higher in low N treatment than in control and high N treatments at July and August, while it was higher in high N treatment than in control and low N treatments at September; the mean diameter had insignificant change along with the extension of time at every N level. The specific root length (SRL) increased significantly with increasing N concentrations supplied at July; however, it was higher in control than in low N treatment and high N treatments at August and September; which decreased significantly along with the extension of time at every N level. At the seeding different growth phase, significant decrease in height, collar diameter, overground, underground, total biomass and S/R in low N treatment compared to the control, while the high N treatments just the opposite whit low N treatment; The above growth Index increased along with the extension of time at every N level besides of the S/R.The mean surface area and length of the first three order individual roots increased significantly with increasing N concentrations supplied at July, August and September; which increased significantly along with the extension of time at every N level. Low N treatment resulted higher diameter comparing with control or high N treatments at the seeding different growth month; the mean diameter had also insignificant change along with the extension of time at every N level. The SRL decreased obvious in low N treatment at July and August; while it was the highest in control at September; the SRL of the first three order individual roots decreased significantly along with the extension of time at every N level. The low N treatment in the first three order roots increased cortical thickness, while high N treatment increased vascular bundle significantly at the seeding different growth phase. The layer of cortical thickness had insignificant change in the same root order indifferent N concentrations at the seeding different growth month, so the low N treatment increase the diameter of cortical thickness cell compare to the control and high N treatments. The cell lengths in the first three order roots were decreased markedly with the increasing N concentrations supplied at the seeding different growth phase.The N contents decreased with increasing the root order, which increased significantly with increasing N concentrations supplied at July, August and September; N contents increased significantly along with the extension of time at every N level. The soluble sugar, starch and total non-structural carbohydrate content of 1-3 order roots increased with increasing the root order, which decreased obvious with increasing N concentrations supplied the seeding different growth phase; and they increased along with the extension of time at every N level. The root vigor at low N treatment were the greatest of three N levers at first three order individual roots, and it higher at high N treatment then low N treatment; the membrane penetration showed that: low N treatment > high N treatment >control.In conclusion, the effects of N on morphology, structure and physiological of Ash seedling roots' are significant. The low N stress and high N stress all negative to seedling's growth ability, but the seedlings also have the acclimation and adaptation to the disadvantage environment.