Different Ph And Different Forms Of Nitrogen On Several Crop Biomass Accumulation And Root Anatomical Structure

Absorption and utilization of water and nutrients is dependent on plant roots, especially on roots' morphological structure and development. Since growth and development of plant roots is controlled by corresponding genes and complex environmental factors, such as nutrients, water, temperature, illumination and pH, it is significant to study the relationship between nutrients uptake and root structure characteristics. Different plant species and varieties have different response to ammonium and nitrate, partly because of their difference in root structures. This dissertation applied four plants, maize (Suyu 16), rice (Yangdao 6), wheat (Yangmai 11) and lupin to explore the relationship between uptake of inorganic nitrogen and root structure characteristics.The whole experiment was carried out under four conditions: pH 4.0, NH₄⁺; pH 4.0, NO₃^-; pH 6.0, NH₄⁺ pH 6.0, NO₃-. After 20 days' growth biomass of seedlings was weighted, length of main radicles was measured and amount of lateral roots was calculated. At the same time roots of seedlings were sampled for making paraffin dissections, and anatomical structures were observed through a microscope. Conclusions were reached as follows:(1) When NH₄⁺-N was supplied as the sole N resource, plant roots were damaged at pH 4.0, but root growth had no obvious inhibition at pH6.0, which indicated that NH₄⁺ toxicity to plant roots development was related to the medium pH. The reason that maize grew even better at low pH level than at near neutral pH may be explained by that visible damage symptoms still didn't occur. Additionally, maize and wheat preferred NO₃^--N to NH₄⁺-N at the seedling stage, while rice and lupin had more effective responses to NH₄⁺-N than NO₃^--N.(2) At low pH level the presence of NH₄⁺-N not only inhibited root elongation, butdecreased the amount of lateral roots and hampered the development of them. At near neutral pH level the presence of NH4+-N hindered elongation of lateral roots, but had no negative effects on the development of them. Especially, roots of lupin didn't affected by the presence of NH4+-N and grew even better at low pH level than at near neutral pH. so it was reasonable to assume that there was a special adaptation mechanic in lupin, which could resist or tolerate the stress of acid environment. Therefore, the presence of NH/-N didn't always inhibit the growth of plant roots and its effects related to plant species and growth environment, such as medium pH.(3) Paraffin sections of rice and maize indicated that when NH/-N was applied as the sole N resources at low pH level, root cells at 10mm behind the apex represented the following characteristics: cortex comprised a large proportion of cross section; cortical parenchyma cells had larger volume and arranged loosely in more layers than when NC^'-N was applied as the sole N resources; vascular cylinder matured early and vessel elements had large cross-section area. Low pH level and the presence of NH/-N accelerated the aerenchyma formation of rice roots. When NH/-N was supplied, lupin root cells at 25mm behind the apex of lupin roots showed the following characteristics: cell volume was apparently larger than when NCV-N was supplied; vascular tissue developed better and matured earlier; and xylem thickened obviously.(4) Effects of both N forms on arrangement of parenchyma cells in roots of maize and rice had no significant difference at near neutral pH level. The presence of NH4+-N stimulated the development of vascular cylinder, where xylem vessel elements developed early and had large radius. Additionally, effects of both N forms on aerenchyma formation in rice roots had no significant difference at near neutral pH level.