Effects Of Nitrogen On The Absorption And Physiological Characteristics Of Hosta Ventricosa (Salisb.) Stearn To Lead Stress

This study compared the effects of nitrogen on Hosta ventricosa (Salisb.) Stearn under different concentration lead stress in order to deeply understand the absorption characteristics and physiological responses of Hosta ventricosa (Salisb.) Stearn to lead, and also explore the effects of nitrogen on the lead behavior and absorption, and the composite effects of nitrogen and lead on physiology. The results would find a suitable plant to remedy the urban lead contaminated soil and expand the application of garden plants in the city further, which have practical significance for ecological construction of hilly urban human settlement. The results of the studies were listed as follows:1、Appling lead alone did not have obvious influence on the whole biomass, only the dry leaf weight reduced significantly with750-1000mg/kg lead. The growth of Hosta ventricosa (Salisb.) Stearn was restrained with the application of200-600mg/kg nitrogen in all lead concentrations. The root, stem and leaf biomass decreased. The whole plant biomass decreased with the nitrogen concentrations increased, but it did not reach a significant level.2、Adding lead to soil elevated PH value and the elevation was rising first, and then falling slightly with the lead content increased. In the whole lead concentrations processing, appling nitrogen leaded the PH value of soil decreased with the increase of nitrogen concentrations. PH value had no significant difference between the three nitrogen levels under the same lead stress, besides250mg/kg lead processing.Under a single Pb stress, the content of three forms of lead increased with lead concentration going up, nitrogen had different influence on the chemical behavior of lead under four lead levels. When applied with nitrogen, the content of weak acid extraction lead increased under250-1000mg/kg lead stress, the content of reducible lead reduced under250-750mg/kg lead treatment and increased under1000mg/kg lead treatment, the content of the oxidizable lead changed smaller under250mg/kg lead stress and rised under500-1000mg/kg lead process. The distribution of lead in organs was:root> stem> leaf, the maximum enrichment coefficient was0.73and transfer coefficient was about0.25under four lead levels. Nitrogen inhibited the lead absorbtion of the plant roots, except the promotion of400mg/kg nitrogen treatment under high concentration lead stress. Adding nitrogen increased the transfer coefficient in all lead treatments.The subcellular distribution of lead in stems and leaves in all processing were: cell wall> soluble ingredients> organelles. The application of nitrogen decreased the proportion of lead content in cell wall and increased the proportion of lead content in organelles and soluble ingredients both in stems and leaves under250mg/kg lead processing. However, the proportion of lead content in cell wall declined and other two parts showed little change with the addtion of nitrogen under500-750mg/kg lead stress. Nitrogen did not effect the subecellular distribution of lead in stems and leaves under1000mg/kg lead stress.3、Lead had little influence on the chlorophyll content, which increased slightly with low concentrations lead stress and lowered weakly under high concentrations lead stress. In250-500mg/kg lead processing, the chlorophyll content decreased with applying nitrogen; In750-1000mg/kg lead processing, nitrogen inhibited the synthesis of chlorophyll in early period and promoted the synthesis of chlorophyll at the later stage. The lead stress and lead-nitrogen combined stress both reduced the photo synthetic rate, which were consistent with the change of Gs and Tr and were the opposite of the Ci.4、Lead increased the content of soluble protein and free pro line, and remained the soluble sugar content. The content of three osmotic adjustment materials were unchanged with the addition of nitrogen in the early time, soluble protein increased and played the main role in the regulation of oslmotic balance in the middle time, free proline and soluble sugar content increased and adjusted the osmotic balance in the later time. According to the results, Hosta ventricosa (Salisb.) Steam grew well and had strong ability to enrich lead, so it could be used as ornamental plant and remediation plants in lead-contaminated area. The supply of nitrogen greatly inhibited plant growth and reduced the enrichment coefficient. we should find some new avenues to improve the ability of Hosta ventricosa (Salisb.) Steam to repair the lead pollution soil.