【作者】 高明霞；

【导师】 王国栋； 胡正义；

【作者基本信息】 西北农林科技大学 ， 土壤学， 2009， 博士

【摘要】 硫(S)素是植物必需营养元素之一。人类活动极大地扰动了陆地生态系统S循环,导致土壤-植物系统S呈明显时空变异性。我国水稻土S过量、不足并存。近年来,在矿区和经济发达地区,水稻土受重金属镉(Cd)污染较普遍,对稻米食品安全形成威胁。因此,研究和调控水稻对Cd的吸收过程,控制Cd通过食物链传递危及人类健康具有重要的现实意义。本研究在研发了水稻根表胶膜浸提体系和元素测定新方法的基础上,以水稻为研究对象,采用土-砂联合培养方法结合扫描电镜技术,研究了硫和镉对水稻根表微观结构、根际胶膜、水稻镉吸收的影响及其交互作用。主要试验结果如下:研发的抗坏血酸-柠檬酸钠-乙酸钠根表胶膜元素浸提剂(ACA)对胶膜元素的浸提率高于传统浸提剂DCB,能测定包含S、铁、锰、磷、重金属等元素,为进一步开展S对水稻根胶膜形成及其生态环境效应研究奠定了方法学基础。在硫丰富土壤上施硫(过量硫胁迫)对水稻根表微观结构、根表胶膜具有一定影响,影响程度与硫形态、硫水平有关。硫酸盐施用有减少水稻根表铁浓度趋势,而元素硫则相反。硫胁迫和镉污染对水稻吸收镉具有显著交互作用。硫对水稻吸收镉影响与硫形态、硫水平、镉胁迫程度有关。施硫酸盐和元素硫均导致水稻地上部镉浓度下降,元素硫施用减少镉污染土壤中水稻根镉浓度,硫酸盐施用却增加镉污染土壤中水稻根镉浓度。硫形态不同,对水稻幼苗镉吸收影响机理不同。无论是施元素硫还是施硫酸根硫,由于铁膜-Cd所占水稻吸收镉的比例较大,铁膜都是阻止水稻吸收和转运Cd的重要机制。元素硫没有改变Cd在水稻幼苗不同部位的分布,而硫酸根硫明显改变了Cd在水稻幼苗不同部位的分布。随硫酸根硫施用量增加,水稻苗期根Cd含量显著增加,说明根组织在硫酸根含量较多情况下,其阻止水稻吸收镉和向地上部转运的作用逐渐增强,成为阻止镉进入水稻可食部位的另一主要机制。施硫、施镉对铁膜在水稻幼苗根表不同部位的形成、结构、厚度都有明显的影响,但对整个根系来说,施硫、施镉对根膜铁锰浓度的影响差异不大。根表铁膜形成是在根表皮细胞壁外成层堆积,没有发生向根表皮细胞内的渗透。硫对水稻镉吸收影响机理应与硫对水稻根胶膜、硫对镉在土壤活性等因素的影响有关。本文研究结果证实硫能减少镉污染土壤中水稻对镉的吸收,其对于减少尾矿区的高硫高镉水稻土中镉向食物链传递具有重要的理论和实践意义。更多还原

【Abstract】 Sulfur (S) is one of the essential elements for plant growth. Human activities, such as fossil fuel consumption, fertilization, irrigation of wastewater containing S, have greatly perturbed the S cycle in terrestrial ecosystem and resulted in spatial variability of S in soil-plant system. The excessive S was observed in paddy soil at acid rain area, and/or irrigation fields of wastewater containing S, while S deficiency also occurred in some area of China. It was reported that paddy soils have been contaminated by cadmium (Cd) in many mining and developed areas. It becomes more and more urgent to understand the mechanism of Cd uptake and accumulation in rice to control its harm to human health through food chain. In the present study, an effective method for the extraction and element analysis of the iron plaque on the root surface of rice was developed, and pot experiments were conducted to study the effect of S supply on the formation of iron plaque on the rice root surface, microstructure, and Cd uptake by rice. The major results were reported as follows.An effective extraction solution (ACA: ascorbic-citrate-acetic) for the extraction and elemental analysis of iron plaque from the root surface of rice was developed. It has a higher extracting efficiency of Fe, Mn, P than DCB. Moreover, S concentration in the solution could be simultaneously determined together with Fe, Mn, P and other heavy elements. It is the basis of investigating the effect of S on iron plaque formation and their ecological effects.Differences of sulfur supply on micro structure of root surface, iron plaque from the root surface of rice were determined in dependence on sulfur form, sulfur levels. Supply of sulfate-S tended to decrease concentration of Fe in iron plaque from the root surface of rice, otherwise it’s opposite for elemental S. There were significant interaction between S stress and Cd pollution to Cd uptake by rice. Significantly differences of sulfur supply on Cd uptake by rice seedlings were demonstrated in dependence on sulfur form, sulfur level, Cd levels. Supply of sulfate and/or elemental sulfur resulted in a decrease of Cd in shoot of rice cultivated in Cd stressed soil; supply of elemental sulfur decreased Cd in roots of rice seedlings cultivated in Cd stressed soils, but supply of sulfate increased Cd in roots of rice seedlings cultivated in Cd stressed soils. Supply of sulfate and elemental sulfur < 30 mg S·kg-1 increased concentrations of Cd in shoots of rice seedlings cultivated in low Cd soils, but excessive sulfur supply resulted in decrease of Cd in shoots of rice seedlings cultivated in low Cd soils.The effect mechanisms of Cd uptake by rice seedling are different under different sulfur forms. The iron plaque is an important barrier to prevent the uptake and transportation of Cd from rice because of a large proportion of plaque-Cd in total Cd uptake by rice whatever to supply elemental sulfur or sulfate. Element S doesn’t change the distribution of Cd in rice seedlings, otherwise sulfate changes the distribution significantly. The root Cd of rice seedling increased with the increasing of sulfate supply, showing that under the condition of more sulfate, the effect of the root tissue to prevent the Cd uptake into rice and Cd transportation to shoots increased gradually, and it is another important mechanism to prevent Cd to enter into edible parts.The supply of sulfur and Cd had significant effects on the formation, structure and thickness of iron plaque in different parts of root surface of rice seedling, but there were no significant differences to the concentration of Fe and Mn of plaque for total root. The formation of iron plaque was to accumulate stratified out of the cytoderms on the surface of root, but not to penetrate into the cells on the surface of root.Effect of S on Cd uptake into rice could be related to S induced activity of Cd in soil, S induced transformation of iron plaque formation in the root surface. Therefore, S supply could effectively reduce Cd accumulation in rice exposed to Cd contaminated soils.The mechanism of sulfur to affect Cd uptake was related to the effects of sulfur on iron plaque and Cd activities of soil. The present research demonstrated that sulfur could decrease the Cd uptake by rice in soils contaminated by Cd, which had important theoretical and practical meaning to decrease the Cd transportation from paddy soil with high level of sulfur and Cd in mining area to food chains.更多还原