生态学
污染生态学污染生态学
      多环芳烃污染是近年来受到广泛关注的一个环境问题，但是由于相关研究开展较晚，目前对于多环芳烃污染的植物修复、农产品安全等方面的机理研究仍不充分。
      本文以多年生黑麦草（Lolium perenne L.）为研究对象，以菲为多环芳烃的代表，采用溶液培养的手段，探讨了植物对多环芳烃的吸收、积累和体内运输以及植物生长、根系分泌、体内解毒酶的响应，研究结果如下：
      （1）黑麦草对菲的吸收、积累、运输：黑麦草能够从溶液中吸收菲，并且能够将根系吸收的菲向地上部分运输；黑麦草根系和地上部分吸收菲的浓度与溶液中菲的浓度有关，处理浓度越高，黑麦草体内菲的浓度也越高；黑麦草体内菲的积累与处理时间也有关系，处理6d后地上部分和根系菲的浓度都比处理3d时显著降低，进一步研究其积累的绝对量发现，处理6d后黑麦草地上部分菲积累量较3d处理减少，说明在黑麦草地上部分存在明显的菲降解、而处理6d后，黑麦草根系积累菲的绝对量较3d处理仍有上升，说明黑麦草根系持续吸收溶液中的菲，并且吸收速率远高于根系将菲向地上部分运输的速率，从而造成根系内菲的不断积累；通过计算菲在黑麦草体内的富集系数和传导系数发现，菲在黑麦草体内传导系数小，不超过0.0262，说明黑麦草吸收的菲主要被根部积累，能够在体内向地上部分运输的量很有限；经过一段时间的培养，黑麦草生长的溶液中菲的含量显著降低，但进一步分析黑麦草积累菲对溶液中菲消散的贡献率发现，黑麦草的积累对溶液中菲的消散贡献不大，不超过0.724%，由此得出，植物吸收不是溶液中菲消失的主要原因，推测是由于黑麦草存在下，溶液中微生物与植物的共同作用导致溶液中菲含量显著下降。
      （2）菲对黑麦草根系分泌物的影响：菲处理下，黑麦草根系分泌的低分子量有机分泌物含量发生变化，低浓度菲处理能够刺激根系分泌氨基酸和总糖，但浓度升高后，根系分泌的氨基酸和总糖含量下降，而菲对根系有机酸的分泌都表现为促进作用；分析了根系分泌的低分子量有机物组成后发现，低分子量有机酸是根系分泌的主要低分子量有机物，而草酸又是黑麦草分泌的主要低分子量有机酸；在对黑麦草根系积累的有机酸进行分析后发现，黑麦草根系内部积累的低分子量有机酸在组成上与根系分泌的低分子量有机酸一致，在菲处理下，黑麦草根系有机酸总量变化不大，推测黑麦草根系有机酸的代谢受菲的影响较小；随着菲处理浓度的升高，黑麦草根系有机酸分泌、积累比持续上升，结合其他研究推测，这种促进作用可能对土壤中菲的解吸附有重要意义；各浓度的菲处理均没有引起黑麦草根系活力的下降，黑麦草根系对菲表现出了较强的抗性。
      （3）菲对黑麦草萌发生长的影响：从萌发率的角度看，当菲处理浓度不超过8 mg/L时，黑麦草的种子萌发率与空白对照无显著差异；从种子萌发的时间看，在萌发前4天，菲对黑麦草种子的萌发有显著的延迟作用，但是到了6天后，这种延迟现象消失；从黑麦草幼苗的生长情况来看，幼苗根长和生物量受菲处理的影响表现相同，均在低浓度菲处理下升高，而随着处理浓度继续上升，表现出下降趋势；从黑麦草叶绿素含量来看，菲处理下，黑麦草的叶绿素含量没有下降，且叶绿素a / b的值保持稳定；综合以上各指标发现，黑麦草对菲具有一定的耐受能力。
      （4）黑麦草体内与菲代谢相关的生理响应：由于进入体内的菲代谢产生氧自由基，诱导了黑麦草的超氧化物歧化酶活性在高浓度菲处理6d后显著提高，以清除自由基，避免细胞损伤；在菲处理3d后，最高浓度（8 mg/L）处理下，黑麦草谷胱甘肽－S－转移酶（GST）活性较对照组显著上升、在菲处理6d后，菲处理组的GST活性均显著高于对照组，而各个菲处理浓度组GST 活性又随处理浓度升高显示出上升趋势；菲处理下，还原型谷胱甘肽（GSH）在植物体内含量增加，且增加趋势随处理时间延长和处理浓度升高而愈加明显；这些生理指标显示：黑麦草吸收到体内的菲进行了代谢，并且刺激相关代谢生理指标的上升。 [英文摘要]：     Polycyclic Aromatic Hydrocarbons (PAHs) pollution is an environmental problem which is focused by many researchers in recent years. But due to the short research history, many aspects in this field such as phytoremediation mechanism and the safety of agricultural products are not sufficiently discussed.
    In this research, we chose perennial ryegrass (Lolium perenne L.) as our research material and phenanthrene as a typical PAH, and a solution culture experiment was performed to discuss such problems: the absorption, transfer and accumulation of phenanthrene by ryegrass; the response of plant growth, root exudates and detoxification enzymes to phenanthrene. Our main results were listed as below:
    (1) The absorption, transfer and accumulation of phenanthrene by ryegrass: ryegrass was able to absorb phenanthrene from culture solution, and phenanthrene which had been absorbed by ryegrass root could been transferred to the overground part; the concentrations of phenanthrene in ryegrass root, overground part were related to both the concentration of phenanthrene in culture solution and the exposure time, the higher concentration of phenanthrene in culture solution, the more phenanthrene in plant tissue. After been exposed to phenanthrene for 6 days, the phenanthrene concentrations in plant root and over ground part were all lower then the plant which were exposed for 3 days, considering the plant growth during exposure time, we found that the content of phenanthrene in overground part declined which meant phenanthrene degradation happened in overground part, however, the content in root kept increasing which meant the root was continuously absorbing phenanthrene from culture solution. Plant Concentration Factor and Translocation Factor were all calculated to understand the transfer of phenanthrene in ryegrass; we found that the transfer of phenanthrene in plant was quite limited; the phenanthrene uptake by plant was mainly absorbed in root. Plant uptake and accumulation of phenanthrene was not the main reason which induced the decline of phenanthrene concentration.
    (2) The impact of phenanthrene on root exudates: phenanthrene affected the organic contents in ryegrass root exudates, relatively lower concentration of phenanthrene stimulated the secretion of amino acids and saccharide, but under high concentration of phenanthrene treatment, the secretion of amino acids and saccharide were restrained. Organic acids were the main part of organic content in ryegrass root exudates, and oxalic acid was the dominant organic acids secreted by ryegrass, under all treatments of phenanthrene in this experiment, oxalic acid secretion were stimulated compared with control. In ryegrass root, oxalic acid was also the dominant organic acid accumulated in root, after calculation we found that the total organic acid ( organic acids in root exudates + organic acids accumulated in root ) seemed to be stable under phenanthrene treatments, while the organic acids secretion was enhanced with the phenanthrene concentration increased. The root activity also tested, data showed that, in all treatment the activity of plant root didn’t decline. Considering other researches in this field, we speculated that the stimulated organic acids secretion may play an import part in the absorption-desorption of phenanthrene in soil.
    (3) The effect of phenanthrene on ryegrass growth: the germination rate of ryegrass wasn’t affected by phenanthrene when its concentration didn’t exceed 8 mg/L, while all concentration of phenanthrene showed delay effect on ryegrass germination at the first 4 days of germination. Phenanthrene had the same effect on the root length and biomass, at relatively low concentrations, the root elongation and seedling growth were stimulated by phenanthrene, but at relatively high concentrations, they were restrained by phenanthrene. Under all treatments, the chlorophyll contents and chlorophyll a/b maintained stability. All these indexes showed that ryegrass had a certain degree of tolerance to phenanthrene.
    (4) The physiological response related to the phenanthrene metabolism in ryegrass under phenanthrene treatment: the plant could metabolize phenanthrene, and oxygen radicals were the by-product in this procedure. In this study, we found that the SOD activity rose significantly after treated by relatively high concentration of phenanthrene for 6 days. GST activity significantly rose under 8 mg/L treatment for 3 days, after 6 days, GST activity of all the samples treated by phenanthrene were higher than control. Phenanthrene also could induce the increasing of GSH in plant. These physiological responses indicated that the ryegrass could metabolize phenanthrene in its tissues.