【作者】 张琴；

【导师】 黄建国；

【作者基本信息】 西南农业大学 ， 微生物学， 2003， 硕士

【摘要】 外生菌根真菌是土壤中非常重要的一类真菌，能与70～75％的造林树种形成外生菌根。优良的外生菌根真菌与木本植物的根系形成外生菌根后，能促进寄主植物的生长，改善它们的营养状况，提高其抗逆(干旱、病虫害，盐害等)能力。因此，外生菌根真菌被在林业生产和植树造林中广泛应用。 某些外生菌根真菌能不同程度的通过多种方式增强寄主植物抵御不良环境的能力，估计对减轻重金属的危害也具积极作用，在污染土壤和矿墟的植树造林中可能有着广阔的应用前景。但是，目前所研究的供试菌种(株)和重金属的代表性和数量不足，尚不能完全弄清外生菌根真菌抗(耐)重金属的能力、机理及应用价值，因此，选择更多的有一定研究基础和应用前景的外生菌根真菌作为供试菌种(株)，研究它们对重金属的抗(耐)性及其机理很有必要。 Cd、Hg是人类活动向环境释放较多的重金属。试验选用彩色豆马勃Pisolithus tinctorius 715(1996年从四川西昌桉树红壤中分离获得)和土生空团菌Cenococcum geophilum SIV(上世纪80年代从西班牙欧洲火炬松土壤中分离获得)两种外生菌根真菌作为供试菌种，在培养基中加入不同浓度的Hg或Cd进行培养，研究了它们的生长状况、氮磷钾吸收、H~+及草酸分泌作用等。目的是了解它们对Hg、Cd的抗(耐)能力和有关机理，为在Hg、Cd污染的土壤和矿墟进行植树造林，防止Hg、Cd进一步迁移释放，污染其它陆生或水生生态环境提供科学依据。研究结果如下： 1．在培养液中加入较低浓度的Hg，外生菌根真菌的生长受到轻微抑制；继续增加Hg的浓度，外生菌根真菌表现出一定的耐受性，生长量不因Hg浓度的提高而显著降低；当Hg的浓度超过一定的阈值后，外生菌根真菌的生长速率迅速降低或停止。Hg对两种外生菌根真菌生长的影响有所差异，Pt 715的生长对Hg比Cg SIV相对敏感。 2．Cg SIV的生长对Cd十分敏感，随着培养液中Cd的浓度逐渐增加，Cg SIV的生长量也随之降低，二者呈直线负相关(y=81.61-3.88X，r=-0.987)。但是，Pt 715对Cd表现出极高的抗(耐)性。在Cd浓度为15mg／L时，Cg SIV的生长量比对照降低74.40％，而在Cd浓度为140mg／L时，Pt 715的生长量仍为对照的73.64％。 3．Hg、Cd对外生菌根真菌生长的抑制作用因重金属元素不同而异。对Pt 715而言，Hg张琴：汞、隔对外生菌根真菌生长、分泌作用和养分吸收的影响 一中文摘要一 对其生长的抑制作用大于Cd，二者的毒性指数分别为：1．614（Hg）和0．576（Cd人 对 Cg SIV而言人d对其生长的抑制作用大于 Hg，二者的毒性指数分别为：0．931（Hg） 和4．59（Cd）。4．外生菌根真菌吸收阳离于和分泌有机酸会释放H＼重金属对外生菌根真菌H”分泌的 影响因菌种不同而异。较低浓度的蝴对 Cg SS的 H”分泌无显著影响，但降低 Pt715 的H“分泌数量，高浓度的Hg同时显著抑制Pt715和Cg SIV的H”分泌。在培养液 中加入 Hg后，外生菌根真菌的生长量和 H”分泌量的关系可用回归方程 y二 0．567＋ 0027X，r＝O．987（Cg SIV）和 y o．653＋O．08’7X， r＝0．998（Pt 715）表示，说明 Hg 对H”分泌的影响与生长同步，即生长量降低减少了H”的分泌量。 低浓度的 Cd促进 Cg SS但抑制 Pt715的 H”分泌，但较高浓度 Cd却显著抑制 Cg SIV 而促进Pt715的 H“分泌。培养基加 Cd处理下，菌根真菌分泌的 H“数量与生长量间 无显著相关性，说明Hg、Cd两种重金属对H”分泌的影响机理不同。5．在不添加重金属的处理中，两种外生菌根真菌分泌草酸的能力差异显著，Pt 715明 显大于 Cg SIV。Hg、Cd可促进 Cg SIV但抑制 Pt 715的草酸分泌作用。向培养液中 添加 Hg或 Cd，Cg SIV的草酸分泌率显著增加，培养液中草酸的数量无显著改变（Hg） 或显著升高（Cd人但 Pt 715的草酸分泌率和培养液中草酸的数量均显著降低。草酸 对重金属有很强的络合能力，在重金属胁迫的条件下，许多抗（耐）能力强的微生物 通过增加草酸分泌以络合重金属，降低它们的危害作用。但本项研究未能支持这种理 论，看来供试外生菌根真菌可能通过某些其它机制抵抗Hg、h对生长的危害作用。6．Cd、Hg两种重金属对外生菌根真菌菌丝体内的氮、磷、钾含量或吸收量的影响因 菌种和金属元素不同而异，但从总体上看，重金属不会显著降低氮、磷、钾含量和 吸收量。 在培养液中加入 Hg之后，Cg SIV菌丝的氮、磷含量和吸收量显著增加，含钾量和 吸收量无显著变化；Hg对 Pt 715菌丝体内的氮、磷、钾含量，以及磷、钾吸收量 无显著影响，但对吸氮量有一定影响。 在培养液中加人 Cd之后，Cg SIV菌丝的磷、钾含量无显著变化，含氮量随培养液 中 Cd浓度上升而增加灯4．20＋12．16X，r＝0．956人与此同时，Cg SIV的吸氮 量显著升高，吸磷量显著降低，吸钾量无显著变化，其中磷素的吸收量与培养液中 Cd的浓度呈显著负相关ha30．23—7．49X，r＝一0．906人对Pt 715而言，菌丝体 内的氮、钾含量显著升高，磷含量随培养液中 Cd浓度上升而缓慢降低h纶7．34更多还原

【Abstract】 Ectomycorrhizal fungi, a group of important fungi in soil, can form symbioint with 70-75% of the trees for artificial reforestation. Selected mycorrhizal fungi could benefit potentially the growth, nutrient status of the host plants as well as their resistance to drought, salt and diseases caused by insects and microorganisms after the infection of the host roots. Therefore, they are widely used in forestry and artificial forestation.Some ectomycorrhizal fungus could, to some extent, improve the abilities of their hosts to resist adverse conditions by variable ways. It seems thus reasonable to suggest that they could effectively alleviate the toxicities of heavy metals and be applied in artificial forestation for the soils and ore debris contaminated by heavy metals. The mycorrhizal fungus and heavy metals studied previously in regard to toxicology are, however, too limited to summarize the fungal resistance to heavy metals. It is not thoroughly clear to understand the abilities of mycorrhizal fungi to resist heavy metal pollution, mechanisms related and potentiality in application in that case. It is thus necessary for us to use more mycorrhizal fungal species and strains intensively studied, which could be applied potentially in artificial forestation in the future, to investigate their resistance to heavy metal toxicities and mechanisms.Cd and Hg are heavy metals largely released, compared to other ones, into environment by human activities. In the present experiment, Pisolithus tinctorius 715, isolated from an eucalyptus growing red soil in Xichang, China, in 1996, and Cenococcum geophilum SIV, isolated from pine growing soil in Spain in 1970s, were adopted. Cd and Hg were added into culture solutions with different concentration gradients. The fungal growth, efflux of protons and oxalate and influx of nitrogen, phosphorus and potassium were observed. The objectives were (i) to realize their resistances to Cd and Hg and the possible mechanisms, (ii) to provide some information for the artificial forestation for soils and ore debris contaminated and (iii) to prevent the continual release of the heavy metals from polluting other territorial and aquatic ecology systems. Following are the results obtain in our experiment.Mycorrhizal fungal growth was slightly inhibited in low Hg concentrations and depressed less with the concentrations increased, indicating the resistance and adaptation to Hg toxicity. But the growth reduced suddenly or stopped as the concentrations go beyond critical ones. Fungal species varied in growth rate under Hg stress. Pt 715 was sensitive and Cg SIV was less sensitive to Hg stress. Cg SIV was quite susceptible to Cd in growth. Thebiomass lowered with Cd concentration increased. Negative correlation was found between biomass and Gd concentration gradients (y = 81.61 - 3.88X, r = -0.987). However, Pt 715 was much less susceptible to Cd compared to Cg SIV. The biomass of Cg SIV cultivated in 15mg Cd / L culture solution reduced 74.40% on the base of blank control, while it reached 73.64% of blank when Pt 715 in 140mg Cd / L solution.Mycorrhizal fungal growth was depressed variously in culture solutions with Cd or Hg added. The growth inhibition of Pt 715 by Hg was more obvious than Cd. The toxic indexes were 1.614 for Hg and 0.576 for Cd. In contrast, it behaved otherwise for Cg SIV. The toxic indexes were 0.931 for Hg and 4.59 for Cd.Efflux of organic acids and protons companied with influx of cation ions in mycorrhizal fungi in the growing period. The fungal species differentiated in proton efflux in heavy metal solutions. The proton efflux by Cg SIV changed very little if any in low Hg culture solutions compared with the blank treatment in contrast to Pt 715, which emitted less protons in this case. The efflux of protons by both Pt 715 and Cg SIV was, however, depressed in high ones. There were positive linear correlations between the proton efflux and fungal biomass, i.e. y = 0.567 + 0.027X for Cg SIV (r = 0.987) and y =0.653 + 0.087X for Pt 715 (r = 0.998). The re更多还原