Jentschke Georg, Winter Susanne, Godbold Douglas L.
Forest Ecosystem Research Centre, Institute of Forest Botany, University of Göttingen, Büsgenweg 2, D-37077 Göttingen, Germany.
Tree Physiol. 1999 Jan;19(1):23-30. doi: 10.1093/treephys/19.1.23.
We studied the effects of ectomycorrhizal colonization by Laccaria bicolor (Maire) Orton S238 and Paxillus involutus (Batsch) Fr. 533 on cadmium (Cd) toxicity in Norway spruce seedlings (Picea abies (L.) Karst.). Both mycorrhizal and nonmycorrhizal seedlings were exposed to 0 (control), 0.5 or 5 &mgr;M CdSO(4) for 9 weeks in a sand culture system with frequent addition of nutrient solutions. In pure culture, P. involutus and L. bicolor showed similar Cd tolerance. However, in symbiosis, the Cd treatments decreased colonization by L. bicolor but not by P. involutus. Paxillus involutus ameliorated the negative effects of 0.5 &mgr;M Cd on shoot and root growth and chlorophyll content of old needles, whereas L. bicolor did not. Mycorrhizal colonization did not affect Cd concentrations of old needles and roots of seedlings. Despite differences between the ectomycorrhizal fungi in colonization and ability to alleviate Cd toxicity of seedlings, both species reduced Cd concentrations of young needles to a similar degree compared with nonmycorrhizal seedlings. However, in the 0.5 &mgr;M Cd treatment, the Cd content of needles of seedlings colonized by P. involutus was increased, whereas the Cd content of needles of seedlings colonized by L. bicolor was similar to that of needles of nonmycorrhizal seedings. When the amount of Cd translocated to needles was expressed on a root length basis to account for differences in the size of the root systems, the amount of Cd translocated to the needles was similar in seedlings mycorrhizal with P. involutus and in nonmycorrhizal seedlings. All mycorrhizal seedlings were similarly affected by 5 &mgr;M Cd, indicating that the amelioration efficiency of ectomycorrhizal fungi is dependent on the metal concentration to which the roots are exposed. Concentrations of P, K, Ca, Mg and Mn were decreased by 5 &mgr;M Cd to a similar extent in both nonmycorrhizal and mycorrhizal seedlings. In contrast to L. bicolor, P. involutus increased P uptake and altered patterns of root branching. We conclude that mycorrhizas alleviate Cd-induced reductions in growth of Picea abies seedlings. Although the two mycorrhizal fungi examined differed in their ability to alleviate Cd toxicity, these differences were not related to differences in Cd uptake or translocation to the shoot of the mycorrhizal seedlings. We suggest that amelioration of Cd toxicity by P. involutus may be a result of improved P nutrition or changes in root morphology, or both.
我们研究了双色蜡蘑（Maire）Orton S238和卷缘桩菇（Batsch）Fr. 533的外生菌根定殖对挪威云杉幼苗（欧洲云杉（L.）Karst.）镉（Cd）毒性的影响。在频繁添加营养液的砂培系统中，将菌根化和非菌根化的幼苗暴露于0（对照）、0.5或5 μM的CdSO₄中9周。在纯培养中，卷缘桩菇和双色蜡蘑表现出相似的Cd耐受性。然而，在共生状态下，Cd处理降低了双色蜡蘑的定殖率，但未降低卷缘桩菇的定殖率。卷缘桩菇改善了0.5 μM Cd对新梢和根系生长以及老针叶叶绿素含量的负面影响，而双色蜡蘑则没有。菌根定殖不影响幼苗老针叶和根系中的Cd浓度。尽管外生菌根真菌在定殖和缓解幼苗Cd毒性的能力上存在差异，但与非菌根化幼苗相比，这两个物种都将新针叶中的Cd浓度降低到了相似的程度。然而，在0.5 μM Cd处理中，卷缘桩菇定殖的幼苗针叶中的Cd含量增加，而双色蜡蘑定殖的幼苗针叶中的Cd含量与非菌根化幼苗的针叶中的Cd含量相似。当以根长为基础表示转运到针叶中的Cd量以考虑根系大小的差异时，卷缘桩菇菌根化的幼苗和非菌根化的幼苗中转运到针叶中的Cd量相似。所有菌根化幼苗受到5 μM Cd的影响相似，这表明外生菌根真菌的改善效率取决于根系所暴露的金属浓度。在非菌根化和菌根化的幼苗中，P、K、Ca Mg和Mn的浓度都因5 μM Cd而在相似程度上降低。与双色蜡蘑不同，卷缘桩菇增加了P的吸收并改变了根分支模式。我们得出结论，菌根可缓解Cd诱导的欧洲云杉幼苗生长减少。尽管所研究的两种菌根真菌在缓解Cd毒性的能力上存在差异，但这些差异与菌根化幼苗对Cd的吸收或向地上部分的转运差异无关。我们认为，卷缘桩菇对Cd毒性的改善可能是P营养改善或根形态变化或两者兼有的结果。
