111 Koshland Hall, College of Natural Resources, University of California at Berkeley, Berkeley, California 94720-3102, USA.
Am J Bot. 2000 Dec;87(12):1783-8.
Sarcodes sanguinea is a nonphotosynthetic mycoheterotrophic plant that obtains all of its fixed carbon from neighboring trees through a shared ectomycorrhizal fungus. We studied the spatial structuring of this tripartite symbiosis in a forest where Sarcodes is abundant, and its only fungal and photosynthetic plant associates are Rhizopogon ellenae and Abies magnifica, respectively. We found disproportionately high concentrations of Abies roots adjacent to Sarcodes roots compared to the surrounding soil. Rhizopogon ellenae colonizes the vast majority of those Abies roots (86-98%), and its abundance tends to decrease with increasing distance from Sarcodes plants. At 500 cm from Sarcodes plants we did not detect R. ellenae, and the ectomycorrhizal community instead was dominated by members of the Russulaceae and Thelephoraceae, which are commonly dominant in other California pinaceous forests. The highly clumped distribution of Abies-R. ellenae ectomycorrhizas indicates that Sarcodes plants either establish within pre-existing clumps, or they stimulate clump formation. Several lines of evidence favor the latter interpretation, suggesting an unexpected mutualistic aspect to the symbiosis. However, the mechanism involved remains unknown.
血叶兰是一种非光合的菌根异养植物，它通过与外生菌根真菌共享从邻近的树木中获取所有固定碳。我们研究了在一个森林中这种三方共生关系的空间结构，其中血叶兰丰富，其唯一的真菌和光合植物伴生物分别是蜡伞和华山松。我们发现，与周围土壤相比，血叶兰根旁的华山松根的浓度异常高。蜡伞菌会定植在绝大多数华山松根上（86-98%），并且其丰度随着与血叶兰植株的距离增加而降低。在距离血叶兰植株 500 厘米处，我们未检测到蜡伞菌，而外生菌根群落则由鹅膏菌科和地衣菌科的成员主导，这些成员在其他加利福尼亚松树林中通常占优势。华山松-蜡伞菌外生菌根的高度聚集分布表明，血叶兰植物要么在已有的菌根簇中建立，要么刺激菌根簇的形成。有几条证据支持后一种解释，表明共生关系具有意想不到的互利方面。然而，所涉及的机制仍然未知。
