林冠郁闭度对美国北红橡幼苗外生菌根形态类型的影响(英文)

Effects of Canopy Cover on Morphological Types of Ectomycorrhizae of Northern Red Oak Seedlings *

在密之根州（美国）南半岛北部地区林龄大约９０年的北红橡（ｎｏｒｔｈｅｒｎｒｅｄｏａｋ，ＱｕｅｒｃｕｓｒｕｂｒａＬ．）林中，调查了北红橡幼苗外生菌根形态类型。实验地的立地质量为中等水平。通过砍伐不同数量的上层林木，形成０％（皆伐）、２５％（第一年５０％）、７５％、１００％（高度郁闭）４种林冠郁闭度。北红橡幼苗是由模仿自然更新人工播育种出，种源一致。在头２年，将幼苗上的外生菌根分类、描述和计数，同时收集菌根菌子实体进行鉴定和分析。根据形态特征，将外生菌根分为７个类型，其中４个类型占菌根总数的９４％。据现有资料（已发表的论文及图片等），把这些菌根类型的共生菌种或菌种组归纳。发现，在林冠高度郁闭并由此降低土壤水分的情况下，类型Ⅲ的菌根最多，表明这类菌根具有耐旱性；类型Ⅰ的菌根在皆伐区最多，表明其有耐较高土壤温度能力，因为皆伐后土壤温度比对照林分高出５℃以上。菌根类型随林冠郁闭度变化而变化的现象，反映了菌根关系的复杂性和多样性。本研究结果表明，探明菌根的形态类型比探明菌根菌的种类更有意义。

Morphological types of ectomycorrhizae (ECM) on northern red oak ( Quercus rubra L.) seedlings were investigated at four levels of canopy cover in approximately 90 year old northern red oak forests in intermediate quality sites of northern Lower Michigan. Four levels of canopy cover (clearcut, 25%(50% first year), 75%, and uncut) were created by removing various amounts of overstory trees. Northern red oak seedlings, originated from a common seed source, were established artificially to simulate natural regeneration. The seedlings were sampled to classify and quantify their ECM by morphological type during each of the first two growing seasons. ECM fruiting bodies were also collected, identified and analyzed. Based on ECM morphology, a total of seven ECM morpho types was recognized on the northern red oak seedlings during the first two growing seasons. More than 94% of the ECM were from four of the seven types. None of the ECM types were identified into definite fungal associates. However, attempt has been made to relate these ECM types to the most likely fungal species or species groups based on references to published descriptions and/ or photographies. A greater percentage of type III (shiny white) ECM was found in the closed canopy plots where soil moisture is the lowest among canopy treatments. This incident indicated that type III ECM may tolerate low levels of soil moisture by their abundant extramatrical hyphae and/or rhizomorphs. The percentage of type I ( Cenococcum like) ECM was greatest in clearcuts, suggesting that it may be resistant to high soil temperatures after canopy removal (soil temperature in clearcut was 5℃ higher than that in uncut stands). These shift in ECM types reflects the complexity and importance of ECM diversity in response to different levels of canopy cover. From ecological perspective, ECM morphology may be more meaningful than ECM fungal species.