Association of ectomycorrhizal mats with Pacific yew and other understory trees at the Andrews Experimental Forest and the southern and western Cascades, Oregon

This study was designed to determine if ectomycorrhizal mats are more likely to be present in soils at the base of common understory trees than in soils distant from trees and to determine if there is a relationship between the occurrence of mats and tree size. The understory trees studied included the Pacific yew (Taxus brevifolia Nutt.) western hemlock (Tsuga heterophylla (Raf.)Sarg) and vine maple (Acer circinatum Pursh). Twelve sites were studied representing a range of climatic conditions and management histories. More than 2,900 plots were surveyed over an 18-month period. It was found that the incidence of ectomycorrhizal mats was higher at the base of all three species of trees when compared with control plots. A statistically significant positive correlation was also observed between the incidence of mats and tree size. When comparing saplings with larger trees, the saplings consistently had a lower incidence of mats. These observations are not consistent with the hypothesis that ectomycorrhizal mats are required for T. brevifolia establishment or survival.

本研究旨在探明外生菌根垫（ectomycorrhizal mats）在常见林下树木基部土壤中的出现概率是否高于远离树木的土壤，并探究菌根垫的出现与树木尺寸之间是否存在关联。本次研究涉及的林下树木包括太平洋红豆杉（Taxus brevifolia Nutt.）、西部铁杉（Tsuga heterophylla (Raf.) Sarg）以及藤枫（Acer circinatum Pursh）。研究共设置12个样地，覆盖了多样的气候条件与经营历史，在18个月的周期内累计调查了超过2900个样方。结果显示，相较于对照样方，三种目标树木基部的外生菌根垫发生率均显著更高；同时，菌根垫发生率与树木尺寸之间存在统计学意义上的显著正相关关系。对比幼树与大型成熟树木后发现，幼树的菌根垫发生率始终更低。上述观测结果与“外生菌根垫是太平洋红豆杉（T. brevifolia）定植或存活所必需”的假说并不相符。