Proportion of fungal mantle, cortex and stele of ectomycorrhizas in Picea abies (L.) Karst. in different soils and site conditions

Anatomical variability of ectomycorrhizal short roots in Norway spruce (Picea abies (L.) Karst) stands was investigated in five stands differing in site quality class (Ia-V) and soil type. Ten root samples per stand were randomly collected from the forest floor and the subsequent 20 cm soil layer. Thin transverse or axial sections (5 (mu)m) of randomly taken short roots were examined by light microscopy (AXIOPHOT; magnification 200-800*). All analyzed short root tips of Norway spruce in different stands were colonized by ectomycorrhizal fungi. Thickness of the mantle (Tmantle) and cortex (Tcortex) and diameter of the root (Droot) were measured in four crossing radial directions for transverse sections and in two radial directions for axial sections. The proportions of the mantle (PSmantle), cortex (PScortex) and stele (PSstele) of the root cross-sectional area (CSA) were calculated. Mean Tmantle and Tcortex varied from 16.5 +- 0.6 to 29 +- 1.3 (mu)m and 83.9 +- 1.7 to 108.4 +- 2.4 (mu)m, respectively; significant differences between stands were found. The number of cell rows in the cortex (4-6) did not vary between different stands, thus thickness of cortex depended on cell size. Mean PSmantle, PScortex and PSstele of the root CSA varied from 17.7 to 28.1%, from 58.9 to 66.9%, and from 13.4 to 15.8%, respectively. No differences between stands were revealed in mean CSA ratio of cortex and stele. It can be concluded that irrespective of big differences in soil and site conditions, including the influence of fungal symbionts, a 4:1 relation on a CSA basis between the cortex and stele is inherent to Norway spruce.