Impact of drought and stand edge on mycorrhizal density on the fine roots of Norway spruce

This paper evaluates the mycorrhizal status and root system of Norway spruce (Picea abies (L.) Karst.) with respect to trees’ position within the stand and artificially induced drought stress. Root systems were sampled during autumn of 2008, 2009 and 2013 from spruces exposed to varying conditions (totalling 18 trees, 47 samples). The experiment involved six groups of 3 spruces each. Three groups were growing within the stand and three groups at the stand’s edge. One tree from each group (total 6) was exposed to artificial drought using shelters deflecting rainfall away from the root system. For each sample, the number of active and non-active mycorrhizae on 20 root segments about 5 cm long was assessed. The densities of active and non-active mycorrhizae, proportion of active mycorrhizae, and root dry biomass weight were assessed. Factors’ significances were determined using ANOVA and the Tukey-Kramer test or the Kruskal-Wallis and Dunn’s tests. Samples from outside the sheltered area were characterized by higher numbers of active mycorrhizae than were those sampled within the sheltered area. Induced drought stress significantly influenced active mycorrhizae density. Significantly higher root dry biomass (roots <1 mm in diameter) was found at the stand’s interior versus its edge.