Effects of forest management history on fine roots and mycorrhizal colonization in Norwegian boreal spruce forests

Abstract

Fine roots play critical roles in carbon cycling in boreal forests. However, they are poorly represented in the studies of forest management effects on forest soil, likely due to the labour- intensive methods of soil sample collecting and time-consuming root sorting. Thus, measurements of fine root biomass and mycorrhizal colonization in near-natural and clear- cut stands, based on the soil core sampling, represent an important contribution to the understudied belowground biomass of boreal forests.

We collected 144 soil samples in 12 pairs of near-natural and clear-cut forests of South-East Norway. After dividing collected soil samples into soil layers, roots were sorted out and classified according to the type and size. Fine roots (diameter <2mm) were further analysed with the WinRhizo root analysis system to obtain data on the average root diameter, root length, and number of root tips. In the final stage, roots were dried and weighed to determine dry weight.

There were no significant differences in any of the analysed root traits, average root diameter, root biomass per surface area, specific root length, and number of root tips per surface area, between the two forest types. The non-significant observation may be explained by relatively low number of samples, the development of clear-cuts over time, high variability among the root traits and soil depth. Further analysis of collected soil samples resulting in a larger number of replicates, would increase the accuracy and reliability of the results. The obtained results on fine root biomass and mycorrhizal colonization provide a valuable contribution to the estimates of belowground carbon storage in Norwegian boreal forest.