Abstract

Fine roots of trees can be sensitive indicators of environmental change. This thesis analyses the response of tree fine-root (<1 and <2 mm in diameter) systems in deciduous and conifer stands to different sustainable management regimes. Separate studies were conducted in plantations and in natural stands of the Baltic Sea region. Clones of Salix viminalis and S. dasyclados in an unfertilised short-rotation forestry (SRF) plantation in Estonia (58°42¢N, 26°55¢E) were studied to compare the decomposition dynamics of fine roots, and the amount, structure and species diversity of associated ectomycorrhizal (EM) communities. The level of EM colonisation was estimated in stands of Alnus incana (Sweden, Estonia). The effect of granulated wood ash (GWA) on the distribution, morphology and chemistry of fine roots was analysed in a Picea abies stand in SW Sweden (56o33¢N, 13o13¢E), a site exposed to high acid deposition. The fine roots of S. dasyclados were a more recalcitrant substrate for decomposition (k=0.162) than those of S. viminalis (k=0.325), because of the higher initial concentration of acid detergent lignin of the former. The N in decomposing fine roots was retained in the system, as indicated by its decrease and immobilisation in the substrates. The level of EM was high in studied Salix spp. and Alnus incana roots. Salix dasyclados was characterised by a higher proportion of colonised root tips (94%) than S. viminalis (75%). Nine EM fungal taxa were identified in Salix spp. roots in SRF - a relatively low diversity compared with established forest ecosystems. The long-term effect of GWA on fine roots of Picea abies was mainly revealed in decreased necromass (1-2 mm root fraction), in decreased specific root length, and in increased P/N and Ca/N proportions by mass (1-2 mm). Fine-root biomass (<1 mm) was significantly greater in the lower humus in the GWA treatment, but this did not affect the total biomass in the whole soil profile. Wood ash in granulated form and in the long term caused only modest changes in the fine-root system, and can be used as a compensatory fertiliser in Picea abies stands. The results are applicable for maintaining sustainable forest ecosystems.