Root turnover and root necromass accumulation of Norway spruce (Picea abies) are affected by soil acidity

Fine root distribution and turnover were investigated in ca. 40-year-old pure Norway spruce (Picea abies Karst.) stands in Germany, growing on four sites that differed in soil acidity (Ebergotzen < Barbis < Fichtelgebirge = Harz). The density of fine root biomass and necromass in different soil horizons differed among the sites. At one of the most acidic sites (Harz), fine root density in the humus layer was more than twice that at the least acidic site (Ebergotzen). At the two most acidic sites, Fichtelgebirge and Harz, the ratio of biomass to necromass was significantly lower than at Ebergotzen and Barbis, particularly in the subsoil layer. In each stand, clear vertical gradients in fine root length density and root tip density were observed. Most of the roots and the root tips were in the humus layer and in the first mineral soil horizon (0-10 cm). There was a significantly different decrease in specific root length (cm gDM (-1)) and specific root tip density (root tips gDM (-1)) in the more acidified stands Fichtelgebirge and Harz compared with Ebergotzen and Barbis. Fine root production estimated by ingrowth cores and a net method was approximately twice as high in the more acidic stands Fichtelgebirge and Harz compared with Ebergotzen and Barbis. Rates of living fine root biomass turnover were higher at the Fichtelgebirge and Harz sites than at the Ebergotzen site. Rates of necromass turnover were similar at all sites. The results suggest that the accumulation of necromass was not due to a slower disappearance at the more acid sites, but to earlier root death. Roots contributed 46% to root + needle litter and 32% to root + total aboveground litter at the Harz site in 1997.