Fine root biomass, production and its proportion of NPP in a fertile middle-aged Norway spruce forest: Comparison of soil core and ingrowth core methods

The mean biomass of fine (<2 mm) and finest (<1 mm) roots in ingrowth cores collected in the third year after installation was two times smaller than that in soil cores. The mean fine root biomass was 1420 ± 170 kg ha −1 in soil cores and 700 ± 105 kg ha−1 in the third year ingrowth cores. The finest roots formed ca. 2/3 of fine root biomass. The fine root NPP estimated by the sequential core method was 2510 and 965 kg ha−1 year−1 by the ingrowth core method (third year after installation). The fine root turnover rate was 1.8 year−1 for sequential cores and 1.4 year−1 for third-year ingrowth cores. The inverse of the root turnover rate is, in turn, a measure of average root longevity; it was smaller for the finest roots in both cases. In the investigated spruce stand the annual NPP of trees at the age of 40 years is estimated as 21.4 t ha−1 year−1, the share of the belowground part forming 31%. Fine roots accounted for 13% of the NPP, which is a relatively small value compared to the results revealed in most studies.