Changes in quantity, morphology and nitrogen content of fine roots with stand development in a subalpine fir-wave forest

To determine the change in nutrient absorption capacity with stand development, we aimed to clarify the changes in fine root characteristics with stand development and stand characteristics. Stand characteristics (stand age, maximum tree height, tree density and basal area) and fine root characteristics were examined in three fir-wave stands that aged sequentially along the slope in a subalpine Abies forest in central Japan. The biomass, length, surface area and N content of fine roots did not change, but the specific root length (SRL) decreased with stand development, i.e. distance from the upper side of each transect. On the other hand, we observed an increase in fine root biomass with stand characteristics, i.e. maximum tree height and basal area of the Abies community, while a decrease in SRL was also observed. These changes resulted in an increase in surface area and N content of fine roots. However, the surface area of absorptive roots that were <0.5 mm in diameter did not change with stand characteristics. Thus, we suggest that the nutrient absorption capacity of the subalpine Abies community increased with aboveground biomass from the viewpoint of comprehensive activity of fine roots, but not from the viewpoint of fine root morphology. We further confirmed that the ratios of surface area and N content of fine roots to basal area decreased with stand development. Future research is needed to understand the actual effect of surface area and N content of fine roots on the maintenance of aboveground organs.