Fine root traits in Chamaecyparis obtusa forest soils with different acid buffering capacities

Low soil acid buffering capacity (ABC) accelerates soil acidification because of the lower concentrations of base cations (BC) and higher concentrations of aluminum (Al) present under such conditions. More information on fine root traits across soil ABC gradients is required to evaluate the effects of accelerated soil acidification in mature forests, especially in East Asia. We investigated the biomass, morphology (specific root length; SRL), and respiration rates of fine roots and analyzed the soil nitrogen status in seven Chamaecyparis obtusa stands with two highly contrasting ABC soils. There were no significant differences in the biomass, SRL, and respiration rates of fine roots between high- and low-ABC stands. However, fine roots in the low-ABC stands were concentrated in the uppermost soil layers and the biomass proportion of roots < 0.5 mm in diameter was higher in low-ABC stands than in high-ABC stands. The fine root biomass increased with increasing soil Al, NH4 (+)-N, and C and with decreasing soil BC and bulk density. The SRL and respiration rates of fine roots were positively correlated with soil NO3 (-)-N. We conclude that the fine root traits were affected not only by soil ABC but also by other soil properties in the forest.