Morphological traits of Chamaecyparis obtusa fine roots are sensitive to soil acid buffering capacity

Aims The purpose of this study was to clarify how the morphological traits of Chamaecyparis obtusa (Sieb. & Zucc.) Endl. roots vary with soil acid buffering capacity (ABC), i.e., along a gradient in soil acidification. We used an order-based root classification system instead of a diameter-based root classification system, as the former relates better to root function. Methods We sampled 210 intact fine root systems up to the fourth order and measured the morphological traits of a total of 16,657 individual branch-order roots in three C. obtusa stands with high soil ABC and four stands with low soil ABC. Results We found significant differences in the morphological traits of the first- to fourth-order roots between the soil ABCs. In the low-ABC soils, the fine root systems consisted of more and thinner roots than in the high-ABC soils. The diameter of the second-order roots was positively correlated with the soil pH and the concentration of base cations, but negatively with soil aluminum. Conclusion Morphological traits of fine roots are sensitive indicators of soil acidification in C. obtusa forests.