Biomass and morphology of fine roots in eight Cryptomeria japonica stands in soils with different acid-buffering capacities

Abstract

Cryptomeria japonica, which is one of the main silvicultural species in Japan, accumulates calcium (Ca) in soils with high acid buffering capacity (ABC) but has depleted Ca in soils with low-ABC over the past two decades. However, the contribution of fine roots in C. japonica to the accumulation or depletion of Ca in soils with different ABCs has not been evaluated. The aim of this study was to clarify the responses of C. japonica fine roots in terms of biomass and morphology in eight plantation stands to soils with two contrasting ABCs, which have different trends of soil acidification. We evaluated the biomass and specific root length (SRL) of fine roots divided into three diameter classes (<0.5, 0.5–1.0, and 1.0–2.0mm), obtained from the organic layer and two mineral soil layers from 0 to 10 and 10 to 20cm depths, in soils with high- and low-ABCs. We also investigated root traits of seedlings grown in soil monoliths in-situ in a greenhouse condition to compare the response of mature trees in stands. The biomass of fine roots (<2.0mm) in mature C. japonica was significantly higher and the SRL was significantly lower in low-ABC soils than in high-ABC soils. In the organic layer, the biomass of very fine roots (<0.5mm) at the organic soil layer in low ABC soils was higher than that in high ABC soils. However, the SRL and the dry weight of the seedlings in the greenhouse condition showed no differences between the soils with two contrasting ABCs. We concluded that fine roots of C. japonica stands could have changed and contributed differently to soils with contrasting ABCs. The conflicting root responses of mature trees in stand and seedlings under controlled conditions suggest that careful caution should be taken to extrapolate in-situ mature trees from the results of seedlings, particularly when evaluating the effects of soil degradation such as soil acidifications on sustainable C. japonica plantation forests.