Effects of fine root characteristics of beech on carbon turnover in the topsoil and subsoil of a sandy Cambisol

Abstract

Fine roots that enter mineral soil at different depths are a major source of organic carbon stored in forest soil. Little is known about the key factors that govern the mineralization kinetics of fine roots in topsoil compared with subsoil. Therefore, we analysed the effects of concentration, spatial distribution and size of fine beech roots on their rates of decomposition in the topsoil and subsoil of a sandy Cambisol. Undisturbed (intact soil columns) and disturbed (soil sieved < 2 mm) samples from the topsoil (2–10 cm) and subsoil (145–153 cm) were incubated for 365 days to determine the carbon dioxide emissions. The treatments included applications of fine roots that varied in size (length: <2 mm and 1–2 cm), different rates of application (2 and 8 g kg‐1) and spatial distribution (homogeneous and locally concentrated, i.e. localized). The mineralization was affected significantly at both depths by the rate of application (large rate > small rate) and in the topsoil by distribution (localized > homogeneous). The spatial distribution of large roots, but not smaller ones, affected rates of emission in subsoil but not in topsoil. Correlation analyses suggest an effect of the calcium and potassium supply on the microbial biomass and on the turnover of roots if these are locally concentrated. The data of this study suggest that in sandy soil the availability of macronutrients has to be considered complementary to root characteristics such as concentration, size and distribution to elucidate their decomposition kinetics throughout the soil profile.HighlightsAnalysis of effects of characteristics of fine beech roots on organic matter decomposition in top‐ and subsoil. The rate of decomposition in the topsoil was larger if the fine roots were locally concentrated. The rate of mineralization of fine beech roots in the subsoil increased with increasing root size. Soil microbial biomass carbon is affected by the supply of calcium and potassium if the fine beech roots are locally concentrated.