Mechanisms and regulating factors of dissolved organic matter production in forest soils of Japan and Indonesia

Kazumichi Fujii1, Chie Hayakawa, Mari Uemura, Yuji Nakata, Makoto Yoshida, Shinya Funakawa
1 Department of Forest Soil Environment, Forestry and Forest Products Researc Institute

P 7.7 in Controls of dissolved organic matter fluxes in ecosystems

Poster Session 1 on Monday, 16:30-18:30

In forest ecosystems, most of the organic matter supplied to the soil mineralizes to CO2, but a proportion is leached as dissolved organic matter (DOM) from the organic horizon. DOM flux plays important roles in C and nutrient cycling in forest soils, however, the mechanisms and regulating factors of DOM production remain to be clarified. Since DOM contains high concentrations of aromatic compounds derived from lignin, we hypothesized that large DOM fluxes are produced by fungal ligninolytic activities. To test this, we investigated the DOC fluxes in the soil profiles and their relationships with lignin decomposition activity.

The DOC fluxes in precipitation, throughfall, and soil solution were quantified in three forest sites of Japan and five forest sites of Indonesia. The organic horizon and mineral soil solutions were collected using tension-free lysimeter and their DOC concentrations were measured. The aromaticity of DOM in soil solution samples was estimated from the specific UV absorbance at 280 nm. The activities of lignin-degrading enzymes [lignin peroxidase (LiP) and manganese peroxidase (MnP)] were measured for the samples of organic horizons. To confirm the presence of the potential enzyme producer in the organic horizon of beech forest (Japan), we also analyzed the fungal community composition from DNA.

The annual DOC fluxes within ecosystems were greatest in the organic horizon, and they decreased with depth in the mineral soil horizons. The proportions of DOC flux from the organic horizon relative to C input were consistently high (13-16%) in the highly acidic soils. The DOC concentration increased with aromaticity of DOM, suggesting that DOM production is driven by release of aromatic compounds through lignin solubilization and their co-bonding with carbohydrates. The activities of both MnP and LiP were detected in the organic horizons, and the LiP activities in the FH layers were highest at beech and dipterocarp forests where the highest DOC concentrations were observed. The DNA analyses of fungal community confirmed the presence of white-rot basidiomycete fungi (e.g., Trechispora spp.) and ectomycorrhizal fungi in the beech forest. Since wood-rot fungi are known to be the only producers of LiP, their presence suggests production of ligninolytic enzymes and lignin solubilization to aromatic compounds in the beech forest. The increased activity of ligninolitic enzymes at low pH appeared to increase production of aromatic DOM. Ectomycorrhizal fungi cannot produce LiP and MnP, however, organic acid exudation from ectomycorrhizal roots could solubilize Al bonded to DOM and increase DOM mobility, especially in beech and dipterocarp forests associated with ectomycorrhizae.

The large DOM fluxes from the organic horizons in the beech and dipterocarp forest soils can be explained by high activity of lignin solubilization by LiP of white-rot fungi at low pH and organic acids from ectomycorrhizal roots.

Letzte Änderung 19.06.2014