Characteristics of decomposition of dissolved organic carbon by microbes in water of forest ecosystems

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A flow-through bioreactor method is useful for measurement of biodegradable dissolved organic carbon(BDOC) in water of forest ecosystems. We determined the condition of BDOC measurement as follows ; over 20℃ for air temperature, 0.25 ml/min for solution flow rate and 10 mg/L for DOC concentration of samples. The percentages of BDOC on DOC(BDOC%) in percolated water of organic layer were 20-30% in Japanese cedar (Cryptomeria japonica), Japanese cypress (Chamecyparis obutsa) and red pine (Pinus densiflora) stand, while 50% in mizunara (Quercus mongolica var.grosseserrata) stand. This result suggested that the large amount of nitrogen influenced the BDOC% in mizunara stand.In a small watershed of aged Japanese cedar and cypress plantation, DOC in order of high concentrations were organic layer percolation > through fall > precipitation, and was rapidly low in soil water. The DOC annual discharge in steam water was small (6.4 kg/ha), suggesting the DOC in soil water was consumed by soil microbes and adsorbed on soil colloid. The amount of consumption of water soluble organic carbon (WSOC) had positive correlations with the rate of carbon mineralization in surface soil. Therefore, DOC and WSOC amounts were important indicators for microbe activities. However, these amounts were remarkably smaller than mineralized carbon, so we considered that determination of available organic carbon was necessary.The percentages of lignin on humus increased with increases of decomposition class in forest floor of six species. Especially, the organic carbon in the humus class insoluble by alkaline solution had 70% of carbon in lignin. On the other hand, the amounts of lignin decreased with decreases of mass weight due to decomposition of the leaf litter of six deciduous broad-leaved trees species. We need to make more detailed classification of organic matter, such as easily or hard decomposed lignin.