Abstract
Dissolved organic matter (DOM) derived from the litter layer under Norway spruce (Picea abies (L.) Karst) was separated into different molecular size fractions (<1, 1–10, 10–100, and >100 kDa) with tangential ultrafiltration technique. The chemical characteristics of the molecular size fractions were studied. The degradability of size fractions was assessed as the degradability of DOC and availability of a fraction to soil bacteria and fungi. The molecular size fractions appeared to differ chemically and microbiologically. The smallest molecular size fraction had the highest pH and lowest DOC/DON ratio. The two smallest molecular size fractions contained more carbohydrates and phenolic compounds than the two largest fractions. In all fractions DOC was degraded. The smallest fraction was the most degradable. It had the highest evolution of CO2–C and loss of DOC during the incubation and the highest estimated proportion of labile DOC. The NPK addition increased the evolution of CO2 in the total solution and in all fractions indicating nutrient shortage in all fractions. The smallest molecular size fraction was the most available to soil bacteria and the least available to soil fungi. Due to observed differences between the molecular size fractions tangential ultrafiltration may be useful in characterizing DOM.
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