Fig. 2. The maximum percentage of dissolved organic C precipitated from the dissolved organic matter solutions from the Oa and Oi horizons of a beech and a spruce forest (at pH 4.5 and Al/C ratio of 0.3, except for the Oi-spruce solution, which had an Al/C ratio of 0.1) after Al addition in relation to the content of aromatic C and aromatic H.