EFFECTS OF DISTURBANCE AND SOIL AMENDMENTS ON DISSOLVED ORGANIC-CARBON AND ORGANIC ACIDITY IN RED PINE FOREST FLOORS

A site manipulation experiment was conducted to test the effects o liming, drought, fertilization, sawdust amendment, and root trenching on water-soluble humic substances in the 0 horizon of a mature red pine (Pinus resinosa Ait.) stand in Maine. Concentrations of water-extractable dissolved organic carbon (DOC) in the sawdust and root trenching treatments were approximately twice as high as DOC in the untreated controls and other treatments. Mean carboxyl group contents of DOC ranged from 4.8 to 6.3 mol/kg C among treatments and controls. Control and drought treatments contained the highest carboxyl contents, whereas the sawdust and fertilizer treatments had the lowest carboxyl densities. Synchronous scan fluorescence spectra for the water extracts contained major peaks at 350, 395, and 470 nm, and these peaks were similar to those obtained for reference humic and fulvic acid standards, as well as selected aromatic model compounds. Overall, the fertilizer treatment produced a 20% decrease, the root trenching generated a 70% increase, and the sawdust treatment yielded a 120% increase in the release of organic acid ligands as compared with the control plots. The twofold range of variation in DOC and organic acidity associated with different substrate conditions in this experiment was considerably smaller than the tenfold range of variation reported in the literature for sites from diverse geographic locations. This suggests that the quantitative fluxes of DOC and organic acidity from forest soil 0 horizons are determined by the interactive effects of substrate conditions, climate, and other local site factors.