Effects of calcium treatment on forest floor organic matter composition along an elevation gradient

Calcium amendment is a restorative option for nutrient-depleted, acidic soils in the forests of the northeastern United States. We studied the effects of watershed-scale wollastonite (CaSiO₃) application on the structural composition of soil organic matter (SOM) and hot-water-extractable organic matter (HWEOM) at the Hubbard Brook Experiment Forest in New Hampshire 7-9 years after treatment, along an elevation gradient. Soils in the high-elevation spruce-fir-birch (SFB) zone contained significantly greater amounts of HWEOM compared with lower elevation hardwood soils, likely due to differences in litter quality and slower decomposition rates in colder soils at higher elevation. The only significant difference in hot-water-extractable organic carbon concentration between reference and calcium-treated watersheds was in Oie horizons of the SFB zone, which also exhibited the greatest degree of soil chemical change after treatment. The ¹³C nuclear magnetic resonance (NMR) spectra showed no significant patterns in O-alkyl C abundance for either soil or HWEOM along the elevation gradient, suggesting that there were no elevation-related patterns in carbohydrate concentration. The general absence of long-term effects in this study suggests that effects of Ca amendment at this dosage on the composition of SOM were small or short-lived.