Influence of parent material mineralogy on forest soil nutrient release rates across a nutrient richness gradient

The influence of parent material mineralogy on nutrient release rates in wood production forests remains poorly understood, despite its importance for sustainable forest management. This study investigated how parent material mineralogy impacts soil nutrient abundance and release rates. We studied three forests in Vermont and New Hampshire across a Ca and Mg richness gradient within the soil parent material. We found that both exchangeable and total nutrient concentrations followed the nutrient richness gradient with exchangeable Ca concentrations highest at the rich (758 mg/kg) and lowest at the poor (51.3 mg/kg) sites. Exchangeable Mg concentrations were higher at the rich (41.5 mg/kg) and moderate (42.9 mg/kg) sites relative to the poor (7.04 mg/kg) sites. Total concentrations of Ca were highest at the rich sites (13 mg/g) compared to the moderate (5.73 mg/g) and poor (5.89 mg/g). Total Mg concentrations were higher at the rich (27.3 mg/g) than the moderate (9.47 mg/g) and poor (3.07 mg/g) sites. Using τ values throughout the soil profile compared to the parent material, we found that all three forests were moderate to weakly depleted in Ca, Mg, and K in the upper 30 cm, but P was slightly enriched due to biological uplift. Additionally, we found that calculated field nutrient release rates did not significantly differ among forest nutrient status (p > 0.05), indicating the limited effects from across parent materials. We also conducted a follow up batch reactor experiment at varying pH conditions (4, 5, 6) with organic acids (NaCl, catechol, and citric acid). As expected, pH 4 had the highest Mg release rate (2.19 mg/m²/day) compared to pH 5 (1.27 mg/m²/day), and pH 6 (0.888 mg/m²/day), but surprisingly no effect on Ca release rates, suggesting the more acidic soils of the base cation poor soils results in higher release rates. Our results highlight the dominant contributions of parent material mineralogy has on Ca and Mg release rates, but also that weathering of primary minerals can sustain forest ecosystem productivity.