Soil Terpenoid Storage and Emissions Are Shaped by Litter Chemistry and Soil Depth

Aims Soil VOCs, particularly reactive terpenoids, play a crucial role in atmospheric chemistry but remain poorly quantified. This study investigates how soil terpenoid storage and emissions vary with depth and tree species in a mixed temperate forest and evaluates the role of litter chemistry in shaping these patterns. Methods Soil samples were collected from Douglas fir ( Pseudotsuga menziesii ) and European beech ( Fagus sylvatica ) plots under identical climatic and edaphic conditions. Soil terpenoid storage was assessed via solvent extraction, while emissions were captured using dynamic headspace sampling; both were analyzed by gas chromatography-mass spectrometry. Results Soil terpenoid storage and emissions were significantly higher in Douglas fir soils (627,386 ± 650,060 ng g⁻¹; 4,718 ± 5,978 ng g⁻¹ h⁻¹) than in European beech soils (17,868 ± 19,981 ng g⁻¹; 234 ± 123 ng g⁻¹ h⁻¹) (p < 0.01). In the Douglas fir plot, storage peaked in the Oi horizon, whereas in the European beech plot, it was highest in the Oe horizon, likely due to differences in litter chemistry, decomposition rates, and soil adsorption. Emissions were highest in the Oi horizon of Douglas fir soils, reflecting direct volatilization from resin-rich litter, while European beech soils showed consistently low emissions. Terpenoid composition differed between the two plots, further suggesting that litter chemistry influences VOC transformation and release. Conclusions These findings highlight the importance of integrating soil VOC fluxes, litter characteristics, and vegetation-specific influences into forest VOC models to improve atmospheric VOC budget prediction.