Fig. 2: Cumulative carbon mineralization, dissolved organic carbon and nitrogen concentrations, and δ¹⁸O isotopic enrichment during litter decomposition.

A Cumulative mineralization of plant litter carbon from incubations for day 7 and day 60 conducted in parallel to isotope addition microcosms for biotic microcosms. B Non-purgeable organic carbon (NPOC) and C dissolved organic nitrogen (DON) concentrations from water extractions. Isotope composition (δ¹⁸O) was determined by isotope ratio mass spectrometry (IRMS) from D water extractable organic matter (WEOM) and E chloroform extractable organic matter (CEOM). Carbon dioxide (CO₂) respiration normalized to grams of litter (mg C-CO₂ g litter⁻¹) within each microcosm, measured via alkaline traps, are cumulative; the value for day 7 is the sum of CO₂ mineralization for the first 7 days of the incubation, and the value for day 60 is the total cumulative CO₂ respiration during the incubation. Thus, the CO₂ mineralization on day 7 represents 40% of the total cumulative mineralization throughout the incubation. Boxplots show distributions (median, interquartile range, and full range) with individual replicate values (n = 3) overlaid as filled purple circles for samples at early (day 7) and late (day 60) incubation time points. Asterisks denote significance in means comparing day 7 and day 60 time points for biotic samples using independent two-sample Welch’s t-tests: (.) <0.10; **<0.01; **** <0.0001.