Short-Distance Variation of Carbon Stocks and Growing-Season Flux Components in Kola Tundra

Carbon accounting in tundra ecosystems is constrained by spatial heterogeneity below conventional inventory scales. We quantified carbon (C) stocks and growing-season flux components across five 50 × 50 m plots within a 250 × 250 m lichen–dwarf shrub tundra site on the Kola Peninsula, Russia. The study included 15 soil profiles, 15 biomass quadrats, and 30 permanent soil-respiration collars measured on seven dates. Biomass, litter, soil chemical and microbial properties, respiration, temperature, and moisture were assessed across contrasting microrelief positions and Podzol groups. Total standing C pools ranged from 10.8 to 26.0 kg C m−2 among plots (mean ± SD: 15.8 ± 6.1 kg C m−2), with soil contributing 60–85%. Stagnic Podzols in local depressions had the largest organic-horizon C stocks, whereas deeper and better-drained profiles stored a larger fraction in mineral horizons. A repeated-measures linear mixed-effects model with a collar-level random intercept and continuous temporal autocorrelation showed that soil temperature improved the fit to log-transformed soil CO2 efflux (likelihood-ratio statistic = 55.54, p < 0.0001). The evidence for an additional linear moisture effect was weak (p = 0.079), and the temperature × moisture interaction was unsupported (p = 0.932). Scenario-based growing-season heterotrophic C efflux ranged from 41 to 52, 48 to 62, and 59 to 76 g C m−2 for Rh/Rs fractions of 0.45, 0.53, and 0.65, respectively. The results support stratification by coupled microrelief–soil–vegetation units for local inventories, while broader inference requires independent replication and year-round flux measurements.