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As the largest biogeochemically active terrestrial reserve of carbon (C), soils have the potential to either mitigate or amplify rates of climate change. Ecosystems with large C stocks and high rates of soil C sequestration, in particular, may have outsized impacts on regional and global C cycles. Montane meadows have large soil C stocks relative to surrounding ecosystems. However, anthropogenic disturbances in many meadows may have altered the balance of C inputs and outputs, potentially converting these soils from net C sinks to net sources of C to the atmosphere. Here, we quantified ecosystem-level C inputs and outputs to estimate the annual net soil C flux from 13 montane meadows spanning a range of conditions throughout the California Sierra Nevada. Our results suggest that meadow soils can be either large net C sinks (577.6 ± 250.5 g C m−2 y−1) or sources of C to the atmosphere (− 391.6 ± 154.2 g C m−2 y−1). Variation in the direction and magnitude of net soil C flux appears to be driven by belowground C inputs. Vegetation species and functional group composition were not associated with the direction of net C flux, but climate and watershed characteristics were. Our results demonstrate that, per unit area, montane meadows hold a greater potential for C sequestration than the surrounding forest. However, legacies of disturbance have converted some meadows to strong net C sources. Accurate quantification of ecosystem-level C fluxes is critical for the development of regional C budgets and achieving global emissions goals. [ABSTRACT FROM AUTHOR]

Though typically limited in aerial extent, soils of high-elevation riparian wetlands have among the highest density of soil carbon (C) and nitrogen (N) of terrestrial ecosystems and therefore contribute disproportionally to ecosystem services such as water retention, forage production, wildlife habitat, and reactive N removal. Because much soil C and N is stored in labile forms in anaerobic conditions, management activities or environmental changes that lead to drying cause mineralization of labile soil organic matter, and loss of C and N. Meadows are focal points of human activities in mountain regions, often with incised stream channels from historically heavy grazing exacerbated by extreme runoff events. To quantify soil C and N stores in montane riparian meadows across hydrologic conditions, 17 meadows between 1950- and 2675-m elevation were selected in the central Sierra Nevada Range, California, that were classified using the proper functioning condition (PFC) system. Results indicate that C and N density in whole-solum soil cores were equivalent at forest edge positions of properly functioning, functioning at-risk, and nonfunctioning condition. Soils under more moist meadow positions in properly functioning meadows have at least twice the C, N, dissolved organic C, and dissolved organic N (DON) than those under nonfunctioning meadows. Densities of total N and DON, but not C, of functioning at-risk meadows are significantly lower ( P < 0.05) than those of properly functioning meadows at mid-slope and stream-bank positions, suggesting accelerated loss of N early in degradation processes. Though variable, the soil attributes measured correspond well to the PFC riparian wetland classification system. [ABSTRACT FROM AUTHOR]