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.

作为最大的生物地球化学活性碳储量，土壤具有缓解或加剧气候变化速率的潜力。尤其是具有大量碳储量和高碳固存率的生态系统可能会对区域和全球碳循环产生巨大影响。相对于周围的生态系统，山地草甸的土壤碳储量很大。但是，许多草甸的人为干扰可能已经改变了碳输入和输出的平衡，可能会将这些土壤从净碳汇转换为净碳源再排放到大气中。在这里，我们量化了生态系统级C的输入和输出，以估算横跨整个内华达山脉的13种山地草甸的年土壤净C通量。我们的结果表明，草甸土壤可以是大型的净碳汇（577.6±250.5 g C m^-2 y ^-1）或大气中的C来源（-391.6±154.2 g C m ^-2 y ^-1）。土壤净碳通量的方向和大小的变化似乎是由地下碳输入驱动的。植被种类和功能组组成与净碳通量的方向无关，但气候和分水岭特征却与之相关。我们的结果表明，每单位面积的山地草甸比附近的森林具有更大的固碳潜力。但是，干扰的影响已使一些草甸转变为强大的净碳源。准确量化生态系统水平的碳通量对于制定区域碳预算和实现全球排放目标至关重要。