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Grasslands are globally abundant and provide many ecosystem services, including carbon (C) storage. While grasslands are widely subject to livestock grazing, the influence of grazing on grassland ecosystem C remains unclear. We studied the effect of long-term livestock grazing on C densities of different ecosystem components in 110 northern temperate grasslands across a broad agroclimatic gradient in Alberta, Canada. These grasslands stored 50 to 180 t ha -1 C in live and dead vegetation, as well as soil C to 30 cm depth, with the majority as soil organic C (SOC). The mulch layer comprised a large amount of C (~18 t ha -1 C) especially within humid grasslands. Although grazing reduced C densities in litter mass, total ecosystem C was 8.5 % greater under grazing (127.8 t ha -1 ) compared to those non-grazed (117.8 t ha -1 ), primarily due to increases in SOC and roots. Increases in SOC were consistently observed in the 0-15 cm layer across all climatic conditions, with changes in SOC of the 15-30 cm layer inversely related to aridity. A structural equation model revealed that increased SOC under grazing was indirectly attributed to increases in eudicot rather than graminoid biomass. In addition, SOC increased with graminoid quality (i.e., a reduced carbon to nitrogen ratio), which together with elevated eudicots, increased litter and mulch C, and ultimately enhanced SOC densities. When applied to spatial maps of habitat type and land use (livestock grazing) activity across the region, an area of ~3.8 M ha of grassland was projected to contain an additional 17.1 M t of C under grazing, primarily in mesic grasslands, worth an estimated $3.1 B (Cdn.) under current C valuation guidelines in Canada. Overall, these results highlight the importance of grasslands for C storage and establishing policies that maintain and promote their sustainable use, including light to moderate grazing., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Long-term livestock grazing (here after 'grazing') affects carbon (C) and nutrient cycling in grassland ecosystems, in part by altering the quantity and quality of litter inputs. Despite their spatial extent and size of carbon and nutrient stocks, the effect of grazing on grassland biogeochemical cycling through the mediation of microbial activity remains poorly understood. To better understand the relationship between grazing and C and nutrient cycling in litter, we conducted an 18-month long study in paired grasslands previously grazed and nongrazed by cattle for 25 years, measuring extracellular enzyme activity (EEA) in various plant litter samples. Litter sources, including seven grass species dominant in one or more subregions and possessing divergent responses to grazing, as well as a community mix of litter sourced from each site, were tested at 15 sites spanning three grassland subregions in Alberta, Canada. We quantified EEAs associated with C cycling (β-glucosidase, β-Cellobiosidase and β-xylosidase), nitrogen (N) cycling (N-acetyl-glucosaminidase) and phosphorus (P) cycling (phosphatase). In general, litter in grasslands exposed to grazing had greater activity of C-liberating and P-liberating enzyme (β-xylosidase and phosphatase) in the mesic grasslands of the Foothills Fescue subregion (P ≤ 0.10). Observed EEAs were strongly mediated by litter type, with greater EEAs in litter of grass species known to increase in abundance under long-term grazing, including Poa pratensis in the Foothills Fescue subregion, and Bouteloua gracilis in arid grasslands of the Mixedgrass Prairie. In contrast, Pascopyrum smithii litter had the lowest enzyme activities in all subregions. We also found that EEAs changed through time (0-18 months) with consistently high levels detected at 1 (June 2014), 6 (October 2014) and 18 months (October 2015) after placement. Overall, these findings indicate grazing enhances EEA, and thus C and N-cycling, in northern temperate grasslands., (Copyright © 2019 Elsevier B.V. All rights reserved.)