Carbon accumulation and storage in semi-arid sagebrush steppe: Effects of long-term grazing exclusion

The potential of grazing lands to sequester carbon has been investigated in different terrestrial environments but the results are often inconclusive. Our study examined the soil organic carbon (SOC) and soil microbial biomass carbon (MBC) contents inside and outside four grazing exclosures that had been established more than four decades ago in the semi-arid sagebrush steppe of Wyoming. Non-grazed soil carbon parameters were compared to those of the adjacent grazed soils to examine the effects of long-term grazing exclusion on the soil carbon accumulation and storage of this particular ecological region. Soil organic carbon concentration in these soils ranged from 3.67 to 53.8 mg g−1 dry soil. There was no significant difference in SOC due to treatment (grazing exclusion) in three of the four sites. Carbon to nitrogen ratios ranged from 10 to 11 with only one site exhibiting greater C:N ratio in ungrazed soil than in grazed soil. Microbial biomass carbon concentrations ranged from 99 to 1011 μg g−1 dry soil in the study sites. All pairwise comparisons (with correlation coefficients from 0 to 1 at α = 0.05 level) between MBC and SOC were significantly positive and strong for ungrazed soil in all four sites. Greater MBC was observed in the ungrazed soil than in the grazed soil at two sites, demonstrating that long-term grazing exclusion promoted enrichment of the labile soil carbon pool.