PS 20-6 - Effects of grazing management and plant cover on the soil microbiome in a semi-arid grassland ecosystem

Abstract: The soil microbiome, through interactions with associated flora and fauna, plays a vital role in preserving ecosystem resilience and increasing productivity. Cattle grazing in grassland ecosystems is known to impact the soil microbiome directly and indirectly through soil compaction, changes in plant cover, and input of nutrients through excrements. Previous studies have found that grazing management practices and related changes to plant composition can affect microbial regulation of nutrient cycling. This study used a long-term grazing experiment (est. 2001) in southwestern Saskatchewan, Canada to further explore the importance of grazing management in plant-soil-microbe interactions and their potential role in carbon cycling. Pastures were originally seeded with either a 7 species mixture (simple) including six C3 grasses and one legume, or 12 species mixture (complex) with six C3 grasses, three C4 grasses, and one legume. The pastures were split by four grazing treatments including continuous grazing, or rotational grazing starting in spring, summer, or fall. Soil samples were collected from grazed and non-grazed (grazing exclosures) areas of the 16 pastures at one sampling date (September 2020) to assess the cumulative effect of these grazing management practices on soil chemical and microbial properties linked to C. Continuous grazing significantly reduced soil microbial biomass C (MBC) compared to rotational grazing. Grazing (i.e., grazed vs. non-grazed) effects on soil MBC were only observed under continuous grazing management practices as we observed significantly lower levels of MBC in grazed compared to non-grazed areas of these pastures. In addition, soil MBC in the continuous grazing treatment was positively correlated with fungal:bacterial ratio. The fungal:bacterial ratio was also significantly impacted by the plant species mixtures as higher ratios were observed in pastures with the simple plant mixture. To dig a little deeper, we used shotgun metagenomic sequencing to better understand the effects of grazing management on the composition and functional potential of the soil microbiome and more specifically how these practices alter microbial-mediated C cycling processes. This data set will help us better understand how the soil microbiome responds to grazing management practices and its functional role in rangeland systems.