Soil fungal composition changes with shrub encroachment in the northern Chihuahuan Desert

Abstract

Woody species encroachment of grasslands globally causes many socioecological impacts, including loss of grazing pastures and decreased biodiversity. Soil microbial communities may partially regulate the pace of shrub encroachment, as plant-microbial interactions can strongly influence plant success. We measured fungal composition and activity under dominant plant species across a grassland to shrubland transition to determine if shrubs cultivate soil microbial communities as they invade. Specifically, soil microbial communities, abiotic soil properties, and extracellular enzyme activities were quantified for soils under four common Chihuahuan Desert plant species (three grasses, one shrub) in central New Mexico, U.S.A. Extracellular enzyme activity levels were fairly consistent under different plant species across the grassland to shrubland transition. Activity levels of two enzymes (alkaline phosphatase and beta-N-acetyl-glucosaminidase) were lower in the ecotone, presumably because soil organic matter content was also lower in ecotone soils. Community composition of soil fungi mirrored patterns in the plant community, with distinct plant and fungal communities in the shrubland and grassland, while grassland-shrubland ecotone soils hosted a mix of taxa from both habitats. We show that shrubs cultivate a distinct microbial community on the leading edge of the invasion, which may be necessary for shrub colonization, establishment, and persistence.