Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Invasive annual cheatgrass enhances the abundance of native microbial and microinvertebrate eukaryotes but reduces invasive earthworms.

Abstract

Aims: The invasive annual grass cheatgrass (Bromus tectorum) has been previously correlated with changes in soil labile nitrogen (N) and soil organic matter (SOM) that have not been consistent across sites and studies. Here we investigated the size and structure of the soil food webs of cheatgrass and perennial grass soils to understand how seemingly contradictory patterns in SOM abundance and N mineralization could result from cheatgrass invasions of perennial grasslands. Methods: Molecular DNA metabarcoding was used to examine diversity and structure of microbial and microfaunal communities beneath cheatgrass and perennial grasses interspersed within a Colorado grassland. In addition, morphological methods were used to enumerate nematodes, microarthropods and earthworms. Results: Cheatgrass and perennial grasses supported distinct communities of all investigated soil groups including bacteria, fungi, nematodes, and other non-fungal non-nematode microbial eukaryotes. Abundances of bacterial-feeding nematodes, collembolans, prostigmatid mites, and SAR eukaryotes were higher beneath cheatgrass than native perennial grasses. Earthworms were about four times less abundant beneath cheatgrass than under perennial grasses. Conclusions: Compositional differences and increased abundance of microbial and micro- and mesofaunal communities were consistent with the increase in labile N previously reported beneath invasive cheatgrass. Likewise, the large densities of exotic earthworms beneath our perennial grasses were consistent with the literature suggesting their role in SOM reduction. We hypothesize that the mechanism for reduced densities of exotic earthworms (and hence preservation of SOM) in our soils invaded by cheatgrass relates to the dry-down and reduction of soil moisture content in this semiarid grassland.