Plant, insect, and soil microbial communities vary across brome invasion gradients in northern mixed-grass prairies

Authors: FROST, MORGAN - University Of North Carolina Greensboro; KOMATSU, KIMBERLY - University Of North Carolina Greensboro; Porensky, Lauren; Reinhart, Kurt; WILCOX, KEVIN - University Of North Carolina Greensboro; BUNCH, ZACHARY - University Of North Carolina Greensboro; JOLIN, ASHLEY - University Of North Carolina Greensboro; JOHNSTON, KATIELYN - University Of North Carolina Greensboro; TRIMAS, GRACEN - University Of North Carolina Greensboro; KOERNER, SALLY - University Of North Carolina Greensboro

Submitted to: Oikos
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2024
Publication Date: 3/8/2024
Citation: Frost, M.D., Komatsu, K.J., Porensky, L.M., Reinhart, K.O., Wilcox, K.R., Bunch, Z.L., Jolin, A.D., Johnston, K.A., Trimas, G.E., Koerner, S.E. 2024. Plant, insect, and soil microbial communities vary across brome invasion gradients in northern mixed-grass prairies. Oikos. Article e10515. https://doi.org/10.1111/oik.10515.
DOI: https://doi.org/10.1111/oik.10515

Interpretive Summary: Invasive plants can have negative effects on many other organisms, including other plants as well as insects and microbes. However, the extent and consequences of these wide-ranging effects remains unclear for many ecosystems. In northern mixed-grass prairies, invasive annual brome grasses like field brome (Bromus arvensis) and cheatgrass (Bromus tectorum) can negatively affect rangeland plants, but their effects on insects and soil microbes are unclear. To address this knowledge gap, we explored the effects of brome invasion on plants, insects, and soil microbes at sites in Montana and Wyoming. We found that invasion by either brome species led to altered plant and insect communities. However, associations between invasion and soil microbes were species specific. We only saw strong relationships between invasion and microbial communities under cheatgrass invasion, implying that cheatgrass invasion may have stronger consequences for ecosystem function and rangeland management than field brome invasion. This work shows that the effects of invasion on natural communities and ecosystems depend on both invader identity and the type of community affected (for example, plants vs. microbes).

Technical Abstract: Species interactions shape native plant communities, influencing both composition and ecosystem processes, with invasion by non-native species threatening these dynamic relationships, native species, and function. The consequences of invasive plants in particular may stretch across taxa to impact plant, insect, and soil microbial communities directly and indirectly, with consequences for ecological functioning. In northern mixed-grass prairies, invasion by two annual brome grasses, Bromus arvensis and B. tectorum, negatively impacts rangeland plants; however, the simultaneous effects on insects and soil microbes (bacteria and archaea), and the implications for ecological function, have received less attention. Here, using observational field studies conducted at two mixed-grass prairie sites in Montana and Wyoming, we assessed the relationships between plants, insects, and soil microbes across gradients of invasion by B. arvensis and B. tectorum. Overall, we found differences in plant and insect communities and functional groups with increasing invasion abundance for both brome species. However, associations between invasion and the soil microbial community were species specific, as we only saw these relationships under B. tectorum invasion, implying B. tectorum may have more substantial consequences for rangeland management. While invasion by annual bromes may cause changes in certain plant and insect functional groups, such as C4 perennial grasses and certain insect herbivores, soil microbial functional groups may be less impacted, especially under B. arvensis invasion. This work sheds light on the need to explore changes in natural communities across taxa and to all invasive species, as ecosystem effects are likely to be contingent upon both.