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Background and Aims <p>Exotic annual grasses including cheatgrass (<i>Bromus tectorum</i> L.) are invading semiarid rangelands of North America and promoting damaging wildfires, motivating use of soil-borne <i>Pseudomonas</i>&#xa0;bacteria strains such as “D7” as bioherbicides.</p> Methods <p>We asked if D7 could be detected via targeted sequencing of its rRNA genes from soils under or adjacent to cheatgrass, before and 4x after broadcast spraying it onto a mixed cheatgrass and perennial bunchgrass (<i>Agropyron cristatum</i> (L.) Gaertn.) grassland. Soil-microbial- and plant-community responses were measured for 1–2&#xa0;years post-spraying, respectively.</p> Results <p>D7 decreased cheatgrass 15% from its &gt; 50% background foliar cover and resulted in doubled native annual grasses (<i>Vulpia octoflora</i> (Walter) Rydb.) to &gt; 25% cover. Interannual cover variation unrelated to D7 exceeded D7 effects, and the extent of cheatgrass reductions did not meet typical vegetation-management needs. Moreover, rRNA sequences from D7-sprayed plots differed from reference sequences for <i>Pseudomonas</i>-D7 except initial, trace detection. Furthermore, <i>Pseudomonas</i> sequences were less abundant in D7 than control plots and scarce overall (0.18% relative abundance). D7 also did not affect bacterial + archaeal or fungal community composition, especially compared to variation among natural microsites and sampling events.</p> Conclusion <p>The D7 effect of increasing the ratio of&#xa0;native:exotic grasses despite absence of molecular markers for D7 in the microbial-community could have resulted from lingering effects of D7’s active ingredient, i.e. pathogenic metabolites,&#xa0;produced after, or more likely before the D7 culture was broadcast-sprayed onto the grassland. A mechanistic understanding of these effects could identify additional methods for longer-term control of cheatgrass using bioherbicide.</p>

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Bacterial bioherbicide increased the ratio of native-to-exotic annual grasses, despite no molecular signature of establishment

  • 期刊论文

  • 发表日期：

    2026年7月1日

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  • Brynne E. Lazarus,
  • Rebecca C. Mueller,
  • Matthew J. Germino

摘要

Background and Aims

Exotic annual grasses including cheatgrass (Bromus tectorum L.) are invading semiarid rangelands of North America and promoting damaging wildfires, motivating use of soil-borne Pseudomonas bacteria strains such as “D7” as bioherbicides.

Methods

We asked if D7 could be detected via targeted sequencing of its rRNA genes from soils under or adjacent to cheatgrass, before and 4x after broadcast spraying it onto a mixed cheatgrass and perennial bunchgrass (Agropyron cristatum (L.) Gaertn.) grassland. Soil-microbial- and plant-community responses were measured for 1–2 years post-spraying, respectively.

Results

D7 decreased cheatgrass 15% from its > 50% background foliar cover and resulted in doubled native annual grasses (Vulpia octoflora (Walter) Rydb.) to > 25% cover. Interannual cover variation unrelated to D7 exceeded D7 effects, and the extent of cheatgrass reductions did not meet typical vegetation-management needs. Moreover, rRNA sequences from D7-sprayed plots differed from reference sequences for Pseudomonas-D7 except initial, trace detection. Furthermore, Pseudomonas sequences were less abundant in D7 than control plots and scarce overall (0.18% relative abundance). D7 also did not affect bacterial + archaeal or fungal community composition, especially compared to variation among natural microsites and sampling events.

Conclusion

The D7 effect of increasing the ratio of native:exotic grasses despite absence of molecular markers for D7 in the microbial-community could have resulted from lingering effects of D7’s active ingredient, i.e. pathogenic metabolites, produced after, or more likely before the D7 culture was broadcast-sprayed onto the grassland. A mechanistic understanding of these effects could identify additional methods for longer-term control of cheatgrass using bioherbicide.