Bacterial endophytes enhance competition by invasive plants

Marnie E. Rout, Thomas H. Chrzanowski, Tara K. Westlie, Thomas H. DeLuca, Ragan M. Callaway, William E. Holben

Research output: Contribution to journalArticlepeer-review

Abstract

Premise of the study: Invasive plants can alter soil microbial communities and profoundly alter ecosystem processes. In the invasive grass Sorghum halepense, these disruptions are consequences of rhizome-associated bacterial endophytes. We describe the effects of N 2-fixing bacterial strains from S. halepense (Rout and Chrzanowski, 2009) on plant growth and show that bacteria interact with the plant to alter soil nutrient cycles, enabling persistence of the invasive. Methods: We assessed fl uxes in soil nutrients for ~4 yr across a site invaded by S. halepense. We assayed the N 2-fixing bacteria in vitro for phosphate solubilization, iron chelation, and production of the plant-growth hormone indole-3-acetic acid (IAA). We assessed the plant's ability to recruit bacterial partners from substrates and vertically transmit endophytes to seeds and used an antibiotic approach to inhibit bacterial activity in planta and assess microbial contributions to plant growth. Key results: We found persistent alterations to eight biogeochemical cycles (including nitrogen, phosphorus, and iron) in soils invaded by S. halepense. In this context, three bacterial isolates solubilized phosphate, and all produced iron siderophores and IAA in vitro. In growth chamber experiments, bacteria were transmitted vertically, and molecular analysis of bacterial community fingerprints from rhizomes indicated that endophytes are also horizontally recruited. Inhibiting bacterial activity with antibiotics resulted in significant declines in plant growth rate and biomass, with pronounced rhizome reductions. Conclusions: This work suggests a major role of endophytes on growth and resource allocation of an invasive plant. Indeed, bacterial isolate physiology is correlated with invader effects on biogeochemical cycles of nitrogen, phosphate, and iron.

Original languageEnglish
Pages (from-to)1726-1737
Number of pages12
JournalAmerican Journal of Botany
Volume100
Issue number9
DOIs
StatePublished - Sep 2013

Keywords

  • Bacterial endophytes
  • Biogeochemical cycles
  • Gramineae
  • Indole-3-acetic acid
  • Iron chelation
  • Microbially enhanced competitiveness
  • Phosphate solubilization
  • Plant invasions
  • Sorghum halepense

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