Bacterial endophytes enhance competition by invasive plants.
OBJECTIVE
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 N2-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 fluxes in soil nutrients for ∼4 yr across a site invaded by S. halepense. We assayed the N2-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. •


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.
Division of Biological Sciences, The University of Montana, Missoula, Montana 59812, USA.
Marnie E
ME
Rout
Thomas H
TH
Chrzanowski
Tara K
TK
Westlie
Thomas H
TH
DeLuca
Ragan M
RM
Callaway
William E
WE
Holben
D001419:Bacteria / Q000145:classification / Q000302:isolation & purification*; D018533:Biomass; D017753:Ecosystem; D060026:Endophytes; D007210:Indoleacetic Acids / Q000378:metabolism; D058865:Introduced Species; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation; D010710:Phosphates / Q000378:metabolism; D010937:Plant Growth Regulators / Q000378:metabolism; D017262:Siderophores / Q000378:metabolism; D012987:Soil / Q000737:chemistry; D012988:Soil Microbiology; D045868:Sorghum / Q000254:growth & development / Q000382:microbiology* / Q000502:physiology*; D013559:Symbiosis / Q000502:physiology*
D007210:Indoleacetic Acids; D010710:Phosphates; D010937:Plant Growth Regulators; D017262:Siderophores; D012987:Soil; C030737:indoleacetic acid; D009584:Nitrogen
Gramineae; Sorghum halepense; bacterial endophytes; biogeochemical cycles; indole-3-acetic acid; iron chelation; microbially enhanced competitiveness; phosphate solubilization; plant invasions