Plant and Soil

, Volume 315, Issue 1, pp 163–172

The invasive Sorghum halepense harbors endophytic N2-fixing bacteria and alters soil biogeochemistry

Regular Article

DOI: 10.1007/s11104-008-9740-z

Cite this article as:
Rout, M.E. & Chrzanowski, T.H. Plant Soil (2009) 315: 163. doi:10.1007/s11104-008-9740-z


Exotic plants invading new habitats frequently initiate broad changes in ecosystem functioning. Sorghum halepense is an invasive grass capable of growing in nitrogen (N)-poor tallgrass prairie soils that creates near monocultures in once phylogenetically diverse-communities. The biogeochemistry of soils invaded by S. halepense was compared to that of un-invaded native prairie soils. Invaded soils contained two to four times greater concentrations of alkaline metals, micronutrients, and essential plant nutrients than native prairie soils. The notable exception was Ca+2, which was always significantly lower in invaded soils. The N-content of S. halepense above-ground biomass was 6.4 mg g−1 (320 mg N plant−1) and suggested a supplemental N source supporting plant growth. Altered soil biogeochemistry in invaded areas coupled with high above-ground biomass in N-poor soils suggested N2-fixing activity associated with S. halepense. Nitrogenase activity of plant tissues indicated that N2-fixation was occurring in, and largely restricted to, S. halepense rhizomes and roots. A culture approach was used to isolate these N2-fixing bacteria from plant tissues, and 16S rRNA gene sequencing was used to identify these bacterial isolates. Nitrogenase activity of bacterial isolates indicated several were capable of N2-fixation. In addition to N2-fixation, other roles involved in promoting plant growth, namely mobilizing phosphorus and iron chelation, are known for closest matching relatives of the bacterial isolates identified in this work. Our results indicate that these plant growth-promoting bacteria may enhance the ability of S. halepense to invade and persist by altering fundamental ecosystem properties via significant changes in soil biogeochemistry.


N2-fixing bacteria Endophytes Invasive plants Soil biogeochemistry Sorghum halepense 


The following symbols are used in this paper:


phosphate buffered saline


acetylene reduction assay

Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  1. 1.Division of Biological SciencesThe University of MontanaMissoulaUSA
  2. 2.Department of BiologyThe University of Texas at ArlingtonArlingtonUSA