N 2 -fixation and growth promotion in cedar colonized by an endophytic strain of Paenibacillus polymyxa
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N2-fixation and growth promotion in cedar colonized by an endophytic strain of Paenibacillus polymyxa Richa Anand & Christopher Chanway
Received: 11 July 2012 / Revised: 13 August 2012 / Accepted: 16 August 2012 / Published online: 30 August 2012 # Springer-Verlag 2012
Abstract Inoculation of western red cedar with Paenibacillus polymyxa P2b-2R, an endophytic diazotroph of a pine, was previously shown to result in biological nitrogen fixation (BNF) in seedlings grown under N-limited conditions, but biomass accumulation was reduced after a 9-month growth period. To determine if the seedling growth reduction was temporary, we inoculated cedar seed with strain P2b-2R and grew seedlings for up to 13 months in a Nlimited soil mix containing 0.7 mM of available N labeled as Ca(15NO3)2. P2b-2R developed a persistent endophytic population comprising 102–106 cfu g−1 plant tissue inside pine roots, stems, and needles. At the end of the growth period, P2b-2R had reduced 15N foliar N abundance by 36 % and increased shoot biomass by 46 % compared to controls. Our results indicate that inoculated seedlings derived 36 % of foliar N from the atmosphere and suggest that BNF by P. polymyxa can significantly enhance growth of cedar in a Nlimited soil if seedlings are grown for a sufficient amount of time. These findings support the hypothesis that endophytic R. Anand : C. Chanway Department of Forest Sciences, University of British Columbia, 3041-2424 Main Mall, Vancouver, BC V6T 1Z4, Canada R. Anand e-mail: [email protected] C. Chanway (*) Faculty of Land and Food Systems, University of British Columbia, 248-2357 Main Mall, Vancouver V6H 3V4 V6T 1Z4, Canada e-mail: [email protected] Present Address: R. Anand IL-7, BC Children’s Hospital, 4480 Oak Street, Vancouver, BC V6H 3V4, Canada
diazotrophs may facilitate regeneration and growth of western red cedar at N-poor sites. Keywords Western red cedar . Paenibacillus polymyxa . Inoculation . Endophyte . N2-fixation
Introduction Certain tree species, such as western red cedar (Thuja plicata Donn.) are capable of growing at very N-limited sites. However, well-known mechanisms such as N uptake from mineralization by soil microorganisms or direct uptake from the soil organic pool by roots or mycorrhizae (Näsholm et al. 2009) do not explain N accretion at sites with little or no inorganic N or organic matter. Biological nitrogen fixation (BNF) in non-legume crops such as rice (Oryza sativa L.) and sugar cane (Saccharum officinarum L.) has been postulated to occur through the activity of endophytic bacteria including Gluconoacetobacter and Herbaspirillum. While there is some evidence to support a role for these microorganisms in BNF (Sevilla et al. 2001), other root-colonizing microorganisms may also be involved, but not yet identified, in part because they may not be amenable to culturing in the laboratory (Burbano et al. 2011; Taulé et al. 2012). Based on initial reports that the microorganism responsible for BNF in sugarcane was a culturable endophyte, we search
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