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Weeds as a source of plant growth promoting rhizobacteria in agricultural soils

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The influence of plant growth promoting (PGP) activity of bacterial communities recovered from each of six weed species (barnyard grass (Echinochloa crusfalli (L.) Beauv.), corn spurrey (Spergula arvensis L.), goldenrod (Sonchus sp.), Italian ryegrass (Lolium multiflorum L.), lamb's-quarters (Chenopodium album L.), and quack grass (Agropyron repens (L.) Beauv.)) was examined in relation to the effect it had on the growth of the potato cultivar Russet Burbank. Bacterial species composition and community structure were compared, species-abundance relationships were determined, and those members conferring positive benefits for potato growth and development were identified. Of the genera identified, Bacillus, Arthrobacter, Stenotrophomonas, Acinetobacter, and Pseudomonas were the most common, and Stenotrophomonas maltophilia was the most frequent species recovered across all sources. Significantly higher population densities were found in the root zones of quack grass, compared with Italian ryegrass and lamb's-quarters. There were no significant differences in species richness among the root zones; however, evenness indices (species distribution) were significantly lower in corn spurrey (P = 0.05). Significantly higher diversity indices (Hill-1 and Hill-2 numbers) (P = 0.05) were found in the root zone soil communities of potato and goldenrod, indicating a decrease in the proportional abundance of common and very abundant species, respectively, while in barnyard grass, corn spurrey, and Italian ryegrass the reverse was the case. In both years of the study, Italian ryegrass and corn spurrey were consistently better sources of PGP rhizobacteria for potatoes, significantly (P < 0.001) increasing the mean wet weight of shoots and roots in in vitro bacterization studies. Barnyard grass was a consistently poor source of such isolates. Species-abundance measures of root zone bacterial biodiversity were not found, in this instance, to be a particularly good predictor of the presence or absence of PGP rhizobacteria. We consider that the study of complementary crops and soil-conditioning treatments should not preclude the examination of weed species as possible beneficials, as alterations in rhizobacterial biodiversity and functional versatility can influence the numbers and types of PGP bacterial strains, and consequently may serve to improve soil quality.Key words: biodiversity, bioindicator, allelopathy, functional versatility, ecosystem function.

Nous avons etudie la capacite de promouvoir la croissance des plantes par des populations bacteriennes isolees de six especes de mauvaises herbes dont l'echinochloa pied-de-coq (Echinochloa crusfalli (L.) Beauv.), la spargoute des champs (Spergula arvensis L.), la verge d'or (Sonchus sp.), le raygrass italien (Lolium multiflorum L.), le chinopode blanc (Chenopodium album L.) et le chiendent (Agropyron repens (L.) Beauv.). L'influence de ces bacteries a ete evaluee chez la pomme de terre du cultivar Russet Burbank. L'organisation de la population bacterienne et la composition des especes ont ete comparees, la relation espece-abondance a ete mesuree et les bacteries promotrices de la croissance et du developpement de la pomme de terre ont ete identifiees. Les genres identifies les plus communs etaient Bacillus, Arthrobacter, Stenotrophomonas, Acinetobacter et Pseudomonas et c'est l'espece Stenotrophomonas maltophilia qui a ete la plus souvent isolee a partir de toutes ces mauvaises herbes. Des populations bacteriennes significativement plus denses ont ete retrouvees dans les zones racinaires du chiendent comparativement au raygrass italien et au chinopode blanc. On n'a pas note de difference significative dans l'abondance des especes dans les zones racinaires, mais par contre les index de ressemblance (distribution des especes) etaient significativement plus faibles chez la spargoute des champs (P = 0,05). Des index de diversite (nombres Hill-1 et Hill-2) significativement plus eleves (P = 0,05) ont ete observes dans les populations bacteriennes du sol de la zone racinaire de la pomme de terre et de la verge d'or indiquant une diminution de l'abondance proportionnelle des especes communes et tres abondantes respectivement alors que c'etait le contraire chez l'echinochloa pied-de-coq, la spargoute des champs et le raygrass italien.

Keywords: allelopathy; allélopathie; biodiversity; biodiversité; bioindicateur; bioindicator; ecosystem function; fonction de l'écosystème; fonctionnelle; functional versatility; versatilité

Document Type: Research Article

Publication date: 2001-11-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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