Plant growth-promoting bacteria and desert soil erosion, dust pollution and re-vegetation

      When naturally vegetated deserts are cleared, either to develop marginal agricultural land that is later abandoned or to build urban settlements lacking paved roads, the natural, organic safeguards that hold the topsoil against wind erosion are destroyed. The result is a severe loss of soil and dust pollution. The latter significantly increases chronic respiratory illnesses. This phenomenon is on the increase throughout the developing world. In North America, it is common in the semi-arid region of northwestern Mexico, where abandoned fields quickly become dust bowls, barren flats without any vegetation. Re-establishing a plant cover in these areas cannot occur naturally, since the nurse plants, especially mesquite and other leguminous shrubs and small trees under whose canopies many climax-vegetation plants (cacti and agave) depend for successful establishment, have been removed.

      Many desert plants, especially cacti, are excellent topsoil stabilizers. These plants can be used to prevent soil erosion and reduce dust pollution in urban areas, but their low rate of establishment and slow development, when transferred from natural habitats or nurseries to eroded urban soil, limit their use. Cacti (as all plants) not only benefit from, but also depend on the presence of soil microbes for early establishment and subsequent growth.

      Inoculation with soil microorganisms is a common practice in agriculture and forestry in developed countries. We find that microorganisms, such as plant-growth-promoting bacteria (PGPB) and mycorrhizal fungi (MF), are integral parts of the re-vegetation process and can be used as a biotechnological tool to reduce soil erosion and dust pollution.

      PGPB Azospirillum strains are commonly used to improve agricultural crop yields and to serve as a common model of rhizosphere microbes for genetic studies. Their potential exceeds agricultural practices and can be extended to environmental applications. In arid regions, they promote cacti survival and growth during the crucial first-year stage of development, allowing the small cactus seedling to prosper after germination, when most seedlings die.

      Survival and development of transplanted cacti in urban and disturbed areas of the Sonoran Desert of Baja California Sur was monitored. For 3.5 years after transplantation, young plants of three species of columnar pachycereid cacti (Pachycereus pringlei, Stenocereus thurberi, and Lophocereus schottii) that were inoculated with A. brasilense had a high survival rate and developed more rapidly than control plants without inoculation. Soil erosion in the eroded area (dirt road) where inoculated cacti were planted was diminished, and soil accumulated was significant, as the fine, surface cactus roots penetrated wind-deposited dust.

      In another investigation in central Baja California Sur, field observations, combined with chemical and physical analyses, mineral analysis, and scanning electron microscopy of unweathered and weathered volcanic rocks, revealed rock-colonizing plants (most were tree-shaped cacti) growing in volcanic rocks without benefit of soil. Many were at the seedling stage and were capable of cracking, growing in, and colonizing cliffs and rocks formed from ancient lava flows, and consequently, forming soil for other plants. Microorganisms heavily colonized the rhizoplane of these plants, as well as the root interiors. The dominant bacterial groups colonizing the roots were fluorescent pseudomonads and endophytic bacteria. Unidentified fungal and actimomycete species were also present. Nitrogen fixation by some of the endophytic, root-colonizing microorganisms was significant. Several bacterial strains capable of solubilizing relatively insoluble phosphate minerals (Al and Fe phosphate) and bacteria capable of dissolving rocks were isolated and identified. The microbial community survived in the rhizoplane of cactus plants during the 10-month dry season, and when inoculated onto young cardon cacti, was capable of enhancing plant growth.

      These studies demonstrate that beneficial microorganisms plays a significant role in desert vegetative processes and can be used to re-vegetate deserts.

 

Variations of this presentation were presented at the following scientific conferences.
  1. Bashan, Y. and Rojas, A. 1997. Improved establishment and development of three cactus species in eroded urban soils by inoculation with Azospirillum brasilense. In: First National Congress on Cacti. 26-29 Nov. 97. Montecillo, México, México.
  2. Bashan, Y. Rojas, A. and Puente, M. E. 1998. Prevention of soil erosion by improved establishment and development of three cacti species inoculated with Azospirillum brasilense in eroded, disturbed urban soil. 4th Annual Conference. Professional Association for Cactus Development.16-19 Sep. 1998. San Antonio, USA.
  3. Bashan, Y. 1998. Prevention of soil erosion with bacterial-inoculated plants and its impact on society. Special seminar in the 2nd Workshop on Environmental Biotechnology. Pontificia Universidad Javeriana. 22 Oct. 1998. Santa Fe de Bogotá, Colombia.
  4. Bashan, Y. 1998. Prevention of soil erosion with bacterial-inoculated plants and its impact on society. Special seminar in the Program of Microbiology, Department of Biological Sciences, Universidad de los Andes, 21 Oct. 1998. Santa Fe de Bogotá, Colombia.
  5. Bashan, Y. 1998. Prevention of soil erosion with bacterial-inoculated cacti plants. Special seminar at El Paso Research Center, Texas A&M University. 17 Dec. 1998. El Paso, USA.
  6. Bashan, Y. 1999. Environmental applications of Azospirillum, a plant growth promoting bacterium commonly used for agriculture, 10th Scientific Summer Week of the Mexican Academy of Science, Benemérita Universidad Autónoma de Puebla. 8-12 Nov. 1999. Puebla, México.
  7. Bashan, Y. 2000. Development of mixed bacterial inoculants for agricultural crops in semiarid zones, reforestation, and biotreatment of wastewater. First Congress for Responsible of Projects in Applied Biological Science of the National Research Council of Science and Technology of México, 14-17 Mar. 2000, Acapulco, México.
  8. Gonzalez, L. E. and Bashan, Y. 2000. Environmental applications of plant growth-promoting bacteria. 10th International Conference on Plant Pathogenic Bacteria. 23-27 Jul. 2000. Charlottetown, P. E. I., Canadá.
  9. Bashan, Y. and Bashan, L. E. 2000. Environmental applications of Azospirillum sp. 5th International Plant Growth-Promoting Rhizobacteria Conference. 29 Oct.-3 Nov. 2000, Villa Carlos Paz, Argentina.
  10. Bashan, Y., Carrillo, A., Bethlenfalvay, G. J., Rojas, A. and Puente, M. E. 2000. Prevention of desert soil erosion and enhancing soil stabilization by mycorrhizal fungi and by cactus plants inoculated with Azospirillum brasilense. 5th International Plant Growth-Promoting Rhizobacteria Workshop. 29 Oct.-3 Nov. 2000. Villa Carlos Paz, Argentina.
  11. Bashan, Y., González-Bashan, L. E., Lebsky, V. K., Moreno, M., Puente, M. E., Rojas, A., Carrillo, A. E., Hernandez, J. P., Troyo, E., Li. C. Y., and Bethlenfalvay, G. 2001. The role of Azospirillum as plant growth promoter. 3rd International Congress of Environmental Microbiology. 9-11 May 2001. Santa Fe de Bogotá, Colombia.
  12. Bashan, Y. 2001. Environmental applications of the plant growth-promoting bacterium Azospirillum. First International Symposium on Microbial Ecology of Soils. Universidad de Los Andes, 29-30 Mar. 2001, Santa Fe de Bogotá, Colombia.
  13. Bashan, Y. 2001. Environmental applications for Azospirillum sp. 10th National Congress for Biochemistry and Molecular Biology of Plants. 27-30 Oct. 2001. La Paz, B. C. S., México.
  14. Bashan, Y. 2001. Environmental applications of plant growth-promoting bacteria. Horticultural Research Center, Universite Laval, 29 Aug. 2001; Quebec city, Quebec, Canadá.
  15. Bashan, Y. 2001. Plant-Microbe interactions in aquatic and terrestrial environments: restoration of disturbed ecosystems: conservation and creation of natural reserves. Special seminar at: Institute Federatif de Recherche 41, Institute des Sciences et Methods de L’ecologie et de L’evolution, Universite Claude Bernard Lyon 1, 20 Sep. 2001. Lyon, France.
  16. Bashan, Y. 2001. Desert revegetation aided by plant growth-promoting bacteria. Special seminar at: Combined Center for Tropical and Mediterranean Symbioses (INRA/IRD/CIRAD/AGRO-M), 21 Sep. 2001. Montpellier, France.
  17. Bashan, Y. 2002. Re-vegetation of eroded desert areas aided by microorganisms. Special seminar at: Department of Biology, University of Arizona, 15 Feb. 2002.Tucson, USA.
  18. Bashan, Y. 2002. Re-vegetation of eroded desert areas aided by plant growth-promoting bacteria. Special seminar at: Center of genetic biotechnology. 8 Mar. 2002. Reynosa, Tamaulipas, México.
  19. Bashan, Y., Puente, M. E., Bethlenfalvay, G. J., Li, C. Y., Bacilio, M., Carrillo, A. E., Moreno M., Vazquez P., Holguin, G., and de-Bashan, L. E. 2003. Plant growth-promoting bacteria and desert re-vegetation. Arid Southwest Lands Habitat Restoration Conference. 3-7 Mar. 2003, Palm Springs, USA.

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