Rhizosphere Microbial Densities and Trace Metal Tolerance of the Nickel Hyperaccumulator Alyssum Serpyllifolium Subsp. Lusitanicum

Abstract

In this study we determine culturable microbial densities (total heterotrophs, ammonifiers, amylolytics and cellulolytics) and bacterial resistance to Co, Cr, and Ni in bulk and rhizosphere soils of three populations of the Ni-hyperaccumulator Alyssum serpyllifolium subsp. lusitanicum and the excluder Dactylis glomerata from ultramafic sites (two populations in Northeast (NE) Portugal (Samil (S), Morais (M)) and one population in Northwest (NW) Spain (Melide (L)). The relationship between bioavailable metal concentrations (H₂O-soluble) and microbial densities were analysed. Significant differences in microbial densities and metal-resistance were observed between the two species and their three populations. The hyperaccumulator showed higher microbial densities (except cellulolytics) and a greater rhizosphere effect, but this was only observed in S and M populations. These populations of A. serpyllifolium also showed selective enrichment of Ni-tolerant bacteria at the rhizosphere where Ni solubility was enhanced (densities of Ni-resistant bacteria were positively correlated with H₂O-soluble Ni). These rhizobacteria could solubilise Ni in the soil and potentially improve phytoextraction strategies.

KEYWORDS:

• Alyssum serpyllifolium
• hyperaccumulation
• metal-tolerance
• microbial groups
• nickel
• rhizosphere

ACKNOWLEDGMENTS

This research was supported by the Ministerio de Educación y Ciencia and EU (FEDER) (CTM2006-13862-CO2) and presented in the Special Symposium “Plant-based technologies to remediate contaminated soils and sediments: processes, bioavailability, sustainability, consequences for ecosystems and human health” at the 9th ICOBTE (International Conference on the Biogeochemistry of Trace Elements) held in Beijing, China in July 2007.

Notes

*P < 0.05;

**P < 0.01;

***P < 0.001

*P < 0.05;

**P < 0.01;

***P < 0.001.