María A. Pérez-Fernández

Biodiversity of Root-Nodule Bacteria Associated With the Leguminous Plant Biserrula pelecinus

Biserrula pelecinus is a noteworthy forage legume known for its drought- and acid-resistant properties and nitrogen-fixing ability that forms an extremely specific symbiotic relationship with bacteria from genera Mesorhizobium. To investigate the biodiversity of root-nodule bacteria associated with B. pelecinus, a total of 88 bacterial strains were examined using rep-polymerase chain reaction amplification. The 16S rRNA gene sequencing was also used to determine the phylogenetic relationship with type strains of different genera of rhizobia. Our results show that although a considerable genetic variability among Biserrula isolates was found, most isolates were phylogenetically related to Mesorhizobium ciceri. Curiously, a new symbiotic partner was found to nodulate Biserrula, suggesting possible lateral gene transfer of nodulation and nitrogen fixation genes between Mesorhizobium and Rhizobium.

Broad environmental tolerance of native root-nodule bacteria of Biserrula pelecinus indicate potential for soil fertility restoration

Background: Biserrula pelecinus is an annual legume native to the Mediterranean basin, found in pastureland, alone or in association with other legumes (Leguminosae) and grasses (Poaceae). It has been used in revegetation programmes of mining wastes showing phytoremediation potentials and thus becoming potentially highly attractive for plant ecology and restoration management of natural ecosystems. Aims: To characterise native root-nodule bacteria isolated from B. pelecinus from the Iberian Peninsula, and to select suitable N fixers for field-application and soil rehabilitation. Methods: Strains were isolated and molecularly identified by 16S rRNA amplification and sequencing. Strains were phenotypically characterised in different abiotic conditions (acidity, salinity and heavy metals) and tested for their ability to fix atmospheric N2. The most suitable N fixers were applied in greenhouse experiments with B. pelecinus under different fertilization levels to assess their tolerance to fertilized and polluted soils, commonly encountered in restoration projects. Results: B. pelecinus root-nodule isolates tolerated pH from 4.5 to 9.5 grew in saline conditions (2.5% of NaCl), and tolerated 50 µM of Al3+ and Mn2+. Three isolates efficient in N2 fixation, relative to the reference Mesorhizobium strain, were considered excellent candidates for the amelioration of nutrient poor sites. Conclusions: These results provide valuable information for the potential use in soil restoration of B. pelecinus in a wide-range of conditions, exploiting the natural variability of its root-nodule bacteria.

Mycorrhizal Colonization Improves Growth and Nutrition of an Invasive Legume in a Mediterranean Ecosystem

The Fynbos biome is a unique flora. It is the only kingdom contained in its entirety within a single country and is characterised by a high richness of some 8,700 species and a high endemicity with 68% are confined to the Cape Floristic Kingdom (CFK). Many of the aliens present in the Western Cape originate from Australia. One of the main invaders is a woody legume, Acacia cyclops A.Cunn. ex G.Don. Since low soil fertility, due to nitrogen (N) and phosphorus (P) deficiencies and low soil organic matter, is the major limiting factor in Mediterranean-type ecosystems, symbiotic association with both Rhizobium and arbuscular mycorrhizae (AM) may be a major advantage to these invading legumes.