Abstract:
Total and diazotrophic bacteria were assessed in the rhizosphere soils of native and
encroaching legumes growing in the Succulent Karoo Biome (SKB), South Africa. These were
Calobota sericea, Lessertia diffusa, Vachellia karroo, and Wiborgia monoptera, of Fabaceae family near
Springbok (Northern Cape Province) and neighboring refugia of the Fynbos biome for C. sericea
for comparison purposes. Metabarcoding approach using 16S rRNA gene revealed Actinobacteria
(26.7%), Proteobacteria (23.6%), Planctomycetes, and Acidobacteria (10%), while the nifH gene revealed
Proteobacteria (70.3%) and Cyanobacteria (29.5%) of the total sequences recovered as the dominant phyla.
Some of the diazotrophs measured were assigned to families; Phyllobacteriaceae (39%) and Nostocaceae
(24.4%) (all legumes), Rhodospirillaceae (7.9%), Bradyrhizobiaceae (4.6%) and Methylobacteriaceae (3%) (C.
sericea, V. karroo, W. monoptera), Rhizobiaceae (4.2%; C. sericea, L. diffusa, V. Karroo), Microchaetaceae (4%;
W. monoptera, V. karroo), Scytonemataceae (3.1%; L. diffusa, W. monoptera), and Pseudomonadaceae (2.7%;
V. karroo) of the total sequences recovered. These families have the potential to fix the atmospheric
nitrogen. While some diazotrophs were specific or shared across several legumes, a member of
Mesorhizobium species was common in all rhizosphere soils considered. V. karroo had statistically
significantly higher Alpha and distinct Beta-diversity values, than other legumes, supporting its
influence on soil microbes. Overall, this work showed diverse bacteria that support plant life in harsh
environments such as the SKB, and shows how they are influenced by legumes.
Description:
SUPPLEMENTARY MATERIAL : TABLE S1: Statistical analysis of soil chemical properties of the study sites showing main effects of different legume species and sites, TABLE S2: Diverse bacterial phyla in the Succulent Karoo biome in South Africa, their inherent properties and possible impacts on plant communities, TABLE S3: Families containing diazotrophic bacteria (nifH gene) in the rhizosphere soils examined and their possible roles in plant growth promotion of legume species in the Succulent Karoo biome in South Africa, TABLE S4: Analysis of variance (ANOVA) and Permutations analysis of variance (PERMANOVA) to test the effects of factors ‘legume species’, ‘sites’ and their interactions on the respective alpha and beta diversity matrices, using the 16S rRNA and nifH gene barcodes.
