Purpose Cycads are the only known gymnosperms associated with nitrogen-fixing bacteria housed in coralloid roots. Plant-associated bacteria, soil bacteria, and extracellular enzymes play a significant role in nutrient cycling. This study isolated and identified culturable bacteria in Encephalartos villosus coralloid roots, rhizosphere, and non-rhizosphere soils and investigated the role of soil bacteria and associated enzyme activities on soil nutrition in forest ecosystem soils in Rhebu and Oceanview, Eastern Cape, South Africa. Methods Encephalartos villosus coralloid roots were collected from mature cycad individuals for bacterial extraction and identification. Soil samples from E. villosus rhizosphere and non-rhizosphere soils were collected for bacterial identification, extracellular enzyme activity analysis, and soil characteristics (nutrient concentrations, pH, total cation, and exchange acidity). Results The bacteria isolated from the coralloid roots of E. villosus growing in Rhebu and Oceanview belonged to the Bacillus, Enterobacter, Peribacillus, Lysinibacillus, Stenotrophomonas, Rhizobium, and Paenibacillus genera. The Pseudomonas, Paraburkholderia, Burkholderia, Variovorax, Caballeronia, Stenotrophomonas, Novosphingobium, Caulobacter, Olivibacter, Cupriavidus, Arthrobacter, Gottfrieder, Dyella, Lysobacter, Xanthomonas, Neobacillus, Bradyrhizobium, Rhizobium, Enisfer, Chitinophaga, Paenarthrobacter, and Paenibacillus genera were isolated from rhizosphere and non-rhizosphere soils in Rhebu and Ocean View farm. There were no significant differences in the concentrations of soil macronutrients (N, P, K), alkaline and acid phosphatase, glucosaminidase, and nitrate reductase activity of E. villosus rhizosphere and non-rhizosphere soils in both localities, this may be attributed to dung and urine deposited by grazing cattle. Conclusion Our results show that soil bacterial communities with nutrient cycling and fixing functions may be linked to nutrient bioavailability contributing to nutrient enrichments in E. villosus rhizosphere soils.
Background Encephalartos villosus is a forest understory dwarf cycad growing in nutrient-deficient and acidic soils due to their association with plant growth promoting bacteria. This study investigated the effects of soil characteristics (pH, nutrition, total cation, and exchange acidity) on cycad-microbe symbiosis and the nitrogen (N) source preference of E. villosus growing in Rhebu and Oceanview, Eastern Cape, South Africa. Methods Coralloid roots and leaf material from targeted E. villosus individuals in both locations were analysed for N isotope, total plant N, and total plant phosphorus (P). Results Plant growth promoting bacteria were associated with E. villosus growing in Rhebu and Oceanview. The culturable bacteria strains isolated from the coralloid roots of E. villosus growing in Rhebu and Oceanview with N-fixing traits were Lysinibacillus fusiformis, Rhizobium huautlense, Stenotrophomonas sp., Enterobacter cloacae, and Paenibacillus polymyxa. Encephalartos villosus growing in Rhebu and Oceanview effectively fixed more than 70% of its total N from the atmosphere. Less than 25% of the total N utilized by E. villosus was derived from the soil. There were no significant variations in the leaf number, length, total N, and P in E. villosus growing in Rhebu and Oceanview. Conclusions The findings of this study revealed that E. villosus maintains growth and plant nutrition in nutrient-deficient and acidic soils by establishing symbiotic associations with plant growth-promoting bacteria and relying mostly in atmospheric N.
Cycads are ancient plants that establish symbiotic associations with plant growth-promoting (PGP) microbes. These ancient associations are rarely contrasted with more recent associations involving PGP microbes and legumes. This study investigated if V. unguiculata growing in Encephalartos villosus acidic, and nutrient-deficient rhizosphere and surrounding soils may share similar symbionts. In addition, the biomass accumulation and plant nutrition in V. unguiculata growing in these soils was investigated. Vigna unguiculata seeds were grown in E. villosus rhizosphere and surrounding soils for 45 days. Thereafter, growth characteristics and plant nutrition were calculated. Vigna unguiculata plants grown in E. villosus rhizosphere and surrounding soils were nodulated by Paenibacillus, Bacillus, Peribacillus, Brevibacillus, Alkalihalobacillus, and Lysinibacillus species that were also identified in E. villosus coralloid roots. There were no significant differences in the total plant biomass, however, V. unguiculata plants in rhizosphere and surrounding soils invested more resources in belowground biomass. The findings of this study show that V. unguiculata and E. villosus growing in similar soil conditions may share the same symbionts promoting plant nutrient assimilation and growth.
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