Encephalartos villosus associated bacterial communities and extracellular enzymes improve soil nutrition in rhizosphere soils in forest ecosystem soils

Abstract

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.