Encephalartos lanatus-associated bacteria and extracellular enzyme activities improve soil nutrition in nutrient-deficient grassland ecosystems.

Abstract

Encephalartos lanatus, commonly called ‘Olifants River Cycad’, is slow-growing and thrives in nutrient-deficient and acidic grassland soils. Like other Encephalartos spp., E. lanatus possess coralloid roots that host nutrient cycling microbes that may enhance soil and plant health and landscape productivity. However, identification of these microbes and their role in soil nutrient improvement have been documented for forest and savanna woodland Encephalartos spp., with limited knowledge on grassland species. The knowledge gap challenges the development of a holistic conservation strategy for grassland cycads. This study identified E. lanatus coralloid roots, rhizosphere, and bulk soils bacterial communities, and assessed the nutrient status and enzyme activities of both soils. Bulk and rhizosphere soils, and E. lanatus coralloid roots were sampled from a > 300 E. lanatus plant population growing in a rocky grassland at Botshabelo in Middleburg, Mpumalanga for nutrient analysis, enzyme activity assays, and bacterial identification. Nutrient concentration was higher in rhizosphere (20.54±3.40) than bulk (17.47±3.24) soils but not significantly different (p = 0.55). Concentration of magnesium and manganese were significantly higher (p < 0.05) in rhizosphere than bulk soils. Nitrogen, phosphorus, potassium and calcium were higher in rhizosphere than bulk soils but did not differ significantly (p > 0.05). Acid phosphatase and nitrate reductase enzyme activities were significantly (p < 0.05) higher in rhizosphere than bulk soils. Nutrient cycling bacteria of the genera Bacillus, Burkholderia, Enterobacter, Paraburkholderia, Pseudomonas and Rhizobium characterised coralloid roots, rhizosphere and bulk soils bacterial communities. The high nitrogen, phosphorus and potassium concentrations in rhizosphere as compared to bulk soils suggest that nutrient cycling bacteria in the coralloid roots, rhizosphere and bulk soils, and increased enzyme activities may be contributing to improving soil and E. lanatus health and productivity in nutrient-poor grassland ecosystem. This underscores the role of E. lanatus in soil nutrient improvement and the need to develop holistic conservation approaches for grassland cycads. I