Encephalartos natalensis association with non- cyanobacterial species increased reliance on atmospheric nitrogen in acidic and nutrient-deficient savanna woodland ecosystem soils.

Abstract

Encephalartos natalensis, commonly known as the “Natal Giant,” is an evergreen cycad growing in nutrient-deficient and acidic savanna woodland ecosystem soils. The ability of E. natalensis to grow in nutrient-deprived and acidic soils may be linked to its association with nitrogen (N2) fixing bacteria housed in the coralloid roots. This study investigated the effects of soil characteristics (pH, total cation, nutrient concentrations, and total exchange acidity) on plant nutrition and N source (soil and atmosphere) reliance of E. natalensis growing in Edendale, KwaZulu-Natal. Leaves and coralloid roots were harvested from E. natalensis cycads in a disturbed savanna woodland for bacterial identification, N-isotope analysis, and plant nutrition. Encephalartos natalensis rhizosphere soils were phosphorus (P) deficient and had a pH of 5.75. The culturable bacteria isolated for E. natalensis coralloid roots belonged to the Bacillus, Paenibacillus, Lysinibacillus, and Beijerinckia genera. Encephalartos natalensis plants relied more on N derived from the atmosphere (72.61%) than N derived from the soil (36.99%). Correlations were observed between soil N, percentage N derived from the atmosphere, and percentage N derived from the soil. Soil P was correlated with pH. The findings of this study suggest that E. natalensis established symbioses with non-cyanobacterial N2-fixing bacteria and relieson atmospheric N for N nutrition in acidic and nutrient-deficient savanna woodland ecosystem soils.