Encephalartos villosus relies on atmospheric nitrogen than soil derived nitrogen to maintain growth in nutrient-deficient and acidic soils

Abstract

AbstractBackgroundEncephalartos villosusis 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 ofE. villosusgrowing in Rhebu and Oceanview, Eastern Cape, South Africa. Methods Coralloid roots and leaf material from targetedE. villosusindividuals in both locations were analysed for N isotope, total plant N, and total plant phosphorus (P). Results Plant growth promoting bacteria were associated withE. villosusgrowing in Rhebu and Oceanview. The culturable bacteria strains isolated from the coralloid roots ofE. villosusgrowing in Rhebu and Oceanview with N-fixing traits wereLysinibacillus fusiformis, Rhizobium huautlense, Stenotrophomonas sp., Enterobacter cloacae, andPaenibacillus polymyxa.Encephalartos villosusgrowing in Rhebu and Oceanview effectively fixed more than 70% of its total N from the atmosphere. Less than 25% of the total N utilized byE. villosuswas derived from the soil. There were no significant variations in the leaf number, length, total N, and P inE. villosusgrowing in Rhebu and Oceanview. Conclusions The findings of this study revealed thatE. villosusmaintains 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.