Symbionts in<i>Mucuna pruriens</i>stimulate plant performance through nitrogen fixation and improved phosphorus acquisition

Abstract Aims South Africa is mainly dominated by savanna and grasslands ecosystems which have been previously reported to be acidic and nutrient deficient, specifically with regard to phosphorus (P) and nitrogen (N). Mucuna pruriens (L.) DC, commonly known as velvet bean, is an indigenous legume in most African countries and has been reported to withstand these adverse soil conditions. The legume is used in many countries of the world for their medicinal value as well as for soil fertilization purposes. Although there are reports on M. pruriens growth and establishment in nutrient stressed ecosystems, no investigation has been conducted on M. pruriens symbiotic interactions, N source preference and associated growth carbon costs when subjected to P deficiency. In this study, we determined the impact of microbial symbionts on N nutrition and growth carbon costs of M. pruriens under P deficiency. Methods Microbe inoculation soils were collected from four geographical distinct KwaZulu-Natal locations. Thereafter, seeds were germinated in these natural soils and in early stages of nodule development, then seedlings were transferred in sterile quartz sand and supplied with Long Ashton nutrient media with varying P concentrations. Important Findings The 16S RNA sequence results revealed that M. pruriens was nodulated by Burkholderia sp., Paenibacillus sp. and Bacillus irrespective of P concentrations. Even though P deficiency resulted in decreased overall biomass/growth, the root biomass, nodule number and carbon costs increased. In addition, low P supplied saplings showed the highest arbuscular mycorrhiza fungi percentage root colonization. In M. pruriens, nitrogen derived from atmosphere had a positive correlation with P level and the saplings had a dual reliance on atmospheric derived N and soil derived N with increased reliance on soil N in low P supplied plants. Therefore, M. pruriens exhibited different morphological and microbial symbiosis when subjected to P deficiency.