Alien Invasive Successfully Acquires Nutrients by Investing in Below-ground Biomass Compared to Native in Nutrient-amended Soils in South Africa

Soils in grasslands and savannas of southern Africa are acidic and nutrient-poor. Legume plants, such as and alien invasive , are a major component of the vegetation there. can establish in drought-prone environments, and is invasive in high rainfall areas. is an emerging invasive in South Africa and is ranked among the world's 100 most invasive alien species. Alien plants can invade native habitats through their adaptability to low-resource soils, and thus can out-compete and displace native vegetation. We investigated the effects of phosphorus (P) deficiency and soil acidity on legume-microbe symbiosis, nitrogen (N) nutrition and carbon (C) growth costs of these two legumes in grassland soils. We used as inoculum and growth substrate soils collected from a long-term (>65 years) nutrient and lime-addition trial, the Veld Fertilizer Trial (VFT), located at Ukulinga Research Farm near Pietermaritzburg in South Africa. We used soils from three VFT treatments: soils fertilized with superphosphate (336 kg ha) applied once per year (+P), soils fertilized with superphosphate (336 kg ha) applied once per year with dolomitic lime (2250 kg ha) applied once every 5 years (P+L) and soils with no superphosphate and no dolomitic lime applications (Control). Seeds of and were germinated and grown independently in these soils in green house conditions and harvested after 125 days for measurement of growth, legume-microbe symbiosis, N nutrition and C growth costs. Results showed that the two legumes had different growth adaptations. grown in control soils and +P soils nodulated with various spp., while did not nodulate in all soil treatments. Both legumes utilized for growth both atmospheric- and soil-derived N across all treatments thereby decreasing C growth costs. grown in +P soils accumulated the most biomass and N nutrition. maximized specific N assimilation rates by investing in below-ground biomass accumulation in control soils. This shows that possesses traits that are successful in acquiring nutrients by investing in below-ground biomass and relying on utilization of N from both the soil and the atmosphere.