Plant competition reshapes nitrogen utilisation in native Vachellia nilotica (Fabaceae)

Anathi Magadlela; Zinhle Lembede; Zivanai Tsvuura; Naledi Zama; Nqobile Motsomane; María Perez-Fernandez

Just Accepted

This article has been peer reviewed and accepted for publication. It is in production and has not been edited, so may differ from the final published form.

Plant competition reshapes nitrogen utilisation in native Vachellia nilotica (Fabaceae)

Anathi Magadlela , Zinhle Lembede, Zivanai Tsvuura , Naledi Zama, Nqobile Motsomane, María Perez-Fernandez

Abstract

Context Vachellia nilotica (Benth.) Kyal. & Boatwr is a leguminous species subjected to competition from co-occurring grassland species in mesic grasslands including Themeda triandra Forssk.. In South Africa, Vachellia nilotica enhances soil nitrogen in nutrient-deficient mesic savanna. The addition of phosphorus and competition between the grass and legume may assist in maintaining balance between the two plant groups. Aims Improved P supply in nutrient-poor soils favours growth of legumes over grasses. This study aimed to assess how nutrient deficiency, P fertilisation, and competition with a dominant grass species, particularly Themeda triandra, affects the aboveground and belowground growth, N nutrition, and nodulation potential of Vachellia nilotica in the Ukulinga Grassland Nutrient Experiment. Methods Soils used in the study were collected from superphosphate (+P, i.e. P-enriched) and non-superphosphate (-P, i.e. no P enrichment) fertilised trials. V. nilotica seedlings were grown independently and in competition with T. triandra seedlings. Key results Our findings confirm that soil in +P treatment had greater P and Ca concentrations than -P soils. Competition from T. triandra decreased the P concentration, Specific Nitrogen Assimilation Rates and the %NDFA in V. nilotica but the opposite effect was observed for Specific Nitrogen Utilization Rates. Conclusions Zero nodule formation in soils with low P levels and competition impacted the N source reliance of V. nilotica. Implications The addition of P might maximize N inputs through increased legume growth performance and weaken the competitive effect of a grass species.

BT24079 Accepted 11 April 2025