Plant competition reshapes nitrogen utilisation in native Vachellia nilotica (Fabaceae)
Anathi Magadlela
A B * , Zinhle Lembede B , Zivanai Tsvuura B , Naledi Zama A B , Nqobile Motsomane B and María A. Pérez-Fernández C
A
B
C
Abstract
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.
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.
Soils used in the study were collected from superphosphate-fertilised trials (+P, i.e. P-enriched) and non-superphosphate trials (−P, i.e. no P enrichment). V. nilotica seedlings were grown independently and in competition with T. triandra seedlings.
Our findings confirmed that soil in +P treatment had greater P and calcium concentrations than did the −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 utilisation rates.
Zero nodule formation in soils with low P concentrations and competition affected the N source reliance of V. nilotica.
The addition of P might maximise N inputs through increased legume growth performance and weaken the competitive effect of a grass species.
Keywords: acidic soils, competition, kangaroo grass, Leguminosae, nitrogen fixation, nutrient deficiency, phosphorus, Ukulinga Grassland nutrient experiment.
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