Accumulation of mineral elements in the rhizosphere and shoots of Cyclopia and Aspalathus species under different settings of the Cape fynbos

Several species of the genus Cyclopia are cultivated for the production of Honeybush tea, largely without mineral fertilization. However, very little is known about the effect of annual harvesting, plant age, and type of planting material (cuttings vs. seedlings) on the mineral nutrition of Cyclopia. The aim of this study was to evaluate mineral nutrition in Cyclopia genistoides, Cyclopiasubternata, Aspalathus caledonensis, and Aspalathusaspalathoides in relation to (i) plant species, (ii) plant age, (iii) farmer's practice, (iv) planting material, and (v) toposequence at Koksrivier, Kanetberg, and Kleinberg in the Cape fynbos. A comparison of mineral concentrations in the rhizosphere and non-rhizosphere of 10-year-old C. genistoides at Koksrivier revealed significantly larger levels of P, Ca, Mg, Cu, Zn, and Mn in the former relative to the latter. There were also significantly greater levels of P, K, Ca, Mg, Na, and Mn in the rhizosphere of 10-year-old C. genistoides compared with 2-year-old plants at Koksrivier. The levels of P, K, Ca, Mg, Na, Fe, and Mn were significantly greater in the rhizosphere than non-rhizosphere soil of 5- and 8-year-old C. subternata plants at Kanetberg. Rhizosphere concentration of minerals were also measured and compared for C. subternata plants raised from cuttings and seedlings at Kanetberg, and P, Ca, and Cu were greater in the rhizosphere of plants cultured from cuttings. The concentration of minerals in the rhizosphere of A. aspalathoides, A. caledonensis, and C. genistoides, which co-occurred within the same tea plantation at Koksrivier, were significantly different, with P, K, Cu, Zn, and Mn being markedly greater in the rhizosphere soil of C. genistoides than the two Aspalathus species. Mineral nutrition under farmers' practice of annual harvesting was compared with unharvested material, and the levels of P, K, Na, Cu, Zn, and Mn were found to be significantly greater in shoots of the annually harvested plants.