Nitrogen nutrition, carbon accumulation and δ13C of Cyclopia and Aspalathus species in different settings of the Cape fynbos, South Africa

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Abstract

Aims

Cyclopia and Aspalathus are legumes harvested for production of Honeybush and Rooibos tea, respectively. Farmers grow these species from either seeds or cuttings over several years with continuous annual harvesting. The aims of this study were to assess the effect of plant age, plant species, toposequence, planting material and farmer practice on nitrogen (N) nutrition and water-use efficiency of two Cyclopia and Aspalathus species in the Cape fynbos.

Methods

The study was conducted using plants from Koksrivier farm located near Gansbaai (33° S 18° E, 39 m.a.s.l), and at Kanetberg farm near Barrydale (33° S 21° E, 830 m.a.s.l). The 15N natural abundance technique was used to determine N2 fixation, carbon (C) assimilation and δ13C in shoot of Cyclopia and Aspalathus species.

Important Findings

Older tea plantations of C. genistoides and C. subternata derived more N from fixation and exhibited greater water-use efficiency than younger plants. At Koksrivier, Aspalathus caledonensis and A. aspalathoides showed greater water-use efficiency and derived more N from fixation than Cyclopia genistoides. Annual harvesting of C. genistoides decreased N2 fixation. At Kanetberg, C. subternata plants on the upper and middle slopes derived more N from atmospheric fixation than those on the lower slope. C. subternata plants grown from seedlings recorded greater %Ndfa than cuttings. N2 fixation and water-use efficiency of Cyclopia was affected by age, slope and planting material. Further, symbiotic N nutrition and water-use efficiency of Cyclopia and Aspalathus were related.

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