Nitrogen nutrition,carbon accumulation andδ^(13)C of Cyclopia and Aspalathus species in different settings of the Cape fynbos,South Africa

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 N_(2)fixation,carbon(C)assimilation andδ^(13)C 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 N_(2)fixation.At Kanetberg,C.subter-nata 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.N_(2)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.

Relationship between acid phosphatase activity and P concentration in organs of Cyclopia and Aspalathus species,and a non-legume of the Cape Floristic Region

Aims The role of tissue acid phosphatase(APase)activity of legumes and non-legumes in their P nutrition and adaptation to low-P soils is not well understood.To better understand this,a relationship between APase activ-ity and P concentration in leaves,stems,roots and nodules of legumes,Cyclopia and Aspalathus and a non-legume,Leucadendron strictum,all native to the P-poor soils of the Cape fynbos biome,was assessed.Methods Plants were collected and each separated into leaves,stems and roots.Phosphatase enzyme activity was assayed in soil using the p-nitrophenol method,while soil P and shoot P were measured using ICP-MS.To measure tissue APase activity,an acetate buffer was added into ground plant material and contents filtered.An ace-tate buffer and a p-nitrophenyl solution were added to the superna-tant and contents incubated.After incubation,NaOH(0.5 M)was added and absorbance read at 405 nm.Important Findings At Koksrivier,Cyclopia genistoides exhibited the highest leaf enzyme activity whilst Aspalathus aspalathoides showed the highest enzyme activity in the stems.At both Kleinberg and Kanetberg,Cyclopia subternata and Cyclopia longifolia showed the highest APase activity in leaves,followed by stems and low-est in roots.P concentration closely mirrored enzyme activity in organs of all test species from each site.APase activity posi-tively correlated with P concentration in organs of all the test Cyclopia and Leucadendron species,indicating that intracellular APase activity is directly linked to P mobilization and transloca-tion in these species.Percentage of N derived from fixation was positively correlated with tissue APase activity in C.genistoides(r=0.911^(*)),A.aspalathoides(r=0.868^(*))and Aspalathus cal-edonensis(r=0.957^(*)),suggesting that APase activity could be directly or indirectly linked to symbiotic functioning in these fynbos legumes,possibly via increased P supply to sites of N2 fixation.