Cape Fynbos Research Articles

Symbiotic N nutrition, carbon accumulation, and water-use efficiency in species of the genus Aspalathus native to the Cape fynbos, South Africa

Low soil moisture and N in the fynbos are a major constraint to plant growth and N2 fixation in legumes, including Aspalathus species. The 15N and 13C natural abundance techniques were used to study N nutrition and plant water relations in different Aspalathus species sampled from 13 study sites in the fynbos. The results showed that A. acuminata shoots recorded lower δ15N values at Kalbaskraal, Worcester Langerug and Roundebosch, resulting in higher %Ndfa at those sites relative to Elim, which registered greater δ15N values. However, A. hispida shoots showed the lowest δ15N at Elim and Dutoitskloof than Yzerfontein, and Silwerstroomstrand, resulting in high %Ndfa at Elim. Of A. cordata, A. astroites, A. hispida, and A. wildenowiana collected from Dutoitskloof differed in δ15N and %Ndfa. A. cordata and A. astroites shoots showed lower δ15N, leading to higher %Ndfa than A. wildenowiana, which exhibited greater shoot δ15N. Of four Aspalathus species (A. cordata, A. carnosa, A. capensis and A. juniperina) sampled from Silvermine, A. cordata revealed the lowest δ15N and hence the highest %Ndfa. Conversely, A. carnosa recorded the highest shoot δ15N and the lowest %Ndfa. At Kokrivier, shoot δ15N was much greater in A. zeyheri and lowest in A. incurvifolia, resulting in higher %Ndfa in the latter than the former. The Aspalathus species differed in water-use efficiency or shoot δ13C values, which ranged from −30.35‰ to −26.93‰. Rainfall, soil moisture deficit and altitude were the major determinants of shoot δ13C values, but how these factors influence shoot δ13C of plants remains to be determined.

Effect of trace element supply on plant growth and mineral nutrition of Cyclopia longifolia Vogel L. a Honeybush tea plant growing on a farmer's field in the Cape fynbos, South Africa

Cyclopia longifolia Vogel L. is endemic to the Cape fynbos, and cultivated for the production of Honeybush tea, a herbal beverage with health benefits and economic potential in the cosmetic and nutraceutical industries. In this study, field plants were supplemented with different levels of Cu, Mo, Mn and Zn using 0, 0.5, 1.0 and 1.5 mM solutions of Na2MoO4·2H2O and MnSO4·2H2O and 0, 1.0 and 1.5 mM solutions of ZnSO4·7H2O and CuSO4·5H2O in a split-application. Plant shoots were harvested at 300 days after fertilization for biomass determination and analysis of mineral nutrients. The results showed significantly increased shoot dry matter yield of C. longifolia in response to Mn, Cu, Zn and Mo supplementation under field conditions, and was highest at the 1.5 mM level of each applied micronutrient. These results suggest that field fertilization of Cyclopia plants can lead to increased plant growth and greater tea yield, in addition to overcoming nutrient mining from the annual harvests of plant shoots for making tea. Furthermore, supplying Mn, Zn, Cu and Mo to C. longifolia also significantly increased the concentrations and amounts of P, K, Ca, Mg, Cu, Zn, Mn and B in shoots relative to the zero controls, suggesting an increase in tea quality with trace element supplementation. However, the shoot concentrations of N and Fe were markedly reduced with increasing supply of Mn, Cu, Zn and Mo to C. longifolia plants, an indication of mineral-to-mineral antagonism in the plant rhizosphere.

Cytotoxic activity of Cape Fynbos against triple-negative breast cancer cell line

• Erica glabella, Hippia frutescens and Salvia africana-lutea ( methanol), and Eriocephalus racemosa ( hexane) extracts IC 50 at < 30 µg/mL • Eriocephalus racemosa induced 21.48±2.86% apoptosis similar to cisplatin 23.72±4.36%. • Metabolite profiling of Salvia africana-lutea extract revealed the presence of phosphatidylcholines, triterpenoids, oxepane and 7-O-methylated flavonoids derivatives. Breast cancer is a leading cause of cancer-related deaths in women globally. Even though a plethora of treatments are available, most patients experience adverse effects which affect their quality of life. The aim of this study was to investigate the utility of nine Fynbos plants ( Erica magnisylvae E.G.H Oliv., Erica canescens J.C. Wendl. , Erica coccinea L. , Erica glabella Thunb. , Erica corifolia L. , Eriocephalus racemosa L. , Hippia frutescens L., Salvia africana-lutea L. and an unknown Fynbos plant) in treating breast cancer. Solvent extraction of fynbos plants was performed, and crude extracts were evaluated against MDA-MB 231 cancer cell line to determine the cytotoxic activity with the mode of cell death confirmed using flow cytometry. Antioxidant activity and mass spectrometry-based metabolite profiling were performed to characterize and identify the phytochemical constituents of the extracts. The methanol extracts from E. glabella ., H. frutescens and S. africana-lutea and the hexane extract from E. racemosa showed promising cytotoxic activities in the screening phase and thus were further evaluated to determine their 50% inhibitory concentrations (IC 50 ) which were found to be < 30 µg/mL. Flow cytometry analysis of treated MDA-MB 231 cells revealed promising results for the hexane crude extract (leaves) of E. racemosa and stem methanol crude extract of H. frutescens which induced apoptosis in MDA-MB-231 cancer cell line, similar to the reference drug cisplatin. Metabolite profiling of S. africana-lutea extract, the most potent apoptosis inducer in this study, revealed the presence of phosphatidylcholines, triterpenoids, oxepane and 7-O-methylated flavonoids derivatives. It was concluded that E. racemosa and S. africana-lutea are excellent candidates for further development of therapeutic agents in the fight against cancer, given the pressing need for novel efficacious agents.

Seasonal Effect on Bacterial Communities Associated with the Rhizospheres of Polhillia, Wiborgia and Wiborgiella Species in the Cape Fynbos, South Africa.

The Cape fynbos biome in South Africa is home to highly diverse and endemic shrub legumes, which include species of Aspalathus, Polhillia, Wiborgia and Wiborgiella. These species play a significant role in improving soil fertility due to their ability to fix N2. However, information regarding their microbiome is still unknown. Using the 16S rRNA Miseq illumina sequencing, this study assessed the bacterial community structure associated with the rhizospheres of Polhillia pallens, Polhillia brevicalyx, Wiborgia obcordata, Wiborgia sericea and Wiborgiella sessilifolia growing at different locations during the wet and dry seasons in the Cape fynbos. The results showed that the most dominant bacterial phylum was Actinobacteria during both the dry (56.2–37.2%) and wet (46.3–33.3%) seasons. Unclassified bacterial genera (19.9–27.7%) were the largest inhabitants in the rhizospheres of all five species during the two seasons. The other dominant phyla included Bacteroidetes, Acidobacteria, Proteobacteria and Firmicutes. Mycobacterium and Conexibacter genera were the biggest populations found in the rhizosphere soil of all five test species during both seasons, except for W. obcordata soil sampled during the dry season, which had Dehalogenimonas as the major inhabitant (6.08%). In this study plant species and growth season were the major drivers of microbial community structure, with W. obcordata having the greatest influence on its microbiome than the other test species. The wet season promoted greater microbial diversity than the dry season.

Modelling cost-effective clearing solutions for invasive alien trees: A case study on wilding conifers

Accurate on-site identification of appropriate alien clearing methods can realize significant cost savings for heterogenous sites. We developed a cost-based model accounting for site parameters such as infestation density, slope, obstructive vegetation density and site-access. These parameters are combined with a unit-costing sub-module to identify the most cost-effective clearing method for a particular site. The model was tested in the heterogenous Cape Fynbos biome of South Africa for three clearing methods for Pinus: traditional felling, drill-and-fill, and the arial-basal bark application (ABBA) method. The model accounts for the above-mentioned site parameters after which it is calibrated with the unit-costing for each method. Various scenarios consisting of different combinations of above-mentioned site parameters are then applied to identify the cost-effective solution for any particular combination of site parameters. Results favoured the drill-and-fill method in most cases, with the ABBA method reserved for sites with isolated Pines situated in dense fynbos with difficult access at slope gradients of 45° and higher. At these site combinations, ground teams experience longer walk times which reduces their productivity to such an extent that ABBA is comparatively more cost-effective. Traditional felling turned out to be prohibitively expensive because of team composition (mandatory higher safety and supervision requirements required for chainsaw operations) and slower on-site walking due to heavier equipment. The information enables site managers to do more accurate planning since the model will ensure that a cost-effective method is chosen for any particular site. It is then up to the manager to implement the chosen clearing method in a cost-efficient way.

Cryptic polymorphic Proteaceae seeds reduce detection by visually-cued predators on post-fire soils

Plant species with large seeds are susceptible to high levels of seed predation. Seeds of serotinous Proteaceae plants display what appears to be background matching, with polymorphic colours or ornamented surfaces reducing their detectability on certain soil types. We investigated whether seed crypsis (background matching) in Proteaceae seeds can reduce seed predation by visually-cued bird granivores using field observations, seed removal trials and spectrophotometry data. We found no difference in seed predation of winged seeds on different substrates by a diurnal rodent granivore. We therefore ruled out rodent granivores as selective agents driving visual seed crypsis in Cape Proteaceae. Light seeds of most polymorphic Leucadendron seeds showed background matching with their native soils, with granivorous birds predicted to have difficulty distinguishing them apart. Monomorphic Protea seeds with hairs generally do not background match with no reduction in detectability from visually cued predators. This is the first widescale documentation of seed colours and first description of crypsis in the seeds of Cape plants. We suggest that seed colour polymorphisms are adaptations to substrate-specific seed predation biases, with visually-cued bird granivores the likely selective agent driving the visual crypsis of Cape fynbos seeds.

Ecological adaptation and phylogenetic analysis of microsymbionts nodulating Polhillia, Wiborgia and Wiborgiella species in the Cape fynbos, South Africa

Polhillia, Wiborgia and Wiborgiella species are shrub legumes endemic to the Cape fynbos of South Africa. They have the ability to fix atmospheric N2 when in symbiosis with soil bacteria called ‘rhizobia’. The aim of this study was to assess the morpho-physiological and phylogenetic characteristics of rhizobia associated with the nodulation of Polhillia, Wiborgia and Wiborgiella species growing in the Cape fynbos. The bacterial isolates from root nodules consisted of a mixture of fast and intermediate growers that differed in colony shape and size. The isolates exhibited tolerance to salinity (0.5–3% NaCl) and pH (pH 5–10) and different antibiotic concentrations, and could produce 0.51 to 51.23 µg mL−1 of indole-3-acetic acid (IAA), as well as solubilize tri-calcium phosphate. The ERIC-PCR results showed high genomic diversity in the rhizobial population and grouped them into two major clusters. Phylogenetic analysis based on 16S rRNA, atpD, glnII, gyrB, nifH and nodC gene sequences revealed distinct and novel evolutionary lineages related to the genus Rhizobium and Mesorhizobium, with some of them being very close to Mesorhizobium australicum. However, the phylogenetic analysis of glnII and nifH genes of some isolates showed incongruency.

Artificial nectar feeders reduce sunbird abundance and plant visitation in Cape Fynbos adjacent to suburban areas

Globally, people feed wild animals to interact with nature. Attracting nectarivorous birds to gardens using artificial nectar feeders is increasingly popular, yet little is known about its influence on birds and the plants they pollinate. We investigated effects of nectar feeders on African birds and their plant mutualists, by conducting feeding experiments in gardens and natural vegetation along the suburban edge of the Cape Peninsula, South Africa. We compared relative abundance and local distribution patterns of nectar-specialist, nectar-opportunist and non-nectarivore bird species between feeder and control treatments. We then tested whether nectar feeders in gardens affected visitation rates to two sunbird-pollinated Erica species in neighbouring vegetation compared to control sites. Nectar feeders increased the density of nectarivores (but not non-nectarivores) in gardens but decreased their density in neighbouring vegetation, even in winter when floral abundance was high. These changes in sunbird distribution patterns had no detectible influence on visitation rates to E. abietina, but decreased visitation to E. plukenetii flowers by on average 16% at least up to 300 m of gardens with feeders. Thus, although supplementary nectar feeding may have conservation value for nectarivorous birds by reducing their urban sensitivity, it can inadvertently interfere with bird-plant pollination networks by competing with native flowers for birds’ attention.

Survival strategy of Watsonia fourcadei (Iridaceae); allocation of resources to sexual reproduction and vegetative survival of the parent plant

Geophytes are abundant in the Cape fynbos vegetation and many of the Cape geophytes, such as Watsonia species, flower mostly only in the first year after a fire. This study investigates the question if these plants have a resource allocation strategy which limits sexual reproduction to the post-fire environment and that they favor resource allocation to the storage organ for the survival of the parent plant at a cost to sexual reproduction. To test the hypothesis that the Cape geophyte Watsonia fourcadei represses sexual reproduction in favor of the survival of the parent plant, three levels of defoliation (20, 50 and 100%) were applied during a phenological stage when resources were least in the parent corms. Resource allocation to different plant parts was investigated when plants were in the seeding phase. Dry mass and nutrient (N, P. K, Ca, Mg and Ca) content were used as indicators of the resource allocation pattern. Dry mass and nutrient allocation patterns were similar, with significantly higher percentages of resources allocated to vegetative survival of the parent plant than to sexual reproductive organs (inflorescence and seeds) after complete defoliation, than after 20 and 50% defoliation. The W. fourcadei plants were able to accumulate adequate resources in the post-fire growth season to support sexual reproduction after up to 50% defoliation, albeit to a lesser extent than in control plants, but sexual reproduction was poorly supported after complete defoliation. Results indicate that W. fourcadei plants must be able to accumulate at least 3.5 g of dry mass in the new developing corm before resources are allocated to sexual reproductive plant parts. Replenishment of nutrient content after defoliation was not a limiting factor for resources allocation to sexual reproduction, except in the case of phosphate. W. fourcadei plants acted as a functional unit and resources allocation to sexual reproduction was controlled and depended on the availability of resources. None of the current resource allocation models are applicable to W. fourcadei and factors that could have selected for the apparent ‘K’ survival strategy in this and other Cape geophyte species are discussed.

Protea maturation rates and fire return intervals in a mediterranean ecosystem: testing the rules of thumb at a local scale

The appropriate fire return interval of prescribed burns is critical in many fire-driven systems. I use a mediterranean-type ecosystem – Cape fynbos, South Africa – to test guidelines for fire return intervals. Guidelines state that at least 50% of a population of the slowest-maturing obligate seeder Protea species must have flowered for three successive seasons, or that 90% of individuals from the slowest-maturing Protea species must have flowered at least once before a fire occurrence. Whether these ‘rules of thumb’ will lead to similar fire return intervals for prescribed burns is unknown. I address this by assessing two obligate seeding Protea species for length of juvenile period and age at three times flowering at 17 sites across a conservation area. For the slowest maturing species, when 50% of the fastest-maturing population had flowered three times (at 11 years), no individuals had flowered three times (happens at 14 years) in the slowest-maturing population. Using the 90% rule, this was reached at 9 years in the fastest-maturing P. neriifolia population and 11 years in the slowest-maturing. The 50% rule is more conservative than the 90% rule and is preferred. I highlight the importance of testing guidelines for fire return intervals to ensure effective biodiversity conservation.

Seed dispersal, directed deterrence and germination in gifboom (Hyaenanche globosa; Picrodendraceae) seeds

We investigated seed dispersal, directed deterrence and germination in the Cape narrow-endemic plant Hyaenanche globosa (gifboom). We found that gifboom seeds were predominantly removed and cached by the known scatter-hoarding specialist, small mammal, Acomys subspinosus, a first case of scatter-hoarding in the Picrodendraceae and the first case of a recalcitrant seed being scatter-hoarded in Cape fynbos. This represents an unusual exception to most hard-seeded, dormant scatter-hoarded seeds. In contrast, the ubiquitous, generalist, small mammal Micaelamys namaquensis, which is known to consume a variety of seeds, ignored gifboom seeds. The seeds, which contain the toxins, appear to have a directed deterrence effect on this common seed predator. We show that imbibed gifboom seeds produce copious mucilage, due to pectins, which aid in germination. Gifboom seeds appear to have two novel mechanisms for increasing seed to seedling survival, including toxins for seed predator deterrence and mucilage production for enhanced germination.

Pollination structures plant and nectar‐feeding bird communities in Cape fynbos, South Africa: Implications for the conservation of plant–bird mutualisms

AbstractWith the current global concerns about pollinators, relationships between species interactions and diversity are pivotal. If pollinator communities depend strongly on the diversity of flowering plants and vice versa, anthropogenic influences—whether positive or negative—on one partner will cause changes in the other. Here we ask whether nectarivorous bird communities are structured by resource abundance (Proteaceae nectar) or Proteaceae diversity at different spatial scales in the Cape fynbos of South Africa. On a small spatial scale, we sampled 34 one‐hectare plots across the Cape Floristic Region (CFR) for flowering Proteaceae species, number of inflorescences, nectar volume, vegetation age, nectar‐feeding bird abundance and species richness. At small scale, nectar—rather than vegetation structure or plant community composition—was the most strongly correlated to nectar‐feeding bird diversity and abundance. On a landscape scale we investigated the spatio‐temporal flowering patterns of ornithophilous Proteaceae throughout the CFR. Similar flowering patterns—with a winter floral abundance peak—were found throughout the region, butProtea,LeucospermumandMimetesshowed complementary flowering periods. At large spatial scales ornithophilous Proteaceae species richness is strongly correlated—more so than plant or floral abundance—to the nectar‐feeding bird community. At large spatial scales resource diversity—and at a smaller scale resource abundance, shapes nectar‐feeding bird communities. Providing high volumes of nectar sugar throughout the year is key to restore the nectar‐feeding bird communities in small conservation areas.

Accumulation of phosphorus and carbon and the dependency on biological N2 fixation for nitrogen nutrition in Polhillia, Wiborgia and Wiborgiella species growing in natural stands in cape fynbos, South Africa

Species of the genera Polhillia, Wiborgia and Wiborgiella are endemic to the Cape fynbos, South Africa. These plants form root nodules with soil rhizobia that fix atmospheric nitrogen. Little is known about their N and P nutrition, as well as their water-use efficiency in this highly dry and nutrient-poor soil environment. Therefore, the aim of this study was to assess P nutrition and water-use efficiency in natural stands of Polhillia, Wiborgia and Wiborgiella species as well as their dependency on Biological N2 fixation for nutrition. The δ15N natural abundance technique was used to measure the symbiotic performance. The Acid and alkaline phosphatase activities were assayed using p-nitrophenol method. 16S rRNA sequence was used to identify microsymbionts nodulating the test plants. The δ15N study showed a high dependency of the tested species on N2 fixation. The N derived from fixation was 76–84% for Polhillia sps., 73–91% for Wiborgia sps., and 61–68% for Wiborgiella sessilifolia. The species differed in water-use efficiency, with δ13C values of −28.1 to −25.1‰ for Polhillia sps., −28.3 to −25.8 ‰ for Wiborgia sps., and − 27.7 to −27.1‰ for Wiborgiella sessilifolia. The rhizosphere acid and alkaline phosphatase activities were higher in P. brevicalyx and P. pollens, than in the other tested species and this resulted in greater available P in the rhizosphere soils and an increased P uptake and accumulation in the plant shoots. Based on 16S rRNA nucleotide sequence and phylogenetic analysis of root nodule isolates, a diverse and novel Mesorhizobium sps. nodulate the tested plant species in the fynbos ecosystem.

Glutamate dehydrogenase is essential in the acclimation of Virgilia divaricata, a legume indigenous to the nutrient-poor Mediterranean-type ecosystems of the Cape Fynbos

Glutamate dehydrogenase (NAD(H)- GDH, EC 1.4.1.2) is an important enzyme in nitrogen (N) metabolism. It serves as a link between C and N metabolism, in its role of assimilating ammonia into glutamine or deaminating glutamate into 2-oxoglutarate and ammonia. GDH may also have a key in the N assimilation of legumes growing in P-poor soils. Virgilia divaricata is such a legume, growing in the nutrient limited soils of the mediterranean-type Cape fynbos ecosystem. In order to understand the role of GDH in the nitrogen nutrition of V. divaricata, the aim of this study was to identify the GDH gene transcripts, their relative expressions and enzyme activity in P-stressed roots and nodules during N metabolism. During P deficiency there was a reduction in total plant biomass as well as total plant P concentration. The analysis of the GDH cDNA sequences in V. divaricata revealed the presence of GHD1 and GHD2 subunits, these corresponding to the GDH1, GDH-B and GDH3 genes of legumes and non-legume plants. The relative expression of GDH1 and GDH2 genes in the roots and nodules, indicates that two the subunits were differently regulated depending on the organ type, rather than P supply. Although both transcripts appeared to be ubiquitously expressed in the roots and nodules, the GDH2 transcript evidently predominated over those of GDH1. Furthermore, the higher expression of both GDH transcripts in the roots than nodules, suggests that roots are more reliant on on GDH in P-poor soils, than nodules. With regards to GHD activity, both aminating and deaminating GDH activities were differently affected by P deficiency in roots and nodules. This may function to assimilate N and regulate internal C and N in the roots and nodules. The variation in GDH1 and GDH2 transcript expression and GDH enzyme activities, indicate that the enzyme may be regulated by post-translational modification, instead of by gene expression during P deficiency in V. divaricata.

Flower colour divergence is associated with post-fire regeneration dimorphism in the fynbos heath Erica coccinea subsp. coccinea (Ericaceae)

The South African Cape fynbos heath Erica coccinea subsp. coccinea is polymorphic for post-fire regeneration mode (seeder/resprouter), flower colour (red/yellow), flowering time (summer-autumn/winter-spring), as well as anther size. These polymorphisms tend to occur between, rather than within, populations. Here, we aimed to understand flower colour divergence in this fynbos heath species and its association with post-fire regeneration. We tested for an association between these polymorphisms. We also examined whether yellow-flowered plants lacked anthocyanins and whether the lack of anthocyanins affected the concentration of other flavonoids, both in flowers and shoots. We found a strong association between flower colour, regeneration mode and flowering phenology. We also detected larger anthers and larger pollen in yellow- than in red-flowered plants, consistently for both resprouter and seeder regeneration strategies. Finally, we ascertained that being yellow-flowered is associated with loss in the capacity of synthesizing anthocyanins in both the flower and in the vegetative tissue. Considering that pollinator availability or preferences do probably not constitute a selection pressure, we propose that both enhanced reproductive success of anthocyaninless, yellow-flowered plants and the avoidance of likely negative pleiotropic effects (early senescence) in seeders would be key to understanding the flower colour divergence in E. coccinea subsp. coccinea.

Priority areas for thein situconservation of crop wild relatives in South Africa

AbstractCrop wild relatives (CWR) are wild plant taxa that have broader genetic diversity than crops hence they are an excellent source of genes and traits to improve crops. The potential value of CWR for agriculture and the need to protect these plants in their natural habitats (in situ) have been recognized globally. South Africa has the richest temperate flora globally, and the checklist of food and fodder CWR for the country considers 258 taxa to be high priority for conservation. A systematic conservation planning approach was used for spatial prioritization forin situconservation actions for CWR. Protected areas were categorized on the basis of their CWR richness. The Kruger National Park has the highest number of CWR (66 taxa), but most of these are widespread and common. Fifty-seven protected areas, most of which are in the Western and Eastern Cape fynbos, are irreplaceable for protecting a number of endemic and threatened CWR. For priority CWR not adequately represented in existing protected areas, a spatial plan was developed to identify the smallest area that aligns with existing targets for the National Protected Areas Expansion Strategy, that are not transformed in terms of habitat, and that are projected to be climate change resilient. Mechanisms for ensuring uptake of the recommendations for thein situconservation of CWR have been documented in a National Strategy and Action Plan and these include making information and data available and promoting the inclusion of CWR in current management and monitoring activities.

Re-opening the case of Frankenflora: Evidence of hybridisation between local and introduced Protea species at Van Stadens Wildflower Reserve

The lack of examples of hybridisation within South African Cape Fynbos lineages gives the impression that interspecific hybridisation events may be rare in this system. If this is the case, then long-distance translocations of plant species across the Cape are unlikely to have any impact on the genetic component of biodiversity. Here we demonstrate that local populations of Protea eximia have hybridised with the non-local and introduced Protea susannae at Van Stadens Wildflower Reserve using morphological and genetic data; DNA sequence data were obtained from the internal transcribed spacer from the nuclear ribosomal cistron and a noncoding region of the chloroplast. Of the 24 plants from the reserve that were analysed, 11 were identified as hybrids, and comparing nuclear and chloroplast signals indicated bidirectional gene-flow between these species. This is the first study demonstrating the potential threat of long-distance dispersal in a Cape lineage to the genetic integrity of local populations.

What predicts the richness of seeder and resprouter species in fire‐prone Cape fynbos: Rainfall reliability or vegetation density?

AbstractIn ecosystems subject to regular canopy fires, woody species have evolved two general strategies of post‐fire regeneration. Seeder species are killed by fire and populations regenerate solely by post‐fire recruitment from a seed bank. Resprouter species survive fire and regenerate by vegetative regrowth from protected organs. Interestingly, the abundance of these strategies varies along environmental gradients and across regions. Two main hypotheses have been proposed to explain this spatial variation: the gap dependence and the environmental‐variability hypotheses. The gap‐dependence model predicts that seeders are favoured in sparse vegetation (vegetation gaps allowing effective post‐fire recruitment of seedlings), while resprouters are favoured in densely vegetated sites (seedlings being outcompeted by the rapid crown regrowth of resprouters). The environmental‐variability model predicts that seeders would prevail in reliable rainfall areas, whereas resprouters would be favoured in areas under highly variable rainfall that are prone to severe dry events (leading to high post‐fire seedling mortality). We tested these two models using distribution data, captured at the scale of quarter‐degree cells, for seeder and resprouter species of two speciose shrub genera (Aspalathus and Erica) common in fire‐prone fynbos ecosystems of the mediterranean‐climate part of the Cape Floristic Region. Contrary to the predictions of the gap‐dependence model, species number of both resprouters and seeders increased with values of the Normalized Difference Vegetation Index (a widely used surrogate for vegetation density), with a more marked increase for seeders. The predictions of the environmental‐variability hypothesis, by contrast, were not refuted by this study. Seeder and resprouter species of both genera showed highest richness in environments with high rainfall reliability. However, with decreasing reliability, seeder numbers dropped more quickly than those of resprouters. We conclude that the environmental‐variability model is better able to explain the abundance of woody seeder and resprouter species in Southern Hemisphere fire‐prone shrublands (fynbos and kwongan) than the gap‐dependence model.

Plant growth and N2 fixation in Cyclopia longifolia (Vogel L.) supplied with mineral nutrients in pot and field experiments

Cyclopia longifolia Vogel L. is indigenous to the Cape fynbos, and widely grown for the production of Honeybush tea, a beverage with health benefits and economic potential in the cosmetic and nutraceutical industries. The aim of this study was to assess plant growth and symbiotic performance of Cyclopia longifolia in field and pot experiments. Field plants were supplemented with different levels of P, Mg and Ca at Kanetberg mountains using 0, 5, 25 and 50mM of K2HPO4, MgCl2·6H2O and CaCl2·2H2O in split application, while P, Ca and Mg were applied as Supergrow (20.3% P), CaMg·(CO3)2, and MgSO4·7H2O) at 0, 10, 20 and 50kg·ha−1 to potted plants. Shoots were harvested at 240 and 300days after last fertilisation for pot and field experiments respectively, and analyzed for nodulation and N2 fixation. The data revealed significantly increased nodule number, nodule dry weight, root and shoot biomass in the pot experiment with P, Ca and Mg supply. Shoot dry matter, N content, amount of N-fixed, soil N uptake and tea yield of C. longifolia was significantly increased with increasing supply of P, Mg and Ca to field plants, and was highest at 50mM level of each element. Applying different levels of Mn, Cu, Zn and Mo to field plants of C. longifolia also markedly increased shoot biomass, N content, δ15N, amount of N-fixed, soil N uptake and tea yield. The increase in δ15N values, and hence reduced %Ndfa, of Cyclopia longifolia plants supplied with P, Mg, Ca, Mn, Cu, Zn and Mo suggests that the endogenous soil concentration of these nutrients were more limiting for plant growth than for nodule functioning. As a result, supplying P, Mg, Ca, Mn, Cu, Zn and Mo increased plant growth and biomass, but not %N derived from fixation.

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.