Cape Fynbos Research Articles

Biological nitrogen fixation and molecular diversity of rhizobia isolated from root nodules of wild legumes: Polhillia, Wiborgia and Wiborgiella species of the South African Cape fynbos

Biological nitrogen fixation and molecular diversity of rhizobia isolated from root nodules of wild legumes: Polhillia, Wiborgia and Wiborgiella species of the South African Cape fynbos

Symbiotic functioning, structural adaptation, and subcellular organization of root nodules from Psoralea pinnata (L.) plants grown naturally under wetland and upland conditions in the Cape Fynbos of South Africa.

In the Cape Fynbos of South Africa, Psoralea pinnata (L.) plants occur naturally in both wetland and well-drained soils and yet effectively fix N2 under the two contrasting conditions. In this study, nodule structure and functioning in P. pinnata plants from the two habitats were evaluated using light and transmission electron microscopy (TEM), as well as the 15N natural abundance technique. The results showed that, structurally, fully developed P. pinnata nodules were spherical in shape with six components (namely, lenticels, periderm, outer cortex, middle cortex, inner cortex, and a central bacteria-infected medulla region). Morphometric analysis revealed 44 and 84% increase in cell area and volume of wetland nodules compared to those from upland. The percentage area of nodules occupied by the middle cortex in wetland nodules was twice that of upland nodules. As a result, the size of the medulla region in wetland nodules was significantly reduced compared to upland nodules. Additionally, the average area of medulla occupied by intercellular air spaces in wetland nodules was about five times that of upland nodules (about 431% increase in wetland over upland nodules). TEM data also showed more bacteroids in symbiosomes of upland nodules when compared to wetland nodules. However, isotopic analysis of above-ground plant parts revealed no differences in symbiotic parameters such as N concentration, ∂15N and %Ndfa between wetland and upland P. pinnata plants. These results suggest that, under limiting O2 conditions especially in wetlands, nodules make structural and functional adjustments to meet the O2 demands of N2-fixing bacteroids.

Nitrogen nutrition, carbon accumulation and δ13C ofCyclopiaandAspalathusspecies 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 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.

Biogeography and evolution of seeder and resprouter forms of Erica coccinea (Ericaceae) in the fire-prone Cape fynbos

The genus Erica represents the epitome of plant biodiversity in the South African Cape fynbos with over 700 species. This genus is composed of seeder and resprouter species, but both species diversity and endemism are strongly linked to the seeder habit and concentrated in the southwestern Cape Floristic Region (CFR). Erica coccinea is a relatively abundant and widespread fynbos species whose most remarkable morphological feature is the existence of distinct seeder and resprouter forms, frequently—but not always—in disjunct populations. Both higher within-population genetic diversity and among-population differentiation have been found in seeders, most likely as a consequence of the shorter generation times and faster population turnovers. Resprouters, despite being less diverse, are suspected to be ancestral. However, no solid evidence has yet been provided for the ancestrality of the resprouter form, or for the demographic processes that have determined the current distribution of genetic diversity in both regeneration forms. Here, we used microsatellites and sequences of the nuclear ribosomal internal transcribed spacers to describe the phylogeographic structure of seeder and resprouter E. c occinea populations and provide good evidence for the ancestral status of the resprouter form and the comparatively high rates of molecular evolution in derived seeder populations. We also reveal that mixed populations, where both seeder and resprouter individuals co-occur, were originated by secondary contacts. This study highlights the role of fire in driving accelerated diversification in seeder lineages of highly speciose CFR fynbos taxa.

Recombination and horizontal transfer of nodulation and ACC deaminase (acdS) genes withinAlpha- andBetaproteobacterianodulating legumes of the Cape Fynbos biome

The goal of this work is to study the evolution and the degree of horizontal gene transfer (HGT) within rhizobial genera of both Alphaproteobacteria (Mesorhizobium, Rhizobium) and Betaproteobacteria (Burkholderia), originating from South African Fynbos legumes. By using a phylogenetic approach and comparing multiple chromosomal and symbiosis genes, we revealed conclusive evidence of high degrees of horizontal transfer of nodulation genes among closely related species of both groups of rhizobia, but also among species with distant genetic backgrounds (Rhizobium and Mesorhizobium), underscoring the importance of lateral transfer of symbiosis traits as an important evolutionary force among rhizobia of the Cape Fynbos biome. The extensive exchange of symbiosis genes in the Fynbos is in contrast with a lack of significant events of HGT among Burkholderia symbionts from the South American Cerrado and Caatinga biome. Furthermore, homologous recombination among selected housekeeping genes had a substantial impact on sequence evolution within Burkholderia and Mesorhizobium. Finally, phylogenetic analyses of the non-symbiosis acdS gene in Mesorhizobium, a gene often located on symbiosis islands, revealed distinct relationships compared to the chromosomal and symbiosis genes, suggesting a different evolutionary history and independent events of gene transfer. The observed events of HGT and incongruence between different genes necessitate caution in interpreting topologies from individual data types.

Variation in organ δ13C and rhizosphere P nutrition of Wiborgiella sessilifolia of the Cape Fynbos

Variation in organ δ13C and rhizosphere P nutrition of Wiborgiella sessilifolia of the Cape Fynbos

Shifts in Köppen-Geiger climate zones over southern Africa in relation to key global temperature goals

Potential changes in Koppen-Geiger climate zones over southern Africa (Africa south of 22 °S) under future climate change are investigated using an ensemble of high-resolution projections of a regional climate model. The projections are performed under the A2 scenario of the Special Report on Emission Scenarios (SRES), and changes are presented for those times in the future when the increase in global average surface temperature reaches thresholds of 1, 2, and 3 °C, relative to the present-day baseline climatology. Widespread shifts in climate regimes are projected, of which the southern and eastern expansion of the hot desert and hot steppe zones is the most prominent. From occupying 33.1 and 19.4 % of southern Africa under present-day climate, these regions are projected to occupy between 47.3 and 59.7 % (hot desert zone) and 24.9 and 29.9 % (hot steppe zone) of the region in a future world where the global temperature has increased by 3 °C. The cold desert and cold steppe zones are projected to decrease correspondingly. The temperate regions of eastern South Africa, the Cape south coast, and winter rainfall region of the southwestern Cape are also projected to contract. An expansion of the hot steppe zone into the cold steppe and temperate zones may favor the intrusion of trees (and therefore the savanna biome) into the most pristine grasslands of southern Africa. However, the correlative climate-vegetation approach of using projected changes in Koppen-Geiger zones to infer future vegetation patterns is of limited value in the savanna complex of southern Africa, where complex feedbacks occur between carbon dioxide (CO2) concentrations, trees, C4 grasses, fire, and climate. The present-day temperate Cape Fynbos regime may come under increasing pressure as the encompassing temperate zone is invaded mainly from the east by the hot steppe climate regime under climate change, with the incidence of Fynbos fires also becoming more likely in a generally warmer and drier climate.

Towards an isotope ecology of Cape Fynbos small mammals

We investigated ecological separation through dietary partitioning of small mammals in the nutrient-poor Fynbos biome using a stable isotope approach. Hair samples from eight species of co-occurring small mammals in two separate locations were analysed for stable carbon (13C/12C) and nitrogen (15N/14N) isotope ratios. In addition, we investigated the seasonal variation in diet again by using variation in isotopic composition of one of the most common small mammal species, the Cape spiny mouse. We also analysed seeds and leaves from the most common plant species at each study site. Results showed that some dietary separation exists among these coexisting small mammals. Geographic differences exist in isotope signatures within the Cape spiny mouse, possibly resulting from area-related variations in isotope values of plants, as well as differences in the animals’ diets. A. subspinosus hair shows little to no seasonal fluctuation of isotopic signals, except in summer, which possibly indicates a stable diet over much of the year. We conclude that the isotopic approach to determine trophic levels is limited by significant geographic variation in plant isotopes and enrichment in seeds compared to leaves.

The Status of Conservation Education in Africa

There are 5 global eco-regions regarded as top conservation priorities in Africa, and each one has a center for conservation studies. Established in 1962, the College of Wildlife Management at Mweka, Tanzania, has trained more than 5000 wildlife managers from 52 countries till date in the Eastern Arc Montane eco-region. The Upper and Lower Guinea eco-region is represented by the Sapo Conservation Center (SCC) in the eponymous National Park in Liberia and the A.P. Levenits Ornithological Research Institute (APLORI), Jos, Nigeria. The SCC offers training programs of up to 2 weeks duration, 2 to 3 times a year for students and academic instructors from the University of Liberia, Monrovia, Forestry Training Institute, Tubmanburg and Nimba County Community College, Nimba. The APLORI, founded in 2002, is a premier institute of ornithological research and conservation training in West Africa, and 66 graduates have left its portals to take up crucial responsibilities in the government, civil society and academia in Africa. The Cape Fynbos eco-region famed for its restioid, ericoid and proteoid components hosts the Southern African Wildlife College (SAWC) for training managers and conservationists in diverse fields such as such as nature-based tourism, trans-frontier conservation area management and capacity building at the community level. SAWC is situated in South Africa in a natural low veld environment, 10km west of the Orpen Gate of the Kruger National Park. The Albertine Rift Montane eco-region with flagship endangered species such as the Mountain and Eastern Lowland gorillas, saw the launch of a conservation primary school in Ilima, Democratic Republic of Congo (DRC) in September 2013; building 14 other unique primary schools over a period of 10 years in key landscapes in Africa is a commitment of the African Wildlife Foundation (AWF). Last but not the least, the Ethiopian highlands eco-region, houses species like the Ethiopian wolf and is served by the Wondo Genet College of Forestry in southern Ethiopia to train conservation professionals in the Horn of Africa region and beyond.

Elemental distribution in tissue components of N2-fixing nodules of Psoralea pinnata plants growing naturally in wetland and upland conditions in the Cape Fynbos of South Africa

There is little information on in situ distribution of nutrient elements in N2-fixing nodules. The aim of this study was to quantify elemental distribution in tissue components of N2-fixing nodules harvested from Psoralea pinnata plants grown naturally in wetland and upland conditions in the Cape Fynbos. The data obtained from particle-induced X-ray emission revealed the occurrence of 20 elements (Si, P, S, Cl, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, As, Br, Rb, Sr, Y, Zr, Mo and Ba) in nodule components. Although, in upland plants, the concentrations of S, Fe, Si, Mn and Cu showed a steady increase from the middle cortex to the medulla region of P. pinnata nodules, in wetland plants, only S, Fe and Mn showed an increase in concentration from the middle cortex to the bacteria-infected medulla of P. pinnata nodules. By contrast, the concentrations of Cl, K, Ca, Zn and Sr decreased from middle cortex to nodule medulla. The alkaline earth, alkali and transition elements Rb, Sr, Y and Zr, never before reported in N2-fixing nodules, were found to occur in root nodules of P. pinnata plants grown in both wetland and upland conditions.

Elucidating patterns in the population size structure and density of Aloe plicatilis, a tree aloe endemic to the Cape fynbos, South Africa

Studies on plant population size structure provide important baseline information for monitoring and conservation. Traditionally, inverse J-shaped size class distributions (SCD) were considered indicative of ‘healthy’, stable plant populations; however, this may not hold true for long-lived, slow-growing species. This study assessed the population size structure of 19 populations of Aloe plicatilis, a Cape fynbos endemic tree aloe, and quantified population size and density. A strong positive linear relationship between stem diameter (SDr) and height was used to align SDr and height SCD bins, and to harmonize stage and size classes. Onset of reproduction occurs at ~15cm SDr and ~0.8m in height. Some A. plicatilis individuals appear to display a ‘bonsai effect’ whereby the growth of individuals in very rocky sites is suppressed. Stunted plants may be non-reproductive ‘suppressed juveniles’ or ‘reproductive dwarfs’. The short, shrub-like growth form of many individuals may also result from height restrictions imposed by persistent strong winds. Population size, extent and density ranged from 31 to >110 000 individuals, 0.05–103ha and 75–3000 plants/ha respectively. Bell-shaped SCDs were the most common (50% of populations). The SDr and height SCDs for all populations combined were also bell-shaped. Seven populations displayed irregular SCDs, but were similar in structure to the bell-shaped SCDs, both of which were attributed to an adult-persistence population survival strategy. This study challenges the suitability of the inverse J as the only SCD indicative of healthy, stable populations for long-lived, slow-growing species. The study provides baseline demographic data on A. plicatilis across its distribution for long-term monitoring, and provides insights useful for examining trends in the demographics of other long-lived, slow-growing species.

Rhizosphere acid and alkaline phosphatase activity as a marker of P nutrition in nodulated Cyclopia and Aspalathus species in the Cape fynbos of South Africa

Cyclopia and Aspalathus species are important economic legumes in the Cape fynbos of South Africa, as they are used for making Honeybush and Rooibos tea, and for trade in the cut wild flower industry. The aim of this study was to assess acid and alkaline phosphatase activity in the rhizosphere of Cyclopia genistoides, Cyclopia subternata, Aspalathus caledonensis and Aspalathus aspalathoides as an indicator of P supply and P nutrition in the nutrient-poor soils of the Cape fynbos. Whether at Kokrivier or Kanetberg, the P enzyme activities were much higher in the rhizospheres of the legumes C. genistoides, C. subternata, A. caledonensis, and A. aspalathoides compared to those of the non-legumes Leucadendron strictum, Elegia thyrsoidea and Mimetes cucullatus, or bulk soil. As a result, plant-available P concentration in the rhizosphere, as well as shoot P levels closely mirrored acid and alkaline phosphatase activity in the rhizosphere of each plant species. Relative to younger plants, older Cyclopia species exhibited, much greater acid and alkaline phosphatase activity in the rhizosphere and this again resulted in much higher plant-available rhizosphere P. C. subternata plants developed from cuttings at Kanetberg showed greater rhizosphere acid and alkaline phosphatase activity than seedlings and bulk soil. As a result, the concentration of plant available-P and organic P were much higher in the rhizosphere of cuttings than seedlings, leading to greater shoot P in cuttings than seedlings. Taken together, these data suggest that rhizosphere P enzyme activity can be used as a good indicator of P supply and P nutrition in Cyclopia cuttings and seedlings, but less so in Aspalathus species in the Cape fynbos. The enhanced P nutrition in plants from cuttings probably accounts for the higher tea yields obtained by farmers when they use cuttings instead of seedlings in their plantations.

Pollination structures plant and nectar-feeding bird communities in Cape Fynbos, South Africa

Pollination structures plant and nectar-feeding bird communities in Cape Fynbos, South Africa

Symbiotic nitrogen contribution and biodiversity of root-nodule bacteria nodulating Psoralea species in the Cape Fynbos, South Africa

The genus Psoralea (tribe Psoraleae, family Leguminosae) is indigenous to the Cape fynbos of South Africa and little is known about its symbiosis and/or adaptation. The aim of this study was to assess root nodulation and N2 fixation in eight of the 50 Psoralea species, as well as the biodiversity of their associated nodulating microsymbionts. The eight species studied (namely, Psoralea pinnata, Psoralea aphylla, Psoralea aculeata, Psoralea monophylla, Psoralea repens, Psoralea laxa, Psoralea asarina and Psoralea restioides) all had round-shaped, determinate type (desmodioid) nodules, and data from 15N natural abundance showed that they obtained 60–88% of their N nutrition from symbiotic fixation. These Psoralea species also transported their fixed-N as ureides (allantoin and allantoic acid) in the xylem stream, a symbiotic trait that links them very closely to the tribe Phaseoleae. Bacteria isolated from root nodules of the eight Psoralea species varied in phenotypic characteristics, nodulation promiscuity, and N2-fixing efficacy. Furthermore, 16S rDNA gene sequence data showed that Psoralea species can form root nodules with different soil bacteria, including Rhizobium, Mesorhizobium and Burkholderia strains. This is not only evidence of nodulation promiscuity, but also an indication of the species’ adaptation to the nutrient-poor, low-N, sandy acidic soils of the Cape fynbos.

Effect of N and P nutrition on extracellular secretion of lumichrome, riboflavin and indole acetic acid by N2-fixing bacteria and endophytes isolated from Psoralea nodules

Soils of the Cape Fynbos in South Africa are very low in nutrients, especially N and P, which affect bacterial growth and metabolism. In this study, the effect of supplying nitrate (14.8 and 59.3 mM NO 3 − ), ammonium (28.1 and 112.0 mM NH 4 + ) and phosphorus (1.4 and 5.7 mM P) to five N2-fixing and 11 non-nodulating bacterial strains isolated from root nodules of Psoralea species in the Cape Fynbos was assessed. The data revealed marked variation in the secretion of lumichrome, riboflavin and IAA into culture filtrate. There was generally greater production of lumichrome, riboflavin and IAA by the N2-fixing bacteria than those unable to nodulate P. pinnata and siratro, with much greater concentrations of lumichrome and riboflavin in culture filtrate at high P than low P. At low and high P, symbiotic strain TUT57pp produced 2.2-fold and 3.2-fold more IAA than TUT65prp and TUT33pap respectively, (two non-nodulating strains also with greater IAA production). Although ammonium nutrition has no effect on riboflavin production, it altered lumichrome concentrations in culture filtrate. While ammonium application had no effect, supplying bacterial cells with high nitrate concentration significantly decreased cellular production of lumichrome and riboflavin, two important symbiotic signal molecules. The observed nitrate inhibition of lumichrome and riboflavin biosynthesis and release is in addition to its depressive effect on nodulation and N2 fixation in symbiotic legumes.

Reduced flower visitation by nectar-feeding birds in response to fire in Cape fynbos vegetation, South Africa

Nectar-feeding birds are important pollinators in fire-prone regions of the world, but the impact of fires on these bird communities has seldom been studied. Nectar-feeding bird communities were censused during peak flowering, before and after fire in the Cape fynbos of South Africa. The abundance and species richness of nectar-feeding birds decreased at all sites. In a controlled experiment, two common bird-pollinated plants, which flower profusely after a fire, were presented in floral arrays in burnt and unburnt vegetation. Birds visited flowers only in the unburnt areas. The results are surprising given the large number of bird-pollinated plants that have fire-stimulated flowering.

Easy technique for assessing pollination rates in the genus Erica reveals road impact on bird pollination in the Cape fynbos, South Africa

AbstractRoad traffic is one of the most pervasive forms of anthropogenic disturbance, but its impact on pollination, a potentially sensitive ecosystem process, has not been investigated. Such an assessment is needed in order to evaluate the potential for roadside verges to act as biodiversity refugia and corridors in otherwise transformed landscapes. Here, we document the impact of a two‐lane tar road on pollination by birds in the Cape fynbos of South Africa. To do so, we developed a quick and widely applicable method of determining pollination rates in bird‐pollinated members of the large genus Erica. Experiments with caged birds showed that the status of the anther ring (broken/perfect) indicated a sunbird visit with 92% accuracy, while field surveys confirmed anther ring status also serves as a proxy for pollen receipt to stigmas. Using this technique we determined pollination rate in Erica perspicua at three distances from the road (0–10, 20–30 and 40–50 m). After controlling for flower colour, robbing rate and plant density, significantly fewer anther rings were disturbed in close proximity to the road. The documented twofold decline in pollination along roadsides could have important implications for the way we view and manage road verges as refugia for species and ecological processes.

Strontium isotope analyses of large herbivore habitat use in the Cape Fynbos region of South Africa

The Cape Fynbos region of South Africa, a global biodiversity hotspot, hosted a diverse large mammal fauna till shortly after permanent European settlement (1652). How these animals survived in this exceptionally nutrient-poor environment is puzzling and it is generally believed that they restricted their movements to the more fertile shale areas. We tested the hypothesis that large herbivores avoid nutrient-poor limestone and sandstone fynbos shrublands in favour of shale-derived renosterveld vegetation using strontium (Sr) isotope analysis. If this technique could reconstruct the preferred feeding habitats of the contemporary fauna, it might also be useful for reconstructing the preferred feeding grounds of an extinct fauna. Using the assumption that small rodents have spatially restricted foraging activities, we determined the (87)Sr/(86)Sr isotope ratios of rodent teeth to establish the isotopic signal characteristic of the different geological substrates in the area. We then analysed (87)Sr/(86)Sr isotope ratios in the bones of a number of different large herbivores found in De Hoop Nature Reserve using laser ablation multi-collector inductively coupled plasma mass spectrometry. These values were compared to the bioavailable (rodent) values on the respective geological substrates. The technique identified differences in feeding substrate selection between different species and groups of the same species. The results also showed that shale renosterveld shrubland is not the exclusive source of nutrition for the large herbivores. Strikingly different isotope ratios among individuals in some populations pointed to significant dispersal events from distant sources. However, we were unable to pinpoint the exact feeding areas using Sr isotope analysis probably because some animals use a combination of substrates for feeding and because the geology of the study area is complex with graded isotope signals. We suggest that this technique is a valuable additional tool for exploring large mammal foraging behaviour on habitats associated with contrasting and less complex geology.

POSTFIRE RESPONSE AND GENETIC DIVERSITY IN ERICA COCCINEA: CONNECTING POPULATION DYNAMICS AND DIVERSIFICATION IN A BIODIVERSITY HOTSPOT

Understanding the processes of biological diversification is a central topic in evolutionary biology. The South African Cape fynbos, one of the major plant biodiversity hotspots out of the tropics, has prompted several hypotheses about the causes of generation and maintenance of biodiversity. Fire has been traditionally invoked as a key element to explain high levels of biodiversity in highly speciose fynbos taxa, such as the genus Erica. In this study, we have implemented a microevolutionary approach to elucidate how plant-response to fire may contribute to explain high levels of diversification in Erica. By using microsatellite markers, we investigated the genetic background of seeder (fire-sensitive) and resprouter (fire-resistant) populations of the fynbos species Erica coccinea. We found higher within-population genetic diversity and higher among-population differentiation in seeder populations and interpreted these higher levels of genetic diversification as a consequence of the comparatively shorter generation times and faster population turnover in the seeder form of this species. Considering that genetic divergence among populations may be seen as the initial step to speciation, the parallelism between these results and the pattern of biodiversity at the genus level offers stimulating insights into understanding causes of speciation of the genus Erica in the Cape fynbos.

Fire management in Mediterranean-climate shrublands: a case study from the Cape fynbos, South Africa

CITATION: Van Wilgen, B. W. et al. 2010. Fire management in Mediterranean-climate shrublands: a case study from the Cape fynbos, South Africa. Journal of Applied Ecology, 47(3):631–638, doi: 10.1111/j.1365-2664.2010.01800.x.