Browsing by Author "Naidoo, Sershen."

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Alleviating delayed field curing-induced deterioration in rice seeds by cathodic water invigoration: a comparison of seed and seedling responses in two upland rice species and their interspecific hybrid.
(2021) Bam, Raphael Kwame.; Varghese, Boby.; Naidoo, Sershen.; Pammenter, Norman William.
Rice constitutes the major source of the world’s food supply. A number of varieties are grown in many parts of the world, all which produce orthodox seeds that are usually stored between growing seasons. As in other crop species, storage-induced loss of seed quality (viability and vigour) is inevitable but considerable research effort has been invested in optimising seed bank storage protocols for rice to ensure acceptably high levels of seed germinability and seedling emergence. However, poor post-harvest practices such as delayed field curing before threshing in developing countries in the humid tropics, such as Ghana, result in curing-induced seed deterioration in the field prior to ex situ storage. Given that many rice growing regions are likely to experience significant levels of climate change, seed processing and storage induced declines in rice seed quality could exacerbate the crop losses incurred by rice farmers in these regions in the future. This motivated the present study which was designed around three aims: 1) to investigate how environmental conditions and the duration of field curing influenced seed macro-structural integrity, susceptibility to microbial infection, and seed germinability and vigour; 2) to identify macro-structural and ultrastructural indicators/ biomarkers of field curing and associated storage-induced stress/ damage; 3) to assess whether the invigoration of field-cured seeds with cathodic water (CW), an established antioxidant-based seed invigoration medium, and deionized water (DW) can alleviate the deteriorative effects of delayed field curing on rice seed cellular integrity, germination and subsequent seedling growth and biomass. The specific objectives of this comparative study, which involved an Asian (Oryza sativa L.) and African (Oryza glaberrima Steud) upland rice species and their interspecific hybrid (O. sativa × O. glaberrima), were as follows: a) to compare the impacts of delayed field curing in wet and dry environments on seed physical, physiological and pathological quality; b) to identify potential ultrastructural biomarkers of seed sensitivity to delayed field curing-induced stress/ damage in embryonic root meristematic cells using transmission electron microscopy (TEM); c) to assess whether CW invigoration alleviates cellular stress/ damage induced by delayed field curing using selected ultrastructural biomarkers of seed sensitivity to such curing-induced stress/ damage; and d) to assess whether invigoration with CW and DW improves seed germinability and emergence, and subsequent plant growth in field cured seeds, relative to non-invigorated (NI) dry seeds.
Bio-guided isolation of biologically active compounds from seeds of selected South African medicinal plants.
(2016) Perumal, Amanda.; Govender, Patrick.; Naidoo, Sershen.; Pillay, Karen.
Abstract available in PDF file.
A biogeographic study of the KwaZulu-Natal sandstone sourveld patches within the eThekwini Municipal Area.
(2016) Drury, Charmaine Crystal.; Ramdhani, Syd.; Naidoo, Sershen.; Carbutt, Clinton.
KwaZulu-Natal Sandstone Sourveld (KZNSS) is an endangered vegetation type in South Africa. Approximately 68% of KZNSS is transformed, with remaining patches existing within an urban and suburban matrix. Fragmented patches of KZNSS found within the eThekwini Municipal Area (EMA) represent a conservation priority but are often not managed/ conserved appropriately as they are sometimes misclassified as Indian Ocean Coastal Grassland Belt (IOCGB) based on their close proximity to the latter vegetation type in a number of areas. This motivated the present study which involved characterising the flora of eight grassland patches within the EMA presently categorised as follows: three KZNSS sites (viz. Giba Gorge Environmental Precinct, Inanda Mountain and Springside Nature Reserve), three IOCBG sites (viz. Spyhill Open Space, Tanglewood Nature Reserve and Edgecliff Open Space) which are currently called Ecotonal given their close proximity to KZNSS, and two IOCGB sites (viz. New Germany Nature Reserve and Roosfontein Nature Reserve). Floristic surveys, which involved quadrats sampling were performed year round (c. 60% in the winter, 30% in the summer and the remaining quadrats performed in spring or autumn) until an 80% sampling effort was achieved. Additionally, transect sampling was performed monthly for a year at each site. Data from both methods were used to determine the vegetation composition and structure at each site. The below-ground flora of each site was also characterized by removing 30 – 35 soil samples after the two main flowering events (late November and early December as well as late April and early May) at each site and allowing germination to occur, with the resulting germinants being identified and quantified. Field observations on levels of disturbance and management practices at each were also considered. When data for quadrats and transects were pooled, 263 species were found to occur across the eight sites, with 110 of these being common to all three vegetation categories. Only one of the eleven endemic taxa characteristic of KZNSS were found across all three vegetation categories, while none of the endemic taxa associated with IOCBG were found, suggesting iv that identifying KZNSS or IOCBG based on endemic (i.e. diagnostic) species may be inappropriate at the sites investigated here. Further comparisons showed KZNSS and Ecotonal to contain more species than IOCBG, which were spread across more plant families (55 found in total), although IOCBG had one less site than KZNSS and Ecotonal. Diversity measures indicated that Ecotonal is more similar to KZNSS, with more species in common between KZNSS and Ecotonal than Ecotonal had with IOCBG. Additionally, diversity measures show very little differentiation between the dominant taxa of IOCBG from KZNSS. Cluster analyses and ordinations confirmed the current classification of Ecotonal sites as part of IOCBG, despite Ecotonal sharing more superficial similarities with KZNSS. Island biogeography theory‟s area and distance effects were not upheld – most likely due to the sites not being truly isolated from each other and a very localised spatial scale, the limited temporal scale (current status a result of the past 200 years), the lack of a true originating mainland and anthropogenic disturbance. Interestingly, the below-ground flora represented only c. 10% of the species found above-ground for all three categories, with Sørenson similarity index ranging from c. 15 – 22% as opposed to the 50% expected for southern African grasslands. This suggests that seedbank health and hence, regenerative potential may be poor at many of these sites and this may necessitate species reintroduction and habitat restoration at a number of these sites. Additionally, the effects of disturbance were evident across sites in all three vegetation categories, with disturbed sites (Edgecliff Open Space, Inanda Mountain and Roosfontein Nature Reserve) containing fewer species of conservation concern, fewer indigenous taxa in general and more alien plant taxa. Diversity indices also suggest that disturbed sites were more heterogeneous. However, disturbance agents such as herbivory appear to have had an enriching effect in term of the abundance of graminoids within the germinable soil seedbank. Alien taxa also occurred frequently in the below-ground flora but were not noted in the above-ground flora which suggests that given further disturbance/transformation, some of these sites are prone to alien plant invasion. The study suggests that IBT is not applicable to vegetation islands (grasslands in this case) with varying levels of transformation in urban matrices. The results confirm the high levels of transformation reported for sub-tropical grasslands within South Africa, specifically KZNSS, and highlight the need for floristic surveys to delimit different grassland types and in turn ensure their appropriate conservation and/or rehabilitation.
Factors governing seed recalcitrance in two species of contrasting storage longevity.
(2017) Moothoo-Padayachie, Anushka.; Naidoo, Sershen.; Varghese, Boby.; Varghese, Dalia.; Pammenter, Norman William.; Govender, Patrick.; Berjak, Patricia.
Abstract available in PDF file.
How green is green? : a socio-spatial analysis of the status of green spaces within the eThekwini Municipality.
(2014) Pillay, Sarushen.; Naidoo, Sershen.; Bob, Urmilla.; Gebreslasie, Michael Teweldemedhin.
Globally, urbanisation is occurring at an alarming rate and urban green spaces are increasingly recognised as essential components in the quest to achieve sustainable urban landscapes. This study, which involved a socio-spatial analysis of the status of green spaces within the eThekwini Municipality (located in KwaZulu-Natal, South Africa), offers a unique opportunity in terms of urban conservation research. The objectives of the study were to examine the socio-economic characteristics and the perspectives of residents on the use and value of green spaces within the eThekwini Municipality using areas surrounding the Bluff Conservancy (all situated within the SDA) as illustrative examples; to develop a spatial representation of the quality/ integrity of selected green spaces within the eThekwini Municipality in relation to land-use patterns; to examine the appropriateness of the typology presently used by the eThekwini Municipality to describe the status of green spaces and to compare the same with Adapted typologies in order to determine the level of deviation; and lastly, to generate recommendations on the conservation and management of these green spaces. A variety of socio-spatial analysis methods were used to collect and analyse primary data. Data was obtained using Geographical Information System mapping and a questionnaire in order to ascertain resident perceptions towards their surrounding green spaces. Thereafter, secondary spatial data acquired from the eThekwini Municipality was processed and subjected to a range of analyses to evaluate the efficacy of the typology presently used by the Municipality to assess the quality/ integrity of green spaces. Six random green space types (settlement, tree crops, woodland, forest, grassland and thicket) were selected and first examined using the eThekwini typology and thereafter with the Adapted typology, developed as part of this study. The results suggested that almost all respondents (75.50%) frequently utilised green spaces in their community, with most respondents favouring the use of recreational and social green spaces (for example, parks, sports field and the golf course). However, respondents also identified numerous challenges associated with accessing and using green spaces; crime, pollution and lack of maintenance in particular, were shown to hamper the optimal use and integrity of a number of green spaces. Additionally, it was found that respondents use of green spaces was not dependent on their gender and income but was significantly influenced by their education. Furthermore, though most respondents indicated that they frequently engage in environmentally-friendly practices, only a small proportion of respondents (9.75%) were aware of the Durban Metropolitan Open Space System (which is a programme that formally allows for the creation and preservation of green spaces). In terms of the spatial analyses, the results revealed that selected green spaces within the Municipality when classified using a more discriminatory typology (Adapted typology), can be shown to contain micro-habitats that are either more degraded or more intact than that reflected by the typology presently used by the eThekwini Municipality. It was found that the five thicket green space sites assessed using the eThekwini typology collectively deviated by approximately 60% from that assessed using the more discriminatory Adapted typology. Overall, it was evident that quality based land cover differed minimally to moderately when selected green space types were compared using the two typologies. This resulted in some green micro-habitats within larger green spaces being potentially misclassified in terms of their ecological integrity when using the eThekwini typology and, possibly not being prioritised for conservation and/ or restoration. The combination of social and spatial results obtained and interpreted in this study was used to generate recommendations for the conservation and management of green spaces within the eThekwini Municipality. Evidence from the social survey clearly showed that respondents expressed a willingness and desire to have and use green spaces. Therefore, it is recommended that the eThekwini Municipality increase the number of green spaces, preferably within densely populated communities as well as improve existing greenery within the Municipality. In addition, these areas should be made more accessible and useable and have value added benefits to communities who are intrinsically supporting them. Furthermore, it was found that the current typology used for the classification of green spaces within the eThekwini Municipality is not discriminative enough to allow for effective management and conservation. This suggests the need for a more nuanced classification of green spaces within the Municipality which ensures that quality characteristics are adequately incorporated into the assessment of these environments.
Implications of land use practices and socio-hydrological vulnerability within a rapidly developing city: a case study of the Umhlatuzana River, Ethekwini, South Africa.
(2020) Webster, Candice Natasha.; Munien, Suveshnee.; Naidoo, Sershen.
Anthropogenic actions affect land uses and land use change concomitantly influencing water quality in a catchment. In a catchment varying levels of income and access to infrastructure and resources result in a lack of access to reliable and clean water, forcing households to rely on nearby water sources such as rivers, dams or lakes to meet their basic needs. Utilisation of river water is influenced by the perception of water quality. The main aim of this study is to explore how land use practices and human-water interactions influence socio-hydrological vulnerability within the Umhlatuzana catchment in a rapidly developing city. Previous research has not focused on the water quality and vulnerability of households within South African catchments. Land use activities and land use changes were observed between 2003 and 2014 to examine the pressures on water and water quality in the catchment. Furthermore, selected water quality parameters were analysed for an 11-year period between 2004 and 2014 in order to examine temporal and spatial variation to unpack influences on vulnerability in the catchment. Moreover, 350 household surveys were administered in order to describe the community perception of land use, land use change and water quality in the catchment. Finally, field observations of areas surrounding the water sampling sites were completed to inform results, and provide a more nuanced understanding of data trends, community perceptions, and experiences with the river. Analysis of the spatial data indicates changes in the catchment that may contribute to the deteriorating water quality in the river. Furthermore, reports of malfunctioning Waste Water Treatment Works (WWTW) link the sewage system to increasing E. coli and T. coli levels in the river, which threatens the health and well-being of all river users. The households in the community are diverse with varying levels of vulnerability and access to resources as many households identified government grants as a source of income. Additionally, although most households perceived the river water in the catchment to be poor and deteriorating, of those that utilised the river water, majority did not treat it before use. The study demonstrates that there are households within the catchment that are vulnerable and at risk to the deteriorating river water in the catchment. Further research is required to identify sources of pollution to improve the water of the Umhlatuzana River and reduce risks to the community in the catchment.
The potential use embryonic shoot apices as explants for cryopreservation of selected recalcitrant-seeded species.
(2017) Nkayi, Anathi Asanda.; Varghese, Dalia.; Pammenter, Norman William.; Naidoo, Sershen.
Abstract available in PDF file.
Restoration of a degraded subtropical forest for climate change mitigation and adaptation in the city of Durban, South Africa.
(2017) Mugwedi, Lutendo Faith.; Rouget, Mathieu.; Egoh, Benis Nchine.; Slotow, Robert Hugh.; Naidoo, Sershen.
With unprecedented changes in climate and land-use patterns, a decrease in global biodiversity and ecosystem services has been occurring at an alarming rate. This has resulted in a widespread damage to the life-support systems upon which every living organism depends on. Reforestation of degraded forest ecosystems is now globally recognized as one of the best natural capital investment options, owing its contribution to biodiversity conservation, climate change mitigation and adaptation, and ecosystem services provision. The aim of this study was (1) to unravel confusions caused by the inconsistent use of terminologies describing different reforestation initiatives; (2) to investigate motivations behind recent reforestation initiatives; (3) to demonstrate the use of a restoration decision-making tool, Robust offsetting (RobOff); (4) to investigate the influence of climatic and edaphic factors on reforestation initiative, (5) to assess reforestation initiative success, and (6) to assess the impact of drought on reforestation initiative. A comprehensive review was conducted to unravel the confusion caused by the inconsistent use terminologies describing different reforestation initiatives, and to gain insight into motivations behind reforestation initiatives in recent literature (2000 to 2016). The results showed that there are 10 most common terminologies used to describe different reforestation initiatives. These terminologies were categorized into five groups based on their motivations, namely, (1) Creation or Fabrication, Reallocation and Replacement, (2) Ecological engineering, (3) Ecological restoration, (4) Reclamation, Reconstruction, Remediation, Renewal or Redemption, and (5) Rehabilitation. The recent reforestation initiatives were motivated by the need to reinstate resilient and more functional forest ecosystems (through planting of a higher diversity of native tree species). This is because species diverse forests are more resilient and functional with significant contributions to biodiversity conservation (fauna and flora), climate change mitigation (carbon storage) and adaptation (e.g., flood control) and ecosystem services that sustain society (e.g., food) and economy (e.g., employment opportunities). Using the Buffelsdraai Landfill Site Community Reforestation Project (BLSCRP) as a case study, RobOff, was employed to plan a complex large-scale reforestation. The complexity was caused by a mosaic of habitats (‗extant forest‘ and ‗former sugarcane fields‘) with varying levels of degradation, diverse reforestation actions (natural regeneration, current action, carbon action and biodiversity action), a limited budget and multiple goals (biodiversity, carbon stock and employment). RobOff results showed that investing in the restoration of ‗former sugarcane fields‘ through biodiversity action is preferable, because it achieved the highest biodiversity, carbon stock and employment opportunities. Field trials were conducted at the Buffelsdraai Landfill Site to assess the influence of microtopographic positions, and soil physical and chemical properties on the growth performance of the four most dominant planted native tree species (Bridelia micrantha, Erythrina lysistemon, Millettia grandis and Vachellia natalitia). Root-collar diameter, stem height and canopy width growth rates were assessed across the chronosequence of three habitats under restoration (0-, 3-, and 5-year-old), in the upland (dry) and lowland (wet) areas of each habitat. Erythrina lysistemon and V. natalitia were found to be good fast growing tree species suitable for restoration in both the upland and lowland areas, while B. micrantha was suitable for lowland area. Reforestation success of the BLSCRP was assessed using measures of plant richness, diversity, vegetation structure, invasive alien plants (IAPs) and ecological processes, contrasted across a chronosequence of habitats under restoration (0-year-old, 3-year-old and 5-year-old) and compared with a reference forest habitat (natural forest). The BLSCRP was largely successful, but low tree density and an increase in IAP cover with an increase in restoration age were identified as threats to the BLSCRP success. The 2015 El Niño event induced serendipitous drought occurrence in South Africa led to the assessment of its effect on planted tree sapling mortality and on the growth performance of the four most dominant planted tree species in the 0-year-old habitat. Drought effected mortality was highest in the lowland area (34.1%) and lower in the upland area (18.9%). Mortality rate of the nine most abundant species ranged from 10% to 52.5%. Erythrina lysistemon and V. natalitia had good growth rates in both the upland and lowland areas, and B. micrantha in the lowland area. The BLSCRP is highly likely to achieve its climate change mitigation and adaptation, biodiversity and ecosystem services restoration and employment creation in the city of Durban, provided the identified threats are addressed as soon as possible. The overall findings from this study showed that future large-scale reforestation initiatives around the globe should be designed to achieve biodiversity conservation, climate change mitigation and adaptation, and ecosystem services supply.
Scotch broom (cytisus scoparius (L.) link) and gorse (ulex europaeus L.) in South Africa: an assessment of invasiveness, management options and feasibility for countrywide eradication.
(2016) Mbatha, Philani Mzameleni.; Ramdhani, Syd.; Naidoo, Sershen.; Wilson, John R.
Abstract available in PDF file.
Studies on factors influencing viability after cryopreservation of excised zygotic embryos from recalcitrant seeds of two amaryllid species.
(2010) Naidoo, Sershen.; Berjak, Patricia.; Pammenter, Norman William.; Wesley-Smith, James.
Recalcitrant unlike orthodox seeds do not show a sharp border between maturation and germination and remain highly hydrated and desiccation-sensitive at all developmental and post-harvest stages. In contrast with recalcitrant seeds, orthodox types retain viability for predictably long periods in the dry state and hence can be stored under low relative humidity and temperature conditions. Storage of recalcitrant seeds under conditions allowing little to no water loss, at moderate temperatures, allows for short- to medium-term storage but only facilitates viability retention for a matter of a few weeks to months, at best, because the seeds are metabolically active and initiate germination while stored. Cryopreservation, i.e. storage at ultra-low temperatures (usually in liquid nitrogen [LN] at -196°C), is a promising option for the long-term germplasm conservation of recalcitrant-seeded species but their seeds present some unavoidable difficulties in terms of the amenability of their germplasm to cryopreservation. Pre-conditioning treatments can reduce the amount of ‘free’ water available for freezing and may increase the chances of cells or tissues surviving exposure to cryogenic temperatures. Such conditioning may be imposed by physical dehydration or cryoprotection, i.e. exposure to compounds that depress the kinetic freezing point of water and so reduce the likelihood of lethal ice-crystal formation during cooling (i.e. exposure to LN at -196°C or sub-cooled LN at -210°C) and subsequent thawing. Partial dehydration is presently a standard pre-treatment for the cryopreservation of recalcitrant zygotic germplasm and explant cryoprotection has been shown to improve postthaw survival in some recalcitrant-seeded species. However, there is a paucity of information on the physiological and biochemical basis of post-thaw survival or death in recalcitrant seeds, and this is the major focus of the current contribution. Additionally, in light of the lack of understanding on how cryo-related stresses imposed at the embryonic stage are translated or manifested during subsequent seedling growth, this study also investigated the effects of partial dehydration and the combination of partial dehydration and cooling of recalcitrant zygotic embryos on subsequent in and ex vitro seedling vigour. All studies were undertaken on the zygotic embryos of two recalcitrant-seeded members of the Amaryllidaceae, viz. Amaryllis belladonna (L.) and Haemanthus montanus (Baker); both of which are indigenous to South Africa. Studies described in Chapter 2 aimed to interpret the interactive effects of partial dehydration (rapidly to water contents > and <0.4 g g-1), cryoprotection (with sucrose [Suc; nonpenetrative] or glycerol [Gly; penetrative]) and cooling rate (rapid and slow) on subsequent zygotic embryo vigour and viability, using three stress markers: electrolyte leakage (an indicator of membrane integrity); spectrophotometric assessment of tetrazolium chloride-reduction (an indicator of respiratory competence); and rate of protein synthesis (an indicator of biochemical competence). These studies showed that in recalcitrant A. belladonna and H. montanus zygotic embryos, stresses and lesions, metabolic and physical, induced at each stage of the cryopreservation protocol appear to be compounded, thus pre-disposing the tissues to further damage and/or viability loss with the progression of each step. Maximum post-thaw viability retention in both species appeared to be based on the balance between desiccation damage and freezing stress, and the mitigation of both of these via Gly cryoprotection. Post-thaw viabilities in both species were best when Gly cryoprotected + partially dried zygotic embryos were rapidly, as opposed to slowly, cooled. However, the rate at which water could be removed during rapid drying was higher in A. belladonna and this may explain why the optimum water content range for post-thaw survival was <0.40 g g-¹ for A. belladonna and >0.40 g g-¹ for H. montanus. These results suggest that to optimise cryopreservation protocols for recalcitrant zygotic germplasm, attention must be paid to pre-cooling dehydration stress, which appears to be the product of both the ‘intensity’ and ‘duration’ of the stress. Cryoprotection and dehydration increased the chances of post-thaw survival in A. belladonna and H. montanus zygotic embryos. However, transmission electron microscopy studies on the root meristematic cells from the radicals of these embryos (described in Chapter 3) suggest that their practical benefits appear to have been realised only when damage to the sub-cellular matrix was minimised: when (a) pre-conditioning involved the combination of cryoprotection and partial dehydration; (b) the cryoprotectant was penetrating (Gly) as opposed to non-penetrating (Suc); and (c) embryos were rapidly cooled at water contents that minimised both dehydration and freezing damage. The ability of A. belladonna and H. montanus embryos to tolerate the various components of cryopreservation in relation to changes in extracellular superoxide (.O2 -) production and lipid peroxidation (a popular ‘marker’ for oxidative stress) was investigated in studies featured in Chapter 4. Pre-conditioning and freeze-thawing led to an increase in oxidative stress and the accompanying decline in viability suggests that oxidative stress was a major component of cryoinjury in the embryos presently investigated. Post-thaw viability retention in Gly cryoprotected + partially dried embryos was significantly higher than noncryoprotected + partially dried embryos, possibly due to the relatively lower post-drying lipid peroxidation levels and relatively higher post-drying and post-thawing enzymic antioxidant activities in the former. Exposure of certain plant tissues to low levels of oxidative or osmotic stress can improve their tolerance to a wide range of stresses. In contrast, exposure of H. montanus zygotic embryos to low levels of oxidative stress provoked by exogenously applied hydrogen peroxide (H2O2) or exposure of A. belladonna embryos to low levels of osmotic stress provoked by low water potential mannitol and polyethylene glycol solutions (in studies featured in Chapter 5) increased their sensitivity to subsequent dehydration and freeze-thaw stresses. Exposure of Gly cryoprotected and non-cryoprotected amaryllid embryos to such stress acclimation treatments may pre-dispose A. belladonna and H. montanus embryos to greater post-drying and post-thaw total antioxidant and viability loss than untreated embryos. To assess the vigour of seedlings recovered from partially dried H. montanus embryos, seedlings recovered from fresh (F) and partially dried (D) embryos in vitro were hardened-off ex vitro, and subsequently subjected to either 42 days of watering or 42 days of water deficit (in studies described in Chapter 6). In a subsequent study (described in Chapter 7), seedlings recovered from fresh (F), partially dried (D) and cryopreserved (C) A. belladonna embryos were regenerated in vitro, hardened-off ex vitro and then exposed to 12 days of watering (W) or 8 days of water stress (S) followed by 3 days of re-watering. Results of these studies suggest that the metabolic and ultrastructural lesions inflicted on A. belladonna and H. montanus zygotic embryos during cryopreservation may compromise the vigour (e.g. development of persistent low leaf water and pressure potentials and reduced photosynthetic rates) and drought tolerance of recovered seedlings, compared with seedlings recovered from fresh embryos. While the adverse effects of freeze-thawing were carried through to the early ex vitro stage, certain adverse effects of partial drying were reversed during ex vitro growth (e.g. the increased relative growth rate of seedlings from partially dried embryos). The reduced vigour and drought tolerance of seedlings recovered from partially dried and cryopreserved embryos in the present work may therefore disappear with an extension in the period afforded to them for hardening-off under green-house conditions, and in the field. The results presented in this thesis reinforce the notion that each successive manipulation involved in the cryopreservation of recalcitrant zygotic germplasm has the potential to inflict damage on tissues and post-thaw survival in such germplasm relies on the minimisation of structural and metabolic damage at each of the procedural steps involved in their cryopreservation. The results also highlight the need to design research programmes aimed not only at developing protocols for cryopreservation of plant genetic resources, but also at elucidating and understanding the fundamental basis of both successes and failures.
Towards understanding alien floristics within an urban matrix: the case of Durban, South Africa.
(2021) Appalasamy, Minoli.; Ramdhani, Syd.; Naidoo, Sershen.
Invasive alien plant species (IAPs) represent a major threat to biodiversity loss and ecosystem functioning globally. Alien species can take advantage of changes in ecosystems brought about by natural and non-natural disturbances and compete with indigenous species for resources. Urban areas are becoming increasingly susceptible to plant invasions due to increasing anthropogenic activity levels as urban human populations increase and changing climatic conditions that favour alien species. If uncontrolled, IAP impacts can bring about the transformation of natural habitats and exclusion of indigenous species. Given the limited financial and human resources available for IAP monitoring and control in developing countries like South Africa, increased efforts to monitor the prevalence of IAPs more efficiently and identify the drivers of invasiveness within cities is urgently needed to prioritise urban green spaces and species for monitoring and control interventions. Frameworks to monitor alien invasions, identify their drivers and impacts and prioritise sites and species for control of alien plants have been limited in the urban context, particularly within developing countries such as South Africa. Where these frameworks have been developed, there are challenges of them not being equally effective at different geographic scales and across different habitats. Furthermore, these frameworks often also suffer the weakness of not capturing the multi-dimensionality of plant invasiveness. This inspired the current study, which aimed to inform the design of an evidence-based framework that aids in prioritising urban green spaces and alien species for monitoring and control interventions by carrying out a set of inter-related investigations that addressed the following research questions: (1) What are the major environmental drivers of alien species (particularly IAPs) distribution? (2) Are alien and indigenous plant functional diversity (FD) and alien-indigenous co-occurrence patterns influenced by non-natural disturbance? (3) What is the influence of non-natural disturbance on the alien and indigenous soil seed bank (SB) floristics? and (4) Can selected seed physical and/or chemical traits be used as potential indicators of IAP persistence in natural SBs? These research questions were addressed using a case study approach: plants occurring within selected natural green spaces in an urban matrix in the rapidly developing city of Durban (eThekwini Metropolitan Area [EMA]), located within the Maputaland-Pondoland-Albany biodiversity hotspot in subtropical KwaZulu-Natal, South Africa. Classical vegetation survey techniques were used to identify and quantify (in terms of richness, density and diversity) aliens within 30 natural green spaces in the study area. Levels of non-natural disturbance were quantified using a scoring matrix, and soil SB samples were collected from each site. Cumulatively, 80 alien plant species were identified, of which 35 are presently categorised as IAPs in the EMA. Once it was established that IAP species richness and density were significantly positively related to disturbance level, selected parameters measured (viz. alien species richness and density) were used to develop an Alien Invasive Index (AII), the utility of which was validated in terms of its ability to discriminate between sites with low and high levels of invasiveness. The findings demonstrate the value of integrating the data generated using vegetation surveys and Geographic Information Systems to monitor and prioritise urban green spaces for alien control interventions. Importantly, the results suggest that the AII could assist in identifying invasive plant hotspots within urban areas. In a related study, alien and indigenous floristic patterns were probed further by comparing alien and indigenous species richness, density, diversity (alpha and functional), and species co-occurrence levels at the 30 sites in relation to non-natural disturbance levels. The ratio of alien to indigenous species was 1:1.5, with Asteraceae being the most dominant family. The relationship between species richness and alpha diversity differed for alien and indigenous species. Alien species were found to have higher FD, except for reproductive mode. Additionally, FD was significantly related to disturbance levels, alien species richness, and alien plant density. Co-occurrence data showed that alien-indigenous species pairs cooccur at high levels in urban spaces. Three notable alien-indigenous pairs (Centella asiaticaConyza sumatrensis, Centella asiatica-Solanum mauritianum and Bidens pilosa-Commelina erecta) co-occurred at more than 40% of sites, while two alien-alien pairs (Solanum mauritianum-Lantana camara and Conyza sumatrensis-Tagetes minuata) co-occurred at more than 50% of sites. The positive interactions between different alien species identified here contribute to the growing amount of evidence that supports the Invasional Meltdown Hypothesis (IMH). The results also showed that non-natural disturbance might lead to high levels of alien plant species diversity and facilitatory alien-alien and alien-indigenous species interactions. Understanding co-occurrence patterns could help design alien control programmes that focus on reducing alien-alien facilitation. For the study examining alien and indigenous species soil SBs in relation to nonnatural disturbance across the 30 sites, samples collected were processed using a modified seedling emergence method, incubated under greenhouse conditions (with irrigation), and monitored for one year. Germinants were identified and quantified, and comparisons were made between the soil SB and standing vegetation (SV). Cumulatively, 70 species belonging to 20 families were identified within the SB, with a higher presence of indigenous (60%) than alien species (40%). Overall, the SB flora was dominated by graminoids. Of the 70 species found in the SB, 69 were shared with the SV. Irrespective of the disturbance level, indigenous was higher than alien plant density within the SB. The findings of this study have implications for managers of urban green spaces since alien species in SBs could exploit niches created by disturbances, promoting urban invasions. In the final investigation, seeds of five IAPs were buried for two years at an experimental site to mimic seed burial within natural SBs. Additionally, the seeds of these species were characterised in terms of selected morphological and anatomical (seed mass, seed size, seed coat thickness) and chemical traits (estimated lipid content and changes in lipid melting properties). This study was designed to assess whether seed physical and/or chemical traits can be used as potential indicators of IAP persistence in natural SBs. Batches of buried seeds were exhumed every three/six months for viability (germinated seeds + seeds that stained positively following a Tetrazolium Chloride Test). Seed mass, size and coat thickness differed significantly across species, with Canna indica having the biggest and heaviest seeds of all species and the thickest seed coat. Solanum mauritianum had the smallest and lightest seed, with one of the thinnest seed coats. Results showed decreases in viability for four species (Canna indica, Melia azedarach, Senna didymobotrya, and Ricinus communis), while Solanum mauritianum maintained a 100% viability throughout the experimental period. However, while the viability of C. indica, R. communis, and S. didymobotrya was dominated by germinable seeds before burial, as viability declined with an increase in burial time, viability was dominated by seeds that were not germinable but stained positively. Melia azedarach differed slightly, where viability declined with burial time, but the majority of the seeds that were viable remained germinable. The longest ageing rate based on P50 was observed for C. indica (lowest estimated lipid content), while M. azedarach had the shortest ageing rate (highest estimated lipid content). Decreases in germination over time for C. indica, R. communis, M. azedarach, and S. didymobotrya led to changes in either/both enthalpy of melting of the lipid, and the temperature of the lipid melt, which could be related to different seed deterioration mechanisms when buried. This study did not identify significant relationships between the seed physical and/or chemical traits and SB longevity using the traits investigated. This could be explained by the relatively low number of species and traits studied and/or the phenotypic plasticity associated with seed post-harvest physiology in wild species. Nevertheless, the study gave rise to the beginnings of a conceptual continuum of IAP seed bank longevity, which, once populated with data for more species, could supplement the criteria currently used for assessing species invasiveness. As mentioned earlier, alien plant invasions are a major challenge for developing countries, particularly in urban settings. In countries like South Africa, the management of IAPs is complicated by heterogeneous combinations of non-natural disturbances, site-specific levels of disturbance intensity, and diverse vegetation types and associated species richness. The results clearly show that IAPs thrive under high levels of non-natural disturbance in urban green spaces and that alien and indigenous species can co-occur in various vegetation types. The AII was able to identify alien hotspots within the study area and may represent a useful tool for conservation practitioners/land managers. Lantana camara and Solanum mauritianum emerged as the most problematic IAPs currently in the study area. It was also evident that disturbance levels play a role in soil SBs of alien and indigenous species richness and plant density, and some problematic IAPs, notably S. mauritianum, can persist in SBs for long periods due to morphological, anatomical, and chemical traits. The results generated were used to design a multi-disciplinary and multi-dimensional framework that aids in prioritising sites and species for alien plant monitoring and control within urban areas. The methods proposed for assessing the prevalence and drivers of alien plant species and the indicators identified as potential indicators of their impacts in the framework can assist land managers, practitioners, and researchers develop recommendations and actions for alien plant monitoring and control in urban areas. The framework is designed to supplement and aid, and not replace, existing EMA policies/guidelines for alien plant control by preceding their planning and preparation phases. It could also help in developing new approaches to monitoring alien plant species in urban spaces.
The use of open top chambers to assess the effects of elevated temperatures on subtropical grassland vegetation in situ : a case study on KwaZulu-Natal sandstone sourveld.
(2016) Buhrmann, Rowan David.; Naidoo, Sershen.; Ramdhani, Syd.; Pammenter, Norman William.
Abstract available in PDF file.
The utility of Brachylaena discolor as a bioindicator of air pollution within selected industrial areas in KwaZulu-Natal.
(2016) Areington, Candyce Ann.; Naidoo, Sershen.; Varghese, Boby.
The negative impacts of air pollution have made monitoring of air quality increasingly important. This is primarily true for industrial areas such as the South Durban Basin (SDB) within the eThekwini Municipal Area (EMA), South Africa. Bioindicators can complement the process of monitoring air quality. For the establishment of Brachylaena discolor DC. tree leaves as a bioindicator of air pollution, this study investigated the effects of sulphur dioxide (SO₂) pollution on various biochemical (intracellular superoxide [·O₂⁻], hydrogen peroxide [H₂O₂] production, total aqueous [TAA] and enzymic antioxidants [superoxide dismutase and catalase], lipid peroxidation [LPO] and electrolyte leakage), physiological (leaf chlorophyll fluorescence and chlorophyll content) and morphological (leaf area [LA]) biomarkers of stress. Leaves were sampled from (four) trees growing at three industrial sites (Prospecton, Ganges and Southern Works) within the SDB and from greenhouse-grown trees that served as an ex situ control. The sampling (n=24, per parameter) accommodated directional and seasonal effects. Annual [SO₂] measured at all three treatment sites (Prospecton [4.39±3.92 ppb], Ganges [5.10±4.73 ppb] and Southern Works [6.71±5.47 ppb]) during the study were high compared to global standards. Values for all biomarkers did not differ significantly for leaves from different cardinal points within sites but seasonal differences were evident in some cases; ·O₂⁻, LPO, electrolyte leakage, leaf chlorophyll fluorescence, and LA were significantly (p<0.05) correlated with seasonal [SO₂]. Except for ·O₂⁻, superoxide dismutase and catalase, all other biomarkers investigated could differentiate between SO₂ exposed and unexposed leaves. However, only electrolyte leakage was sensitive enough to reflect differences in [SO₂] across the treatment sites. Qualitative data on land-use practices at each site suggests that the pollution sources/pollutants differed across the SDB and that the use of SO₂ as the sole proxy of air pollution may not be ideal. Actually, ·O₂⁻, H₂O₂, lipid peroxidation and LA data suggested that trees at Ganges were exposed to the highest levels of stress, even though annual average [SO₂] was highest at Southern Works. Nevertheless, the investigated biomarkers provide motivation for the establishment of B. discolor a bioindicator of air pollution within the SDB. If the appropriate biomarkers are measured (e.g. LPO, electrolyte leakage, leaf chlorophyll fluorescence and LA in this study), B. discolor leaves can serve as reliable bioindicators complementing current air monitoring techniques within the EMA.
The utility of Trichilia dregeana leaves as a bioindicator of air pollution within selected industrial areas in the eThekwini Municipality, South Africa.
(2016) Appalasamy, Minoli.; Naidoo, Sershen.
Increased anthropogenic activities worldwide have led to dangerously high levels of gaseous emissions. Air pollution levels within industrial areas in South Africa, such as South Durban Basin (SDB), are monitored daily at a few monitoring stations; however, limited coverage of, and data generated by, these stations necessitates alternative strategies such as biomonitoring. In this regard, the use of tree leaves as bioindicators of air pollution can generate valuable data on environmental health and pollutant levels. The present study investigated the utility of Trichilia dregeana Sond. leaves as a bioindicator of air pollution within selected industrial areas in SDB. The first part of the study focussed on effects of SO₂ pollution on leaf morphological (leaf area), physiological (leaf chlorophyll content and leaf fluorescence) and biochemical (intracellular superoxide and hydrogen peroxide production, total aqueous antioxidant activity, and electrolyte leakage) biomarkers of environmental stress. Leaves were sampled over four seasons from (four) trees growing at three industrial (treatment) sites (Prospecton, Ganges and Southern Works) within SDB and from greenhouse-located trees, which served as an ex situ control. Results indicated annual SO₂ concentrations ([SO₂]) were high by global standards and significantly different (p<0.001) across sites, with levels being highest at Southern Works. All biomarkers, except leaf chlorophyll fluorescence, could discriminate between SO₂-exposed and -unexposed leaves. Seasonal data for many of these biomarkers were significantly (p<0.001) correlated with seasonal [SO₂]; however, none of them reflected differences in [SO₂] across treatment sites. The second part of the study, partial least squares regression (PLSR) was used to quantify the relationship between two air pollution biomarkers (chlorophyll content and leaf area) and hyperspectral data. Trichilia dregeana leaves (n=28) were sampled in spring and summer only. Spectral reflectance data were able to distinguish between SO₂-exposed and -unexposed leaves and PLSR was able to relate the hyperspectral dataset to both biomarkers. However, the interaction between biomarkers suggests simultaneous prediction of these, using an algorithm such as PLS-2, may be more suitable. The variable importance in projection method identified wavebands within the red-edge region of the electromagnetic spectrum that showed promise in identifying stress in the leaves of T. dregeana. Collectively, the results provide ample motivation for the establishment of T. dregeana leaves as a bioindicator of air pollution.