Assessing the impacts of Lantana camara and opportunities for ecological restoration after its removal: does clearing facilitate both soil and native vegetation recovery?
- Authors: Bolosha, Uviwe
- Date: 2024-10-11
- Subjects: Lantana camara , Restoration and conservation , Restoration ecology , Invasive plants , Physicochemical process , Soil seed banks , Invasion driver
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466524 , vital:76738 , DOI https://doi.org/10.21504/10962/466524
- Description: Invasive alien plants (IAPs) are one of the major contributing factors to biodiversity loss, and Lantana camara is among the top ten alien invaders worldwide. Lantana camara threatens native biodiversity and human health, prevents natural succession, and has an economic and environmental impact globally. With current climate change and future predictions, these IAPs are anticipated to continue posing huge threats to ecosystem composition, structure, and function. Even though L. camara is a widespread IAP, there is still limited knowledge in South Africa on how it influences soil physicochemical properties at the species level, vegetation communities, and soil seed banks at the community level following its invasion. There is also minimal knowledge on the management and control (i.e., clearing for restoration purposes) of L. camara in South Africa, especially in the Eastern Cape province of South Africa. To address the knowledge gap, this thesis was structured into three main aspects: understanding L. camara invasion mechanisms, evaluating invasion impacts on both the aboveground and belowground communities, and invasion management. The main objectives of this thesis were (i) to examine how L. camara invasion (at a species level) affected soil physicochemical properties across different seasons, (ii) to assess how L. camara influences natural vegetation (at a community level), (iii) to examine the effects of L. camara invasion (at the community level) on belowground soil seed banks and also assess the availability of pioneer native species and IAPs in the soil seed banks, and (iv) to evaluate soil and vegetation responses following L. camara clearing in comparison to invaded and uninvaded conditions. To answer these objectives, different studies were carried out in the Eastern Cape province, South Africa, on various farms within the Albany Thicket Biome. The results (Chapter 3) show that L. camara alters and modifies some soil physical properties, such as soil infiltration rate, repellency, and soil penetration resistance, in the communities it invades. A significant decrease in soil penetration under the L. camara canopy was observed compared to soils from the edge and out position. Moreover, significantly faster infiltration rates were observed in the canopy and edge positions than in the out position. The study also observed that these modifications in soil physical properties vary depending on the season. A seasonal comparison in soil penetration showed that soil was more compact in the dry season than the wet season, and significantly faster infiltration rates were observed in summer than in the other seasons. The soil collected under the invaded sampling positions was mostly wettable (80–100%), and not strongly, severely, or extremely repellent across all the seasons. The changes in soil properties caused by L. camara could create favourable conditions for its growth and invasion. Seasonal changes in soil properties also highlight how environmental conditions, especially temperature and rainfall patterns, can affect soil physical properties. The findings in Chapter 4 observed both the negative and positive impacts of L. camara, where the species did not have negative effects on species richness, diversity, or cover of some native species growth forms (i.e., graminoids and forbs). For all species, both species richness and Shannon-Wiener (H’) were significantly higher in the L. camara invaded condition compared to the uninvaded condition. The Simpson’s (J’) and Pielou’s evenness (D’) indices, however, showed no differences between the invasion conditions. Furthermore, the effects of L. camara on vegetation cover were growth form-dependent, with differences being noted for trees and shrubs but not for graminoids and forbs. Changes in vegetation structure and composition were also noted where L. camara created favourable conditions for some species to co-occur with it, meaning that its known trait of changing soil physicochemical properties could benefit some species. Generally, the results of this study showed that the effects of L. camara on vegetation are varied and do not have a predictable pattern, so they should not be generalised. The findings (Chapter 5) also indicate that the L. camara invasion had a negative impact on seedling abundance and composition but not species diversity and richness. This is evident through the decrease in seedling abundance of forbs and graminoids in the L. camara invaded condition. Lantana camara also acted as a refuge for some plant species, mostly native forbs and grasses, including Aptenia cordifolia, Chamaesyce prostrata, Oxalis spp., and Setaria spp., as well as alien forbs such as Bidens pilosa, Plantago lanceolata, and Taraxacum officinale, suggesting L. camara does not entirely eliminate less competitive plant species but can co-exist with them. Lantana camara also displaced some native species, and this could be associated with their displacement in the standing vegetation. Moreover, the species also displaced the seed banks of some alien species, thus showing its competitive ability. Overall, L. camara invasion negatively influenced soil seed bank seedling abundance and composition of some species, but not diversity and richness. The results in Chapter 6 indicated that clearing L. camara is an effective method for reducing its population. However, our findings suggest that clearing alone may not be enough to re-establish these communities with native species. This is because the results of this study showed varied changes in soil properties and native vegetation (species richness, species diversity, percentage cover, and composition) after L. camara clearing. For example, soil moisture and soil penetration resistance showed no significant differences among the invasion conditions; only monthly variations were observed. This is an indication that seasonality influenced these properties. Significantly lower soil infiltration rates were observed in the cleared condition compared to the other conditions and were influenced by the months and the interaction of the clearing conditions and months. The water droplet penetration time showed no significant difference among the clearing conditions over the three months, and all the soil collected from the three clearing conditions was mostly wettable. Soil chemical properties showed that the L. camara invaded and cleared conditions had significantly lower soil pH compared to the uninvaded condition, and an increase in soil pH was observed after clearing L. camara. Vegetation characteristics showed that both the Shannon-Wiener index (H') and the Simpson’s index (D') were lower in the invaded and cleared conditions compared to the uninvaded condition, and significant differences were observed. A slight increase in the H' and D' indices was also observed after clearing L. camara. The mean percentage cover for trees and shrubs was significantly higher in the invaded condition than in the cleared and uninvaded conditions. However, the mean percentage cover of forbs and graminoids was similar among the invaded, cleared, and uninvaded conditions, and no significant differences were observed. When L. camara was cleared, native species recovery was observed and was more notable in the understory species. Overall, some signs of vegetation recovery were observed, although challenges such as secondary invaders and re-invasion by L. camara were noted in the cleared areas. This chapter then concluded that active restoration interventions should be incorporated during restoration to fast-track soil and vegetation recovery. The findings of this thesis will make several significant contributions to the field of biological invasions and provide baseline information that can be used in future studies. These are discussed in the various research chapters. Overall, the thesis concludes that L. camara invasion has varied impacts on native vegetation and soil, and its clearance, should be prioritised to reduce the negative impacts. However, L. camara cleared areas (by WfW in South Africa) require follow-up and monitoring at an early stage to assess vegetation and soil restoration success. In addition, active management measures after L. camara’s removal should be considered for clearing programmes to yield positive ecosystem recovery. , Thesis (PhD) -- Faculty of Science, Environmental Science, 2024
- Full Text:
Towards a bacterial biofertiliser for the rehabilitation of disturbed and degraded land
- Authors: Masudi, Wiya Leon
- Date: 2024-10-11
- Subjects: Biofertilizers , Land degradation , Ecological disturbances , Plant-growth promoting rhizobacteria , Restoration ecology
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466826 , vital:76790 , DOI https://doi.org/10.21504/10962/466826
- Description: Agriculture, mining, industry, and human activity disturb, degrade, and pollute pristine environments and particularly the soil environment. Excessive land exploitation slows or disrupts the soil potential, rendering it incapable of playing its role leading to land degradation. In the mining sector, specifically coal mining, rehabilitation of disturbed and degraded land involves strategies that include importing topsoil and using fossil fuel-derived fertilisers. Both practices are unsustainable. To address the unsustainability, a myco-phytoremediation technology known as Fungcoal was developed to facilitate successful revegetation of mining-disturbed and degraded land following the bioconversion of waste coal into a soil-like humic-rich substrate. To offset the dependence on chemical-based fertilisers, efforts were/are focussed on finding mutualistic and cost-effective microbial resources with plant growth-promoting (PGP) activity as a bacterial biofertiliser. This study made use of 22 isolated bacteria and the three Fungcoal coal-degrading fungi viz., Aspergillus sp. ECCN 84, Aspergillus sp. ECCN 225 and Penicillium sp. ECCN 243 as the microbial resource. Initially, characterisation of the substrate waste coal and molecular identification of the selected bacterial isolates were carried out. Physicochemical analysis of the low-rank coal (LRC) substrate revealed a pH of 3.60 with background S content equivalent to 7.13 g L-1, N at 20 mg L-1, P at 7.8 mg L-1 and K at 3.3 mg L-1. Energy-dispersive X-ray spectroscopy (EDX) analysis revealed a C and O content of 23.09 and 69.03 wt%, respectively. Metagenomic analysis of the microbial population associated with the LRC substrate showed that among the 96.32% of bacteria, 59.46 to 62.18% belonged to Bacillota (also called Firmicutes), a phylum of largely Gram-positive bacteria, and 33.01 to 35.74% to Pseudomonadota (synonymous with Proteobacteria), a phylum of mostly Gram-negative bacteria. Following purification of the selected bacterial isolates and molecular characterisation by PCR, phylogenetic relatedness to known plant growth-promoting bacteria (PGPB) contained in the GenBank database showed that these bacterial isolates clustered with high bootstrap values to the reference PGPB strains. Only Pseudomonas sp. ECCN 10b (MW672582) was outside of the tree and shared significant similarity (100%) with Pseudomonas fluorescens (CP015638). A biochemical study revealed that the two Proteus sp. strains, Exiguobacterium sp., Enterobacter sp., and Ancylobacter, tolerated high salt and a wide range of temperatures. Bacterial isolates showed a high pH tolerance between 3 and 11, with the best growth at pH around 7. Nine of the identified strains, four Bacillus sp., Exiguobacterium sp., Enterobacter sp., Pseudomonas sp., Arthrobacter sp., and Aeromonas sp., were able to grow and increase in a medium containing either glucose, mannitol, sodium L-glutamate, sucrose, or fructose. Growth was highest in media containing either sodium L-glutamate, sucrose, or fructose. All the coal degrading strains and 83% of those isolated from municipal wastewater used more complex carbon sources such as high and LRC. The potential for PGP activity was quantified spectrophotometrically by measuring the production of auxins, as indole-3-acetic acid (IAA) equivalents; gibberellins, as gibberellic acid (GA3) equivalents, along with 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and siderophore activity. Additionally, nutrient mobilisation was evaluated by monitoring an ability to mineralise NH4+, PO43−, and K+. Competent PGP strains for the coal degrading isolates included Proteus strain ECCN 20b, Proteus strain ECCN 23b, and Serratia strain ECCN 24b. In response to L-trp supplementation, the concentration of indolic compounds (measured as indole-3-acetic acid) increased. Production of ammonium and solubilisation of insoluble P by these strains was also apparent. Only Serratia strain ECCN 24b could solubilise insoluble K. Production of indoles increased following exposure to increasing aliquots of LRC, suggesting no negative effect of this material on indole production and that these bacteria may possess PGP potential. Of the twelve bacterial strains isolated from wastewater MaB-flocs, three produced indoles, nine mineralised NH4+, seven solubilised P, and one K. Potential of isolated strains for PGP activity according to a one-way ANOVA on ranks was: ECCN 7b > ECCN 4b > ECCN 6b > ECCN 3b = ECCN 10b > ECCN 1b = ECCN 5b > ECCN 8b > ECCN 2b > ECCN 12b > ECCN 9b = ECCN 11b. Further study revealed that cell-free filtrate from indole-producing cultures of Aeromonas strain ECCN 4b, Enterobacter strain ECCN 7b, and Arthrobacter strain ECCN 6b promoted mung bean adventitious root formation. Based on a biochemical study and the outcome of the ranking of bacterial strains according to PGP-like activities, three bacteria, Enterobacter sp., strain ECCN 7b, Proteus sp., strain ECCN 20b and Serratia sp., strain ECCN 24b that showed great mutualistic relationship with the most effective Fungcoal biocatalyst, A. fischeri ECCN 84, were used to prepare a bacterial bio-fertiliser. This consortium grew well in NB supplemented with L-tryptophan and produced indole compounds that could activate the adventitious rooting of mung bean (Vigna radiata L.) hypocotyls. Finally, the consortium showed no antibiotic resistance activity; however, they produced better biofertiliser with good responses to root/plant biomass production of the same Fabaceae, mung bean (Vigna radiata L.). The further development of this consortium into a cost-effective, environmentally friendly biofertiliser may help reduce dependence on chemical-based fertilisers and improve the sustainability of Fungcoal and other land rehabilitation strategies. Further studies are therefore underway to investigate in greater detail the PGP activity of these isolates individually and in consortium under field conditions to support the Fungcoal myco-phytoremediation strategy. , Thesis (PhD) -- Faculty of Science, Institute for Environmental Biotechnology, 2024
- Full Text:
Innovation in ecological restoration techniques: Enhancing Portulacaria afra survivorship in degraded arid thicket
- Authors: Norman, Yondela Masande
- Date: 2023-03-31
- Subjects: Land degradation South Africa , Subtropical Thicket Ecosystem Planning , Portulacaria afra , Restoration ecology , Nurse plants
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/419276 , vital:71630
- Description: The Albany Thicket Biome has undergone extensive degradation over the past century, particularly from overstocking of livestock in the arid types of thicket. The degradation of the biome, coupled with little to no natural recovery, prompted the South African Government to implement the Subtropical Thicket Restoration Programme (STRP) in the early 2000s to rehabilitate degraded thicket using unrooted Portulacaria afra truncheons. The STRP also sought to create job opportunities, bring about social upliftment, promote biodiversity conservation and incentivise farmers and landowners in the region to promote carbon trading and farming of P. afra using carbon credits. However, the survivorship of P. afra planted using the STRP planting protocol has been less than ⁓30% because they are planted in degraded areas, where the truncheons are subjected to harsh biophysical conditions such as hard, capped soil, high soil temperatures, drought and herbivory. The aim of this study, therefore, was to improve the survivorship of P. afra planted in degraded thicket to at least 30%, using modified planting methods. In this study, four treatments were applied in 210 pondings (or micro-dams), each with P. afra planted in them (the first three treatments used rooted cuttings). The first treatment involved watering regimes where pondings were watered at varying frequencies. The second treatment involved planting companion species alongside P. afra while the third treatment involved planting P. afra underneath a nurse canopy. In the fourth treatment, unrooted P. afra truncheons were planted inside pondings. The mean survivorship of the P. afra cuttings was assessed 18 months after planting. The watering regime treatments, including the control, all yielded a survivorship of over 75%, with the significantly highest levels of survivorship being displayed in the weekly watering treatment (90.9 ± 6.8%) (p < 0.01). The companion plant treatment also produced a high mean survivorship of P. afra (94.9 ± 3.6%), significantly higher than that of the nurse plants (87.5 ± 6.3%) (p < 0.01). Among the unrooted truncheons it was found that untreated truncheons had the highest survivorship (76.2 ± 17.6%), with the lowest mean being found in truncheons that were both pruned and scarified (70.8 ± 20.8%), suggesting that this treatment, out of all of them, is the least successful under the prevailing environmental conditions in the study area. However, there was no significant differences among the unrooted truncheon treatments and their respective survivorship values to further substantiate this assertion (p = 0.26). Findings in this study also suggest that planting P. afra cuttings under a nurse plant was ideal for P. afra survivorship due to the nurse plant’s ability to ameliorate the microclimate under which the cuttings can establish and grow. Despite the soil under the nurse canopy having a significantly lower mean soil water potential (-160.9 ± 200.5 kPa), compared to the open areas (-73.4 ± 55.7 kPa) (p = 0.04), the pondings under the nurse canopy still had a lower mean soil temperature (31.4 ± 5.25°C) than the treatments in the open areas (38.5 ± 2.7°C), during the harsh midday sun. These favourable characteristics are reflected in the P. afra cuttings under a nurse canopy having a higher chlorophyll fluorescence (0.76 ± 0.06). compared to those planted in open areas (0.73 ± 0.13), suggesting that the P. afra cuttings in the former treatment had a higher photosynthetic efficiency compared to those in the latter, despite there being no statistically significant difference in chlorophyll fluorescence between the treatments (p = 0.14). Although these findings suggest that applying these modifications to planting P. afra, having achieved its objective of increasing survivorship to well over 50%, is likely to produce favourable results not only in overall survivorship, but also in fast-tracking arid thicket rehabilitation and restoration, further research on these rehabilitation techniques and their effectiveness is required. Furthermore, the downside to these treatments is that they are costly and time consuming, which puts the feasibility of large-scale programmes using these applications into question. Further investigation is required to determine ways in which the cost-effectiveness of these applications can be enhanced. , Thesis (MSc) -- Faculty of Science, Environmental Science, 2023
- Full Text:
Interaction between arbuscular mycorrhizal fungi and soil microbial populations in the rhizosphere
- Authors: Ike-Izundu, Nnenna Esther
- Date: 2008
- Subjects: Mycorrhizas , Mycorrhizal fungi , Vesicular-arbuscular mycorrhizas , Soil microbiology , Rhizosphere , Revegetation , Restoration ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3962 , http://hdl.handle.net/10962/d1004021 , Mycorrhizas , Mycorrhizal fungi , Vesicular-arbuscular mycorrhizas , Soil microbiology , Rhizosphere , Revegetation , Restoration ecology
- Description: This study examined the rehabilitation potential of AM fungi with organic and inorganic fertilisers under pot and field trial conditions as well as their interaction with rhizospheric organisms and specific functional groups. In addition, the study highlighted the effects of land-use management on AM fungal populations in soil and the mycorrhizal status of some selected plants from one of the study sites. The study focussed on two sites that differ in operational activities and these included a mined area that was to be rehabilitated and a commercial farming site. A pot trial was conducted using an overburdened soil resulting from kaolin clay mining. Pots were seeded with Cynodon dactylon and treated with either Organic Tea or NPK (3:1:5) fertiliser, with or without AM fungal inoculum. The compatibility of these fertilisers with AM fungi was assessed by plant growth and percentage root colonisation. Maximum shoot height and plant biomass were observed at the 28th week with NPK (3:1:5) fertiliser supporting mycorrhizal colonisation by 80%. The result indicated the potential of AM fungi to be used in rehabilitation with minimal phosphate fertiliser. Similarly, a field trial was set-up using 17 x 17 m[superscript 2] plots in the mining site that were treated with the same organic and inorganic fertilisers as well as with AM fungal inoculum in different combinations. The interaction between AM fungi and soil microbial population was determined using culture dependent and culture independent techniques. The culture dependent technique involved the use of soil dilution and plating on general purpose and selective media. The result showed that there was no change in the total culturable bacterial number in the untreated and AM fungal treated plots, while a change in species composition was observed in the functional groups. Different functional groups identified included nitrogen fixing bacteria, pseudomonads, actinomycetes, phosphate solubilisers and the fungal counterparts. Gram-positive bacteria were observed as the predominant phenotypic type, while nitrogen fixers and actinomycetes were the predominant functional groups. Species identified from each functional group were Pseudomonas fulva, Bacillus megaterium, Streptomyces and actinomycetales bacteria. Meanwhile, fungi such as Ampelomyces, Fusarium, Penicillium, Aspergillus, Cephalosporium and Exserohilium were identified morphologically and molecularly. Furthermore, the mining site had a significantly higher bacterial number than the farming site thereby indicating the effects of land-use management on culturable bacterial numbers. The culture independent technique was carried out by cloning of the bacterial 16S rDNA and sequencing. Identified clones were Bradyrhizobium, Propionibacterium and Sporichthya. A cladogram constructed with the nucleotides sequences of identified functional species, clones and closely related nucleotide sequences from the Genbank indicated that nucleotide sequences differed in terms of the method used. The activity and establishment of the introduced AM fungal population was determined by spore enumeration, infectivity assay, percentage root colonisation and assessment of glomalin concentrations. The results indicated that the two land use types affected AM fungal populations. However, the establishment of AM fungi in the farming site was more successful than in the mining site as indicated by the higher infectivity pontential. Selected host plants, which were collected around the mine area, were observed to be mainly colonised by AM fungi and these were identified as Pentzia incana, Elytropappus rhinocerotis, Euphorbia meloformis, Selago corymbosa, Albuca canadensis and Helichrysum rosum. These plant species were able to thrive under harsh environmental conditions, thereby indicating their potential use as rehabilitation host plants. Generally, the findings of this study has provided an insight into the interaction between arbuscular mycorrhizal fungi and other soil microorganisms in two fields with differing land use management practices.
- Full Text: