Exploring the mechanism of transformation in Acacia nilotica (Linn.) triggered by colchicine seed treatment.

BACKGROUND: Acacia nilotica Linn. is a widely distributed tree known for its applications in post-harvest and medicinal horticulture. However, its seed-based growth is relatively slow. Seed is a vital component for the propagation of A. nilotica due to its cost-effectiveness, genetic diversity, and ease of handling. Colchicine, commonly used for polyploidy induction in plants, may act as a pollutant at elevated levels. Its optimal concentration for Acacia nilotica's improved growth and development has not yet been determined, and the precise mechanism underlying this phenomenon has not been established. Therefore, this study investigated the impact of optimized colchicine (0.07%) seed treatment on A. nilotica's morphological, anatomical, physiological, fluorescent, and biochemical attributes under controlled conditions, comparing it with a control. RESULTS: Colchicine seed treatment significantly improved various plant attributes compared to control. This included increased shoot length (84.6%), root length (53.5%), shoot fresh weight (59.1%), root fresh weight (42.8%), shoot dry weight (51.5%), root dry weight (40%), fresh biomass (23.6%), stomatal size (35.9%), stomatal density (41.7%), stomatal index (51.2%), leaf thickness (11 times), leaf angle (2.4 times), photosynthetic rate (40%), water use efficiency (2.2 times), substomatal CO2 (36.6%), quantum yield of photosystem II (13.1%), proton flux (3.1 times), proton conductivity (2.3 times), linear electron flow (46.7%), enzymatic activities of catalase (25%), superoxide dismutase (33%), peroxidase (13.5%), and ascorbate peroxidase (28%), 2,2-diphenyl-1-picrylhydrazyl-radical scavenging activities(23%), total antioxidant capacity (59%), total phenolic (23%), and flavonoid content (37%) with less number of days to 80% germination (57.1%), transpiration rate (53.9%), stomatal conductance (67.1%), non-photochemical quenching (82.8%), non-regulatory energy dissipation (24.3%), and H2O2 (25%) and O-2 levels (30%). CONCLUSION: These findings elucidate the intricate mechanism behind the morphological, anatomical, physiological, fluorescent, and biochemical transformative effects of colchicine seed treatment on Acacia nilotica Linn. and offer valuable insights for quick production of A. nilotica's plants with modification and enhancement from seeds through an eco-friendly approach.

Hydroponic Screening of Fast-growing Tree Species for Lead Phytoremediation Potential.

Using trees as phytoremediators has become a powerful tool to remediate lead from contaminated environments. This study aims to identify potential candidates among fast-growing trees by comparing their ability to tolerate and accumulate Pb. Cuttings from Acacia mangium, Azadirachta indica, Eucalyptus camaldulensis, and Senna siamea were cultured in 25% modified Hoagland's solutions supplemented with 10, 30, and 50 mg/L Pb for 15 days. Lead concentrations were determined by a flame atomic absorption spectrophotometer. All species showed high Pb tolerance (over 78%) and low translocation factor (<1) in all treatments. The highest Pb content in roots (>40000 mg/kg) was recorded in A. mangium and E. camaldulensis grown in 50 mg/L Pb solution. Based on high biomass, tolerance index, and Pb content in plants, A. mangium and E. camaldulensis are good candidates for phytoremediation.

Tolerance, arsenic uptake, and oxidative stress in Acacia farnesiana under arsenate-stress.

Acacia farnesiana is a shrub widely distributed in soils heavily polluted with arsenic in Mexico. However, the mechanisms by which this species tolerates the phytotoxic effects of arsenic are unknown. This study aimed to investigate the tolerance and bioaccumulation of As by A. farnesiana seedlings exposed to high doses of arsenate (AsV) and the role of peroxidases (POX) and glutathione S-transferases (GST) in alleviating As-stress. For that, long-period tests were performed in vitro under different AsV treatments. A. farnesiana showed a remarkable tolerance to AsV, achieving a half-inhibitory concentration (IC50) of about 2.8 mM. Bioaccumulation reached about 940 and 4380 mg As·kg(-1) of dry weight in shoots and roots, respectively, exposed for 60 days to 0.58 mM AsV. Seedlings exposed to such conditions registered a growth delay during the first 15 days, when the fastest As uptake rate (117 mg kg(-1) day(-1)) occurred, coinciding with both the highest rate of lipid peroxidation and the strongest up-regulation of enzyme activities. GST activity showed a strong correlation with the As bioaccumulated, suggesting its role in imparting AsV tolerance. This study demonstrated that besides tolerance to AsV, A. farnesiana bioaccumulates considerable amounts of As, suggesting that it may be useful for phytostabilization purposes.

Structural changes in soil communities after triclopyr application in soils invaded by Acacia dealbata Link.

Triclopyr is a commonly used herbicide in the control of woody plants and can exhibit toxic effects to soil microorganisms. However, the impact on soils invaded by plant exotics has not yet been addressed. Here, we present the results of an 18-month field study conducted to evaluate the impact of triclopyr on the structure of fungal and bacterial communities in soils invaded by Acacia dealbata Link, through the use of denature gradient gel electrophoresis. After triclopyr application, analyses of bacterial fingerprints suggested a change in the structure of the soil bacterial community, whereas the structure of the soil fungal community remained unaltered. Bacterial density and F:B ratio values changed across the year but were not altered due to herbicide spraying. On the contrary, fungal diversity was increased in plots sprayed with triclopyr 5 months after the first application. Richness and diversity (H') of both bacteria and fungi were not modified after triclopyr application.

Gibberellin mediates the development of gelatinous fibres in the tension wood of inclined Acacia mangium seedlings.

BACKGROUND AND AIMS: Gibberellin stimulates negative gravitropism and the formation of tension wood in tilted Acacia mangium seedlings, while inhibitors of gibberellin synthesis strongly inhibit the return to vertical growth and suppress the formation of tension wood. To characterize the role of gibberellin in tension wood formation and gravitropism, this study investigated the role of gibberellin in the development of gelatinous fibres and in the changes in anatomical characteristics of woody elements in Acacia mangium seedlings exposed to a gravitational stimulus. METHODS: Gibberellin, paclobutrazol and uniconazole-P were applied to the soil in which seedlings were growing, using distilled water as the control. Three days after the start of treatment, seedlings were inclined at 45 ° to the vertical and samples were harvested 2 months later. The effects of the treatments on wood fibres, vessel elements and ray parenchyma cells were analysed in tension wood in the upper part of inclined stems and in the opposite wood on the lower side of inclined stems. KEY RESULTS: Application of paclobutrazol or uniconazole-P inhibited the increase in the thickness of gelatinous layers and prevented the elongation of gelatinous fibres in the tension wood of inclined stems. By contrast, gibberellin stimulated the elongation of these fibres. Application of gibberellin and inhibitors of gibberellin biosynthesis had only minor effects on the anatomical characteristics of vessel and ray parenchyma cells. CONCLUSIONS: The results suggest that gibberellin is important for the development of gelatinous fibres in the tension wood of A. mangium seedlings and therefore in gravitropism.

Cu2+ inhibition of gel secretion in the xylem and its potential implications for water uptake of cut Acacia holosericea stems.

Maintaining a high rate of water uptake is crucial for maximum longevity of cut stems. Physiological gel/tylosis formation decreases water transport efficiency in the xylem. The primary mechanism of action for post-harvest Cu(2+) treatments in improving cut flower and foliage longevity has been elusive. The effect of Cu(2+) on wound-induced xylem vessel occlusion was investigated for Acacia holosericea A. Cunn. ex G. Don. Experiments were conducted using a Cu(2+) pulse (5 h, 2.2 mM) and a Cu(2+) vase solution (0.5 mM) vs a deionized water (DIW) control. Development of xylem blockage in the stem-end region 10 mm proximal to the wounded stem surface was examined over 21 days by light and transmission electron microscopy. Xylem vessels of stems stood into DIW were occluded with gels secreted into vessel lumens via pits from surrounding axial parenchyma cells. Gel secretion was initiated within 1-2 days post-wounding and gels were detected in the xylem from day 3. In contrast, Cu(2+) treatments disrupted the surrounding parenchyma cells, thereby inhibiting gel secretion and maintaining the vessel lumens devoid of occlusions. The Cu(2+) treatments significantly improved water uptake by the cut stems as compared to the control.

The breeding systems of diploid and neoautotetraploid clones of Acacia mangium Willd. in a synthetic sympatric population in Vietnam.

Colchicine-induced neoautotetraploid genotypes of Acacia mangium were cloned and planted in mixture with a set of diploid clones in an orchard in southern Vietnam. Following good general flowering, open-pollinated seed was collected from trees of both cytotypes and microsatellite markers were used to determine the breeding system as characterised by the proportion of outcrosses in young seedling progeny. As predicted from the literature, the progeny of diploid clones were predominantly outcrossed (t(m) = 0.97). In contrast, the progeny of the tetraploid clones were almost entirely selfs (t(m) = 0.02; 3 of 161 seedlings assayed were tetraploid outcrosses and there were no triploids). Segregation at loci heterozygous in the tetraploid mothers followed expected ratios, indicating sexual reproduction rather than apomixis. Post-zygotic factors are primarily responsible for divergence of the breeding systems. Commonly, less than 1 % of Acacia flowers mature as a pod, and after mixed pollination, diploid outcrossed seed normally develops at the expense of selfs. Selfs of the tetraploid trees appear to express less genetic load and have a higher probability of maturing. However, this does not fully explain the observed deficiency of outcross tetraploid progeny. Presumably, there are cytogenetic reasons which remain to be investigated. In nature, selfing would increase the probability of establishment of neotetraploids irrespective of cytotype frequency in the population. Breeders need to review their open-pollinated breeding and seed production strategies. It remains to be seen whether this is an ephemeral problem, with strong fertility selection restoring potential for outcrossing over generations.

Gibberellin is required for the formation of tension wood and stem gravitropism in Acacia mangium seedlings.

BACKGROUND AND AIMS: Angiosperm trees generally form tension wood on the upper sides of leaning stems. The formation of tension wood is an important response to gravitational stimulus. Gibberellin appears to be involved in the differentiation of secondary xylem, but it remains unclear whether gibberellin plays a key role in the formation of tension wood and plant gravitropism. Therefore, a study was designed to investigate the effects of gibberellin and of inhibitors of the synthesis of gibberellin, namely paclobutrazole and uniconazole-P, on the formation of tension wood and negative stem gravitropism in Acacia mangium seedlings. METHODS: Gibberellic acid (GA(3)), paclobutrazole and uniconazole-P were applied to seedlings via the soil in which they were growing. Distilled water was applied similarly as a control. Three days after such treatment, seedlings were tilted at an angle of 45° from the vertical, and samples of stems were collected for analysis 2 weeks, 2 months and 6 months after tilting. The effects of treatments on the stem recovery degree (Rº) were analysed as an index of the negative gravitropism of seedlings, together the width of the region of tension wood in the upper part of inclined stems. KEY RESULTS: It was found that GA(3) stimulated the negative gravitropism of tilted seedling stems of A. mangium, while paclobutrazole and uniconazole-P inhibited recovery to vertical growth. Moreover, GA(3) stimulated the formation of tension wood in tilted A. mangium seedlings, while paclobutrazole and uniconazole-P strongly suppressed the formation of tension wood, as assessed 2 weeks after tilting. CONCLUSIONS: The results suggest that gibberellin plays an important role at the initial stages of formation of tension wood and in stem gravitropism in A. mangium seedlings in response to a gravitational stimulus.

Copper phytotoxicity in native and agronomical plant species.

Copper (Cu) is a widespread soil contaminant that is known to be highly toxic to soil biota. Limited information is available on the response of wild endemic species to Cu in the literature, which hinders ecological risk assessments and revegetation. In the present study, the phytotoxicity of Cu in nutrient solution was studied in five Australian endemic plant species (Acacia decurrens, Austrodanthonia richardsonii (Wallaby Grass), Bothriochloa macra (Redgrass), Eucalyptus camaldulensis var. camaldulensis (River Red-Gum) and Dichanthium sericeum (Bluegrass) and two vegetable plants species (Lactuca sativa L. 'Great lakes' and Raphanus sativa L.). Vegetable species were grown in a more concentrated nutrient solution. The response of B. macra was also compared between the two nutrient solutions (dilute and concentrated nutrient solution). In the first experiment, D. sericeum and E. camaldulensis were found to be highly sensitive to Cu exposure in nutrient culture. Critical exogenous Cu concentrations (50 percent reduction in roots) for E. camaldulensis, D. sericeum, A. richardsonii, B. macra (dilute), L. sativa, B. macra (concentrated), R. sativa and A. decurrens were, respectively, (µg/L) 16, 35, 83, 88, 97, 105, 128 and 186. Copper tolerance in B. macra was observed to be higher in the more concentrated nutrient solution despite the estimated Cu(2+) concentration being very similar in treatment solutions. Additional short-term rhizo-accumulation studies showed that neither Ca(2+) not K(+) was responsible for reduced uptake at the roots. However, the estimated maximum shoot Cu was reduced from 41 to 24mg/kg in the more concentrated solution.

Elemental composition of arbuscular mycorrhizal fungi at high salinity.

We investigated the elemental composition of spores and hyphae of arbuscular mycorrhizal fungi (AMF) collected from two saline sites at the desert border in Tunisia, and of Glomus intraradices grown in vitro with or without addition of NaCl to the medium, by proton-induced X-ray emission. We compared the elemental composition of the field AMF to those of the soil and the associated plants. The spores and hyphae from the saline soils showed strongly elevated levels of Ca, Cl, Mg, Fe, Si, and K compared to their growth environment. In contrast, the spores of both the field-derived AMF and the in vitro grown G. intraradices contained lower or not elevated Na levels compared to their growth environment. This resulted in higher K:Na and Ca:Na ratios in spores than in soil, but lower than in the associated plants for the field AMF. The K:Na and Ca:Na ratios of G. intraradices grown in monoxenic cultures were also in the same range as those of the field AMF and did not change even when those ratios in the growth medium were lowered several orders of magnitude by adding NaCl. These results indicate that AMF can selectively take up elements such as K and Ca, which act as osmotic equivalents while they avoid uptake of toxic Na. This could make them important in the alleviation of salinity stress in their plant hosts.

Evolutionary change from induced to constitutive expression of an indirect plant resistance.

Induced plant resistance traits are expressed in response to attack and occur throughout the plant kingdom. Despite their general occurrence, the evolution of such resistances has rarely been investigated. Here we report that extrafloral nectar, a usually inducible trait, is constitutively secreted by Central American Acacia species that are obligately inhabited by ants. Extrafloral nectar is secreted as an indirect resistance, attracting ants that defend plants against herbivores. Leaf damage induces extrafloral nectar secretion in several plant species; among these are various Acacia species and other Fabaceae investigated here. In contrast, Acacia species obligately inhabited by symbiotic ants nourish these ants by secreting extrafloral nectar constitutively at high rates that are not affected by leaf damage. The phylogeny of the genus Acacia and closely related genera indicate that the inducibility of extrafloral nectar is the plesiomorphic or 'original' state, whereas the constitutive extrafloral nectar flow is derived within Acacia. A constitutive resistance trait has evolved from an inducible one, obviously in response to particular functional demands.

Suadian Acacia Gerrardii: Antidiabetic Effect in Rats Suffering from Diabetic Nephropathy and DNA Fingerprinting Using ISSR.

BACKGROUND AND OBJECTIVE: There is a widespread use of medicinal herbs with beneficial uses against different diseased conditions. This study was carried out to identify and study the biological effect of Acacia gerrardii leaf extract on lowering blood sugar in rats suffering from diabetic nephropathy. MATERIALS AND METHODS: It studied the effects of leaf extract at concentrations ranging from 100-500 mg kg-1 b.wt. per day for 4 weeks. Serum glucose levels, total lipids profile and kidney functions were estimated. Plasma levels of sodium and potassium as well as total bilirubin levels were assessed and kidneys from different groups were histopathologically examined. RESULTS: The results showed that leaves were rich in the major compounds of phenolic acids, including salicylic acid and flavonoids with reduction of total lipids, triglycerides and total cholesterol in diabetic rats with renal failure together with reduction in uric acid, creatinine and urea with reduced vacuolar degeneration of tubules and basement membrane thickening. Additionally, the phylogenetic analysis using ISSR primers detected a genetic divergence among different samples. The results showed that the rich antioxidant content of Acacia gerrardii improved lipid, serum antioxidant and kidney function profiles in diabetic rats. CONCLUSION: Acacia gerrardii could be used as a safe source of antioxidants. Moreover, the ISSR assay proved its usefulness in detecting genetic variations among different Acacia gerrardii samples.

Heteroblastic development and the optimal partitioning of traits among contrasting environments in Acacia implexa.

BACKGROUND AND AIMS: Optimal partitioning theory (OPT) predicts plants will allocate biomass to organs where resources are limiting. Studies of OPT focus on root, stem and leaf mass ratios where roots and stems are often further sub-divided into organs such as fine roots/tap roots or branches/main stem. Leaves, however, are rarely sub-divided into different organs. Heteroblastic species develop juvenile and adult foliage and provide an opportunity of sub-dividing leaf mass ratio into distinct organs. Acacia implexa (Mimosaceae) is a heteroblastic species that develops compound (juvenile), transitional and phyllode (adult) leaves that differ dramatically in form and function. The aims of the present study were to grow A. implexa to examine patterns of plastic development of whole-plant and leaf traits under the OPT framework. METHODS: Plants were grown in a glasshouse under contrasting nutrient, light and water environments in a full factorial design. Allocation to whole-plant and leaf-level traits was measured and analysed with multivariate statistics. KEY RESULTS: Whole-plant traits strongly followed patterns predicted by OPT. Leaf-level traits showed a more complex pattern in response to experimental treatments. Compound leaves on low nutrient plants had significantly lower specific leaf area (SLA) and were retained for longer as quantified by a significantly greater compound leaf mass ratio after 120 d. There was no significant difference in SLA of compound leaves in the light treatment, yet transitional SLA was significantly higher under the low light treatment. The timing of heteroblastic shift from compound to transitional leaves was significantly delayed only in the low light treatment. Therefore, plants in the light treatment responded at the whole-plant level by adjusting allocation to productive compound leaves and at the leaf-level by adjusting SLA. There were no significant SLA differences in the water treatment despite strong trends at the whole-plant level. CONCLUSION: Explicitly sub-dividing leaves into different types provided greater insights into OPT.

Phosphate treatment alleviated acute phytotoxicity of heavy metals in sulfidic Pb-Zn mine tailings.

Phytostabilization of sulfidic PbZn tailing landscapes may be one of interim options of tailings management, but which is limited by acute phytotoxicity of heavy metals in the tailings. The present study aimed to investigate the effectiveness of soluble phosphate (i.e., K2HPO4) in immobilizing soluble Pb, Cd and Zn and lowering their acute phytotoxicity. The addition of soluble phosphate improved the growth of native plants Acacia chisholmii and survival rate of A. ligulata, where the latter exhibited 100% survival rate. This was in contrast to effects of conventional organic amendment in the tailings on metal solubility (e.g., elevated metal levels in porewater) and plant survival (e.g., only 42%). Organic amendment with mulch did not lower the levels of water-soluble Cd, Pb and Zn and their concentrations in plant tissues after 56 days of plant growth in the treatment. In contrast, the tailings amended with K2HPO4 significantly decreased metal concentrations in the porewater and plant tissues by about 80-92% and 56-88%, respectively. The metal immobilization by phosphate was due to the formation of insoluble or sparingly soluble metal (Pb, Cd and Zn)-phosphate minerals in the tailings with circumneutral pH conditions, as revealed by using X-ray diffraction and scanning electron microanalyses. The reduced metal concentrations in roots and shoots of Acacia species after direct root contact with the K2HPO4 amended tailings suggested that metals (i.e., Pb, Cd and Zn) were effectively immobilized by the phosphate treatment of the tailings. These findings indicate that addition of high dosage of soluble phosphate may provide a low cost option to treat sulfidic PbZn tailings for rapid phytostabilization of the tailings surface, as an interim option to manage environmental risks of sulfidic PbZn tailings.

Assessing germination characteristics of Australian native plant species in metal/metalloid solution.

This study investigated tolerance of Australian native grass species Astrebla lappacea, Themeda australis, and Austrostipa scabra and a tree species Acacia harpophylla to different concentrations of arsenic As(V) (13.34-667.36 µM), Cu2+ (0.5-200 µM), Zn2+ (9-500 µM), Mn2+ (8-10240 µM) and Pb2+ (240-9600 µM) in single solutions in germination experiments. Metal/loid tolerance indicators used were maximum germination percentage (Gmax), mean germination time (MGT), radicle and shoot tolerance indexes (RTI & STI). Radicle tolerance index was the most sensitive indicator of metal tolerance in germinating seeds. All native species were highly tolerant to the metal/loids tested, however, they showed different metal toxicity thresholds and levels of tolerance based on RTI as a metal tolerance indicator during germination. Overall, all four species could be classified as metallophytes, confirming their current suitability for and established use in mine site rehabilitation. This work may also serve as a basis for future studies on metal/loid tolerance of other plant species during germination.

Regulatory roles of 24-epibrassinolide in tolerance of Acacia gerrardii Benth to salt stress.

This experiment aimed to investigate the role of 24-epibrassinolide (EBL) against NaCl-induced salinity stress in Acacia gerrardii Benth. NaCl (200 mM) imparted deleterious effects on the growth and chlorophyll contents of A. gerrardii, but foliar application of EBL (1.0 mg/l; each plant received 2.5 ml) mitigated the negative effect considerably. NaCl reduced chlorophyll content but this was significantly ameliorated by the application of EBL. EBL reduced significantly NaCl-induced oxidative stress hence protect membranes and also improved the relative water content significantly by 6.6% as compared with control. Nitrate reductase activity declined after NaCl treatment but EBL application sustained its activity under normal and stressed conditions. Exogenous application of EBL significantly improved the activity of superoxide dismutase, catalase and the enzymes of the ascorbate-glutathione pathway thereby protecting the photosynthetic electron transport chain and other metabolic processes in A. gerrardii from NaCl-induced oxidative stress.

Germination, physiological and biochemical responses of acacia seedlings (Acacia raddiana and Acacia tortilis) to petroleum contaminated soils.

Along the arid Arava, southern Israel, acacia trees (Acacia raddiana and Acacia tortilis) are considered keystone species. Yet they are threatened by the ongoing aquifer depletion for agriculture, the conversion of natural land to agricultural land, seed infestation by bruchid beetles, and the reduction in precipitation level in the region. In the acacia dominated Evrona reserve (southern Arava), adding to these threats are recurrent oil spills from an underground pipeline. We report here a study of the effects of contaminated soils, from a recent (December 2014) and a much older (1975) oil spills. The effects of local petroleum oil-contaminated soils on germination and early growing stages of the two acacia species were studied by comparisons with uncontaminated (control) soils from the same sites. For both acacia species, germination was significantly reduced in the 2014 oil-contaminated soils, whereas delayed in the 1975 oil-contaminated soil. There was no significant effect of oil volatile compounds on seed germination. At 105 days post transplanting (DPT), height, leaf number, stem diameter, and root growth were significantly smaller in the oil-contaminated soils. While photosynthetic performance (quantum yield of photosystem II) did not differ considerably between treatments, reductions of chlorophylls content and protein content were found in seedlings growing in the contaminated soils. Significant increases in superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities were found in roots of seedlings growing in oil-contaminated soils. These results demonstrate that seed germination and seedling growth of both acacia species were strongly restricted by oil contamination in soils, from both recent (2014) and a 40-year old (1975) oil spills. Such long-term effects of oil spills on local acacia seedlings could shift the structure of local acacia communities. These results should be taken into account by local authorities aiming to clean up and restore such polluted areas.

Phytotoxicity data safeguard the performance of the recipient plants in leachate irrigation.

Leachates from an operating and a closed landfill were examined for their phytotoxicity by seed germination/root elongation tests using seeds of Brassica chinensis and Lolium perenne. Their EC50s ranged from 3% to 46% v/v, which varied remarkably with the operating status of the landfills. Seedlings of twelve tree species were grown in pots, which were irrigated with landfill leachate at the EC50 levels, with tap water as control. No tree mortality or growth inhibition was observed after 90 days of leachate application. Chlorophyll fluorescence measurement also showed that plants receiving leachate did not suffer from a decline in photosynthetic efficiency. Litsea glutinosa and Hibiscus tiliaceus had remarkable growth, and other non-N-fixers were not inferior to the N-fixing Acacia auriculiformis. Leachate irrigation improved soil N content, though P deficiency is still a problem. The seed bioassay provided a conservative estimate of the phytotoxicity of landfill leachate. Plants irrigated can be protected from growth inhibition when the leachate irrigation plan is designed with reference to phytotoxicity data.

A preliminary assessment of the potential of using an acacia--biochar system for spent mine site rehabilitation.

Mining activities result in extensive soil degradation by removing the top soil, disturbing soil structure and altering microbial communities. Rehabilitation of spent mine sites through revegetation thus requires proper soil amendments. In this study, a pot trial was conducted to investigate the effects of a jarrah biochar on the growth and nutrient status of a native legume, Acacia tetragonophylla, grown in a mixture of topsoil and mine rejects. Two biochar application rates (37 and 74 t ha(-1)) and two types of biochar, namely nutrient-enriched and non-enriched, were tested. We measured the soil pH and electrical conductivity, the carbon (C) and nitrogen (N) contents and C and N isotope composition (δ(13)C and δ(15)N) of soil and plants, the foliar phosphorus content and the growth and leaf biomass of the plants. Whilst no significant effect of biochar was observed on plant growth, biochar amendment affected soil properties and plant nutritional status. The highest rate of biochar application increased soil pH, C content and C/N ratio, and decreased soil δ(13)C. Biochar application also enhanced photosynthetic N use efficiency, as showed by the increase in foliar C/N ratio, and biological N fixation rates, as indicated by foliar δ(15)N. These positive effects were not observed when biochar was nutrient-enriched due to the associated increase in soil N. Revegetation of mine sites with acacia in combination with biochar amendment constitutes a plausible alternative to the wide use of N fertiliser through the supply of additional N to the system, even though other nutrients may be required in order to enhance plant early growth.

The effectiveness of lime, chicken manure and leaf litter ash in ameliorating acidity in a soil previously under black wattle (Acacia mearnsii) plantation.

There are about 130,000 hectares of land in South Africa that have been under black wattle plantation for a long time and whose soils have become more acidic than those from contiguous land without the tree. This incubation study investigated the effectiveness of lime, chicken manure and leaf litter ash to ameliorate the soil acidity. Lime and chicken manure were applied in pots at rates equivalent to 0, 5, 10 and 20 Mg ha(-1) while ash was applied at 0, 3 and 5 Mg ha(-1). In comparison to the control, the application of all the three amendments caused significant increases in soil pH(KCL) (4.1-5.6) and reduced the exchangeable acidity. The liming effectiveness of the amendments varied with rate and type of amendment and were in the order: lime > chicken manure > ash. A similar trend was evident in the concentration of exchangeable bases (Ca, Mg and K) in the soil. The effectiveness of ash and chicken manure as liming material was 0.12 and 0.26 respectively compared to lime. The difference in liming effect between ash and chicken manure was related to their alkalinity concentration. It was concluded that both amendments have the potential to be used as liming materials and merit further field evaluation.