Microbial perspective on restoration of degraded urban soil using ornamental plants.

The urban soil where abandoned buildings are demolished is barren and structurally poor, and this degraded soil requires restoration. Ornamental plants enhance the urban environment, increase biodiversity, and affect soil physicochemical properties, microbial diversity; however, their effects remain unclear. Thus, in this study, a mixed-planting meadow consisting of 14 perennial ornamental flower species, including Iris tectorum, Iris lacteal, and Patrinia scabiosaefolia, etc. Was planted at a demolition site with sewage-contaminated soil in Beijing. Simultaneously, a single-planting lawn of I. tectorum was established in a nearby park. We aimed to examine soil physicochemical properties, sequence soil bacterial 16S rRNA and fungal ITS amplicons, and analyze soil microbial diversity and community structure at both sites at five time points in the year after planting, To explore the effect of herbaceous ornamental plants on degraded urban soil, we used FAPROTAX and FUNGuild to predict bacterial and fungal functions, the bin-based null model to evaluate the soil microbial community, and random matrix theory to construct soil microbial molecular networks. The mixed-planting meadow produced a visually appealing landscape and dynamic seasonal enrichment, significantly increasing soil total nitrogen (TN) and organic matter (SOM) contents by 1.99 and 1.21 times, respectively. TN had a positive correlation with soil microbial α diversity and community structure. Dominant phyla at both sites included Proteobacteria, Actinobacteria, and Ascomycota. Although soil microorganisms were primarily influenced by stochastic processes, stochasticity was notably higher in the mixed-planting meadow than in the single-planting lawn. The mixed-planting meadow significantly increased the relative abundance of beneficial microorganisms, improving nitrification and aerobic ammonium oxidation of soil bacteria, as well as symbiotroph of fungi. No significant changes were observed in the single-planting lawn. The mixed-planting meadow established a complex soil microbial molecular network, enhancing the correlation between bacteria and fungi and increasing the number of key microorganisms. Our findings suggest the potential of mixed-planting meadow in restoring degraded urban soils by influencing the soil microbial community and enhancing the ecological service function. Our study provides theoretical support for applying mixed-planting meadow communities to improve the soil environment of urban green spaces.

Plant growth-promoting rhizobacteria: a potential bio-asset for restoration of degraded soil and crop productivity with sustainable emerging techniques.

The rapid expansion of degraded soil puts pressure on agricultural crop yield while also increasing the likelihood of food scarcity in the near future at the global level. The degraded soil does not suit plants growth owing to the alteration in biogeochemical cycles of nutrients, soil microbial diversity, soil organic matter, and increasing concentration of heavy metals and organic chemicals. Therefore, it is imperative that a solution should be found for such emerging issues in order to establish a sustainable future. In this context, the importance of plant growth-promoting rhizobacteria (PGPR) for their ability to reduce plant stress has been recognized. A direct and indirect mechanism in plant growth promotion is facilitated by PGPR via phytostimulation, biofertilizers, and biocontrol activities. However, plant stress mediated by deteriorated soil at the field level is not entirely addressed by the implementation of PGPR at the field level. Thus, emerging methods such as CRISPR and nanotechnological approaches along with PGPR could manage degraded soil effectively. In the pursuit of the critical gaps in this respect, the present review discusses the recent advancement in PGPR action when used along with nanomaterials and CRISPR, impacting plant growth under degraded soil, thereby opening a new horizon for researchers in this field to mitigate the challenges of degraded soil.

Occurrence and Distribution of Heavy Metals in Mining Degraded Soil and Medicinal Plants: A Case Study of Pb/Zn Sulfide Terrain Northern Areas, Pakistan.

Mining activities have serious environmental impacts, thus releasing heavy metals (HMs) such as cadmium (Cd), lead (Pb), chromium (Cr), zinc (Zn) and nickel (Ni) into the surrounding environment. The current paper investigated the impacts of mining activities of Pb-Zn sulfide on soil and medicinal plants. Hence, soil samples (n = 36) and medicinal plants (n = 36) samples were collected, acid extracted and were analyzed through Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for HMs quantification. Our results showed that mineralized zones showed high HMs enrichment levels as compared to non-mineralized zones. Various Indices for HMs assessment revealed that the contaminated soil of the study area had low to extreme level. The mean concentrations of HMs in mining degraded soil and medicinal plants were significantly higher (p ≤ 0.01) and were found in order of Zn > Pb > Cr > Ni > Cd and Cr > Zn > Pb > Ni > Cd respectively. Similarly, some widely consumable medicinal plants showed good metal accumulation for Cd, Cr and Pb i.e., 3.57 mg kg1, 350 mg kg-1 and 335 mg kg-1 in C. sativa, while 5.9 mg kg-1, 276.9 mg kg-1 and 188.7 mg kg-1 in R. hestatus respectively. Hence, the present study recommended that medicinal plants grown in mining areas should be analyzed for HMs concentration before consumption.

Phytotoxicity assay to assess sewage sludge phytoremediation rate using guaiacol peroxidase activity (GPX): A comparison of four growth substrates.

Waste disposal such as sewage sludge (biosolids) in phytoremediation is a sustainable remediation alternative for fertilizers, therefore there is a need to develop a test that will allow to determine phytoremediation dose of biosolids from the best-for-plant-growth point of view. In order to determine the doses of biosolids to degraded soils, tests based on germination of seeds and root elongation are commonly used, but also, they are subjected to large errors caused by low repeatability of results and differentiation. That is why there is a need to introduce new testing solutions that will be of use based on more reliable indicators such as biochemical activity of selected plant enzymes. The aim of the study was to demonstrate high efficiency of the guaiacol peroxidase activity (GPX) in plant-based toxicity tests used as an optimal dose amendments indicator in heavy metal degraded soil phytoremediation process. GPX were measured in underground and above ground parts of Sinapis alba L. and Brassica rapa L. in relation to germination index (GI) and biomass cultivated on four different substrates (raw degraded soil, sterilized degraded soil, water extract from degraded soil solidified with agar, water extract from degraded soil solidified with Murashige-Skoog medium). Each testing soil substrate was enriched with sewage sludge (food industry origin) in the percentage share (w/w) of 5, 10, 15, 20 and 25. The process was carried out under controlled conditions of the phytotronic chamber for a period of 14 days. The obtained values were compared for each plant separately and for all substrates and amendments rates of sewage sludge. GPX activity was expressed as a percentage increase or decrease in relation to the GPX in soil substrates without addition of sewage sludge which allowed to determine their positive or negative impact on substrate toxicity. Results of GPX activity showed that the water-based soil extracts solidified with agar give more accurate results in relation to the tests on raw soil. It has been demonstrated that the optimal phytoremediation dose of sewage sludge was in the range of 15-20%, with values of 5% and 25% respectively favoring or inhibiting plant development expressed in GPX activity. The most differentiating GPX values were obtained for the roots.Measurement of GPX activity in the roots of Sinapis alba L. cultivated on soil agar-based tests is a good, new and easy additional or alternative to the old tests based on germination and increase biomass measuring as an indicator in the assessment of optimal phytoremediation sewage sludge.

Chemical and ecotoxicological effects of the use of drinking-water treatment residuals for the remediation of soils degraded by mining activities.

The aim of this study was to evaluate the use of drinking-water treatment residuals (DWTR) in the amendment of a soil affected by mining activities (Aljustrel mine, Portuguese sector of the Iberian Pyrite Belt), considering the effects on its chemical, biochemical and ecotoxicological characteristics. The DWTR had neutral characteristics (pH 6.7) and an organic matter (OM) content of 575 g kg-1 dry matter (DM), which makes them a potential amendment for the remediation of mine degraded soils, as they may correct soil acidity and reduce the extractable metal fraction. An incubation assay, with soil and DWTR, with or without lime, was carried out to test the doses to be used in the assisted-phytostabilization experiment. Based on the results obtained, the doses of DWTR used were the equivalent to 48, 96, and 144 t DM ha-1, with and without lime application (CaCO3 11 t DM ha-1). Agrostis tenuis Sibth was used as the test plant. Some amendments doses were able to improve soil characteristics (pH and OM content), to decrease metal extractability by 0.01 M CaCl2 (especially for Cu and Zn), and to allow plant growth, that did not occur in the non-amended soil. Copper, Pb and Zn concentrations in the plant material were lower than the maximum tolerable level for cattle feed, used as an indicator of risk of entry of those metals into the human food chain. The simultaneous application of DWTR (96 and 144 t ha-1), with lime, allowed a reduction in the mine soil ecotoxicity, as evaluated by some lethal and sub-lethal bioassays, including luminescence inhibition of Vibrio fischeri, Daphnia magna acute immobilization test, mortality of Thamnocephalus platyurus, and 72-h growth inhibition of the green microalgae Pseudokirchneriella subcapitata. However, DWTR were unable to increase soil microbial activity, evaluated by dehydrogenase activity, an important soil-health indicator. Also, OM content and NKjeldahl, concentrations increased slightly but remained low or very low (P and K extractable concentrations were not affected). In general, the bioassays highlighted a decrease in soil ecotoxicity with the presence of lime and DWTR (144 t DM ha-1). In conclusion, DWTR are recommended to amend acidic soils, with high concentrations of trace elements, but an additional application of organic or mineral fertilizers should be considered.

Modification of properties of energy crops under Polish condition as an effect of sewage sludge application onto degraded soil.

Energy crops are one of the possible solutions for reclamation of degraded or contaminated terrain. Their cultivation requires adequate fertilization typically containing high content of organic matter, nitrogen and phosphorous. While sewage sludge may be one source of these necessary nutrients, it may also modify some plant biomass properties, such as total carbon content. In our study, we determined whether sewage sludge (containing different value of heavy metals) could be an effective fertilizer to obtain good quality energy crops (such as Miscanthus x gigantheus and reed canary grass, Phalaris arundinacea) and simultaneously play positive role for improvement of phytoremediation. The 3-year experiment was performed on degraded soil from terrain of steel mill of Czestochowa (Silesian region, Poland). During the study, it was confirmed that sewage sludge (also in combination with urea, CH4N2O) influences the mobility of Pb, Zn, Cd in soil solution, however the intensity of the process can be limited by plant species and time. Both miscanthus, and reed canary grass were characterized by the low value of bioconcentration factor (BCF), but because biomass was high, the total concentration of heavy metals in crops was comparable with hyperaccumulators. Additionally, modification of the fertilization affected energetic parameters, such as the content of carbon, S/Cl ratio, unitary CO2 emission. However, this effect was not statistically significant.

Comparative effect of compost and technosol enhanced with biochar on the fertility of a degraded soil.

A large number of studies on the reclamation of mine soils focused on the problem caused by metals and did not explore in depth the issue of nutrients and vegetation after the application of organic materials. The aim of this study was to compare the effect of two treatments made of wastes and vegetated with Brassica juncea L. on the fertility of a settling pond mine soil. The first treatment was compost, biochar, and B. juncea (SCBP) and the second treatment was technosol, biochar, and B. juncea (STBP). This study evaluated the effect of the treatments on the soil nutrient concentrations and fertility conditions in the soil amendment mixtures, after 11 months of greenhouse experiment. Total carbon and nitrogen concentrations were higher in treatment SCBP than in treatment STBP after 7 months but, after 11 months, carbon concentration was higher in STBP. The used technosol could have forms of carbon more stable than compost, which could be released slower than in the compost-amended soils. Both compost and technosol mixed with biochar also increased the concentration of calcium, potassium, magnesium, and sodium in exchangeable form in the mine soil.

Field approach to mining-dump revegetation by application of sewage sludge co-compost and a commercial biofertilizer.

An approach was devised for revegetation of a mining dump soil, sited in a semiarid region, with basic pH as well as Fe and Mn enrichment. A field experiment was conducted involving the use of co-compost (a mixture of urban sewage sludge and plant remains) along with a commercial biofertilizer (a gel suspension which contains arbuscular mycorrhizal fungus) to reinforce the benefits of the former. Four treatments were studied: unamended soil; application of conditioners separately and in combination. Pistachio, caper, rosemary, thyme and juniper were planted. We evaluated the effects of the treatments using soil quality (physicochemical properties, total content of hazardous elements, nutrient availability, microbial biomass and enzyme activities) and plant establishment indicators (survival, growth, vigor, nutrient content in leaves, nutrient balances and mycorrhizal root colonization). Thyme and juniper did not show a suitable survival rate (<50%) whereas 70-100% of the pistachio, rosemary and caper survived for at least 27 months. In unamended soil, plant growth was severely hampered by P, N, K and Zn deficiencies as well as Fe and Mn excess. Overall, the treatments affected the soil and plant indicators as follows: biofertilizer + co-compost > co-compost > biofertilizer > unamended. The application of co-compost was therefore essential with regard to improving soil fertility; furthermore, it increased leaf N and P content, whereas leaf Fe and Mn concentrations showed a decrease. The combined treatment, however, provided the best results. The positive interaction between the two soil conditioners might be related to the capacity of the biofertilizer to increase nutrient uptake from the composted residue, and to protect plants against Fe and Mn toxicity.

Microbial inoculants and organic amendment improves plant establishment and soil rehabilitation under semiarid conditions.

The re-establishment of autochthonous shrub species is an essential strategy for recovering degraded soils under semiarid Mediterranean conditions. A field assay was carried out to determine the combined effects of the inoculation with native rhizobacteria (Bacillus megaterium, Enterobacter sp, Bacillus thuringiensis and Bacillus sp) and the addition of composted sugar beet (SB) residue on physicochemical soil properties and Lavandula dentata L. establishment. One year after planting, Bacillus sp. and B. megaterium + SB were the most effective treatments for increasing shoot dry biomass (by 5-fold with respect to control) and Enterobacter sp + SB was the most effective treatments for increasing dry root biomass. All the treatments evaluated significantly increased the foliar nutrient content (NPK) compared to control values (except B. thuringiensis + SB). The organic amendment had significantly increased available phosphorus content in rhizosphere soil by 29% respect to the control. Enterobacter sp combined with sugar beet residue improved total N content in soil (by 46% respect to the control) as well as microbiological and biochemical properties. The selection of the most efficient rhizobacteria strains and their combined effect with organic residue seems to be a critical point that drives the effectiveness of using these biotechnological tools for the revegetation and rehabilitation of degraded soils under semiarid conditions.

The shaping of onion seedlings performance through substrate formulation and co-inoculation with beneficial microorganism consortia.

Introduction: Smart management in crop cultivation is increasingly supported by application of arbuscular mycorrhizal fungi (AMF) and plant growth-promoting microorganisms (PGPM), which sustain soil fertility and plant performance. The aim of this study was the evaluation of the effects of consortia composed of (Claroideoglomus claroideum BEG96, Claroideoglomus etunicatum BEG92, Funneliformis geosporum BEG199, Funneliformis mosseae BEG 95, and Rhizophagus irregularis BEG140) and PGPM (Azospirillum brasilense - AZ, or Saccharothrix sp. - S) on onion cultivated in growing media with a composition corresponding to a degraded soil. Methods: Three types of substrate formulations were used, with peat:sand ratios of 50:50, 70:30, 100:0 (v:v). The analysis of substrate parameters crucial for its fertility (pH, salinity, sorption complex capacity, and elements' content) and characteristics reflecting onion seedlings' performance (fresh weight, stress biomarkers, and elements' content) was performed. Results: AMF colonized onion roots in all treatments, showing increasing potential to form intercellular structures in the substrates rich in organic matter. Additionally, co-inoculation with PGPM microorganisms accelerated arbuscular mycorrhiza establishment. Increased antioxidant activity and glutathione peroxidase (GPOX) activity of onion roots sampled from the formulations composed of peat and sand in the ratio of 100:0, inoculated with AMF+S, and positive correlation between GPOX, fresh weight and antioxidant activity of onion roots reflected the successful induction of plant acclimatization response. Total phenols content was the highest in roots and leaves of onion grown in substrates with 70:30 peat:sand ratio, and, in the case of roots, it was correlated with AMF colonization parameters but not with antioxidant activity. Discussion: AMF and PGPM efficiency in supporting onion growth should be linked to the increased onion root system capacity in mineral salts absorption, resulting in more efficient aboveground biomass production. AMF and PGPM consortia were effective in releasing minerals to soluble fraction in substrates rich in organic matter, making elements available for uptake by onion root system, though this phenomenon depended on the PGPM species. Microorganism consortia enhanced onion seedlings' performance also in substrates with lower content of organic carbon through plant biofertilization and phytostimulation.

Impact of Biochar Amendment on Soil Properties and Organic Matter Composition in Trace Element-Contaminated Soil.

The application of biochar as an organic amendment in polluted soils can facilitate their recovery by reducing the availability of contaminants. In the present work, the effect of biochar application to acid soils contaminated by heavy metal spillage is studied to assess its effect on the quantity and composition of soil organic matter (SOM), with special attention given to soil humic acids (HAs). This effect is poorly known and of great importance, as HA is one of the most active components of SOM. The field experiment was carried out in 12 field plots of fluvisols, with moderate and high contamination by trace elements (called MAS and AS, respectively), that are located in the Guadiamar Green Corridor (SW Spain), which were amended with 8 Mg·ha-1 of olive pit biochar (OB) and rice husk biochar (RB). The results indicate that 22 months after biochar application, a noticeable increase in soil water holding capacity, total organic carbon content, and soil pH were observed. The amounts of oxidisable carbon (C) and extracted HAs in the soils were not altered due to biochar addition. Thermogravimetric analyses of HAs showed an increase in the abundance of the most thermostable OM fraction of the MAS (375-650 °C), whereas the HAs of AS were enriched in the intermediate fraction (200-375 °C). Spectroscopic and chromatographic analyses indicate that the addition of biochar did not alter the composition of the organic fraction of HAs, while Cu, Fe, and as were considerably accumulated at HAs.

Nano-Restoration for Sustaining Soil Fertility: A Pictorial and Diagrammatic Review Article.

Soil is a real treasure that humans cannot live without. Therefore, it is very important to sustain and conserve soils to guarantee food, fiber, fuel, and other human necessities. Healthy or high-quality soils that include adequate fertility, diverse ecosystems, and good physical properties are important to allow soil to produce healthy food in support of human health. When a soil suffers from degradation, the soil's productivity decreases. Soil restoration refers to the reversal of degradational processes. This study is a pictorial review on the nano-restoration of soil to return its fertility. Restoring soil fertility for zero hunger and restoration of degraded soils are also discussed. Sustainable production of nanoparticles using plants and microbes is part of the process of soil nano-restoration. The nexus of nanoparticle-plant-microbe (NPM) is a crucial issue for soil fertility. This nexus itself has several internal interactions or relationships, which control the bioavailability of nutrients, agrochemicals, or pollutants for cultivated plants. The NPM nexus is also controlled by many factors that are related to soil fertility and its restoration. This is the first photographic review on nano-restoration to return and sustain soil fertility. However, several additional open questions need to be answered and will be discussed in this work.

Effects of field scale in situ biochar incorporation on soil environment in a tropical highly weathered soil.

Biochar has been proven as a soil amendment to improve soil environment. However, mechanistic understanding of biochar on soil physical properties and microbial community remains unclear. In this study, a wood biochar (WB), was incorporated into a highly weathered tropical soil, and after 1 year the in situ changes in soil properties and microbial community were evaluated. A field trial was conducted for application of compost, wood biochar, and polyacrylamide. Microstructure and morphological features of the soils were characterized through 3D X-ray microscopy and polarized microscopy. Soil microbial communities were identified through next-generation sequencing (NGS). After incubation, the number of pores and connection throats between the pores of biochar treated soil increased by 3.8 and 7.2 times, respectively, compared to the control. According to NGS results, most sequences belonged to Anaerolinea thermolimosa, Caldithrix palaeochoryensis, Chthoniobacter flavus, and Cohnella soli. Canonical correlation analysis (CCA) further demonstrated that the microbial community structure was determined by inorganic N (IN), available P (AP), pH, soil organic C (SOC), porosity, bulk density (BD), and aggregate stability. The treatments with co-application of biochar and compost facilitated the dominance of Cal. palaeochoryensis, Cht. flavus, and Coh. soli, all of which promoted organic matter decomposition and ammonia oxidation in the soil. The apparent increases in IN, AP, porosity, and SOC caused by the addition of biochar and compost may be the proponents of changes in soil microbial communities. The co-application of compost and biochar may be a suitable strategy for real world biochar incorporation in highly weathered soil.

Improving the Properties of Degraded Soils from Industrial Areas by Using Livestock Waste with Calcium Peroxide as a Green Oxidizer.

Over the past years, the treatment and use of livestock waste has posed a significant problem in environmental engineering. This paper outlines a new approach to application of calcium peroxide (CaO2) as a green oxidizer and microbiocidal agent in the treatment of poultry manure. It also presents the application of pretreated waste in improvement of degraded soils in industrial areas. The CCD (Central Composite Design) and RSM (Response Surface Methodology) were employed for optimizing the process parameters (CaO2 concentration 1.6-8.4 wt %, temperature 5.2-38.8 °C and contact time 7-209 h). The analysis of variance (ANOVA) was used to analyze the experimental results, which indicated good fit of the approximated to the experimental data (R2 = 0.8901, R2adj = 0.8168). The amendment of CaO2 in optimal conditions (8 wt % of CaO2, temperature 22 °C and contact time 108 h) caused a decrease in bacteria Escherichia coli (E. coli) in poultry manure from 8.7 log10 CFU/g to the acceptable level of 3 log10 CFU/g. The application of pretreated livestock waste on degraded soils and the studies on germination and growth of grass seed mixture (Lollum perenne-Naki, Lollum perenne-Grilla, Poa pratensis-Oxford, Festuca rubbra-Relevant, Festuca rubbra-Adio and Festuca trachypylla-Fornito) showed that a dose of 0.08 g of CaO2 per 1 gram of poultry manure induced higher yield of grass plants. The calculated indicators for growth of roots (GFR) and shoots (GFS) in soils treated with poultry manure were 10-20% lower compared to soils with amended CaO2. The evidence from this study suggests that CaO2 could be used as an environmentally friendly oxidizer and microbiocidal agent for livestock waste.

Biowastes to augment the essential oil production of Leptospermum scoparium and Kunzea robusta in low-fertility soil.

Biowastes are unwanted materials of biological origin. They include biosolids, dairy shed effluent, and sawdust. When applied to soil, biowastes can provide plant nutrients, but also introduce heavy metals, pathogens, or xenobiotics. Biowastes could improve degraded or low-fertility soils and generate revenue through the production of non-food products such as essential oils. We grew New Zealand native plants, manuka (Leptospermum scoparium J.R. Forst & G. Forst) and kanuka (Kunzea robusta de Lange & Toelken) in series of greenhouse experiments in low-to-medium-fertility soils (Bideford clay loam, Lismore stony silt loam, and Pawson silt loam) amended with either biosolids (up to 13500 kg N ha-1 equiv.), biosolids + sawdust (1:0.5-1250 kg N ha-1 equiv.) and dairy shed effluent (200 kg N ha-1 equiv.). Two types of biosolids from Kaikoura (KB) and Christchurch City Council (CB) were used in the experiments. CB (1500 kg N ha-1 equiv.) and dairy shed effluent (200 kg N ha-1 equiv.) increased the biomass of L. scoparium by up to 120% and 31%, and K. robusta by up to 170% and 34%, respectively. Adding sawdust to KB increased the biomass of L. scoparium and K. robusta although it offset the L. scoparium growth increase in the KB-only treatment. The growth response of K. robusta to biowastes was greater than L. scoparium with oil production in K. robusta increasing by up to 211% when 1500 kg N ha-1 equiv. of CB was applied to Lismore stony silt loam. Generally, the treatments had a negligible effect on oil concentration in all the soil types, except for the KB + sawdust treatment, which increased the oil concentration by 82%. Most of the EOs' major components were unaffected by biowaste addition in the soils, although some components increased in the Bideford clay loam following KB and KB + sawdust application. Biosolids increased foliar concentrations of Zn, Cu, and Cd, but these were below risk-threshold concentrations. Applying CB (up to 1500 kg N ha-1 equiv.) to low-fertility soils is recommended to establish ecosystems dominated by L. scoparium and K. robusta that annually would produce ca. 100 kg ha-1 of EOs worth US$ 26k and 24k, respectively. Adding sawdust to CB could have environmental benefits through reduction of N leaching. Field trials are warranted to elucidate critical ecological variables and production economics in biowaste management.

N2-fixing black locust intercropping improves ecosystem nutrition at the vulnerable semi-arid Loess Plateau region, China.

The Loess Plateau in northwestern China constitutes one of the most vulnerable semi-arid regions in the world due to long-term decline in forest cover, soil nutrient depletion by agricultural use, and attendant soil erosion. Here, we characterize the significance of N2-fixing Robinia pseudoacacia L. and non-N2-fixing Juglans regia L. for improving nutrient availability and water retention in soil by comparing a range of biological and physicochemical features in monoculture and mixed plantations of both species. We found that N2-fixing Robinia facilitates the nitrogen and phosphorus composition of non-N2-fixing Juglans in the mixed stand as a consequence of improved soil nutrient availability, evident as higher levels of nitrogen and labile carbon compared to mono-specific stands. This demonstrates that intercropping N2-fixing Robinia with non-N2-fixing woody plants can greatly improve soil carbon and nitrogen bioavailability as well as whole-plant nutrition and can potentially mediate water retention with additional sequestration of soil organic carbon in the range of 1 t C ha-1 year-1. Thus, intercropping N2-fixing woody species (e.g. Robinia pseudoacacia or Hippophae rhamnoides L.) with locally important non-N2-fixing tree and shrub species should be considered in afforestation strategies for landscape restoration.

The influence of various organic amendments on the bioavailability and plant uptake of cadmium present in mine-degraded soil.

Mining of minerals and precious elements leads to land degradation that need to be reclaimed using environmentally friendly and cost effective techniques. The present study investigated the potential effects of different organic amendments on cadmium (Cd) bioavailability in mining-degraded soil and its subsequent bioaccumulation in tomato and cucumber. The selected organic geosorbents (hard wood biochar (HWB), bagasse (BG), rice husk (RH), and maize comb waste (MCW)) were added at application rates of 3% and 5% to chromite mine-degraded soil containing Cd. Tomato and cucumber plants were then grown in the soil, and the roots, shoots, leaves, and fruits of each plant were analysed for Cd concentration, biomass production, and chlorophyll content. The results indicated that the different organic materials have variable effects on physiochemical characteristics of vegetables and Cd bioavailability. The biochar amendment significantly (P < 0.01) increased chlorophyll contents (20-40%) and biomass (40-63%), as did RH to a lesser extent (increase of 10-18% in chlorophyll content and 3-45% in biomass). Among the amendments, HWB was the most effective at reducing Cd bioavailability, wherein significant decreases were observed in Cd uptake by fruits of tomato (24-30%) and cucumber (36-54%). The higher application rate of 5% was found to be more effective for mitigation of Cd mobility and bioaccumulation in plants grown in mine degraded soil. The study results indicate that effective use of organic amendments, especially HWB, can significantly reduce Cd levels in vegetables, improve food quality, and reduce human-health risk while increasing biomass production.

Response of Leptospermum scoparium, Kunzea robusta and Pinus radiata to contrasting biowastes.

The myrtaceae family has a cosmopolitan distribution and includes the Australasian native species Leptospermum scoparium (manuka) and Kunzea robusta (kanuka), which are of economic interest for the production of high-value honey and essential oils. Potentially, these species could be established on low-fertility or degraded soils that have been amended with biowastes, including biosolids and sawdust. We aimed to determine the effect of these biowastes on nitrate leaching and the growth and chemical composition of these plant species compared to Pinus radiata (pine), a common forestry species. The addition of biosolids (1250kgNha-1 equiv.) increased the total dry biomass of manuka, kanuka, and pine by 117, 90, and 86% respectively. Mixing sawdust with biosolids stimulated growth of manuka (52%), kanuka (121%) but not pine. Biosolids increased plant uptake of N, P, and trace elements, but not to levels of concern. Nitrate leaching from all treatments was negligible (<2kgha-1).

Effect of two different composts on soil quality and on the growth of various plant species in a polymetallic acidic mine soil.

The effect of the addition (0-10%) of two types of sewage sludge composts (composted sewage sludge [CS] and sewage sludge co-composted with olive prune wastes [CSO]) on a polymetallic acidic soil from the Riotinto mining area was evaluated by i) a soil incubation experiment and ii) a greenhouse pot experiment using tomato (Solanum lycopersicum Mill.), ryegrass (Lolium perenne L.) and ahipa (Pachyrhizus ahipa (Wedd.) Parodi). Compost addition improved the soil organic carbon content, increased the pH and the electrical conductivity and enhanced enzyme activities and soil respiration, more for CSO than for CS. Plant growth was generally enhanced after compost addition, but not proportionally to the dose. Foliar concentrations of some hazardous elements (As, Cr, Fe) in tomato growing in non-amended soil were above the thresholds, questioning the adequacy of using this plant species. However, leaf concentrations of essential and potentially toxic elements (Fe, As, Cr and Pb) in tomato and/or ryegrass were reduced after the amendment with both composts, generally more for CSO than for CS. Conversely, foliar concentrations in ahipa, a plant species which is able to grow without the need of compost addition, were safe except for As and were only slightly affected by compost addition. This plant species would be a suitable candidate due to its low requirements and due to the limited element translocation to the leaves. Concerning the composts, amelioration of plant and soil properties was better accomplished when using CSO, a compost of sewage sludge and plant remains, than when using CS, which only contained the sludge.

Use of phytoproductivity data in the choice of native plant species to restore a degraded coal mining site amended with a stabilized industrial organic sludge.

Coal mining-related activities result in a degraded landscape and sites associated with large amounts of dumped waste material. The arid soil resulting from acid mine drainage affects terrestrial and aquatic ecosystems, and thus, site remediation programs must be implemented to mitigate this sequential deleterious processes. A low-cost alternative material to counterbalance the affected physico-chemical-microbiological aspects of the degraded soil is the amendment with low contaminated and stabilized industrial organic sludge. The content of nutrients P and N, together with stabilized organic matter, makes this material an excellent fertilizer and soil conditioner, fostering biota colonization and succession in the degraded site. However, choice of native plant species to restore a degraded site must be guided by some minimal criteria, such as plant survival/adaptation and plant biomass productivity. Thus, in this 3-month study under environmental conditions, phytoproductivity tests with five native plant species (Surinam cherry Eugenia uniflora L., C. myrianthum-Citharexylum myrianthum, Inga-Inga spp., Brazilian peppertree Schinus terebinthifolius, and Sour cherry Prunus cerasus) were performed to assess these criteria, and additional biochemical parameters were measured in plant tissues (i.e., protein content and peroxidase activity) exposed to different soil/sludge mixture proportions. The results show that three native plants were more adequate to restore vegetation on degraded sites: Surinam cherry, C. myrianthum, and Brazilian peppertree. Thus, this study demonstrates that phytoproductivity tests associated with biochemical endpoint measurements can help in the choice of native plant species, as well as aiding in the choice of the most appropriate soil/stabilized sludge proportion in order to optimize biomass production.