The significance of magnesium for crop quality

Background

The quality of agricultural and horticultural products and its modulation by fertilization has increasingly received attention. However, whereas the importance of magnesium (Mg) as an essential plant nutrient is well established, the impact of Mg nutrition on quality parameters has only been rarely addressed.

Scope

This review aims at evaluating the available knowledge on the influence of Mg on produce quality. A short discussion on the term quality as used in this review is followed by an overview of the various functions of Mg in plant metabolism in relation to quality aspects. Finally, the available literature on Mg-associated effects on crop quality is critically surveyed. The question whether Mg application beyond yield optimum further improves crop quality is specifically addressed.

Conclusion

Increasing Mg supply on Mg-deficient sites tends to increase the quality of agricultural crops, particularly when the formation of quality traits is dependent on Mg-driven photosynthesis and assimilate translocation within the plant. In fruits and vegetables, ratios of Mg to other nutrients like Ca and K were shown to be a more reliable indicator of the quality response than the Mg status alone. Moreover, it is concluded that Mg doses beyond those required for maximum yield rarely induce a further improvement of produce quality.     

Interaction of aluminium and drought stress on root growth and crop yield on acid soils

Background

Aluminium (Al) toxicity and drought stress are two major constraints for crop production in the world, particularly in the tropics. The variation in rainfall distribution and longer dry spells in much of the tropics during the main growing period of crops are becoming increasingly important yield-limiting factors with the global climate change. As a result, crop genotypes that are tolerant of both drought and Al toxicity need to be developed.

Scope

The present review mainly focuses on the interaction of Al and drought on root development, crop growth and yield on acid soils. It summarizes evidence from our own studies and other published/related work, and provides novel insights into the breeding for the adaptation to these combined abiotic stresses. The primary symptom of Al phytotoxicity is the inhibition of root growth. The impeded root system will restrict the roots for exploring the acid subsoil to absorb water and nutrients which is particularly important under condition of low soil moisture in the surface soil under drought. Whereas drought primarily affects shoot growth, effects of phytotoxic Al on shoot growth are mostly secondary effects that are induced by Al affecting root growth and function, while under drought stress root growth may even be promoted. Much progress has recently been made in the understanding of the physiology and molecular biology of the interaction between Al toxicity and drought stress in common bean (Phaseolus vulgaris L.) in hydroponics and in an Al-toxic soil.

Conclusions

Crops growing on acid soils yield less than their potential because of the poorly developed root system that limits nutrient and water uptake. Breeding for drought resistance must be combined with Al resistance, to assure that drought resistance is expressed adequately in crops grown on soils with acid Al-toxic subsoils.     

Adequate magnesium nutrition mitigates adverse effects of heat stress on maize and wheat

Aims

Heat stress is a growing concern in crop production because of global warming. In many cropping systems heat stress often occurs simultaneously with other environmental stress factors such as mineral nutrient deficiencies. This study aimed to investigate the role of adequate magnesium (Mg) nutrition in mitigating the detrimental effects of heat stress on wheat (Triticum aestivum) and maize (Zea mays).

Methods

Wheat and maize plants were grown in solution culture with low or adequate Mg supply at 25/22 °C (light/dark). Half of the plants were, then, exposed to heat stress at 35/28 °C (light/dark). Development of leaf chlorosis and changes in root and shoot growth, chlorophyll and Mg concentrations as well as the activities of major antioxidative enzymes were quantified in the experimental plants. Additionally, maize plants were analyzed for the specific weights (e.g., dry or fresh weight per a given leaf surface area) and soluble carbohydrate concentrations of sink and source leaves.

Results

Visual leaf symptoms of Mg deficiency were aggravated in wheat and maize when exposed to heat stress. In both species, root growth was more sensitive to Mg deficiency than shoot growth, and the shoot-to-root ratios peaked when heat stress was combined with Mg deficiency. Magnesium deficiency markedly reduced soluble carbohydrate concentrations in young leaf; but resulted in substantial increase in source leaves. Magnesium deficiency also increased activities of antioxidative enzymes, especially when combined with heat stress. The highest activities of superoxide dismutase (up to 80 % above the control), glutathione reductase (up to 250 % above the control) and ascorbate peroxidase (up to 300 % above the control) were measured when Mg-deficient plants were subjected to heat, indicating stimulated formation of reactive oxygen species (ROS) in Mg deficient leaves under heat stress.

Conclusions

Magnesium deficiency increases susceptibility of wheat and maize plants to heat stress, probably by increasing oxidative cellular damage caused by ROS. Ensuring a sufficiently high Mg supply for crop plants through Mg fertilization is a critical factor for minimizing heat-related losses in crop production.     

The effect of rate and Cd concentration of repeated phosphate fertilizer applications on seed Cd concentration varies with crop type and environment

Background and aims

Limited information is available on how cadmium (Cd) applied in phosphate fertilizer interacts with soil and environmental conditions over time to affect crop Cd concentrations.

Methods

Field studies from 2002 to 2009 at seven locations evaluated the cumulative effects of P fertilizer rate and Cd concentration on seed Cd concentration of durum wheat (Triticum turgidum L.) and flax (Linum usitatissiumum L.).

Results

Soil characteristics and environment affected Cd availability. Durum wheat grain Cd increased with P fertilizer rate but effect on flaxseed Cd concentration was smaller. Cadmium concentration in fertilizer had a greater effect on flaxseed than durum wheat Cd concentration. Seed Cd concentration of both crops was greatest with the highest rate P fertilizer containing the highest Cd concentration. There was not a strong cumulative effect of fertilization over the 8 years of the study, indicating attenuation of Cd availability over time.

Conclusions

Cadmium in phosphate fertilizer increases Cd available for crop uptake, but crop Cd concentration is also affected by soil characteristics and annual environmental conditions. Type of crop produced and soil and environmental characteristics that affect phytoavailability must be taken into account when assessing the Cd risk from P fertilization.     

Properties of anthropogenic soils in ancient run-off capturing agricultural terraces in the Central Negev desert (Israel) and related effects of biochar and ash on crop growth

Background and aims

In the Central Negev hills (Israel) many ancient terraced wadis exist, which captured run-off and caused gradual soil aggradation, which enabled agricultural practices. In these terraces, dark colored soil horizons were observed, containing charcoal, as can be found in Terra Preta soils, suggesting higher fertility compared to natural soils. The aim of our investigation was to investigate these anthropogenic soils and to study the effects of charcoal and ash addition on soil properties and crop growth.

Methods

We investigated 12 soil profiles, focusing on possible differences between light and dark colored soil horizons. We also investigated the effects of amendment of charcoal and ash on the growth of wheat (Triticum Aestivum L.) in a 40-day pot experiment involving two water regimes.

Results

Results show that charcoal content in light and dark horizons were both low (<0.2 %), but significantly lower bulk densities were found in dark colored horizons. In the crop experiment, charcoal addition resulted in decreased crop growth, while, in the water deficit regime, ash addition resulted in increased crop growth.

Conclusions

Considering the observed charcoal and the results from the crop experiment, we hypothesize that, in ancient run-off capturing agricultural systems, ash was purposefully added as fertilizer.     

Influence of agricultural practices and seasons on the abundance and community structure of culturable pseudomonads in soils under no-till management in Argentina

Background and aims

Members of the genus Pseudomonas are common inhabitants of rhizospheres and soils, and it is known that soil types and crop species influence their population density and structure. 20?×?10⁶ ha are cultivated under no-tillage in Argentina and there is a need to find new biologically-based soil quality indexes to distinguish between sustainable and non-sustainable agricultural practices. Pseudomonads abundance and community structure were analyzed in no-till soils with different agricultural practices, in productive fields along 400 km of Argentinean Pampas.

Methods

We sampled soils and root systems from agricultural plots in which sustainable or non-sustainable agricultural practices have been applied. Samples were collected in summer and winter during 2010 and 2011. Culturable fluorescent and total pseudomonads were enumerated by plating on Gould’s selective medium S1. Colonies from these plates served as DNA source to carry out PCR-RFLP community structure analysis of the pseudomonads-specific marker genes oprF and gacA.

Results

Abundance of total and fluorescent culturable pseudomonads in bulk soils was influenced by seasonal changes and agricultural practices. Rhizospheric counts from the same crop were affected by agricultural treatments. Also, crop species influenced pseudomonads density in the rhizosphere. Combined PCR-RFLP profile of both genes showed a seasonal grouping of samples.

Conclusions

Sustainable soil management seems to promote pseudomonads development in soils, favoring root colonization of crops from those plots. Crop species influence total pseudomonads load of rhizospheres and its community structure. Total or relative pseudomonads load could function as soil quality indicator of good agricultural practices.     

Past, present and future of organic nutrients

Background

Slowing crop yield increases despite high fertiliser application rates, declining soil health and off-site pollution are testimony that many bioproduction systems require innovative nutrient supply strategies. One avenue is a greater contribution of organic compounds as nutrient sources for crops. That plants take up and metabolise organic molecules (‘organic nutrients’) has been discovered prior to more recent interest with scientific roots reaching far into the 19th century. Research on organic nutrients continued in the early decades of the 20th century, but after two world wars and yield increases achieved with mineral and synthetic fertilisers, a smooth continuation of the research was not to be expected, and we find major gaps in the transmission of methods and knowledge.

Scope

Addressing the antagonism of ‘organicists’ and ‘mineralists’ in plant nutrition, we illustrate how the focus of crop nutrition has shifted from organic to inorganic nutrients. We discuss reasons and provide evidence for a role of organic compounds as nutrients and signalling agents.

Conclusion

After decades of focussing on inorganic nutrients, perspectives have greatly widened again. As has occurred before in agricultural history, science has to validate agronomic practises. We argue that a framework that views plants as mixotrophs with an inherent ability to use organic nutrients, via direct uptake or aided by exoenzyme-mediated degradation, will transform nutrient management and crop breeding to complement inorganic and synthetic fertilisers with organic nutrients.     

Biochar’s effect on crop productivity and the dependence on experimental conditions—a meta-analysis of literature data

Background and aims

For the last decade, there has been an increasing global interest in using biochar to mitigate climate change by storing carbon in soil. However, there is a lack of detailed knowledge on the impact of biochar on the crop productivity in different agricultural systems. The objective of this study was to quantify the effect of biochar soil amendment (BSA) on crop productivity and to analyze the dependence of responses on experimental conditions.

Methods

A weighted meta-analysis was conducted based on data from 103 studies published up to April, 2013. The effect of BSA on crop productivity was quantified by characterizing experimental conditions.

Results

In the published experiments, with biochar amendment rates generally <30 t ha^?1, BSA increased crop productivity by 11.0 % on average, while the responses varied with experimental conditions. Greater responses were found in pot experiments than in field, in acid than in neutral soils, in sandy textured than in loam and silt soils. Crop response in field experiments was greater for dry land crops (10.6 % on average) than for paddy rice (5.6 % on average). This result, associated with the higher response in acid and sandy textured soils, suggests both a liming and an aggregating/moistening effect of BSA.

Conclusions

The analysis suggests a promising role for BSA in improving crop productivity especially for dry land crops, and in acid, poor-structured soils though there was wide variation with soil, crop and biochar properties. Long-term field studies are needed to elucidate the persistence of BSA’s effect and the mechanisms for improving crop production in a wide range of agricultural conditions. At current prices and C-trading schemes, however, BSA would not be cost-effective unless persistent soil improvement and crop response can be demonstrated.     

Isolates of dark septate endophytes reduce metal uptake and improve physiology of Salix caprea L.

Background and aims

Dark septate endophyte (DSE) fungi are the most frequent colonists on the roots of Salix caprea in highly metal-contaminated soils. The present study was performed to obtain insights into the physiology and potential role(s) of DSE fungi for Salix caprea growing in metal-enriched sites.

Methods

Fungal isolates from S. caprea roots were identified using molecular methods, and tested for their tolerance and metal accumulation in axenic cultures. In addition, an inoculation experiment was performed to monitor the effects of the fungi on the metal uptake by the plant host. Fitness of S. caprea cuttings was assessed by photosynthetic pigment quantification and measurements of transpiration.

Results

Fungal isolates were identified as members of the Phialophora/Cadophora complex. They showed different levels of metal tolerance and maintained growth on metal-enriched media. In comparison to non-inoculated cuttings, the DSE-inoculated cuttings had lower leaf Cd content, and for isolates DB146 and DB148, also lower Zn concentrations. All DSE isolates increased the chlorophyll levels of the cuttings, with isolate DB146 also positively affecting the transpiration rate of S. caprea.

Conclusions

Our findings suggest that DSE reduced the metal uptake by the S. caprea cuttings, thus suggesting a beneficial role for S. caprea in metal-enriched soils.     

Effect of selenium fertilization on the accumulation of cadmium and lead in rice plants

Background and Aims

The accumulation of cadmium and lead in rice (Oryza sativa L.) grains is a potential threat to human health. In this study, the effect of selenium fertilization on the uptake and translocation of cadmium and lead in rice plants was investigated.

Methods

Rice plants were cultivated using cadmium and lead contaminated soils with selenium addition at three concentrations (0, 0.5 and 1 mg kg^?1). At maturity, plants were harvested, and element concentrations in rice tissues were analyzed by using ICP-MS.

Results

Selenium application significantly increased selenium accumulation in rice grain, and markedly decreased cadmium and lead concentrations in rice tissues. In brown rice grains, selenium application reduced cadmium concentrations by 44.4 %, but had no significant effect on lead accumulation. Selenium application significantly decreased metal mobility in soils, at 0.5 mg kg^?1 treatment, the translocation factor of cadmium and lead from soil to iron plaque decreased by 71 and 33 % respectively.

Conclusions

The mechanism of selenium mitigating of heavy metal accumulation in rice could be decreasing metal bioavailability in soil. Selenium fertilization could be an effective and feasible method to enrich selenium and reduce cadmium levels in brown rice.     

The effect of soil water status on fertiliser, topsoil and subsoil phosphorus utilisation by wheat

Background and aims

Crop phosphorus (P) content is controlled by P uptake from both banded P fertiliser and from P throughout the soil profile. These P supply factors are in turn controlled by soil, climatic and plant factors. The aim of this experiment was to measure the contribution of fertiliser, topsoil and subsoil P to wheat plants under wet and dry growing season conditions.

Methods

An isotopic tracer technique was used to measure P uptake from fertiliser at seven agricultural field sites under wet and dry growing season conditions. At three of these sites a dual isotopic technique was used to distinguish between wheat uptake of P from fertiliser, topsoil (0–15 cm) and subsoil (below 15 cm).

Results

The amount of P fertiliser used by wheat was in the order of 3–30% of the P applied and increased with increasing rainfall. Topsoil P was the most important P source, but when sufficient P was present in the subsoil, P fertiliser addition stimulated the use of subsoil P.

Conclusions

Most crop P uptake was from the topsoil, however P fertiliser banded below the seed increased plant P uptake and stimulated the use of subsoil P in one soil type in a decile 7 (above average rainfall) growing season.     

Effects of biochar amendment on root traits and contaminant availability of maize plants in a copper and arsenic impacted soil

Background and aims

Biochar has been proposed as a tool to enhance phytostabilisation of contaminated soils but little data are available to illustrate the direct effect on roots in contaminated soils. This work aimed to investigate specific root traits and to assess the effect of biochar amendment on contaminant availability.

Methods

Amendment with two different types of biochar, pine woodchip and olive tree pruning, was assessed in a rhizobox experiment with maize planted in a soil contaminated with significant levels of copper and arsenic.

Results

Amendment was found to significantly improve root traits compared to the control soil, particularly root mass density and root length density. Copper uptake to plants and ammonium sulphate extractable copper was significantly less in the biochar amended soils. Arsenic uptake and extractability varied with type of biochar used but was not considered to be the limiting factor affecting root and shoot development.

Conclusions

Root establishment in contaminated soils can be enhanced by biochar amendment but choice of biochar is key to maximising soil improvement and controlling contaminant availability.     

Mitigating zinc deficiency and achieving high grain Zn in rice through integration of soil chemistry and plant physiology research

Background

Zinc deficiency has been recognized as an important factor affecting both human health and crop production. Rice (Oryza sativa) is relevant to both concerns, as it is susceptible to soil Zn deficiency and is a staple food for some of the Zn-deficient human population. Improving the processes by which Zn moves from the soil into the plant and eventually into the edible part of the grain has the potential to mitigate problems associated with Zn deficiency in crops and humans. This review article focuses on soil- and plant-related processes affecting Zn chemistry in rice-grown soils and Zn uptake and transport in a rice plant.

Scope

This review covers advances in soil chemistry regarding the reasons for inconsistent Zn deficiency in rice soils and the limitations of soil test methods for predicting Zn response for rice. We then review advances in plant physiology related to root Zn uptake and internal Zn distribution mechanisms in rice and explore interactions between specific root processes and the soil chemistry of particular environments. We aim to provide an overview of the soil science research for plant scientists and vice versa, in order to promote and facilitate future interdisciplinary collaborations.

Conclusions

Priority research areas to fill in knowledge gaps are: 1) improving our ability to predict Zn deficiency in rice soils, 2) understanding the relationship between Zn-deficiency tolerance mechanisms and grain Zn accumulation, 3) exploring the effectiveness of root Zn uptake mechanisms in contrasting soil environments.     

Effects of magnesium deficiency on magnesium uptake activity of rice root,evaluated using <Superscript>28</Superscript> Mg as a tracer

Aims

The mechanisms underlying magnesium (Mg) uptake by plant roots remain to be fully elucidated. In particular, there is little information about the effects of Mg deficiency on Mg uptake activity. A Mg uptake kinetic study is essential for better understanding the Mg uptake system.

Methods

We performed a Mg uptake tracer experiment in rice plants using ²⁸?Mg.

Results

Mg uptake was mediated by high- and low-affinity transport systems. The K _m value of the high-affinity transport system was approximately 70 μM under Mg-deficient conditions. The Mg uptake activity was promoted by Mg deficiency, which in turn fell to the basal level after 5- min of Mg resupply. The induced uptake rate was inhibited by ionophore treatment, suggesting that an energy-dependent uptake system is enhanced by Mg deficiency.

Conclusions

The Mg uptake changes rapidly with Mg conditions in rice, as revealed by a ²⁸?Mg tracer experiment. This technique is expected to be applicable for Mg uptake analyses, particularly in mutants or other lines.

     

Relationships between serpentine soils and vegetation in a xeric inner-Alpine environment

Aims

In serpentinitic areas non-endemic plants suffer from the serpentine syndrome, due to high Ni and Mg concentrations, low nutrients and Ca/Mg ratio. We evaluated the environment-soil-vegetation relationships in a xeric inner-alpine area (NW Italy), where the inhibited pedogenesis should enhance parent material influences on vegetation.

Methods

Site conditions, topsoil properties, plant associations and species on and off serpentinite were statistically associated (51 sites).

Results

Serpentine soils had higher Mg and Ni concentrations, but did not differ from non-serpentine ones in nutrient contents. The 15 vegetation clusters often showed substrate specificity. Two components of the Canonical Analysis of Principal Coordinates, respectively related to Mg and to Ni and heat load, identified serpentine vegetation. Random Forests showed that several species were positively correlated with Ni and/or Ca/Mg or Mg, some were negatively associated with high Ni, Mg excess affected only few species. Considering only serpentine sites, nutrients and microclimate were most important.

Conclusions

Ni excess most often precludes the presence of plant species on serpentinite, while an exclusion due to Mg is rarer. Endemic species are mostly adapted to both factors. Nutrient scarcity was not specific of serpentine soils in the considered environment. Considering only serpentine sites, nutrient and microclimatic gradients drove vegetation variability.     

Interactions between root hair length and arbuscular mycorrhizal colonisation in phosphorus deficient barley (Hordeum vulgare)

Aims

Phosphorus (P) limits crop yield and P-fertilisers are frequently applied to agricultural soils. However, supplies of quality rock phosphate are diminishing. Plants have evolved mechanisms to improve P-acquisition and understanding these could improve the long-term sustainability of agriculture. Here we examined interactions between root hairs and arbuscular mycorrhizal (AM) colonisation in barley (Hordeum vulgare L.).

Methods

Barley mutants exhibiting different root hair phenotypes, wild type barley and narrowleaf plantain (Plantago lanceolata L.) were grown in the glasshouse in P-sufficient and P-deficient treatments and allowed to develop AM colonization from the natural soil community. Plants were harvested after 6 weeks growth and root hair length, AM-fungal colonisation, shoot biomass and P-accumulation measured.

Results

Under P-deficient conditions, root hair length and AM colonisation were negatively related suggesting that resources are allocated to root hairs rather than to AM fungi in response to P-deficiency. There was evidence that barley and narrowleaf plantain employed different strategies to increase P-acquisition under identical conditions, but root hairs were more effective.

Conclusions

This research suggests future barley breeding programmes should focus on maintaining or improving root hair phenotypes and that pursuing enhancements to AM associations under the prevalent agricultural conditions tested here would be ineffectual.     

Potassium release characteristics, potassium balance, and fingermillet (Eleusine coracana G.) yield sustainability in a 27- year long experiment on an Alfisol in the semi-arid tropical India

Aims

In Alfisols, potassium (K) deficiency limits productivity, as these soils are poor in K-bearing minerals such as mica. As nutrient management practices greatly influence K nutrition of crops especially in the longer term, we evaluated the effects of 27 (1978–2004) years of cropping fingermillet (Eleusine coracana G.) under different manure and mineral fertilizer treatments on K release, balance and yield sustainability on K deficient Alfisols in the semi-arid tropical region of southern India.

Methods

Fingermillet (variety: PR-202) was grown each year under rainfed conditions with 5 different nutrient management treatments: control (no amendment), 10 Mg ha^?1 farm yard manure (FYM), 10 Mg ha^?1 FYM +50 % NPK, 10 Mg ha^?1 FYM +100 % NPK and 100 % NPK. Potassium release characteristics in the soil profile were determined using 1 N boiling HNO₃ (strong extracting solution), 0.01 M HCl (medium extracting solution) and 0.01 M CaCl₂ (mild extracting solution).

Results

Continuous cropping of Alfisols for 27 years resulted in a decrease in K supplying capacity due to soil K depletion through crop K uptake. In soils without K addition, inherent soil supply could not meet the K requirement of fingermillet; thus, a negative K balance following 27 years of cropping affected K nutrition of the crop in all the treatments. As a result, the highest sustainable yield index (SYI) was observed using an integrated nutrient supply (combined application of nutrients from organic and inorganic sources), and the lowest index was obtained without K additions.

Conclusion

For balanced nutrient management in cereal production systems, K nutrition needs urgent attention in the K deficient Alfisol region of southern India. Addition of any amount of organic manures available at field level offers an alternative strategy for maintaining soil K fertility to improve and sustain crop productivity.     

Prehistoric settlement activities changed soil pH, nutrient availability, and growth of contemporary crops in Central Europe

Background and aims

How prehistoric human settlement activities have changed soil chemical properties, plant nutrition and growth of contemporary crops is a question that has not been satisfactorily addressed. The aim of this paper was to study to what extent nutrient availability in the soil, together with nutrition and growth of spring barley (Hordeum vulgare), improved on sites of former sunken buildings (cropmarks) in comparison to their surroundings (controls) 1,700 years after abandonment of the buildings.

Methods

In the Czech Republic, a unique prehistoric settlement with many sunken buildings was discovered during aerial reconnaissance from cropmarks in stands of cereals. Soil and biomass samples were collected from cropmarks and controls in a barley crop in June 2012.

Results

A substantially higher content of organic matter, higher pH and concentrations of plant-available (Mehlich III) P, Ca, Mg, Cu and Zn were recorded in the sub-soil layer in cropmarks compared with controls, indicating the accumulation of wood ash and organic waste. In the arable layer, pH and concentrations of P, Ca and Mg were generally very high in both positions. Cropmarks were characterised by barley plants that were twice as tall as the controls, with significantly higher Ca, Mg and P concentrations.

Conclusions

Prehistoric settlement activity affected nutrient availability and plant growth in the previously settled area even after 1,700 years. We conclude that the chemical signature of prehistoric settlement activity can be detected from chemical analysis of the sub-soil layer as well as analysis of the contemporary arable layer and crop biomass.     

Dynamics of plant metal uptake and metal changes in whole soil and soil particle fractions during repeated phytoextraction

Aims

Phytoextration of metal polluted soils using hyperaccumulators is a promising technology but requires long term successive cropping. This study investigated the dynamics of plant metal uptake and changes in soil metals over a long remediation time.

Methods

A soil slightly polluted with metals (S1) was mixed with highly polluted soil (S4) to give two intermediate pollution levels (S2, S3). The four resulting soils were repeatedly phyto-extracted using nine successive crops of Cd/Zn-hyperaccumulator Sedum plumbizincicola over a period of 4 years.

Results

Shoot Cd concentration decreased with harvest time in all soils but shoot Zn declined in S1 only. Similar shoot Zn concentrations were found in S2, S3 and S4 although these soils differed markedly in metal availability, and their available metals decreased during phytoextraction. A possible explanation is that plant active acquisition ability served to maintain plant metal uptake. Plant uptake resulted in the largest decrease in the acid-soluble metal fraction followed by reducible metals. Oxidisable and residual fractions were less available to plants. The coarse soil particle fractions made the major contribution to metal decline overall than the fine fractions.

Conclusion

Sedum plumbizincicola maintained long term metal uptake and the coarse soil particles played the most important role in phytoextraction.