Aluminum, a Friend or Foe of Higher Plants in Acid Soils

Effects of acid and aluminum stress on seed germination and physiological characteristics of seedling growth in Sophora davidii

Sophora davidii, a vital forage species, predominantly thrives in the subtropical karst mountains of Southwest China. Its resilience to poor soil conditions and arid environments renders it an ideal pioneer species for ecological restoration in these regions. This study investigates the influence of acidic, aluminum-rich local soil on the germination and seedling growth physiology of S. davidii. Experiments were conducted under varying degrees of acidity and aluminum stress, employing three pH levels (3.5 to 5.5) and four aluminum concentrations (0.5 to 2.0 mmol·L-1). The results showed that germination rate, germination index, and vigor index of S. davidii seeds were decreased but not significantly under slightly acidic conditions (pH 4.5-5.5), while strong acid (pH = 3.5) significantly inhibited the germination rate, germination index, and vigor index of white spurge seeds compared with the control group. Aluminum stress (≥0.5 mmol·L-1) significantly inhibited the germination rate, germination index, and vigor index of S. davidii seed. Moreover, the seedlings' root systems were sensitive to the changes of aluminum concentration, evident from significant root growth inhibition, characterized by root shortening and color deepening. Notably, under aluminum stress (pH = 4.3), the levels of malondialdehyde and proline in S. davidii escalated with increasing aluminum concentration, while antioxidant enzyme activities demonstrated an initial increase followed by a decline. The study underscores the pivotal role of cellular osmoregulatory substances and protective enzymes in combating aluminum toxicity in S. davidii, a key factor exacerbating growth inhibition in acidic environments. These findings offer preliminary theoretical insights for the practical agricultural utilization of S. davidii in challenging soil conditions.

Fluorescent and colorimetric dual-mode recognition of Al3+ in tablets based on chrome azurol S and pH-switchable boron, nitrogen co-doped carbon dots

The synthesis and characterization of pH-sensitive boron and nitrogen co-doped CDs (B, N-CDs) is reported. The fluorescence of B, N-CDs exhibited pH-responsive behavior within the range pH 3.0-6.0, attributed to their controlled aggregation and disaggregation. Interestingly, the fluorescence of B, N-CDs was quenched by the inner filter effect from chrome azurol S (CAS). With the subsequent addition of Al3+, the fluorescence of B, N-CDs was restored due to the formation of blue Al3+-CAS and B, N-CDs-Al3+ complexes. Consequently, a fluorescent and colorimetric dual-mode sensor for Al3+ detection was developed. The proposed sensor enabled Al3+ detection in the ranges and limits of detection of 3.75-22.5 μM and 2.67 μM for the fluorescent mode and 5-20 μM and 4.8 μM for the colorimetric mode, respectively. Furthermore, the efficacy of the sensor was validated through successful detection of Al3+ in tablet samples. The obtained B, N-CDs promised the application in acid condition and the proposed sensor is expected to be applied to in situ on-line detection of Al3+.

Potential protection of resveratrol-tempeh against nephrotoxic and hepatotoxic histological damage in mice induced by aluminum

Aluminum is a widely distributed metal that, while generally safe at low levels, can become toxic when accumulated in the body. Its exposure is daily through various sources, including food, water, and medications. High levels of aluminum have been shown to adversely affect the kidneys and liver, leading to significant organ damage. Resveratrol-tempeh is a safe protective agent against organ damage caused by aluminum. Here, we investigated the impact of resveratrol on liver and kidney toxicity and Al-induced levels of catalase and malondialdehyde. The mice group was the control group, Al-group, Al+REST5-group, and Al+REST10-group. Aluminum and resveratrol were administered intraperitoneally to mice for four weeks, but resveratrol was administered one hour after exposure to aluminum. Mice were killed by cervical dislocation; the liver and kidney were isolated for slide, and the level of an antioxidant enzyme of catalase and oxidant of malondialdehyde was measured. The results showed that administration of aluminum at a dose of 200 mg/kg body weight caused glomerular shrinkage and proximal tubule degeneration in the kidneys. In addition, it also caused liver tissue damage, with hepatocytes undergoing degeneration, sinusoids dilating, and decreased body weight in the mice. Administration of resveratrol-tempeh tended to decrease malondialdehyde levels and increase catalase activity, although the changes were not significant. It seems that resveratrol-tempeh can repair liver and kidney damage and restore them to normal conditions. Conclusion: Aluminum at 200 mg/kg is toxic to mice. Resveratrol-tempeh can be considered a potential candidate to protect kidney and liver damage caused by aluminum chloride toxicity.

Physiological alterations and genotoxic damage under combined aluminum and cadmium treatments in Bryophyllum daigremontianum clones

BACKGROUND

Cadmium (Cd) is one of the most important stress factors in plants, with its high mobility in soils, ease of uptake by plants and toxicity at low concentrations. Aluminum (Al) is another phytotoxic metal, the accumulation of which is a crucial agricultural complication for plants, especially in acidic soils.

METHODS AND RESULTS

In this study, Bryophyllum daigremontianum clone plantlets were obtained from bulbiferous spurs of a mother plant and separated into four different groups and watered with Hoagland solution and mixtures containing 0, 50, 100, and 200 µM of AlCl3 and CdCl2 each for 75 days. Control groups were maintained under the same conditions without Al and Cd treatment. To simulate acidic soil conditions typical of environments where Al toxicity is prevalent, the soil pH was adjusted to 4.5 by spraying the sulphuric acid (0.2%) with 2-day intervals after each irrigation day. After harvesting, growth parameters such as shoot length and thickness, root, shoot and leaf fresh and dry weights were measured, along with physiological parameters like mineral nutrient status, total protein, and photosynthetic pigment concentrations (chlorophyll a, b, a/b, total chlorophyll, and carotenoid) in both control and experimental groups of B. daigremontianum clones. In response to Al and Cd applications, the plant height, shoot thickness and carotenoid levels were declined, whereas the increments were found in leaf/shoot/root fresh weight, root dry weight, and total protein content. Moreover, differences in genomic alterations were investigated using 21 ISSR and 19 RAPD markers, which both have been used extensively as genetic markers to specify phylogenetic relationships among different cultivars as well as stress-dependent genetic alterations. RAPD primers were used due to their arbitrary sequences and the unknown genome sequence of the plant material used. In contrast, ISSR primers were preferred for a genome-wide genotoxic effect scan via non-arbitrary and more common genetic markers. Distinct types of band polymorphisms detected via RAPD and ISSR markers include band loss, and new band formation under a combination of Al and Cd stress. 17 ISSR and 14 RAPD primers generated clear electrophoretic bands.

CONCLUSION

The study revealed that combined application of Al and Cd affect B. daigremontianum clones in terms of growth, physiology and genotoxicity related to the increasing concentrations.

Calibrated SoilOptix ® estimates of soil pH and exchangeable cations in three agricultural fields in western Canada - implications for managing spatially variable soil acidity

Spatial variability in soil pH is a major contributor to within-field variations in soil fertility and crop productivity. An improved understanding of the spatial variability of soil pH within agricultural fields is required to determine liming requirements for precision farming. This study with the use of proximal sensors, firstly assessed the spatial pattern of soil pH and how it can be used to determine site-specific, spatially variable lime requirements. Secondly, the effects of soil pH on soil concentrations of nitrate nitrogen (N03-N), phosphorus (P), potassium (K), sulfur (SO4-S), calcium (Ca), magnesium (Mg), soil organic matter (SOM), aluminum (Al), and manganese (Mn) were assessed in three study fields in central Alberta, Canada. Soil pH varied between 4.5 and 7.5 across all field sites. The field-scale coefficient of variation (CV %) for soil pH, Al and Mn ranged between 4.39 and 7.50 %, 7.33-13.72 %, and 7.33-13.72 % across the three sites. The other soil properties showed low, moderate, and high variability, with field-scale CVs ranging between 6.39 and 17.70 % for SOM and 24.33-91.39 % for SO4-S. Soil pH exhibited positive correlations with both Ca and Mg, across all fields. Negative correlations were observed between soil pH and Al across all fields. A principal component analysis (PCA) was performed for all soil parameters and two principal components accounted for 50 %, 54.9 %, and 76.8 % of the total variance in field 1, field 2, and field 3, respectively. Geostatistical semivariance indicated a strong spatial dependence of all chemical parameters across fields. Large regions within a field were strongly acidic (pH < 5.5) and required lime applications ranging from 0 to 6 t ha-1. We conclude that proximal soil sensors can be calibrated to soil properties, enabling variable rate lime recommendations on spatially variable fields for the management of soil acidity.

Both hormones and energy-rich compounds play a role in the mitigation of elevated pH on aluminum toxicity in Citrus sinensis leaves

The contribution of plant hormones and energy-rich compounds and their metabolites (ECMs) in alleviating aluminum (Al) toxicity by elevated pH remains to be clarified. For the first time, a targeted metabolome was applied to identify Al-pH-interaction-responsive hormones and ECMs in Citrus sinensis leaves. More Al-toxicity-responsive hormones and ECMs were identified at pH 4.0 [4 (10) upregulated and 7 (17) downregulated hormones (ECMs)] than those at pH 3.0 [1 (9) upregulated and 4 (14) downregulated hormones (ECMs)], suggesting that the elevated pH improved the adaptation of hormones and ECMs to Al toxicity in leaves. The roles of hormones and ECMs in reducing leaf Al toxicity mediated by elevated pH might include the following aspects: (a) improved leaf growth by upregulating the levels of jasmonoyl-L-isoleucine (JA-ILE), 6-benzyladenosine (BAPR), N6-isopentenyladenosine (IPR), cis-zeatin-O-glucoside riboside (cZROG), and auxins (AUXs), preventing Al toxicity-induced reduction of gibberellin (GA) biosynthesis, and avoiding jasmonic acid (JA)-mediated defense; (b) enhanced biosynthesis and accumulation of tryptophan (TRP), as well as the resulting increase in biosynthesis of auxin, melatonin and secondary metabolites (SMs); (c) improved ability to maintain the homeostasis of ATP and other phosphorus (P)-containing ECMs; and (d) enhanced internal detoxification of Al due to increased organic acid (OA) and SM accumulation and elevated ability to detoxify reactive oxygen species (ROS) due to enhanced SM accumulation. To conclude, the current results corroborate the hypotheses that elevated pH reduces Al toxicity by upregulating the ability to maintain the homeostasis of ATP and other P-containing ECMs in leaves under Al toxicity and (b) hormones participate in the elevated pH-mediated alleviation of Al toxicity by positively regulating growth, the ability to detoxify ROS, and the internal detoxification of Al in leaves under Al toxicity. Our findings provide novel insights into the roles of hormones and ECMs in mitigating Al toxicity mediated by the elevated pH.

Role of cotyledons in aluminium accumulation as a tolerance strategy in Fagopyrum esculentum Moench (Polygonaceae) seedlings

Acidic soils have increased due to agricultural practices, climate factors, and the excessive use of nitrogen fertilizers to meet food demand. In these soils, aluminium (Al) is soluble and can be taken up by roots, but it is toxic to most plant species. Fagopyrum esculentum is able to adapt to acidic toxic aluminium conditions. Anatomical studies identifying novel potential cellular structures as sites of Al accumulation are currently lacking. This study provides an anatomical description of the cotyledons, revealing the presence of papillae and glandular trichomes at their margins. In seedlings treated with 100 μM Al, energy-dispersive x-ray spectroscopy (ESEM-EDS) analysis of the cotyledons revealed that the margin has the highest concentration of Al. The margin containing the epidermal papillae was subjected to laser microdissection, and Al was quantified using mass spectrometry with an inductively coupled plasma source ICP-MS and compared with the Al in the remaining leaf blades. The concentration of Al in the microdissected papillae was 3,460 mg Al kg-1 Dry Weight (DW), whereas the blades contained only 1,390 mg Al kg-1 DW. Moreover, histochemical tests for Al and total phenols in the epidermal papillae revealed that Al may be bound to phenolic compounds. Thus, this study demonstrated that the cotyledons of F. esculentum have epidermal papillae that can accumulate Al.

Systematic Investigation of Aluminum Stress-Related Genes and Their Critical Roles in Plants

Aluminum (Al) stress is a dominant obstacle for plant growth in acidic soil, which accounts for approximately 40-50% of the world's potential arable land. The identification and characterization of Al stress response (Al-SR) genes in Arabidopsis, rice, and other plants have deepened our understanding of Al's molecular mechanisms. However, as a crop sensitive to acidic soil, only eight Al-SR genes have been identified and functionally characterized in maize. In this review, we summarize the Al-SR genes in plants, including their classifications, subcellular localizations, expression organs, functions, and primarily molecular regulatory networks. Moreover, we predict 166 putative Al-SR genes in maize based on orthologue analyses, facilitating a comprehensive understanding of the impact of Al stress on maize growth and development. Finally, we highlight the potential applications of alleviating Al toxicity in crop production. This review deepens our understanding of the Al response in plants and provides a blueprint for alleviating Al toxicity in crop production.

How tree species have modified the potentially toxic elements distributed in the developed soil-plant system in a post-fire site in highly industrialized region

The biogeochemical cycles of trace elements are changed by fire as a result of the mineralization of organic matter. Monitoring the accumulation of trace elements in both the environment and the tree biomass during the post-fire (PF) forest ecosystem regeneration process is important for tree species selection for reforestation in ecosystems under anthropogenic pressure. We analyzed the soil concentrations of different groups of potentially toxic elements (PTEs), including beneficial (Al), toxic (Cd, Cr, Pb), and microelements (Cu, Mn, Ni, Zn), and their bioaccumulation in the tree species (Pinus sylvestris, Betula pendula, Alnus glutinosa) biomass introduced after a fire in a forest weakened by long-term emissions of industrial pollutants. The results indicated no direct threat from the PTEs tested at the PF site. The tree species introduced 30 years ago may have modified the biogeochemical cycles of the PTEs through different strategies of bioaccumulation in the belowground and aboveground biomass. Alder had relatively high Al concentrations in the roots and a low translocation factor (TF). Pine and birch had lower Al concentrations in the roots and higher TFs. Foliage concentrations and the TF of Cd increased from alder to pine to birch. However, the highest concentration and bioaccumulation factor of Cd was found in the alder roots. The concentrations of Cr in the foliage and the Cr TFs in the studied species increased from pine to birch to alder. Higher concentrations of Cu and Ni were found in the foliage of birch and alder than of pine. Among the species, birch also had the highest Pb and Zn concentrations in the roots and foliage. We found that different tree species had different patterns of PTE phytostabilization and ways they incorporated these elements into the biological cycle, and these patterns were not dependent on fire disturbance. This suggests that similar patterns might also occur in more polluted soils. Therefore, species-dependent bioaccumulation patterns could also be used to design phytostabilization and remediation treatments for polluted sites under industrial pressure.

Effects of copper, and aluminium in ionic, and nanoparticulate form on growth rate and gene expression of Setaria italica seedlings

This study aims to determine the effects of copper, copper oxide nanoparticles, aluminium, and aluminium oxide nanoparticles on the growth rate and expression of ACT-1, CDPK, LIP, NFC, P5CR, P5CS, GR, and SiZIP1 genes in five days old seedling of Setaria italica ssp. maxima, cultivated in hydroponic culture. Depending on their concentration (ranging from 0.1 to 1.8 mg L-1), all tested substances had both stimulating and inhibiting effects on the growth rate of the seedlings. Copper and copper oxide-NPs had generally a stimulating effect whereas aluminium and aluminium oxide-NPs at first had a positive effect but in higher concentrations they inhibited the growth. Treating the seedlings with 0.4 mg L-1 of each tested toxicant was mostly stimulating to the expression of the genes and reduced the differences between the transcript levels of the coleoptiles and roots. Increasing concentrations of the tested substances had both stimulating and inhibiting effects on the expression levels of the genes. The highest expression levels were usually noted at concentrations between 0.4 and 1.0 mg/L of each metal and metal nanoparticle, except for SiZIP1, which had the highest transcript amount at 1.6 mg L-1 of Cu2+ and at 0.1-0.8 mg L-1 of CuO-NPs, and LIP and GR from the seedling treated with Al2O3-NPs at concentrations of 0.1 and 1.6 mg L-1, respectively.

Guidelines for efficient nitrogen preservation in sewage sludge-based fertilizers

This study explores sustainable methods to mitigate nitrogen (N) loss in agriculture amid rising food demands and limited arable land. It examines sewage sludge (SS) as an alternative to synthetic N fertilizers. SS is rich in nitrogen (4.21 ± 0.42 %) and phosphorus (3.60 ± 0.72 %), making it suitable for nutrient recovery and soil enhancement. Unfavorable sludge management methods result in the loss of 950,000 tons of nitrogen, meeting almost 10 % of the EU's nitrogen fertilization demand. This research evaluates SS treatment methods, including chemical conversion, thermal treatment, and biological composting, focusing on nitrogen conservation efficiency. Results show nitrogen loss during hydrolysis is minimized at pH 4 to 8 but increases significantly as ammonia (NH3) at pH 9 to 11, ranging from 4.2 % to 9 %. Neutralizing the hydrolysate is crucial; using solid KOH resulted in 13.5 % nitrogen loss, 11 times more than using slightly alkaline ash (1.22 %). Adding ash during drying reduced nitrogen emissions by 30 % compared to traditional drying at 105 °C. Improving the C/N ratio with food residues reduced nitrogen losses by 46.3 % during composting. These findings highlight the importance of pH control in chemical processes and temperature regulation in thermal treatments. Adding residues from other processes, such as biomass combustion waste, enhances SS processing conditions. Understanding nitrogen retention mechanisms is crucial for the environmental sustainability of SS usage. Efficient nitrogen retention strategies improve the fertilization value of SS and reduce its environmental footprint by lowering greenhouse gas emissions, particularly ammonia. Reducing nitrogen loss during SS treatment significantly lowers ammonia emissions, a major contributor to greenhouse gas emissions. These results help determine optimal methods for managing and processing SS to minimize emissions and increase agricultural usability.

Mitigating salt stress by conditioning seeds with ultraviolet light (UV-C) in white oats (Avena sativa L.)

Seed conditioning with ultraviolet light (UV-C) might (1) improve crop yield and quality, (2) reduce the use of agrochemicals during cultivation, and (3) increase plant survival in high salinity environments. The aim of this study was to examine the effects of UV-C conditioning of white oat seeds at two doses (0.85 and 3.42 kJ m-2) under salinity stress (100 mM NaCl). Seeds were sown on germination paper and kept in a germination chamber at 20°C. Germination and seedling growth parameters were evaluated after 5 and 10 days. Data demonstrated that excess salt reduced germination and initial growth of white oat seedlings. In all the variables analyzed, exposure of seeds to UV-C under salt stress exerted a positive effect compared to non-irradiated control. The attenuating influence of UV-C in germination was greater at 0.85 than at 3.42 kJ m-2. Thus, data indicate that conditioning white oat seeds in UV-C light produced greater tolerance to salt stress. These findings suggest that UV-C conditioning of white oat seeds may be considered as a simple and economical strategy to alleviate salt-induced stress.

Quantifying aluminum toxicity effects on corn phenotype using advanced imaging technologies

Soil acidity (pH <5.5) limits agricultural production due to aluminum (Al) toxicity. The primary target of Al toxicity is the plant root. However, symptoms can be observed on the shoots. This study aims to determine the potential use of chlorophyll fluorescence imaging, multispectral imaging, and 3D multispectral scanning technology to quantify the effects of Al toxicity on corn. Corn seedlings were grown for 13 days in nutrient solutions (pH 4.0) with four Al treatments: 50, 100, 200, and 400 μM and a control (0 μM AlCl3 L-1). During the experiment, four measurements were performed: four (MT1), six (MT2), 11 (MT3), and 13 (MT4) days after the application of Al treatments. The most sensitive traits affected by Al toxicity were the reduction of plant growth and increased reflectance in the visible wavelength (affected at MT1). The reflectance of red wavelengths increased more significantly compared to near-infrared and green wavelengths, leading to a decrease in the normalized difference vegetation index and the Green Leaf Index. The most sensitive chlorophyll fluorescence traits, effective quantum yield of PSII, and photochemical quenching coefficient were affected after prolonged Al exposure (MT3). This study demonstrates the usability of selected phenotypic traits in remote sensing studies to map Al-toxic soils and in high-throughput phenotyping studies to screen Al-tolerant genotypes.

OsAlR3 regulates aluminum tolerance through promoting the secretion of organic acids and the expression of antioxidant genes in rice

In acidic soils, aluminum (Al) toxicity inhibits the growth and development of plant roots and affects nutrient and water absorption, leading to reduced yield and quality. Therefore, it is crucial to investigate and identify candidate genes for Al tolerance and elucidate their physiological and molecular mechanisms under Al stress. In this study, we identified a new gene OsAlR3 regulating Al tolerance, and analyzed its mechanism from physiological, transcriptional and metabolic levels. Compared with the WT, malondialdehyde (MDA) and hydrogen peroxide (H2O2) content were significantly increased, superoxide dismutase (SOD) activity and citric acid (CA) content were significantly decreased in the osalr3 mutant lines when exposed to Al stress. Under Al stress, the osalr3 exhibited decreased expression of antioxidant-related genes and lower organic acid content compared with WT. Integrated transcriptome and metabolome analysis showed the phenylpropanoid biosynthetic pathway plays an important role in OsAlR3-mediated Al tolerance. Exogenous CA and oxalic acid (OA) could increase total root length and enhance the antioxidant capacity in the mutant lines under Al stress. Conclusively, we found a new gene OsAlR3 that positively regulates Al tolerance by promoting the chelation of Al ions through the secretion of organic acids, and increasing the expression of antioxidant genes.

The Stylo Cysteine-Rich Peptide SgSnakin1 Is Involved in Aluminum Tolerance through Enhancing Reactive Oxygen Species Scavenging

Stylo (Stylosanthes spp.) is an important pasture legume with strong aluminum (Al) resistance. However, the molecular mechanisms underlying its Al tolerance remain fragmentary. Due to the incomplete genome sequence information of stylo, we first conducted full-length transcriptome sequencing for stylo root tips treated with and without Al and identified three Snakin/GASA genes, namely, SgSnakin1, SgSnakin2, and SgSnakin3. Through quantitative RT-PCR, we found that only SgSnakin1 was significantly upregulated by Al treatments in stylo root tips. Histochemical localization assays further verified the Al-enhanced expression of SgSnakin1 in stylo root tips. Subcellular localization in both tobacco and onion epidermis cells showed that SgSnakin1 localized to the cell wall. Overexpression of SgSnakin1 conferred Al tolerance in transgenic Arabidopsis, as reflected by higher relative root growth and cell vitality, as well as lower Al concentration in the roots of transgenic plants. Additionally, overexpression of SgSnakin1 increased the activities of SOD and POD and decreased the levels of O2·- and H2O2 in transgenic Arabidopsis in response to Al stress. These findings indicate that SgSnakin1 may function in Al resistance by enhancing the scavenging of reactive oxygen species through the regulation of antioxidant enzyme activities.

The Physiological Response Mechanism of Peanut Leaves under Al Stress

Aluminum (Al) toxicity in acidic soils can significantly reduce peanut yield. The physiological response of peanut leaves to Al poisoning stress still has not been fully explored. This research examined the influences of Al toxicity on peanut leaves by observing the leaf phenotype, scanning the leaf area and perimeter, and by measuring photosynthetic pigment content, physiological response indices, leaf hormone levels, and mineral element accumulation. Fluorescence quantitative RT-PCR (qPCR) was utilized to determine the relative transcript level of specific genes. The results indicated that Al toxicity hindered peanut leaf development, reducing their biomass, surface area, and perimeter, although the decrease in photosynthetic pigment content was minimal. Al toxicity notably affected the activity of antioxidative enzymes, proline content, and MDA (malondialdehyde) levels in the leaves. Additionally, Al poisoning resulted in the increased accumulation of iron (Fe), potassium (K), and Al in peanut leaves but reduced the levels of calcium (Ca), manganese (Mn), copper (Cu), zinc (Zn), and magnesium (Mg). There were significant changes in the content of hormones and the expression level of genes connected with hormones in peanut leaves. High Al concentrations may activate cellular defense mechanisms, enhancing antioxidative activity to mitigate excess reactive oxygen species (ROS) and affecting hormone-related gene expression, which may impede leaf biomass and development. This research aimed to elucidate the physiological response mechanisms of peanut leaves to Al poisoning stress, providing insights for breeding new varieties resistant to Al poisoning.

Soil organic matter and total nitrogen as key driving factors promoting the assessment of acid-base buffering characteristics in a tea (Camellia sinensis) plantation habitat

The issue of soil acidification in tea plantations has become a critical concern due to its potential impact on tea quality and plant health. Understanding the factors contributing to soil acidification is essential for implementing effective soil management strategies in tea-growing regions. In this study, a field study was conducted to investigate the effects of tea plantations on soil acidification and the associated acid-base buffering capacity (pHBC). We assessed acidification, pHBC, nutrient concentrations, and cation contents in the top 0-20 cm layer of soil across forty tea gardens of varying stand ages (0-5, 5-10, 10-20, and 20-40 years old) in Anji County, Zhejiang Province, China. The results revealed evident soil acidification due to tea plantation activities, with the lowest soil pH observed in tea gardens aged 10-20 and 20-40 years. Higher levels of soil organic matter (SOM), total nitrogen (TN), Olsen phosphorus (Olsen-P), available iron (Fe), and exchangeable hydrogen (H+) were notably recorded in 10-20 and 20-40 years old tea garden soils, suggesting an increased risk of soil acidification with prolonged tea cultivation. Furthermore, prolonged tea cultivation correlated with increased pHBC, which amplified with tea stand ages. The investigation of the relationship between soil pHBC and various parameters highlighted significant influences from soil pH, SOM, cation exchange capacity, TN, available potassium, Olsen-P, exchangeable acids (including H+ and aluminum), available Fe, and available zinc. Consequently, these findings underscore a substantial risk of soil acidification in tea gardens within the monitored region, with SOM and TN content being key driving factors influencing pHBC.

Exogenous silicon induces aluminum tolerance in white clover (Trifolium repens) by reducing aluminum uptake and enhancing organic acid secretion

Excessive aluminum (Al) in acidic soils is a primary factor that hinders plant growth. The objective of the present study was to investigate the effect and physiological mechanism of exogenous silicon (Si) in alleviating aluminum toxicity. Under hydroponic conditions, 4 mM Al significantly impeded the growth of white clover; however, pretreatments with 1 mM Si mitigated this inhibition, as evidenced by notable changes in growth indicators and physiological parameters. Exogenous silicon notably increased both shoot and root length of white clover and significantly decreased electrolyte leakage (EL) and malondialdehyde (MDA) content compared to aluminum treatments. This positive effect was particularly evident in the roots. Further analysis involving hematoxylin staining, scanning electron microscopy (SEM), and examination of organic acids (OAs) demonstrated that silicon relieved the accumulation of bioactive aluminum and ameliorated damage to root tissues in aluminum-stressed plants. Additionally, energy-dispersive X-ray (EDX) analysis revealed that additional silicon was primarily distributed in the root epidermal and cortical layers, effectively reducing the transport of aluminum and maintaining the balance of exchangeable cations absorption. These findings suggest that gradual silicon deposition in root tissues effectively prevents the absorption of biologically active aluminum, thereby reducing the risk of mineral nutrient deficiencies induced by aluminum stress, promoting organic acids exudation, and compartmentalizing aluminum in the outer layer of root tissues. This mechanism helps white clover alleviate the damage caused by aluminum toxicity.

Low levels of Al stimulate the aboveground growth of Davidia involucrata saplings

Davidia involucrata is a woody perennial and the only living species in the Genus Davidia. It is native to southern China where it holds cultural and scientific importance. However, D. involucrata is now an endangered species and its natural range includes low pH soils which are increasingly impacted by acid rain, nitrogen deposition and imbalanced nutrient cycling. The combination of these stresses also poses the additional risk of aluminum (Al) toxicity. Since the responses of D. involucrata to low pH and aluminum toxicity have not been investigated previously, a hydroponic experiment was conducted to examine the growth of one year old D. involucrata saplings after 50 d growth in a range of pH and Al conditions. Plant biomass, morphology, antioxidant enzyme activity, mineral concentrations and plant ecological strategy were compared at pH 5.8 and pH 4.0 without added Al (AlCl3) and in 0.1, 0.2 and 0.5 mM Al at pH 4.0. Our results showed that compared with pH 5.8, pH 4.0 (without added Al) not only inhibited root and shoot growth but also limited accumulation of nitrogen (N) and phosphorus (P) in leaves of D. involucrate. However, low Al concentrations (0.1 and 0.2 mM Al) at pH 4.0 partially restored the aboveground growth and leaf N concentrations, suggesting an alleviation of H+ toxicity by low Al concentrations. Compared with low Al concentrations, 0.5 mM Al treatment decreased plant growth and concentrations of N, P, and magnesium (Mg) in the leaves, which demonstrated the toxicity of high Al concentration. The results based on plant ecological strategy showed that D. involucrate decreased the competitiveness and favored its stress tolerance as pH changed from 5.8 to 4.0. Meanwhile, the competitiveness and stress tolerance of D. involucrata increased and decreased at low Al concentrations, respectively, and decreased and increased at high Al concentration, respectively. These trade-offs in ecological strategy were consistent with the responses of growth and antioxidant enzyme activity, reflecting a sensitive adaptation of D. involucrata to acid and Al stresses, which may aid in sustaining population dynamics. These findings are meaningful for understanding the population dynamics of D. involucrata in response to aluminum toxicity in acid soils.

Aluminium tolerance and stomata operation: Towards optimising crop performance in acid soil

Stomatal operation is crucial for optimising plant water and gas exchange and represents a major trait conferring abiotic stress tolerance in plants. About 56% of agricultural land around the globe is classified as acidic, and Al toxicity is a major limiting factor affecting plant performance in such soils. While most of the research work in the field discusses the impact of major abiotic stresses such as drought or salinity on stomatal operation, the impact of toxic metals and, specifically aluminium (Al) on stomatal operation receives much less attention. We aim to fill this knowledge gap by summarizing the current knowledge of the adverse effects of acid soils on plant stomatal development and operation. We summarised the knowledge of stomatal responses to both long-term and transient Al exposure, explored molecular mechanisms underlying plant adaptations to Al toxicity, and elucidated regulatory networks that alleviate Al toxicity. It is shown that Al-induced stomatal closure involves regulations of core stomatal signalling components, such as ROS, NO, and CO2 and key elements of ABA signalling. We also discuss possible targets and pathway to modify stomatal operation in plants grown in acid soils thus reducing the impact of Al toxicity on plant growth and yield.

Investigating aluminum toxicity effects on callose deposition, oxidative stress, and nutrient homeostasis in banana genotypes

Aluminum (Al) toxicity poses a significant challenge to agricultural productivity, particularly in acidic soils. The banana crop, predominantly cultivated in tropical and subtropical climates, often grapples with low pH and Al toxicity. This study seeks to explore the differential responses of two banana genotypes with varying Al tolerance (Baodao and Baxi) to Al exposure (100 and 500 µM) for 24 h. Microscopic analysis uncovered distinctive structural modifications in root cells, with Baodao displaying more severe alterations in response to Al stress. There was higher superoxide (O2-.) and hydrogen peroxide (H2O2) production and lipid peroxidation in Baodao indicating enhanced oxidative stress and membrane damage. Al accumulation in root tips was higher in Baxi than Baodao, while the roots of Baodao had a higher accumulation of callose. Nutrient content analysis revealed alterations in ion levels, highlighting the impact of Al exposure on nutrient uptake and homeostasis. In summary, Al differentially affects callose deposition, which, in turn, leads to Al uptake and nutrient homeostasis alteration in two contrasting banana genotypes. This intricate interplay is a key factor in understanding plant responses to aluminum toxicity and can inform strategies for crop improvement and soil management in aluminum-stressed environments.

Unveiling a Technosol-based remediation approach for enhancing plant growth in an iron-rich acidic mine soil from the Rio Tinto Mars analog site

This paper explores the potential of Technosols made from non-hazardous industrial wastes as a sustainable solution for highly acidic iron-rich soils at the Rio Tinto mining site (Spain), a terrestrial Mars analog. These mine soils exhibit extreme acidity (pHH2O = 2.1-3.0), low nutrient availability (non-acid cation saturation < 20 %), and high levels of Pb (3420 mg kg-1), Cu (504 mg kg-1), Zn (415 mg kg-1), and As (319 mg kg-1), hindering plant growth and ecosystem restoration. To address these challenges, the study systematically analyzed selected waste materials, formulated them into Technosols, and conducted a four-month pot trial to evaluate the growth of Brassica juncea under greenhouse conditions. Technosols were tailored by adding varying weight percentages of waste amendments into the mine Technosol, specifically 10 %, 25 %, and 50 %. The waste amendments comprised a blend of organic waste (water clarification sludge, WCS) and inorganic wastes (white steel slag, WSS; and furnace iron slag, FIS). The formulations included: (T0) exclusively mine Technosol (control); (T1) 60 % WCS + 40 % WSS; (T2) 60 % WCS + 40 % FIS; and (T3) 50 % WCS + 16.66 % WSS + 33.33 % FIS. The analyses covered leachate quality, soil pore water chemistry, and plant response (germination and survival rates, plant height, and leaf number). Results revealed a significant reduction in leachable contaminant concentrations, with Pb (26.16 mg kg-1), Zn (4.94 mg kg-1), and Cu (2.29 mg kg-1) dropping to negligible levels and shifting towards less toxic species. These changes improved soil conditions, promoting seed germination and seedling growth. Among the formulations tested, Technosol T1 showed promise in overcoming mine soil limitations, enhancing plant adaptation, buffering against acidification, and stabilizing contaminants through precipitation and adsorption mechanisms. The paper stresses the importance of tailoring waste amendments to specific soil conditions, and highlights the broader implications of the Technosol approach, such as waste valorization, soil stabilization, and insights for Brassica juncea growth in extreme environments, including Martian soil simulants.

Supplemental Silicon and Boron Alleviates Aluminum-Induced Oxidative Damage in Soybean Roots

Aluminum (Al) toxicity in acidic soils is a major abiotic stress that negatively impacts plant growth and development. The toxic effects of Al manifest primarily in the root system, leading to inhibited root elongation and functionality, which impairs the above-ground organs of the plant. Recent research has greatly improved our understanding of the applications of small molecule compounds in alleviating Al toxicity. This study aimed to investigate the role of boron (B), silicon (Si), and their combination in alleviating Al toxicity in soybeans. The results revealed that the combined application significantly improved the biomass and length of soybean roots exposed to Al toxicity compared to B and Si treatments alone. Our results also indicated that Al toxicity causes programmed cell death (PCD) in soybean roots, while B, Si, and their combination all alleviated the PCD induced by Al toxicity. The oxidative damage induced by Al toxicity was noticeably alleviated, as evidenced by lower MAD and H2O2 accumulation in the soybean roots treated with the B and Si combination. Moreover, B, Si, and combined B and Si significantly enhanced plant antioxidant systems by up-regulating antioxidant enzymes including CAT, POD, APX, and SOD. Overall, supplementation with B, Si, and their combination was found to alleviate oxidative damage and reduce PCD caused by Al toxicity, which may be one of the mechanisms by which they alleviate root growth inhibition due to Al toxicity. Our results suggest that supplementation with B, Si, and their combination may be an effective strategy to improve soybean growth and productivity against Al toxicity.

Characterization of mineral composition of leaves and flowers of wild-growing Sambucus nigra

The objective of this study was to determine the mineral content in the leaves and flowers of wild-grown Sambucus nigra collected from eleven different locations in Kosovo. The samples were digested in a microwave system using the wet digestion method. The minerals were determined by the application of inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS). A total of 31 elements were determined, 15 elements by the ICP-AES method (Al, B, Ba, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, P, Sr, V, and Zn) and 16 elements by the ICP-MS method (Ag, As, Be, Bi, Cd, Co, Cs, Ga, Hg, In, Li, Ni, Pb, Rb, Tl, and U). The leaves of S. nigra show a higher content of minerals compared to the flowers, except for the flower of the sample SN-FL10, which is characterized by a high concentration of Fe, Al, Pb, Be, and Tl. The concentration of heavy metals and toxic elements (Pb, Cd, and Hg) was within the permissible concentrations according to Eur. Ph.

Silicon attenuates aluminum toxicity in sugarcane plants by modifying growth, roots morphoanatomy, photosynthetic pigments, and gas exchange parameters

Aluminum (Al) inhibits growth and limits plant productivity in acidic soils. An important strategy to increase Al tolerance is the use of silicon (Si) nutrition. Thus, the aim of this study was to evaluate the interactive role of Si in increasing the growth, physiological and morphoanatomy responses of sugarcane plants under Al toxicity. A 4 × 2 factorial scheme in a completely randomized design was used to study the impact of Si (2 mM) on attenuating Al toxicity (0, 10, 15 and 20 mg L-1, as Al2(SO4)3·18H2O) in sugarcane seedlings. After 45 days, Al toxicity affected sugarcane growth by increasing Al uptake and accumulation, modifying root growth, thickness, and morphoanatomy, and decreasing pigment content, gas exchange parameters, and the number of adaxial and abaxial stomata. However, Si attenuated Al toxicity in the sugarcane seedlings by limiting Al uptake and transport to the shoots, causing positive changes in root morphoanatomy, higher pigment content, improving gas exchange parameters, thereby increased growth. Furthermore, cultivar 'CTC9003' showed beneficial impacts from Si supplementation than 'CTC9002', especially under Al toxicity. The findings of this study suggest that Si plays a notable role in improving anatomical and physiological aspects, particularly the growth of sugarcane seedlings under Al toxicity.

Physiological Mechanism through Which Al Toxicity Inhibits Peanut Root Growth

Al (Aluminum) poisoning is a significant limitation to crop yield in acid soil. However, the physiological process involved in the peanut root response to Al poisoning has not been clarified yet and requires further research. In order to investigate the influence of Al toxicity stress on peanut roots, this study employed various methods, including root phenotype analysis, scanning of the root, measuring the physical response indices of the root, measurement of the hormone level in the root, and quantitative PCR (qPCR). This research aimed to explore the physiological mechanism underlying the reaction of peanut roots to Al toxicity. The findings revealed that Al poisoning inhibits the development of peanut roots, resulting in reduced biomass, length, surface area, and volume. Al also significantly affects antioxidant oxidase activity and proline and malondialdehyde contents in peanut roots. Furthermore, Al toxicity led to increased accumulations of Al and Fe in peanut roots, while the contents of zinc (Zn), cuprum (Cu), manganese (Mn), kalium (K), magnesium (Mg), and calcium (Ca) decreased. The hormone content and related gene expression in peanut roots also exhibited significant changes. High concentrations of Al trigger cellular defense mechanisms, resulting in differentially expressed antioxidase genes and enhanced activity of antioxidases to eliminate excessive ROS (reactive oxygen species). Additionally, the differential expression of hormone-related genes in a high-Al environment affects plant hormones, ultimately leading to various negative effects, for example, decreased biomass of roots and hindered root development. The purpose of this study was to explore the physiological response mechanism of peanut roots subjected to aluminum toxicity stress, and the findings of this research will provide a basis for cultivating Al-resistant peanut varieties.

Spatial distribution of potentially toxic elements in e-waste contaminated site at Akwatia-Line, Kumasi, Ghana

E-waste processing sites abound with potentially toxic elements (PTE) that negatively affect the environment and human health. The study determined the presence of selected PTE (Cu, Zn, Pb, Hg, and Al) and their spatial distribution in an e-waste processing site in a developing country setting. pH, moisture, organic matter/carbon, and particle size were determined in 30 soil samples. The spatial position of each sampling point was picked with a GPS device, and the area was mapped in a GIS environment. The concentrations of PTE were determined with an atomic absorption spectrophotometer. Findings from the study indicate that the soil is polluted with PTE, rich in organic carbon/matter but has low pH. The Geoaccumulation Indices ranged from unpolluted (Al) to strongly/extremely polluted (Cu). Pollution Load Index showed about 77 % of the samples as extremely/heavily polluted, 10 % as heavily polluted, and 13 % as moderately polluted. Contamination Factors of Zn, Pb, and Cu were very high but considerably low for Hg and Al. Regular monitoring and remediation are required for the soil to be restored and put into productive use.

Alteration of Hordeum vulgare and Sinapis alba germination and early growth in response to airborne low-metallic automotive brake wear debris

Road transportation significantly contributes to environmental pollution, both in terms of exhaust and non-exhaust (brake wear) emissions. As was proven, brake wear debris is released in a wide variety of sizes, shapes, and compositions. Although studies confirming the possible adverse health and environmental impact of brake wear debris were published, there is no standardized methodology for their toxicity testing, and most studies focus only on one type of brake pad and/or one test. The lack of methodology is also related to the very small amount of material released during the laboratory testing. For these reasons, this study deals with the mixture of airborne brake wear debris from several commonly used low-metallic brake pads collected following the dynamometer testing. The mixture was chosen for better simulation of the actual state in the environment and to collect a sufficient amount of particles for thorough characterization (SEM, XRPD, XRF, chromatography, and particle size distribution) and phytotoxicity testing. The particle size distribution measurement revealed a wide range of particle sizes from nanometers to hundreds of nanometers, elemental and phase analysis determined the standard elements and compounds used in the brake pad formulation. The Hordeum vulgare and Sinapis alba were chosen as representatives of monocotyledonous and dicotyledonous plants. The germination was not significantly affected by the suspension of brake wear debris; however, the root elongation was negatively influenced in both cases. Sinapis alba (IC50 = 23.13 g L-1) was more affected than Hordeum vulgare (IC50 was not found in the studied concentration range) the growth of which was even slightly stimulated in the lowest concentrations of brake wear debris. The plant biomass was also negatively affected in the case of Sinapis alba, where the IC50 values of wet and dry roots were determined to be 44.83 g L-1 and 86.86 g L-1, respectively.

Physiological mechanisms of exogenous organic acids to alleviate aluminum toxicity in seedlings of mungbean, buckwheat, and rice

One of the major constraints for crop yield in acidic soils is the phytotoxicity of aluminum ions (Al3+), which primarily affects the roots. To mitigate the harmful effects of Al toxicity, plants use organic acids to chelate Al internally and externally. In this study, the effects of exogenous organic acids on Al toxicity in rice, mung bean, and buckwheat were investigated. Specifically, the study examined the ameliorative effect of three organic acids (oxalic acid, malic acid, and citric acid, each at a concentration of (100 μmol/L) on root elongation, fresh weight, Al content, organic acid key enzymes, and rhizosphere pH in hydroponic media containing (100 μmol/L) Al. The experimental results revealed species-specific responses to aluminum tolerance and the alleviating effects of different organic acids. Buckwheat was found to be the most aluminum-tolerant, followed by mung bean, while rice was the least tolerant. Exogenous application of oxalic acid promoted root elongation, increased root fresh weight, and enhanced the activity of the PEPC enzyme in mung bean. Malic acid, on the other hand, alleviated Al toxicity in rice by promoting root elongation, increasing root fresh weight, enhancing the activity of the PEPC enzyme, and decreasing the activity of the MDH enzyme. In buckwheat, citric acid application reduced Al toxicity by promoting root elongation, increasing root weight, and decreasing the activities of CS and GO enzymes. These findings indicate that different organic acids can reduce Al toxicity in different plant species by employing different physiological mechanisms.

Soil acidification and salinity: the importance of biochar application to agricultural soils

Soil acidity is a serious problem in agricultural lands as it directly affects the soil, crop production, and human health. Soil acidification in agricultural lands occurs due to the release of protons (H+) from the transforming reactions of various carbon, nitrogen, and sulfur-containing compounds. The use of biochar (BC) has emerged as an excellent tool to manage soil acidity owing to its alkaline nature and its appreciable ability to improve the soil's physical, chemical, and biological properties. The application of BC to acidic soils improves soil pH, soil organic matter (SOM), cation exchange capacity (CEC), nutrient uptake, microbial activity and diversity, and enzyme activities which mitigate the adverse impacts of acidity on plants. Further, BC application also reduce the concentration of H+ and Al3+ ions and other toxic metals which mitigate the soil acidity and supports plant growth. Similarly, soil salinity (SS) is also a serious concern across the globe and it has a direct impact on global production and food security. Due to its appreciable liming potential BC is also an important amendment to mitigate the adverse impacts of SS. The addition of BC to saline soils improves nutrient homeostasis, nutrient uptake, SOM, CEC, soil microbial activity, enzymatic activity, and water uptake and reduces the accumulation of toxic ions sodium (Na+ and chloride (Cl-). All these BC-mediated changes support plant growth by improving antioxidant activity, photosynthesis efficiency, stomata working, and decrease oxidative damage in plants. Thus, in the present review, we discussed the various mechanisms through which BC improves the soil properties and microbial and enzymatic activities to counter acidity and salinity problems. The present review will increase the existing knowledge about the role of BC to mitigate soil acidity and salinity problems. This will also provide new suggestions to readers on how this knowledge can be used to ameliorate acidic and saline soils.

Designing amendments to improve plant performance for mine tailings revegetation

To provide recommendations for establishment of plants on low-pH Formosa Mine tailings, two greenhouse experiments were conducted to evaluate the use of remedial amendments to improve the survival and growth of Douglas fir (Pseudotsuga menziesii) seedlings. A preliminary experiment indicated that 1% lime (by weight) raised tailings pH, permitting seedling survival. However, high rates of biosolid application (BS; 2% by weight) added to supply nutrients were phytotoxic when added with lime. A gasified conifer biochar (BC) added to tailings at 1%, 2.5%, or 5% (by weight), along with lime and BS, caused an additional increase in pH, decreased electrical conductivity (EC), and tended to increase the survival of Douglas fir. The addition of a locally sourced microbial inoculum (LSM) did not affect survival. A subsequent experiment expanded our experimental design by testing multiple levels of amendments that included lime (0.5% and 1% by weight), three application rates (0.2%, 0.5%, and 2%) of two nutrient sources (BS or mineral fertilizer), BC (0% and 2.5%), and with or without LSM. There were many interactions among amendments. In general, Douglas fir survival was enhanced when lime and BC were added. These experiments suggest that amending with lime, a nutrient source, and BC would enhance revegetation on low-pH, metal-contaminated mine tailings.

Foliar application of enriched banana pseudostem sap influences the nutrient uptake, yield, and quality of sweet corn grown in an acidic soil

Foliar fertilization is a reliable technique for correcting a nutrient deficiency in plants caused by inadequate nutrient supply to the roots in acid soil. Soluble nutrients in banana pseudostem sap might be effective to supplement chemical fertilizers. However, the limited nutrients in sole banana pseudostem sap as foliar fertilization may not meet-up the nutritional demand of the crop. Field trials were, therefore, conducted with the combination of soil-applied fertilizers with foliar spray of banana pseudostem sap to increase nutrient uptake, yield, and quality of sweet corn planted in acidic soil. Three treatments viz., 100% recommended dose of fertilizers (RD) as control (T1), 75% of RD applied in soil with foliar application of non-enriched banana pseudostem sap (T2), and 50% RD applied in soil with foliar spray of enriched banana pseudostem sap (T3) were replicated four times. The combination of soil-applied fertilizer with foliar spray of enriched banana pseudostem sap (T3) showed a significant increase in leaf area index (11.3%), photosynthesis (12%), fresh cob yield (39%), and biomass of corn (29%) over control. Besides, the 50% RD of soil fertilization with foliar spray of enriched pseudostem sap increased nutrient uptake in addition to an increase in sugar content, phenolic content, soluble protein, and amino acids of corn. Considering the economic analysis, the highest net income, BCR (3.74) and MBCR (1.25) values confirmed the economic viability of T3 treatment over the T1. The results suggest that foliar spray of enriched banana pseudostem sap can be used as a supplementary source of nutrients to enhance nutrient uptake by corn while increasing yield and minimizing chemical fertilizer use in acid soil.

Physico-Chemical and Nutritional Properties of Chia Seeds from Latin American Countries

In the last few decades, chia (Salvia hispanica L.) cultivation has expanded around the world, and the seeds have become well known due to their rich composition of nutrients and bioactive compounds. The aim of this work was to evaluate the physical, chemical, and nutritional profile of eight types of chia seeds grown in different Latin-American countries (Argentina, Bolivia, Chile, Ecuador, Mexico, Paraguay, and Peru). The results showed that several nutritional parameters of the seeds, such as the protein content and amino acid profile, dietary fiber content, lipid content, mineral composition, and presence of phytate, depend on the location in which they were grown. Other parameters, such as ash content, fatty acid profile, or various physical parameters, were uniform across locations (except for color parameters). The results support the notion that the nutritional characteristics of seeds are determined by the seeds' origin, and further analysis is needed to determine the exact mechanisms that control the changes in the seed nutritional properties of chia seeds.

Influence of Reagents on Qualitative Indicators of Artificial Anti-Deflationary Phytocenosis on Waste from a Rare Earth Tailing Facility

This paper presents an assessment of the effect of various reagents on the qualitative indicators of anti-deflationary single-species sowing phytocenosis on enrichment waste from rare earth ores. It has been established that tailings of loparite ores are not suitable for biological reclamation due to low values of hygroscopic moisture (0.54-2.85%) and clay particles (17.6 ± 0.6%) and high content of bioavailable forms of aluminum (504 ± 14 mg/kg). Seeds of red fescue (Festuca rubra L.) were grown on the tailings of loparite ore enrichment with the addition of opoka (O), brucite (B), and vermiculite (V). The quality of the seed cenosis was assessed by the dry biomass of the above-ground parts of the plants and the plant height. A positive effect (one-way ANOVA followed by Tukey's HSD test (p < 0.05 and p < 0.01)) of the considered combinations of reagents on the growth of above-ground biomass from 31.5% (V) to 70.3 (V + O), 82.4% (V + B), and 81.8% (V + O+B) and on plant height from 53.8% (V) up to 78.6 (V + O), 83.8% (V + B), and 75.4% (V + O+B) was revealed. The use of a combination of V + O and V + B reagents made it possible to significantly reduce the content of Al (by 19.0% and 52.8%), Sr (by 16.5% and 12.9%), La (by 65.2% and 40.6%), and Ce (by 66.8% and 41.9%) in the aerial part of the sowing phytocenosis compared to control. The results obtained here can become the basis for development of a combined sorption technology for the reclamation of technogenically disturbed lands.

Signaling and crosstalk of rhizobacterial and plant hormones that mediate abiotic stress tolerance in plants

Agricultural areas exhibiting numerous abiotic stressors, such as elevated water stress, temperatures, and salinity, have grown as a result of climate change. As such, abiotic stresses are some of the most pressing issues in contemporary agricultural production. Understanding plant responses to abiotic stressors is important for global food security, climate change adaptation, and improving crop resilience for sustainable agriculture, Over the decades, explorations have been made concerning plant tolerance to these environmental stresses. Plant growth-promoting rhizobacteria (PGPR) and their phytohormones are some of the players involved in developing resistance to abiotic stress in plants. Several studies have investigated the part of phytohormones in the ability of plants to withstand and adapt to non-living environmental factors, but very few have focused on rhizobacterial hormonal signaling and crosstalk that mediate abiotic stress tolerance in plants. The main objective of this review is to evaluate the functions of PGPR phytohormones in plant abiotic stress tolerance and outline the current research on rhizobacterial hormonal communication and crosstalk that govern plant abiotic stress responses. The review also includes the gene networks and regulation under diverse abiotic stressors. The review is important for understanding plant responses to abiotic stresses using PGPR phytohormones and hormonal signaling. It is envisaged that PGPR offer a useful approach to increasing plant tolerance to various abiotic stresses. However, further studies can reveal the unclear patterns of hormonal interactions between plants and rhizobacteria that mediate abiotic stress tolerance.

Molecular network of the oil palm root response to aluminum stress

BACKGROUND

The solubilization of aluminum ions (Al³⁺) that results from soil acidity (pH < 5.5) is a limiting factor in oil palm yield. Al can be uptaken by the plant roots affecting DNA replication and cell division and triggering root morphological alterations, nutrient and water deprivation. In different oil palm-producing countries, oil palm is planted in acidic soils, representing a challenge for achieving high productivity. Several studies have reported the morphological, physiological, and biochemical oil palm mechanisms in response to Al-stress. However, the molecular mechanisms are just partially understood.

RESULTS

Differential gene expression and network analysis of four contrasting oil palm genotypes (IRHO 7001, CTR 3-0-12, CR 10-0-2, and CD 19 - 12) exposed to Al-stress helped to identify a set of genes and modules involved in oil palm early response to the metal. Networks including the ABA-independent transcription factors DREB1F and NAC and the calcium sensor Calmodulin-like (CML) that could induce the expression of internal detoxifying enzymes GRXC1, PER15, ROMT, ZSS1, BBI, and HS1 against Al-stress were identified. Also, some gene networks pinpoint the role of secondary metabolites like polyphenols, sesquiterpenoids, and antimicrobial components in reducing oxidative stress in oil palm seedlings. STOP1 expression could be the first step of the induction of common Al-response genes as an external detoxification mechanism mediated by ABA-dependent pathways.

CONCLUSIONS

Twelve hub genes were validated in this study, supporting the reliability of the experimental design and network analysis. Differential expression analysis and systems biology approaches provide a better understanding of the molecular network mechanisms of the response to aluminum stress in oil palm roots. These findings settled a basis for further functional characterization of candidate genes associated with Al-stress in oil palm.

Two Sweet Sorghum (Sorghum bicolor L.) WRKY Transcription Factors Promote Aluminum Tolerance via the Reduction in Callose Deposition

Aluminum (Al) toxicity is a primary limiting factor for crop production in acidic soils. The WRKY transcription factors play important roles in regulating plant growth and stress resistance. In this study, we identified and characterized two WRKY transcription factors, SbWRKY22 and SbWRKY65, in sweet sorghum (Sorghum bicolor L.). Al induced the transcription of SbWRKY22 and SbWRKY65 in the root apices of sweet sorghum. These two WRKY proteins were localized in the nucleus and exhibited transcriptional activity. SbWRKY22 showed the significant transcriptional regulation of SbMATE, SbGlu1, SbSTAR1, SbSTAR2a, and SbSTAR2b, which are major known Al tolerance genes in sorghum. Interestingly, SbWRKY65 had almost no effect on the aforementioned genes, but it significantly regulated the transcription of SbWRKY22. Therefore, it is speculated that SbWRKY65 might indirectly regulate Al-tolerance genes mediated by SbWRKY22. The heterologous expression of SbWRKY22 and SbWRKY65 greatly improved the Al tolerance of transgenic plants. The enhanced Al tolerance phenotype of transgenic plants is associated with reduced callose deposition in their roots. These findings suggest the existence of SbWRKY22- and SbWRKY65-mediated Al tolerance regulation pathways in sweet sorghum. This study extends our understanding of the complex regulatory mechanisms of WRKY transcription factors in response to Al toxicity.

Traceability of Croatian extra virgin olive oils to the provenance soils by multielement and carbon isotope composition and chemometrics

A capacity to determine the provenance of high-value food products is of high scientific and economic interest. With the aim to develop a tool for geographical traceability of Croatian extra virgin olive oils (EVOO), multielement composition and ¹³C/¹²C isotope ratio in EVOO as well as the geochemistry of the associated soils were analysed in samples collected from three regions along the Croatian Adriatic coast. Soil geochemistry was shown to influence the transfer and elemental composition of EVOO. The most discriminating variables to distinguish EVOO from different regions were S, Mo, Rb, Mg, Pb, Mn, Sn, K, V and δ¹³C. The predictive models achieved high sensitivity and specificity, especially when carbon isotope composition was added. The results suggest that interregional geographical traceability of Croatian EVOO is possible based on matching their multielement composition with that of the soils in the provenance area.

Molecular probes for fluorescent sensing of metal ions in non-mammalian organisms

While metal ions play an important role in the proper functioning of all life, many questions remain unanswered about exactly how different metals contribute to health and disease. The development of fluorescent probes, which respond to metals, has allowed greater understanding of the cellular location, concentration and speciation of metals in living systems, giving a new appreciation of their function. While the focus of studies using these fluorescent tools has largely been on mammalian organisms, there has been relatively little application of these powerful tools to other organisms. In this review, we highlight recent examples of molecular fluorophores, which have been applied to sensing metals in non-mammalian organisms.

The tricarboxylic acid (TCA) cycle: a malleable metabolic network to counter cellular stress

The tricarboxylic acid (TCA) cycle is a primordial metabolic pathway that is conserved from bacteria to humans. Although this network is often viewed primarily as an energy producing engine fueling ATP synthesis via oxidative phosphorylation, mounting evidence reveals that this metabolic hub orchestrates a wide variety of pivotal biological processes. It plays an important part in combatting cellular stress by modulating NADH/NADPH homeostasis, scavenging ROS (reactive oxygen species), producing ATP by substrate-level phosphorylation, signaling and supplying metabolites to quell a range of cellular disruptions. This review elaborates on how the reprogramming of this network prompted by such abiotic stress as metal toxicity, oxidative tension, nutrient challenge and antibiotic insult is critical for countering these conditions in mostly microbial systems. The cross-talk between the stressors and the participants of TCA cycle that results in changes in metabolite and nucleotide concentrations aimed at combatting the abiotic challenge is presented. The fine-tuning of metabolites mediated by disparate enzymes associated with this metabolic hub is discussed. The modulation of enzymatic activities aimed at generating metabolic moieties dedicated to respond to the cellular perturbation is explained. This ancient metabolic network has to be recognized for its ability to execute a plethora of physiological functions beyond its well-established traditional roles.

Bacillus-Loaded Biochar as Soil Amendment for Improved Germination of Maize Seeds

Biochar is considered one of the most promising long-term solutions for soil quality improvement, representing an ideal environment for microorganisms' immobilization. Hence there is a possibility to design microbial products formulated using biochar as a solid carrier. The present study was aimed at development and characterization of Bacillus-loaded biochar to be applied as a soil amendment. The producing microorganism Bacillus sp. BioSol021 was evaluated in terms of plant growth promotion traits, indicating significant potential for production of hydrolytic enzymes, indole acetic acid (IAA) and surfactin and positive tests for ammonia and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase production. Soybean biochar was characterised in terms of physicochemical properties to evaluate its suitability for agricultural applications. The experimental plan for Bacillus sp. BioSol021 immobilisation to biochar included variation of biochar concentration in cultivation broth and adhesion time, while the soil amendment effectiveness was evaluated during maize germination. The best results in terms of maize seed germination and seedling growth promotion were achieved by applying 5% of biochar during the 48 h immobilisation procedure. Germination percentage, root and shoot length and seed vigour index were significantly improved when using Bacillus-biochar soil amendment compared to separate treatments including biochar and Bacillus sp. BioSol021 cultivation broth. The results indicated the synergistic effect of producing microorganism and biochar on maize seed germination and seedling growth promotion, pointing out the promising potential of this proposed multi-beneficial solution for application in agricultural practices.

Comparative assessment of the heavy metal phytoextraction potential of vegetables from agricultural soils: A field experiment

A field study was established to determine the phytoextraction potential of six vegetable species, namely Amaranthus viridis L., Basella alba L., Brassica chinensis var. Parachinensis, Brassica rapa L., Capsicum frutescens L., and Ocimum tenuiflorum L.. These edible plants were selected for their short growth cycles and high biomass production, which are some traits for efficient phytoremediation. Following acid digestion of the soil and vegetable samples using the USEPA 3050B acid digestion method, the extracts were analyzed for Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn using ICP-OES. Results in soil samples showed that the concentrations of both beneficial and essential heavy metals, and non-essential heavy metals are below the WHO, USEPA, and CCME soil quality guidelines. Al is one of the highest concentrations found in the soil samples but it tends to accumulate in the root part of all vegetable species compared to the aboveground parts. In general, B. rapa L. accumulated the highest level of Cd (0.4 mg/kg) and Pb (5.71 mg/kg), while B. alba L. accumulated the highest Cr (2.62 mg/kg) in all plant parts. The findings in this study indicated that Co, Cu, Fe, Mn and Zn were mostly accumulated in leaves of A. viridis L. (Co, Cu, Fe, Mn and Zn), B. alba L. (Co, Fe and Mn), B. chinensis (Mn and Zn) and O. tenuiflorum L. (Mn), and roots of C. frutescens L. (Co, Cu, Fe and Mn), B. alba L. (Co, Cu and Zn), A. viridis L. and B. chinensis (Cu and Fe) and B. rapa L. (Fe). Cr, Pb and Ni were significantly greater in B. alba L. (Cr) And B. rapa L. (Ni and Pb) roots. MTF >1 was observed in the roots of all species for Co, Cd, Zn, and Ni. BTC values varied between the different vegetable species with A. viridis L. having the greatest heavy metal mobility between its plant parts and the best heavy metal phytoextraction potential among other species. The PCA biplots showed that heavy metals were partitioned differently between various plant parts of the vegetable species and can be explained by the first two components (PC1 and PC2) which were associated with the root and/or leaf parts for most vegetable species.

The elements of life: A biocentric tour of the periodic table

Living systems are built from a small subset of the atomic elements, including the bulk macronutrients (C,H,N,O,P,S) and ions (Mg,K,Na,Ca) together with a small but variable set of trace elements (micronutrients). Here, we provide a global survey of how chemical elements contribute to life. We define five classes of elements: those that are (i) essential for all life, (ii) essential for many organisms in all three domains of life, (iii) essential or beneficial for many organisms in at least one domain, (iv) beneficial to at least some species, and (v) of no known beneficial use. The ability of cells to sustain life when individual elements are absent or limiting relies on complex physiological and evolutionary mechanisms (elemental economy). This survey of elemental use across the tree of life is encapsulated in a web-based, interactive periodic table that summarizes the roles chemical elements in biology and highlights corresponding mechanisms of elemental economy.

Deciphering Interactions between Phosphorus Status and Toxic Metal Exposure in Plants and Rhizospheres to Improve Crops Reared on Acid Soil

Acid soils are characterized by deficiencies in essential nutrient elements, oftentimes phosphorus (P), along with toxicities of metal elements, such as aluminum (Al), manganese (Mn), and cadmium (Cd), each of which significantly limits crop production. In recent years, impressive progress has been made in revealing mechanisms underlying tolerance to high concentrations of Al, Mn, and Cd. Phosphorus is an essential nutrient element that can alleviate exposure to potentially toxic levels of Al, Mn, and Cd. In this review, recent advances in elucidating the genes responsible for the uptake, translocation, and redistribution of Al, Mn, and Cd in plants are first summarized, as are descriptions of the mechanisms conferring resistance to these toxicities. Then, literature highlights information on interactions of P nutrition with Al, Mn, and Cd toxicities, particularly possible mechanisms driving P alleviation of these toxicities, along with potential applications for crop improvement on acid soils. The roles of plant phosphate (Pi) signaling and associated gene regulatory networks relevant for coping with Al, Mn, and Cd toxicities, are also discussed. To develop varieties adapted to acid soils, future work needs to further decipher involved signaling pathways and key regulatory elements, including roles fulfilled by intracellular Pi signaling. The development of new strategies for remediation of acid soils should integrate the mechanisms of these interactions between limiting factors in acid soils.

Aluminum phytotoxicity induced structural and ultrastructural changes in submerged plant Vallisneria natans

Aluminum (Al) is a concentration-dependent toxic metal found in the crust of earth that has no recognized biological use. Nonetheless, the mechanism of Al toxicity to submerged plants remains obscure, especially from a cell/subcellular structure and functional group perspective. Therefore, multiple dosages of Al³⁺ (0, 0.3, 0.6, 1.2, and 1.5 mg/L) were applied hydroponically to the submerged plant Vallisneria natans in order to determine the accumulation potential of Al at the subcellular level and their ultrastructural toxicity. More severe structural and ultrastructural damage was determined when V. natans exposed to ≥ 0.6 mg/L Al³⁺. In 1.2 and 1.5 mg/L Al³⁺ treatment groups, the total chlorophyll content of leaves significantly reduced 3.342, 3.838 mg/g FW, some leaves even exhibited chlorosis and fragility. Under 0.3 mg/L Al³⁺ exposure, the middle-age and young leaves were potent phytoexcluders, whereas at 1.5 mg/L Al³⁺, a large amount of Al could be transferred from the roots to other parts, among which the aged leaves were the most receptive tissues (7.306 mg/g). Scanning/Transmission electron microscopy analysis displayed the Al-mediated disruption of vascular bundle structure in leaf cells, intercellular space and several vegetative tissues, and demonstrated that Al in vacuole and chloroplast subcellular segregation into electron dense deposition. Al and P accumulation in the roots, stolons and leaves varied significantly among treatments and different tissues (P < 0.05). Fourier transform infrared spectroscopy of plant biomass also indicated possible metabolites (amine, unsaturated hydrocarbon, etc.) of V. natans that may bind Al³⁺. Conclusively, results revealed that Al³⁺ disrupts the cellular structure of leaves and roots or binds to functional groups of biological tissues, thereby affecting plant nutrient uptake and photosynthesis. Findings might have scientific and practical significance for the restoration of submerged vegetation in Al-contaminated lakes.

Assessment soil cadmium and copper toxicity on barley growth and the influencing soil properties in subtropical agricultural soils

Evaluation joint cadmium (Cd) and copper (Cu) phytotoxicity in wide range of subtropical agricultural soils is highly vital for phytoremediation of soils contaminated with Cd and Cu. In this study, barley root elongation assays were performed in 30 representative soils in response to single and combined Cd and Cu inhibition. The single Cd caused nearly 50% inhibition of barley root elongation, and Cu induced more than 50% inhibition in most soils. Mixed Cd + Cu caused significant inhibition on barley growth with average relative root elongation values of 20.0% and 30.4% in soil with a pH < 7 and pH > 7, respectively. An antagonistic interaction was evaluated in combined Cd + Cu toxicity, which was strong in soils containing low soluble Cu and Cd contents. Soil pH was the controlling factor in predicting single and mixed Cd and Cu phytotoxicity, which could explain 44% and 46% variation of single Cd and Cu toxicity, respectively. Soil organic carbon and effective cation exchange capacity were another important factor positively influencing metal toxicity, which further improved empirical prediction models accuracy, with determined coefficient (r²) values of 0.44-0.84. These results provide a theoretical basis for soils Cd and Cu pollution control.

Aluminum in plant: Benefits, toxicity and tolerance mechanisms

Aluminum (Al) is the third most ubiquitous metal in the earth's crust. A decrease in soil pH below 5 increases its solubility and availability. However, its impact on plants depends largely on concentration, exposure time, plant species, developmental age, and growing conditions. Although Al can be beneficial to plants by stimulating growth and mitigating biotic and abiotic stresses, it remains unknown how Al mediates these effects since its biological significance in cellular systems is still unidentified. Al is considered a major limiting factor restricting plant growth and productivity in acidic soils. It instigates a series of phytotoxic symptoms in several Al-sensitive crops with inhibition of root growth and restriction of water and nutrient uptake as the obvious symptoms. This review explores advances in Al benefits, toxicity and tolerance mechanisms employed by plants on acidic soils. These insights will provide directions and future prospects for potential crop improvement.

Study of the mineral contents of Matricaria pubescens and Brocchia cinerea from Algeria

Two species of plants commonly used for mainly their therapeutic values and available in some herbalists shops, namely: Brocchia cinerea and Matricaria pubescens that both belong to asteraceae family, and encountered mainly in the Algerian desert, have drawn attention in the scope of assessing their mineral contents, in fact minerals play an important role in the plant homeostasis and metabolism, on the other hand they may influence the health conditions mainly due to toxicity, and also the benefits that the plant consumer could have, the current study aimed to assess the contents of Al, Cd, Cr, Cu, Fe, Hg, Ni, Pb, Zn, As, Na, K, Mg, P, S and SI, beside comparing the obtained results to other similar studies, the aerial parts of the plants are collected from several sites then mineralized and analyzed using ICP-AES and AAS, high levels of Na, K and Mg have been noted, on the other hands levels of metals were noted to be overall marginal, except for Al and Hg for the sample of Brocchia cinerea from El oued, the levels of As also seemed to be high in all the samples, inversely to the levels of S and P which seemed lower than those noted for other plants in paralleled studies, while that similar results were found for Zn, Fe, the chemical and geologic features of the soils may be the influencing factor. Additionally the current study may put first milestone for the establishment of national guidelines regarding the mineral contents of medicinal plants.

GOCompare: An R package to compare functional enrichment analysis between two species

Functional enrichment analysis is a cornerstone in bioinformatics as it makes possible to identify functional information by using a gene list as source. Different tools are available to compare gene ontology (GO) terms, based on a directed acyclic graph structure or content-based algorithms which are time-consuming and require a priori information of GO terms. Nevertheless, quantitative procedures to compare GO terms among gene lists and species are not available. Here we present a computational procedure, implemented in R, to infer functional information derived from comparative strategies. GOCompare provides a framework for functional comparative genomics starting from comparable lists from GO terms. The program uses functional enrichment analysis (FEA) results and implement graph theory to identify statistically relevant GO terms for both, GO categories and analyzed species. Thus, GOCompare allows finding new functional information complementing current FEA approaches and extending their use to a comparative perspective. To test our approach GO terms were obtained for a list of aluminum tolerance-associated genes in Oryza sativa subsp. japonica and their orthologues in Arabidopsis thaliana. GOCompare was able to detect functional similarities for reactive oxygen species and ion binding capabilities which are common in plants as molecular mechanisms to tolerate aluminum toxicity. Consequently, the R package exhibited a good performance when implemented in complex datasets, allowing to establish hypothesis that might explain a biological process from a functional perspective, and narrowing down the possible landscapes to design wet lab experiments.