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Purpose: Durum wheat is sensitive of acid soils because it lacks effective genes for Al3+ tolerance. Previous research showed introgression of the TaMATE1B and TaALMT1 genes individually increased the Al3+ tolerance of durum wheat. Here we aimed to (a) combine the genes into a single durum line, (b) compare the various introgression lines and (c) establish the effectiveness of the introgressions in improving the acid soil tolerance in the field. Methods: Durum wheat lines homozygous for Al3+-tolerant alleles of TaMATE1B and TaALMT1 were crossed to develop a line that incorporated both genes. The parental cultivar, lines with the individual genes and the line with both genes introgressed were screened for Al3+ tolerance by hydroponic and soil cultures in a growth cabinet. The lines were also assessed for biomass production and grain yield in the field on acid soils. Results: The durum wheat lines with the various Al3+-tolerance genes introgressed performed better based on root growth than Jandaroi, the parental cultivar, in both hydroponic and soil assays when grown in a cabinet. The various introgression lines were tolerant of acid soils compared to Jandaroi when grown in the field as assessed by shoot biomass and grain yield. Conclusion: The TaALMT1 and TaMATE1B genes improve the acid soil tolerance of durum wheat with indications that combining both genes is the most effective strategy. The various lines will be valuable to breeders who wish to enhance the acid soil tolerance of durum germplasm. [ABSTRACT FROM AUTHOR]

Soil acidity is one of the most important constraints to maize production in Angola, where both yellow and white maize is essential for food and feed requirements. In this study, four yellow acid soil tolerant donor lines from the International Maize and Wheat Improvement Centre (CIMMYT)—Colombia were crossed with ten yellow elite lines adapted to the mid-altitude climatic conditions developed by CIMMYT—Zimbabwe, in order to identify donor lines, which can be potential sources of acid tolerance genes in breeding programs in Angola and within the mid-altitude climatic zones. The two groups of parents were crossed using a line by tester mating design, yielding 36 crosses with sufficient seed, which were evaluated alongside six acid tolerant commercial hybrids, during the 2014–16 cropping seasons at nine sites, representing acid and non-acid soils in Angola and Zimbabwe. A significant (p < 0.05) line and line × tester effect for grain yield performance was observed across acid and non-acid conditions. Acid tolerance donor lines CY3 and CY1 showed the highest positive GCA effects for grain yield. In addition, crosses involving these two donor lines had the best yielding ability and stability under both acid and non-acid conditions. For instance, the crosses CH142464 (ZY2 × CY3) and, CH142447 (ZY2 × CY1) were the best combinations for grain yield performance under both acid and non-acid soil conditions, and were stable compared to the commercial check hybrids. Crosses involving the acid tolerant donor lines mostly flowered earlier than the commercial checks. Overall, the data showed the potential of tropically-adapted exotic yellow maize acid tolerance donor lines in improving productivity of sub-tropical maize under both low-pH and well-managed soil conditions. [ABSTRACT FROM AUTHOR]

Electrochemical experiments, slow strain rate tensile testing (SSRT), and scanning electron microscopy were used to investigate the effect of various applied potentials on the stress corrosion cracking (SCC) of X80 pipeline steel in acidic soil containing sulfate-reducing bacteria (SRB). The results demonstrated that when the anodic potential was applied, X80 steel exhibited sensitivity to SCC, which was attributed to anodic dissolution. The SCC sensitivity initially decreased, but then increased with a negative shift in the applied potential. At −1200 mV, SCC was the most sensitive, which corresponded to the substantial cathodic polarisation and toxic impact of SRB, which increased the risk of hydrogen embrittlement. At −850 mV, the SCC sensitivity was the lowest because cathodic polarisation suppressed anodic dissolution. The experimental results can contribute to the prevention and management of SCC in operational pipelines. [ABSTRACT FROM AUTHOR]

Main conclusion: The 4-coumarate:coenzyme A ligase 4CL4 is involved in enhancing rice P acquisition and use in acid soil by enlarging root growth and boosting functional rhizosphere microbe recruitment. Rice (Oryza sativa L.) cannot easily acquire phosphorus (P) from acid soil, where root growth is inhibited and soil P is fixed. The combination of roots and rhizosphere microbiota is critical for plant P acquisition and soil P mobilization, but the associated molecular mechanism in rice is unclear. 4CL4/RAL1 encodes a 4-coumarate:coenzyme A ligase related to lignin biosynthesis in rice, and its dysfunction results in a small rice root system. In this study, soil culture and hydroponic experiments were conducted to examine the role of RAL1 in regulating rice P acquisition, fertilizer P use, and rhizosphere microbes in acid soil. Disruption of RAL1 markedly decreased root growth. Mutant rice plants exhibited decreased shoot growth, shoot P accumulation, and fertilizer P use efficiency when grown in soil—but not under hydroponic conditions, where all P is soluble and available for plants. Mutant ral1 and wild-type rice rhizospheres had distinct bacterial and fungal community structures, and wild-type rice recruited some genotype-specific microbial taxa associated with P solubilization. Our results highlight the function of 4CL4/RAL1 in enhancing rice P acquisition and use in acid soil, namely by enlarging root growth and boosting functional rhizosphere microbe recruitment. These findings can inform breeding strategies to improve P use efficiency through host genetic manipulation of root growth and rhizosphere microbiota. [ABSTRACT FROM AUTHOR]

Background and Aims: Suitable N source supply is critical to improve plant growth and N uptake, but the importance of nitrate (NO3−) for rice (Oryza sativa L.) and microbiota is often neglected in acidic paddy soils where ammonium (NH4+) is dominant. This study aimed to explore the differential effects of NH4+ and NO3− on rice growth, fertilizer nitrogen recovery efficiency (FNRE), and rhizosphere bacterial community in acid soil. Methods: Two rice varieties, Kasalath (Al-sensitive indica) and Koshihikari (Al-tolerant japonica), were exposed to different N sources with or without lime in an acid soil. Results: Liming and NO3− application solely improved the growth and FNRE of the Al-sensitive rice, namely, by increasing soil pH and alleviating Al toxicity. Compared with liming and rice variety, N source had a more pronounced influence on rhizobacterial community composition. Of the two sources, NO3− had a stronger effect on the rhizobacterial community than NH4+. Remarkably, rice plants fed with NH4+ specifically recruited Desulfosporosinus and Desulfitobacterium associated with ferric NH4+ oxidation in the rhizosphere, whereas those exposed to NO3− recruited Alicyclobacillus with NO3−-reducing iron oxidation ability. Three keystone taxa were identified in a rhizobacterial co-occurrence network analysis: Alicyclobacillus, which was positively associated with rice growth and FNRE, and Acidobacteriales and WPS-2, both with negative associations. Conclusion: Compared with NH4+, NO3− enhances the growth and FNRE of Al-sensitive rice and exerts dominant effects on the rhizobacterial community, which indicates the importance of NO3− for rice and has instructive implications for N management in acid soil. [ABSTRACT FROM AUTHOR]

The form of inorganic N in soil is governed by N transformations, but the relationship between the soil N transformation dynamics and the N uptake by plants is unclear. The effect of liming and nitrification inhibitor on crop N uptake efficiency (NUE) and N loss due to altered soil N processes was investigated using a 15 N tracing approach. Crops with different N uptake strategies (sweet potato (Dioscorea esculenta L.); an ammonium-N preferring plant and pakchoi (Brassica chinensis L.); a nitrate–N preferring plant) were grown in two agricultural soils with different pH values with or without lime and nitrification inhibitor (3,4-dimethylpyrazole phosphate, DMPP). We monitored the effects of 15 N-nitrate or 15 N-ammonium on the plant biomass and NUE, residual soil N, leachate, and emitted gas. The NUE of pakchoi in acidic soil was greater with nitrate than with ammonium; however, when lime was applied, the NUE of pakchoi increased significantly compared to ammonium alone. The NUE of pakchoi was not affected by N source in the alkaline soil, but application of DMPP together with ammonium significantly reduced NUE of pakchoi compared to ammonium alone. The N source had no effect on the NUE of sweet potato in acidic or alkaline soils, while NUE increased significantly after application of lime and ammonium (31.3%) and with application of DMPP (32.4%) compared to ammonium alone (30% in acidic soil and 23% in alkaline soil). Pakchoi NUE was significantly (p < 0.05) related to gross mineralization rate and the inorganic N supply capacity. Nitrous oxide emissions after N fertilization were greater in the alkaline than in acid soil greater after ammonium than after nitrate application. Since DMPP together with ammonium reduced N2O losses from the alkaline soil, this indicates the importance of nitrification as an N2O production process. Nitrate leaching was greater with lime and ammonium application compared to ammonium alone in the acidic soil, whereas the opposite occurred for ammonium leaching. In summary, crop NUE can be significantly increased by lime treatment whereas the addition of DMPP also increased the NUE of sweet potato, which prefer ammonium, grown in the alkaline soil. [ABSTRACT FROM AUTHOR]

Background and aims: High aluminum (Al3+) concentrations associated with subsoil acidity is a major constraint to durum wheat (Triticum turgidum) production as it inhibits root growth affecting crop tolerance to drought. This study evaluated the introgressed TaMATE1B gene on drought resistance and Al3+ toxicity in durum wheat. Methods: Durum wheat lines Jandaroi–TaMATE1B (introgressed with the TaMATE1B gene) and Jandaroi–null (without TaMATE1B gene) were grown in 1-m deep columns filled with re-constructed field soil with Al3+-rich acid subsoil in a glasshouse under well-watered conditions until the onset of ear emergence (Z51), before imposing well-watered and terminal drought treatments. Results: Jandaroi–TaMATE1B produced 25.3 % higher grain yield than Jandaroi–null under well-watered conditions and 49.0 % higher grain yield under terminal drought. Terminal drought reduced grain yield by 47.7 % in Jandaroi–TaMATE1B and 72 % in Jandaroi–null, relative to well-watered conditions. The effects of TaMATE1B on grain yield can be attributed to increased root growth and proliferation below 0.4 m in Al3+-toxic soil. Jandaroi–TaMATE1B had 34.5 and 32.0 % more total root biomass than Jandaroi–null in the well-watered and terminal drought treatments, respectively (P ≤ 0.05). Jandaroi–TaMATE1B had a significantly higher root: shoot ratio than Jandaroi–null at Z51. Introgression of the TaMATE1B gene did not affect grain-filling duration, but terminal drought reduced it by 24 days in both lines. Conclusions: Introgression of the Al3+-tolerant TaMATE1B gene into durum wheat improved terminal drought resistance by enabling root growth and proliferation into deep layers of Al3+-rich acidic soil. [ABSTRACT FROM AUTHOR]

Background: Gypsum is a valuable resource for farmers, supplying essential calcium and sulfur for plant growth. It serves as a crucial soil amendment, particularly in reclaiming alkali and sodic soils. While not a liming material, gypsum is widely recognized as a nutrient source for calcium and sulfur in acidic soils. The presence of calcium in various crops growing in acidic soils is instrumental in alleviating aluminum toxicity and mitigating aluminum phytotoxicity.The application of gypsum positively influences nutrient uptake, thereby enhancing their availability and overall productivity in acidic soils. Synthetic gypsum variants like slag-based gypsum, phosphogypsum, and flue gas desulfurized gypsum have garnered attention due to their elevated silicon content, which enhances plant accessibility in acidic soils. Crucially, gypsum does not significantly alter the pH of acidic soils, although it may induce slight changes depending on specific soil conditions such as mineral composition and cation exchange capacity.Gypsum promotes improved root development in crops, exerting a multifaceted impact on soil physicochemical properties, ultimately bolstering crop productivity and the sustainability of acidic soils. Furthermore, gypsum contributes to mitigating greenhouse gas emissions in acidic soils, particularly in reducing methane emissions. The recent application of industrial gypsum has emerged as a viable strategy for enhancing the immobilization of heavymetals in acidic soils. These versatile applications underscore the potential benefits of gypsum for the sustainable management and utilization of acidic soils.Scope: Gypsum is a valuable resource for farmers, supplying essential calcium and sulfur for plant growth. It serves as a crucial soil amendment, particularly in reclaiming alkali and sodic soils. While not a liming material, gypsum is widely recognized as a nutrient source for calcium and sulfur in acidic soils. The presence of calcium in various crops growing in acidic soils is instrumental in alleviating aluminum toxicity and mitigating aluminum phytotoxicity.The application of gypsum positively influences nutrient uptake, thereby enhancing their availability and overall productivity in acidic soils. Synthetic gypsum variants like slag-based gypsum, phosphogypsum, and flue gas desulfurized gypsum have garnered attention due to their elevated silicon content, which enhances plant accessibility in acidic soils. Crucially, gypsum does not significantly alter the pH of acidic soils, although it may induce slight changes depending on specific soil conditions such as mineral composition and cation exchange capacity.Gypsum promotes improved root development in crops, exerting a multifaceted impact on soil physicochemical properties, ultimately bolstering crop productivity and the sustainability of acidic soils. Furthermore, gypsum contributes to mitigating greenhouse gas emissions in acidic soils, particularly in reducing methane emissions. The recent application of industrial gypsum has emerged as a viable strategy for enhancing the immobilization of heavymetals in acidic soils. These versatile applications underscore the potential benefits of gypsum for the sustainable management and utilization of acidic soils.Conclusion: Gypsum is a valuable resource for farmers, supplying essential calcium and sulfur for plant growth. It serves as a crucial soil amendment, particularly in reclaiming alkali and sodic soils. While not a liming material, gypsum is widely recognized as a nutrient source for calcium and sulfur in acidic soils. The presence of calcium in various crops growing in acidic soils is instrumental in alleviating aluminum toxicity and mitigating aluminum phytotoxicity.The application of gypsum positively influences nutrient uptake, thereby enhancing their availability and overall productivity in acidic soils. Synthetic gypsum variants like slag-based gypsum, phosphogypsum, and flue gas desulfurized gypsum have garnered attention due to their elevated silicon content, which enhances plant accessibility in acidic soils. Crucially, gypsum does not significantly alter the pH of acidic soils, although it may induce slight changes depending on specific soil conditions such as mineral composition and cation exchange capacity.Gypsum promotes improved root development in crops, exerting a multifaceted impact on soil physicochemical properties, ultimately bolstering crop productivity and the sustainability of acidic soils. Furthermore, gypsum contributes to mitigating greenhouse gas emissions in acidic soils, particularly in reducing methane emissions. The recent application of industrial gypsum has emerged as a viable strategy for enhancing the immobilization of heavymetals in acidic soils. These versatile applications underscore the potential benefits of gypsum for the sustainable management and utilization of acidic soils. [ABSTRACT FROM AUTHOR]

Sustainable agricultural practices based on the development of native arbuscular mycorrhizal fungi (AMF) can improve crop growth and stress tolerance in acidic soils with manganese toxicity. The beneficial effects are stronger when crops are colonized early in development by an intact extraradical mycelium (ERM), but are dependent on AMF assemblage. In wheat colonized by AMF associated to Lolium rigidum L. (LOL) or Ornithopus compressus (ORN), growth and stress tolerance are differently influenced. In the present study, this functional diversity was studied by evaluating the activity of ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), guaiacol peroxidase (GPX), superoxide dismutase (SOD) and Mn-SOD. ORN treatment promoted higher wheat shoot and root dry weights, a higher root protein content, decreased root APX, GR and SOD activities but a higher proportion of MnSOD activity. ORN associated microbiota differently manage antioxidant enzyme activity of succeeding wheat to improve growth. [ABSTRACT FROM AUTHOR]

Dephosphorization slag is primarily composed of CaO–SiO2–FeO–P2O5 slag system. As it contains abundant valuable components, dephosphorization slag is considered a potential material to restore the degraded acid soil. To efficiently supply Ca, Si, Fe, and P elements for acid soil, the dissolution behavior of dephosphorization slag with high P2O5 content in the weakly acidic solution was investigated. It was found that the existence of citric acid could significantly promote the dissolution of slag in the aqueous solution. Most of the Ca, Si, and P was dissolved from slag at pH 5, and the Fe dissolution ratio reached 36.9%. In this case, the precipitation of Fe3(PO4)2∙8H2O was suppressed, and the majority of C2S–C3P solid phase and matrix phase was dissolved while wustite remained in the residue. The dissolution ratios of main elements from slag decreased dramatically as the pH increased. Only in the weakly acidic solution, it could make full use of dephosphorization slag, and large amounts of nutrient elements were simultaneously supplied. The dissolution ratios of nutrient elements decreased with the increase in particle size. The dissolution kinetics of slag in the citric acid solution followed the shrinking core model. [ABSTRACT FROM AUTHOR]

A microcosm study was established using three arable soils differing in both physicochemical properties and AOB or AOA dominance of ammonia oxidization. Nitrification and N2O emissions were quantified under 10 Pa C2H2, 1-octyne, or 3,4-dimethylpyrazole phosphate (DMPP), and the community composition and abundance of AOA and AOB were assessed. Amendment of soil with DMPP had a comparable effect to 1-octyne on AOB activities, composition, and N2O emissions across soils. By blocking AOB activity, both DMPP and 1-octyne supported higher rates of AOA growth in both the acid and alkaline soils. Approximately, 50% of ammonia-oxidizing activity in the acid soil was attributed to AOB activity by phylotypes affiliated with Nitrosomonas communis. When AOB were blocked by DMPP or 1-octyne across all soils, recovery of AOA communities was associated with the increased abundance of Nitrososphaera viennesis. [ABSTRACT FROM AUTHOR]

Aims: Characterizing the roles of abundant and rare soil microorganism is vital for clarifying microbial functions and help optimize agricultural management strategies, but their responses to various amendments in acid soils and correlations with crop biomass remain poorly understood.A 5-year field experiment was conducted to evaluate the influence of amendments, including canola straw (SC), animal manure (OM), and alkaline slag (AS), on abundant and rare bacteria or fungi in acidic bulk and rhizosphere soils in aspect of microbial diversity, compositions, potential functions, and their relationship with canola biomass.Amendments and canola planting significantly affected both bacterial and fungal community structures. Applying AS had pronounced effect on bacterial communities and sub-communities, and the addition of OM showed the strong influence on fungal communities and sub-communities. The sub-community structures of rare bacterial and rare fungal significantly correlated to canola biomass; this correlation was stronger in the rhizosphere soil than that in the bulk soil. The α-diversity of rare rhizosphere bacteria, but not rare bulk bacteria and rare fungi, was significantly positively related to canola biomass. Rare bacteria accounted for the high proportion of nodes and most keystone species in microbial networks, and the number of edges belonging to rare bacteria positively correlated to canola biomass. The predicted functions of rare bacteria also make large contributions to crop biomass.These findings highlight the important roles that rare microbes play in ameliorating acid soils and suggest that rare bacteria should be more closely associated with crop growth than rare fungi.Methods: Characterizing the roles of abundant and rare soil microorganism is vital for clarifying microbial functions and help optimize agricultural management strategies, but their responses to various amendments in acid soils and correlations with crop biomass remain poorly understood.A 5-year field experiment was conducted to evaluate the influence of amendments, including canola straw (SC), animal manure (OM), and alkaline slag (AS), on abundant and rare bacteria or fungi in acidic bulk and rhizosphere soils in aspect of microbial diversity, compositions, potential functions, and their relationship with canola biomass.Amendments and canola planting significantly affected both bacterial and fungal community structures. Applying AS had pronounced effect on bacterial communities and sub-communities, and the addition of OM showed the strong influence on fungal communities and sub-communities. The sub-community structures of rare bacterial and rare fungal significantly correlated to canola biomass; this correlation was stronger in the rhizosphere soil than that in the bulk soil. The α-diversity of rare rhizosphere bacteria, but not rare bulk bacteria and rare fungi, was significantly positively related to canola biomass. Rare bacteria accounted for the high proportion of nodes and most keystone species in microbial networks, and the number of edges belonging to rare bacteria positively correlated to canola biomass. The predicted functions of rare bacteria also make large contributions to crop biomass.These findings highlight the important roles that rare microbes play in ameliorating acid soils and suggest that rare bacteria should be more closely associated with crop growth than rare fungi.Results: Characterizing the roles of abundant and rare soil microorganism is vital for clarifying microbial functions and help optimize agricultural management strategies, but their responses to various amendments in acid soils and correlations with crop biomass remain poorly understood.A 5-year field experiment was conducted to evaluate the influence of amendments, including canola straw (SC), animal manure (OM), and alkaline slag (AS), on abundant and rare bacteria or fungi in acidic bulk and rhizosphere soils in aspect of microbial diversity, compositions, potential functions, and their relationship with canola biomass.Amendments and canola planting significantly affected both bacterial and fungal community structures. Applying AS had pronounced effect on bacterial communities and sub-communities, and the addition of OM showed the strong influence on fungal communities and sub-communities. The sub-community structures of rare bacterial and rare fungal significantly correlated to canola biomass; this correlation was stronger in the rhizosphere soil than that in the bulk soil. The α-diversity of rare rhizosphere bacteria, but not rare bulk bacteria and rare fungi, was significantly positively related to canola biomass. Rare bacteria accounted for the high proportion of nodes and most keystone species in microbial networks, and the number of edges belonging to rare bacteria positively correlated to canola biomass. The predicted functions of rare bacteria also make large contributions to crop biomass.These findings highlight the important roles that rare microbes play in ameliorating acid soils and suggest that rare bacteria should be more closely associated with crop growth than rare fungi.Conclusions: Characterizing the roles of abundant and rare soil microorganism is vital for clarifying microbial functions and help optimize agricultural management strategies, but their responses to various amendments in acid soils and correlations with crop biomass remain poorly understood.A 5-year field experiment was conducted to evaluate the influence of amendments, including canola straw (SC), animal manure (OM), and alkaline slag (AS), on abundant and rare bacteria or fungi in acidic bulk and rhizosphere soils in aspect of microbial diversity, compositions, potential functions, and their relationship with canola biomass.Amendments and canola planting significantly affected both bacterial and fungal community structures. Applying AS had pronounced effect on bacterial communities and sub-communities, and the addition of OM showed the strong influence on fungal communities and sub-communities. The sub-community structures of rare bacterial and rare fungal significantly correlated to canola biomass; this correlation was stronger in the rhizosphere soil than that in the bulk soil. The α-diversity of rare rhizosphere bacteria, but not rare bulk bacteria and rare fungi, was significantly positively related to canola biomass. Rare bacteria accounted for the high proportion of nodes and most keystone species in microbial networks, and the number of edges belonging to rare bacteria positively correlated to canola biomass. The predicted functions of rare bacteria also make large contributions to crop biomass.These findings highlight the important roles that rare microbes play in ameliorating acid soils and suggest that rare bacteria should be more closely associated with crop growth than rare fungi. [ABSTRACT FROM AUTHOR]

Changes in root exudates and rhizospheric microbial functional capacities involved in carbon (C) decomposition and nitrogen (N) transformation of aluminum (Al)-tolerant and Al-sensitive soybean genotypes were investigated under Al stress. Rhizosphere soils were collected from rhizobox systems with two soybean genotypes. A wide range of microbial functional capacities were determined by functional gene arrays. Microbial functional capacities of rhizospheres were distinct between Al-tolerant and Al-sensitive genotypes, which were related to exchangeable Al concentrations. Functional capacities associated with decomposition of chemically recalcitrant C were lower in Al-tolerant than Al-sensitive genotypes, which was negatively correlated with the secretion rate of succinic acid. Microbial functional capacities were higher for nitrification but lower for denitrification in the rhizosphere of Al-tolerant than Al-sensitive genotype, which coincided with higher succinic acid secretion and lower abundance of microbial oxygen stress genes. Soybean biomass increased logarithmically with nitrification capacities. We concluded that exchangeable Al concentrations, root exudation, and microbial C and N cycling capacities were intrinsically linked, which served as a key mechanism for legume genotypes toward enhancing tolerance to Al stress occurring in acid soils. [ABSTRACT FROM AUTHOR]

The tea plant [Camellia sinensis (L.) O. Kuntz] is a well-known hyper-accumulator of aluminum (Al3+) that can grow in acidic soils contaminated with excess levels of Al3+. In this work, we used various assays for ascorbate–glutathione cycle components and other antioxidant enzymes to show that the alterations in the redox status after Al3+ treatment on tea cultivars, TV23 (tolerant) and S3A1 (sensitive), is responsible for their differential tolerance to Al3+ stress. A lower dose of Al3+ stress hastened the growth rate as suggested by an increase in biomass with respect to the control in both roots and leaves, but on further increasing the dose, the reverse occurred. Organic acid exudation has a major role in Al3+ detoxification. This study also reports the involvement of oxalate as a major exudate, since the activity of glycolate oxidase (GO) was found to drastically increase under the Al3+ stress condition. The increment in reactive oxygen species production and accumulation was quantitated in terms of malondialdehyde (MDA), super oxide anion (O2−), and hydrogen peroxide (H2O2), which was followed by a rapid increase in the activity of many stress-responsive antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX). The results indicated that differential tolerance to Al3+ toxicity in tea varieties is linked to their oxidative stress response; and, antioxidant enzymes, as a crucial constituent of the defense response, appear to function differentially in the two cultivars. This is the first report showing differential tolerance of two contrasting varieties of 'Assam Tea' to Al3+ stress. [ABSTRACT FROM AUTHOR]

Aims: We tested whether a nurse-plant effect depends on target-seedling tolerance to soil acidity and arbuscular mycorrhizal fungi (AMF) in an acid soil. Methods: A mesocosm experiment was used to assess the acid-tolerance of the seedlings of four target species. Field experiment 1 tested the nurse effects of an adult plant (Lespedeza formosa) on germination rate, seedling survival rate, growth and AMF colonization rate of target seedlings growing in an acid soil. Field experiment 2 tested the influence of AMF root colonization on nurse-plant effects. Results: Target species greatly varied in their tolerance to soil acidity while nurse-effect on target species were mediated by target species acid-tolerance and AMF root colonization. In field experiment 1, as expected, nurse-effect was positive for acid-sensitive species and negative for acid-tolerant species. While nurse plant presence facilitated the germination, survival, growth, and AMF colonization of the two acid-sensitive species it competed with the two acid-tolerant species. In field experiment 2, the nurse plant facilitated the growth of the acid-sensitive seedlings more under AMF not suppressed treatment than AMF suppressed treatment. For the acid-tolerant seedlings, however, the nurse plant reduced their growth under AMF not suppressed treatment, but did not affect their growth under AMF suppressed treatment. Conclusion: Nurse plant facilitated the acid-sensitive species in an acid soil, and the facilitation was enhanced by increasing AMF in the soil. These findings highlight how acid-tolerance of target species and AMF colonization mediates nurse plant facilitation and has important implications for the use of nurse plants in the restoration of acid soils ecosystems. [ABSTRACT FROM AUTHOR]

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Background and aims: Although phosphorus (P) application is known to affect the zinc (Zn) nutrition of crops, the underlying mechanisms and effects of soil type are unclear.Methods: A greenhouse pot experiment was conducted with wheat, two soils (calcareous and acid), and nine P fertilizer rates (0, 50, 100, 200, 400, 1000, 2000, 3000, and 5000 mg P2O5 kg−1 soil).Results: The effects of P application on the Zn content of shoots and roots in wheat and on the levels of available Zn in soil differed on the two soils. The wheat dry weight on both soils was highest with 2000 mg P2O5 kg−1. Total Zn accumulation was reduced above 2000 mg P2O5 kg−1 on the acid soil and above 100 mg P2O5 kg−1 on the calcareous soil. Available soil Zn declined when the Bray-P concentration reached about 34 mg kg−1 in the acid soil and when the Olsen-P concentration exceeded 200 mg kg−1 in the calcareous soil. Shoot Zn concentrations were negatively related to available soil P on the two soils.Conclusion: The negative effects of increasing P application rates on Zn accumulation by wheat differed between the two soils. The effects showed no close relationship to available soil Zn. [ABSTRACT FROM AUTHOR]

Soil acidification is one of major problems limiting crop growth and especially becoming increasingly serious in China owing to excessive use of nitrogen fertilizer. Only the STOP1 of Arabidopsis was identified clearly sensitive to proton rhizotoxicity and the molecular mechanism for proton toxicity tolerance of plants is still poorly understood. The main objective of this study was to investigate the transcriptomic change in plants under the low pH stress. The low pH as a single factor was employed to induce the response of the wheat seedling roots. Wheat cDNA microarray was used to identify differentially expressed genes (DEGs). A total of 1057 DEGs were identified, of which 761 genes were up-regulated and 296 were down-regulated. The greater percentage of up-regulated genes involved in developmental processes, immune system processes, multi-organism processes, positive regulation of biological processes and metabolic processes of the biological processes. The more proportion of down-regulation genes belong to the molecular function category including transporter activity, antioxidant activity and molecular transducer activity and to the extracellular region of the cellular components category. Moreover, most genes among 41 genes involved in ion binding, 17 WAKY transcription factor genes and 17 genes related to transport activity were up-regulated. KEGG analysis showed that the jasmonate signal transduction and flavonoid biosynthesis might play important roles in response to the low pH stress in wheat seedling roots. Based on the data, it is can be deduced that WRKY transcription factors might play a critical role in the transcriptional regulation, and the alkalifying of the rhizosphere might be the earliest response process to low pH stress in wheat seedling roots. These results provide a basis to reveal the molecular mechanism of proton toxicity tolerance in plants. [ABSTRACT FROM AUTHOR]

The tea plant (Camellia sinensis (L.) O. Kuntze) is indigenous to China, where its wild ancestors are broadly distributed in Southwest China. As an aluminum (Al) accumulator, tea plant is very tolerant to Al and accumulates Al at high levelin the leaves. Here an Al tolerant transcription factor of CsSTOP1 was characterized and assumed to regulate multiple genes critical for Al tolerance. The transcriptional regulations by STOP1-like proteins were conserved and conferred the ability to survive in acid soil. Furthermore, a 9-bp deletion was found in five varieties of assamica subspecies and CsSTOP1Mkdy-OE Arabidopsis lines showed more tolerant to Al than CsSTOP1JM1-OE lines, which might be the natural selection of the genetic variation for the tea plant’s adaptation to acidic soil. Given the CsSTOP1Mkdy allele more tolerant to Al and tea plant gradually spreading from the original center of Southwest China, this present study suggests that CsSTOP1 is labelled as an ‘adaptive’ trait that increases tea plant fitness in a particular environmental context of rhizotoxicity Al toxicity in acid soil. The qPCR result suggests the 9-bp deletion is not responsible for transcriptional activity while this deletion may affect the transcriptional regulation level. [ABSTRACT FROM AUTHOR]

Soil contamination with cadmium (Cd) represents a substantial threat to human health and environmental quality. Long-term effectiveness and persistence of remediation are two important criteria for the evaluation of amendment techniques used to remediate soils polluted with potentially toxic metals. In the current study, we investigated the remediation persistence of a natural sepiolite bearing material (NSBM, containing 15% sepiolite) and ground limestone (equivalent to > 98.0% CaO) on soil pH, Cd bioavailability, and Cd accumulation by pak choi (Brassica chinensis L.) during the growth of four consecutive crops in a Cd-contaminated acid soil with different amounts of NSBM (0, 0.2, 0.5, 1, 2, and 5%). Soil pH levels ranged from 5.21 to 7.76 during the first crop, 4.30 to 7.34 during the second, 4.23 to 7.80 during the third, and 4.33 to 6.98 during the fourth, and increased significantly with increasing the application rate of NSBM. Soil CaCl2-Cd and shoot Cd concentrations decreased by 8.11 to 99.2% and 6.58 to 94.5%, respectively, compared with the control throughout the four cropping seasons. A significant negative correlation was found between soil CaCl2-Cd and soil pH. Combined use of 0.1% lime and NSBM showed greater effects than NSBM alone, especially, when the application rate of NSBM was ˂ 2%. Moreover, pak choi tissue Cd concentrations in the treatments with NSBM addition alone at ≥ 2% or at ≥ 1% NSBM combined with 0.1% lime met the maximum permissible concentration (MPC) over the four crops, allowed by the Chinese and European regulations. Based on the present study, safe crop production in the test soil is possible at a soil pH > 6.38 and CaCl2-Cd < 14 μg kg−1, and soil Cd immobilization by NSBM without or with lime is a potentially feasible method of controlling the transfer of soil Cd into the food chain. [ABSTRACT FROM AUTHOR]

Aims: Panax notoginseng is normally cultivated in acidic red soil with high soluble Al, however, the distribution pattern of Al in P. notoginseng is unknown. The aim of this study is to investigate the Al distribution in different organs of P. notoginseng grown in different acid soil, in order to get a deeper insight into the Al tolerance mechanism in this species.Methods: P. notoginseng was sampled from different sites and subjected to Al determination. Al tolerance and accumulation were investigated by exposing the seedlings to different Al concentrations in hydroponic solution. The expression of pectin methylesterase genes was determined by quantitative RT-PCR.Results: The soil pH ranged from 4.68 to 6.13. The total Al concentration in soil was 76.7-168.5 g·kg−1 and active Al was 1.34-5.01 g·kg−1. Al concentration differed with organs of P. notoginseng, following the order: rootlet > rhizome > main root > leaf and stem. Furthermore, Al concentration in the cell wall, organelle and cytoplasmic supernatant of P. notoginseng was approximately 15:2:1 and most Al in the cell wall was bound to pectin component. Al treatment significantly increased the content of pectin and enhanced the expression of PME3, PME7, and PME40 of P. notoginseng root.Conclusions: P. notoginseng was able to grow under high active Al condition and accumulated high Al in its underground parts. The pectin component in the cell wall was the major binding site of Al of P. notoginseng root. [ABSTRACT FROM AUTHOR]

Background and aims: Although silicon (Si) is known to improve plant growth under low phosphorus (P) conditions, the in planta mechanisms responsible for this effect are still unknown. Here, we investigated the role of Si on P uptake along with the expression of Pi transporters in wheat ( Triticum aestivum L.) grown in low P acid soil in comparison with P fertilization and liming. Methods: A combined approach was performed including analyses of rhizosphere soil, tissue P content, the expression of the root Pi transporter genes ( TaPHT1.1 and TaPHT1.2), and the root exudation of citrate and malate. Results: Supply of Si in a form of NaSiO increased shoot P concentration to an adequate level in the range of P-fertilized plants. Silicon ameliorated low soil pH and high Al comparable to the effect of liming. The in planta effect of Si on up-regulating the expression of TaPHT1.1 and TaPHT1.2 was several fold higher and consequently P uptake doubled compared to both P fertilization and liming. In addition, Si directly stimulated root Pi acquisition by prominently increasing both malate and citrate exudation rate. Conclusions: Application of Si increased root exudation of organic acids that mobilize Pi in the rhizosphere and up-regulated Pi transporters in wheat roots. [ABSTRACT FROM AUTHOR]

Maize is not inherently tolerant to soil acidity but due to the ever increasing demand for the crop in the developing world, production of maize on acid soils continues to expand. Breeding for maize acid soil tolerance is the best strategy to improve yield under these conditions. Therefore, the current study was done to determine the general combining ability (GCA) of eight acid-soil tolerant and susceptible inbred lines and the specific combining ability (SCA) of cross combinations of these lines for grain yield under acid and non-acid soils. The eight lines were crossed using a diallel mating design to produce 28 single cross hybrids for evaluation under acid and non-acid soils at four sites for two seasons. Line C2 was the best general combiner under both soil environments while A2/C1 and A1/C2 had the highest desirable SCA effects under optimal conditions. Loss in grain yield and sensitivity to low pH stress was higher among genotypes in light textured soils than heavy soils. Non-additive gene action was more important than additive gene action in conditioning grain yield under both environments. Results revealed that it was feasible to improve grain yield under low pH and optimum soils from the set of genotypes used in the current study. [ABSTRACT FROM AUTHOR]

One Gram-negative, aerobic, motile, rod-shaped bacterium, designated as FH14, was isolated from nodules of Phaseolus vulgaris grown in Hidalgo State of Mexico. Results based upon 16S rRNA gene (≥99.8 % similarities to known species), concatenated sequence ( recA, atpD and glnII) analysis of three housekeeping genes (≤93.4 % similarities to known species) and average nucleotide identity (ANI) values of genome sequence (ranged from 87.6 to 90.0 % to related species) indicated the distinct position of strain FH14 within the genus Rhizobium. In analyses of symbiotic genes, only nitrogen fixation gene nifH was amplified that had nucleotide sequence identical to those of the bean-nodulating strains in R. phaseoli and R. vallis, while nodulation gene nodC gene was not amplified. The failure of nodulation to its original host P. vulgaris and other legumes evidenced the loss of its nodulation capability. Strain FH14 contained summed feature 8 (C ω6 c/C ω7 c, 59.96 %), C (10.6 %) and summed feature 2 (C aldehyde/unknown 10.928, 10.24 %) as the major components of cellular fatty acids. Failure to utilize alaninamide, and utilizing l-alanine, l-asparagine and γ-amino butyric acid as carbon source, distinguished the strain FH14 from the type strains for the related species. The genome size and DNA G+C content of FH14 were 6.94 Mbp and 60.8 mol %, respectively. Based on those results, a novel specie in Rhizobium, named Rhizobium hidalgonense sp. nov., was proposed, with FH14 (=HAMBI 3636 = LMG 29288) as the type strain. [ABSTRACT FROM AUTHOR]

Here, we report results from a field experiment investigating the application of biochars, lime, organic fertilizer, and their combinations. Soil pH was increased by ameliorants. Wheat biochar produced the largest increase, of approximately 2 pH units, and mixed treatment (one third rice husk biochar, one third lime, and one third organic fertilizer) also caused large increases, of almost 1 pH unit. There was strong evidence that the ratio of ammonia-oxidizing archaea to ammonia-oxidizing bacteria (AOB) abundance greatly increased with decreased soil pH, indicating that soil pH was an important factor affecting the abundance of AOB. High-throughput MiSeq sequencing showed that the soil ameliorants significantly increased the relative abundances of Nitrosomonas and Nitrospira. Soil pH was an important determinant of the bacterial community composition and diversity. Our study suggests that the ameliorants (biochar, lime, organic fertilizer, and their combinations) change soil nitrification by altering nitrifying bacteria abundance, diversity, and composition, caused by the changed soil pH. [ABSTRACT FROM AUTHOR]

Aims: The role of different soil types for beech productivity and drought sensitivity is unknown. The aim of this experimental study was to compare mycorrhizal diversity between acid sandy and calcareous soils and to investigate how this diversity affects tree performance, nitrogen uptake and use efficiency (NUE). Methods: Beech trees were germinated and grown in five different soil types (pH 3.8 to 6.7). One-and-a-half-year-old plants were exposed for 6 weeks to sufficient or low soil humidity. Tree biomass, root tip mycorrhizal colonization and community structure, root tip mortality, leaf area, photosynthesis, nitrogen concentrations, NUE and short-term N uptake from glutamine were determined. Results: Soil type did not affect photosynthesis or biomass formation, with one exception in calcareous soil, where root mortality was higher than in the other soil types. Beech in acid soils showed lower mycorrhizal colonization, higher nitrogen tissue concentrations, and lower NUE than those in calcareous soils. Drought had no effect on nitrogen concentrations or NUE but caused reductions in mycorrhizal colonization. Mycorrhizal species richness correlated with nitrogen uptake and NUE. Nitrogen uptake was more sensitive to drought in calcareous soils than in acid soils. Conclusions: Beech may be more drought-susceptible on calcareous sites because of stronger decrease of organic nitrogen uptake than on acid soils. [ABSTRACT FROM AUTHOR]

With the fast growth of world population and climate change, agricultural production is being a main global issue and challenge. Leading to deficiencies of several essential elements and toxicity of heavy metals in plants, acid soil is one of the most important limitations to crop productivity worldwide. Although lime is widely used to ameliorate acid soil, it is not economic and ideal. Identification of the mechanisms and genes conferring tolerance to acid soil stress could be an alternative way to improve the productivity in acid soil through breeding tolerant crops. Aluminum (Al) toxicity and phosphorous (P) deficiency are considered as two severe constraints to plant growth in acid soil. Several genes related to tolerance to Al toxicity and P deficiency have been identified and analysed in various crop plants. This review describes the current understanding of transcription factors involved in the transcriptional regulation of tolerance to Al toxicity and P deficiency in Arabidopsis and rice. [ABSTRACT FROM AUTHOR]

Repeated blocks in the TaALMT1 promoter as well as a transposon insertion in the TaMATE1B upstream region have been correlated with the level of gene expression, organic acid efflux, and ultimately aluminum (Al3+) resistance in wheat (Triticum aestivum L.). In this study, we investigated the allelic polymorphism related to the TaALMT1 and TaMATE1B promoter regions in 300 Brazilian wheat genotypes and the correlation of that variation with root growth on acid soil. In addition, SSR markers were used to determine the genetic variability of the genotypes. Seven TaALMT1 promoter alleles (Types I–VII) were detected based on size of PCR products. The most common alleles were Type V and Type VI (71.3 and 11.9 %, respectively), and these are generally associated with higher levels of TaALMT1 expression and Al3+ resistance. The promoter alleles Type I and Type II, which are usually associated with Al3+ sensitivity, were detected in 12.2 % of the genotypes. The insertion in the TaMATE1B promoter, associated with greater Al3+ resistance, was identified in 80 genotypes. Combination among the alleles allowed the separation in 12 haplotypes were 68 genotypes presented the TaALMT1 promoters Type V and Type VI along with the transposon insertion in the TaMATE1B promoter. However, the most represented haplotype was Type V without the insertion (176 genotypes). Short-term soil experiment, performed in 33 genotypes representing the 12 haplotypes, revealed that the higher relative root length was observed in some genotypes presenting TaALMT1 promoters Type V or Type VI and the transposon insertion in the TaMATE1B promoter. Moreover, when comparing genotypes inside the same haplotype, the transposon insertion was significantly advantageous for a few materials. However, the majority the genotypes presenting the insertion in the TaMATE1B promoter did not outperform the genotypes without the insertion but showing the same TaALMT1 promoter. Analysis using SSR markers, with an average PIC of 0.60, showed high genetic diversity among the genotypes belonging to different haplotypes. The alleles and the genetically diverse genotypes reported here should be considered for wheat-breeding programs aiming increments in wheat Al3+ resistance. [ABSTRACT FROM AUTHOR]

Purpose: Initial soil pH determines the direction and magnitude of pH change after residue addition. This study aimed to evaluate the relative importance of initial soil pH and rate of residue application in determining subsequent pH change, nitrogen (N) mineralization, and soil-exchangeable aluminum (Al). Materials and methods: An incubation experiment was conducted for 102 days on a Plinthudult soil and a Paleudalf soil, where pH gradients were produced after application of direct current (DC). Rates of vetch applications were 0, 5, 15, 30, and 50 g kg soil. Results and discussion: Increasing rates of vetch application caused greater increases in soil pH, but no consistent increase in soil pH at higher initial pH range (4.40∼6.74), because of nitrification. There was a positive correlation between alkalinity production and the initial soil pH at day 14, while correlations became negative at days 56 and 102. Mineral N accumulated as NH-N in low pH soils, due to limited nitrification, while NO-N dominated in higher pH soils. Application of vetch decreased KCl-extractable Al, probably because of complexation of Al by organic matter and precipitation of Al as a result of increased pH, reductions in Al concentration increased with increasing rates of vetch application. However, this amelioration effect on Al concentration weakened with time in higher pH soils. Conclusions: Application of vetch residue can significantly increase soil pH and concentrations of mineral N and reduce exchangeable Al. These amelioration effects are enhanced with increased rate of vetch addition and vary with time depending on the initial pH of the soil. [ABSTRACT FROM AUTHOR]

Aims: Aluminum (Al) toxicity in acid soil significantly reduces plant growth, agricultural productivity and ecosystem health. The Al-tolerant barley cultivars were reported to mainly rely on the Al-activated efflux of citrate from root apices, but the key mechanisms for Al tolerance may differ for wild relatives of barley adapted to acid soil.Here, we investigated plant Al tolerance from evolutionary physiological, molecular, and ecological perspectives.Phylogenetic analysis of Al tolerance-associated gene families showed that most of these genes were conserved from streptophyte algae to angiosperms, indicating land plants have evolved gradually in adaption to Al-rich acid soil during plant terrestrialization. Vacuolar phosphate transporter SPX-major facility superfamily (SPX-MFS) and inorganic phosphate transporter 1 family (PHT1s) of streptophyte algae showed high genetic similarity to land plants. PHT1s exhibited a significant expand during the evolution from streptophyte algae to liverworts and then eudicots. Al-tolerant Tibetan wild barley accession, XZ29 showed high levels of P-containing glycolytic intermediates including Glu-6-P, Fru-6-P, 3-PGA, 2-PGA and PEP under Al stress. Some primary metabolites were evolutionarily conserved in liverwort, gymnosperm and three tested angiosperms. Furthermore, we found that Al-induced Pi efflux from root elongation zone to chelate rhizosphere Al3+, and immobilization of Al with P at the inner epidermal layer of root mature zone to reduce Al accumulation in the cortical layer in barley.These results indicated that Tibetan wild barley has evolved unique P transport and metabolism for the adaptation to harsh conditions in eastern and southeastern Tibet where acid soils contain high P.Methods: Aluminum (Al) toxicity in acid soil significantly reduces plant growth, agricultural productivity and ecosystem health. The Al-tolerant barley cultivars were reported to mainly rely on the Al-activated efflux of citrate from root apices, but the key mechanisms for Al tolerance may differ for wild relatives of barley adapted to acid soil.Here, we investigated plant Al tolerance from evolutionary physiological, molecular, and ecological perspectives.Phylogenetic analysis of Al tolerance-associated gene families showed that most of these genes were conserved from streptophyte algae to angiosperms, indicating land plants have evolved gradually in adaption to Al-rich acid soil during plant terrestrialization. Vacuolar phosphate transporter SPX-major facility superfamily (SPX-MFS) and inorganic phosphate transporter 1 family (PHT1s) of streptophyte algae showed high genetic similarity to land plants. PHT1s exhibited a significant expand during the evolution from streptophyte algae to liverworts and then eudicots. Al-tolerant Tibetan wild barley accession, XZ29 showed high levels of P-containing glycolytic intermediates including Glu-6-P, Fru-6-P, 3-PGA, 2-PGA and PEP under Al stress. Some primary metabolites were evolutionarily conserved in liverwort, gymnosperm and three tested angiosperms. Furthermore, we found that Al-induced Pi efflux from root elongation zone to chelate rhizosphere Al3+, and immobilization of Al with P at the inner epidermal layer of root mature zone to reduce Al accumulation in the cortical layer in barley.These results indicated that Tibetan wild barley has evolved unique P transport and metabolism for the adaptation to harsh conditions in eastern and southeastern Tibet where acid soils contain high P.Results: Aluminum (Al) toxicity in acid soil significantly reduces plant growth, agricultural productivity and ecosystem health. The Al-tolerant barley cultivars were reported to mainly rely on the Al-activated efflux of citrate from root apices, but the key mechanisms for Al tolerance may differ for wild relatives of barley adapted to acid soil.Here, we investigated plant Al tolerance from evolutionary physiological, molecular, and ecological perspectives.Phylogenetic analysis of Al tolerance-associated gene families showed that most of these genes were conserved from streptophyte algae to angiosperms, indicating land plants have evolved gradually in adaption to Al-rich acid soil during plant terrestrialization. Vacuolar phosphate transporter SPX-major facility superfamily (SPX-MFS) and inorganic phosphate transporter 1 family (PHT1s) of streptophyte algae showed high genetic similarity to land plants. PHT1s exhibited a significant expand during the evolution from streptophyte algae to liverworts and then eudicots. Al-tolerant Tibetan wild barley accession, XZ29 showed high levels of P-containing glycolytic intermediates including Glu-6-P, Fru-6-P, 3-PGA, 2-PGA and PEP under Al stress. Some primary metabolites were evolutionarily conserved in liverwort, gymnosperm and three tested angiosperms. Furthermore, we found that Al-induced Pi efflux from root elongation zone to chelate rhizosphere Al3+, and immobilization of Al with P at the inner epidermal layer of root mature zone to reduce Al accumulation in the cortical layer in barley.These results indicated that Tibetan wild barley has evolved unique P transport and metabolism for the adaptation to harsh conditions in eastern and southeastern Tibet where acid soils contain high P.Conclusions: Aluminum (Al) toxicity in acid soil significantly reduces plant growth, agricultural productivity and ecosystem health. The Al-tolerant barley cultivars were reported to mainly rely on the Al-activated efflux of citrate from root apices, but the key mechanisms for Al tolerance may differ for wild relatives of barley adapted to acid soil.Here, we investigated plant Al tolerance from evolutionary physiological, molecular, and ecological perspectives.Phylogenetic analysis of Al tolerance-associated gene families showed that most of these genes were conserved from streptophyte algae to angiosperms, indicating land plants have evolved gradually in adaption to Al-rich acid soil during plant terrestrialization. Vacuolar phosphate transporter SPX-major facility superfamily (SPX-MFS) and inorganic phosphate transporter 1 family (PHT1s) of streptophyte algae showed high genetic similarity to land plants. PHT1s exhibited a significant expand during the evolution from streptophyte algae to liverworts and then eudicots. Al-tolerant Tibetan wild barley accession, XZ29 showed high levels of P-containing glycolytic intermediates including Glu-6-P, Fru-6-P, 3-PGA, 2-PGA and PEP under Al stress. Some primary metabolites were evolutionarily conserved in liverwort, gymnosperm and three tested angiosperms. Furthermore, we found that Al-induced Pi efflux from root elongation zone to chelate rhizosphere Al3+, and immobilization of Al with P at the inner epidermal layer of root mature zone to reduce Al accumulation in the cortical layer in barley.These results indicated that Tibetan wild barley has evolved unique P transport and metabolism for the adaptation to harsh conditions in eastern and southeastern Tibet where acid soils contain high P. [ABSTRACT FROM AUTHOR]

Purpose: Disturbances such as cultivation, logging, and plantation occurred widely in acid red soil area of China, yet little is known about their effects on soil microbial community which is closely related to soil function. In this study, microbial community compositions were investigated in a red soil with different long-term land utilization patterns to understand the potential effects of cultivation and vegetation successions on relevant soil functions. Materials and methods: Land utilization patterns include restoration, degradation (logging), cropland, and pine plantation. Both DNA- and phospholipid fatty acid (PLFA)-based methods were used to measure the abundance and community structure of microorganisms. Results and discussion: In general, DNA- and PLFA-based methods showed similar results of microbial composition, but for some parameters, only one approach showed significant differences between different land utilization patterns. Land utilization patterns showed significant effects on abundance of total microbial community, bacteria, fungi, and actinomycetes which were all lowest in the cropland plot either by PLFA or DNA analyses. 17:0 cyclo/16:1 ω7c and 19:0 cyclo/18:1 ω7c which are possibly associated with environmental stresses also varied among different land utilization patterns. Both PLFA and T-RFLP analyses showed that each land utilization pattern possessed a specific microbial community structure. Conclusions: These results revealed significant effects of different land utilization patterns especially cultivation and logging on soil microbial communities and suggested that we should be cautious in utilizing red soils to sustain soil properties and functions. Combination of DNA- and PLFA-based methods is effective to provide precise results of microbial composition. [ABSTRACT FROM AUTHOR]

To feed the predicted extra two billion people by 2050, crop production must increase on existing cultivated land at a rate that challenges our current capability. Acid soils and aluminium (Al) toxicity restrict productivity worldwide but also offer the greatest opportunity for increases in global food production. Our understanding of the physiology, genetic control and the identification of genomic regions underlying Al resistance in important staple crops has increased greatly over the past 20 years, enabling the application of molecular breeding. In this study, we report the application of an efficient marker-assisted backcrossing (MAB) strategy for the introgression of the HvAACT1 gene which confers Al resistance in barley ( Hordeum vulgare L.). We conducted foreground and background selection using microsatellite (SSR) markers linked to HvAACT1 and SSR-based linkage maps, along with embryo rescue and a cost-effective DNA preparation method shortening the breeding cycle to ~18 months. The MAB strategy enabled the development of homozygous (BCF) Al-resistant lines with the smallest introgressed region and 98.7 % of the recurrent parent genome. The Al-resistant line yielded significantly more seeds (121 %) than its isogenic line in soil-based assays containing 12 % of Al saturation. This MAB strategy could be extended to other staple crops with similar molecular toolboxes, expanding their cultivation onto acid soils, and contributing to greater yield stability and food security, particularly in developing countries. [ABSTRACT FROM AUTHOR]

Many plant species excrete organic acids into the rhizosphere in response to aluminum stress to protect sensitive cells from aluminum rhizotoxicity. When the roots of Eucalyptus camaldulensis, a major source of pulp production, were incubated in aluminum-toxic medium, citrate released into the solution increased as a function of time. Citrate excretion was inducible by aluminum, but not by copper or sodium chloride stresses. This indicated that citrate is the major responsive organic acid released from the roots of this plant species to protect the root tips from aluminum damage. Four genes highly homologs to known citrate-transporting multidrugs and toxic compounds exclusion proteins, named EcMATE1- 4, were isolated using polymerase chain reaction-based cloning techniques. Their predicted proteins included 12 membrane spanning domains, a common structural feature of citrate-transporting MATE proteins, and consisted of 502-579 amino acids with >60 % homology to orthologous genes in other plant species. One of the homologs, designated EcMATE1, was expressed in the roots more abundantly than in the shoots and in response to both Al and low pH stresses. Ectopic expression of EcMATE1 and 3 in tobacco hairy roots enhanced Al-responsive citrate excretion. Pharmacological characterization indicated that Al-responsive citrate excretion involved a protein phosphorylation/dephosphorylation process. These results indicate that citrate excretion through citrate-transporting multidrugs and toxic compounds exclusion proteins is one of the important aluminum-tolerance mechanisms in Eucalyptus camaldulensis. [ABSTRACT FROM AUTHOR]

Background and aims: Soil acidification is known to be one of the constraints of tree growth; however, it is unclear how it affects tree growth at photosynthesis level (i.e., through affecting stomatal conductance vs. carboxylation rate) during the growth of trees. This paper studied the effects of soil acidification on Pinus densiflora foliar chemistry and tree ring C isotope ratio (C/C, expressed as δC) and their relationship with tree growth. Methods: Tree growth (diameter, annual growth ring area, and root biomass), soil chemistry (pH, mineral N, and exchangeable Ca and Al), foliage chemistry (N, Ca/Al, and δC), and tree ring δC in P. densiflora stands along a soil pH gradient (from 4.38 to 4.83, n = 9) in southern Korea were investigated. Results: Overall, trees with relatively poor growth under more acidic soil conditions (low pH and Ca/Al) had lower values of foliar N concentration and δC and tree ring δC, suggesting that restricted N uptake under more acidic soil conditions caused N limitation for photosynthesis, leading to poor tree growth. In addition, relationships between mean annual area increment and carbon isotope discrimination of tree rings at five-yr intervals from 1968 to 2007 revealed that the impact of soil acidification on tree growth became severer during the last 15 yrs as negative correlations between them became significant after 1993. Conclusions: Reduced N uptake under acidic soil conditions resulted in lower radial growth of P. densiflora via non-stomatal limitation of photosynthesis. [ABSTRACT FROM AUTHOR]

In situ remediation with waste material is an inexpensive method to reduce contaminant availability in polluted soil. The experiments were done to investigate the effects of possible in situ application of two different amendments: inorganic material (marble sludge) and organic material (horticultural waste compost) on chemical and biological properties of abandoned metalliferous mine wastes. The results show that the application of inorganic material raises the pH above neutrality and the combination of inorganic and organic material would produce the highest ratio of biological activity. The reductions of available Zn, Pb and As in lime, organic and lime/organic amendments were favoured by incubation time. However, available Cd content increased after 275 days of incubation, except the treatment with inorganic amendment. This work denoted that the application of lime with organic amendments has a better effect than the lime alone because the addition of both amendments improves both soil chemical and biological properties. [ABSTRACT FROM AUTHOR]

Aims: The high concentrations of Mn, Fe and Al in acid soils during waterlogging impair root and shoot growth more severely in intolerant than tolerant wheat genotypes. This study aims to establish whether this difference in vegetative growth and survival during waterlogging (1) is verifiable across a range of tolerant/intolerant genotypes and acid soils, and (2) results in improved recovery after cessation of waterlogging and enhanced grain yield. Methods: Wheat genotypes contrasting in their tolerance to ion toxicities were grown in four acid soils until 63DAS and maturity, with a 42-day waterlogging treatment imposed at 21 DAS. Results: The shoot Al, Mn and Fe concentrations increased by up to 5-, 3- and 9-fold respectively due to waterlogging in various soils. Compared to the intolerant lines, Al-, Mn- and Fe-tolerant genotypes maintained a relatively lower increase in shoot concentrations of Al (79 vs. 117%), Mn (90 vs. 101%) and Fe (171 vs. 252%) and demonstrated better waterlogging tolerance at the vegetative stage expressed in relative root (38% vs. 25%) and shoot (62% vs. 52%) growth. After cessation of waterlogging and the continued growth to maturity, tolerant genotypes maintained a relatively lower plant concentration of Al, Mn and Fe, but produced a higher above-ground biomass (74% vs. 56%) and most importantly demonstrated improved waterlogging tolerance (a relative grain yield of 78% vs. 54%) compared to intolerant genotypes. Maturity following waterlogging stress was delayed less in tolerant than intolerant genotypes (114 vs. 124%, respectively), which would reduce the potential yield loss where post-anthesis coincides with drought. Conclusions: The results confirm the validity of a novel approach of enhancing waterlogging tolerance of wheat genotypes grown in acid soil via increased tolerance to ion toxicities. [ABSTRACT FROM AUTHOR]

Purpose: The key factors influencing pH buffering capacity of acid soils from tropical and subtropical regions, and effects of soil evolution and incorporation of biochars on pH buffering capacity were investigated to develop suitable methods to increase pH buffering capacity of acid soils. Materials and methods: A total of 24 acid soils collected from southern China were used. The pH buffering capacity was determined using acid-base titration. The values of pH buffering capacity were obtained from the slope of titration curves of acid or alkali additions plotted against pH in the pH range 4.0-7.0. Two biochars were prepared from straws of peanut and canola using a low temperature pyrolysis method. After incubation of three acid soils, pH buffering capacity was then determined. Results and discussion: pH buffering capacity had a range of 9.1-32.1 mmol kg pH for 18 acid soils from tropical and subtropical regions of China. The pH buffering capacity was highly correlated ( R = 0.707) with soil cation exchange capacity (CEC) measured with ammonium acetate method at pH 7.0 and decreased with soil evolution due to the decreased CEC. Incorporation of biochars at rates equivalent to 72 and 120 t ha increased soil pH buffering capacity due to the CEC contained in the biochars. Incorporation of peanut straw char which itself contained more CEC and alkalinity induced more increase in soil CEC, and thus greater increase in pH buffering capacity compared with canola straw char. At 5% of peanut straw char added, soil CEC increased by 80.2%, 51.3%, and 82.8% for Ultisol from Liuzhou, Oxisol from Chengmai and Ultisol from Kunlun, respectively, and by 19.8%, 19.6%, and 32.8% with 5% of canola straw char added, respectively; and correspondingly for these soils, the pH buffering capacity increased by 73.6%, 92.0%, and 123.2% with peanut straw char added; and by 31.3%, 25.6%, and 52.3% with canola straw char added, respectively. Protonation/deprotonation of oxygen-containing functional groups of biochars was the main mechanism for the increase of pH buffering capacity of acid soils with the incorporation of biochars. Conclusions: CEC was a key factor determining pH buffering capacity of acid soils from tropical and subtropical regions of China. Decreased CEC and content of 2:1-type clay minerals during evolution of tropical soils led to decreased pH buffering capacity. Incorporation of biochars generated from crop straws did not only ameliorate soil acidity, but also increased soil pH buffering capacity. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the correlation between organic acids secreted by two soybeans genotypes, BX10 [aluminum (Al) tolerant] and BD2 (Al sensitive) and rhizosphere microbial communities in acid soil. The organic acids secreted by BX10 and BD2 were significantly different at each growth stage. Both fungi/bacteria and gram-negative bacteria/gram-positive bacteria ratio values were affected by the two soybean genotypes at different growth periods. Compared with BD2, phospholipid fatty acid of BX10 showed higher Shannon diversity at the seedling and flowering stages, but had lower Shannon diversity at the pod-setting stage. Redundancy analysis and canonical correspondence analysis revealed that the organic acids including tartaric acid, lactic acid, and citric acid significantly affected rhizosphere bacterial communities. Sequence analysis indicated that uncultured Acidobacterium, Chloroflexi, and actinomycete enriched in BD2, whereas some uncultured bacteria enriched in BX10. The two soybean genotypes exhibit distinct rhizosphere microbial communities; root organic acid exudates may affect composition of microbial communities of rhizosphere soil: tartaric acid may negatively affect rhizosphere bacteria at the seedling stage, lactic acid may positively affect rhizosphere actinomycetes at the flowering stage, and succinic acid may stimulate fungi at the pod-setting stage. [ABSTRACT FROM AUTHOR]

Bean species and genotypes show wide phenotypic variability in relation to aluminium (Al) resistance and progressive soil drying. The objective of this study was to identify and characterize sources of resistance to Al toxicity and progressive soil drying among six genotypes of common bean ( Phaseolus vulgaris), four of runner bean ( P. coccineus), and one of tepary bean ( P. acutifolius), using hydroponic and soil cylinder screening methods. One experiment on hydroponic screening of Al resistance was carried out using a basal nutrient solution with and without 20 μM Al. Two experiments were carried out using two oxisols in 80 cm long soil cylinders with high Al (HAl) and low Al (LAl) saturation treatments. The three experiments showed an average of 36.9-53.5% inhibition of root growth with HAl compared with LAl treatments. Differences in root development and distribution were observed among genotypes and species. Two accessions of P. coccineus (G35346-2Q, G35464-5Q) and one Andean common bean genotype (ICA Quimbaya) were outstanding in root and shoot growth in the HAl treatments. P. coccineus accession (G35346-3Q) was outstanding under combined stress of Al-toxic acid soil and progressive soil drying. Accessions of P. coccineus may represent unique sources of Al resistance for the improvement of common bean through interspecific crosses. [ABSTRACT FROM AUTHOR]

We demonstrated that aluminum (Al)-induced oxalate secretion and plasma membrane (PM) H-ATPase activity in tomato ( Lycopersicon esculentum 'Hezuo903') roots were poorly correlated. In addition, vanadate, an inhibitor of PM H-ATPase, had no effect on Al-induced oxalate secretion, but significantly inhibited enzyme activity. An anion channel inhibitor phenylglyoxal inhibited oxalate secretion, but not PM H-ATPase activity. Exposure of tomato roots to 10 μM LaCl also stimulated PM H-ATPase activity; however, La failed to induce oxalate secretion. Furthermore, Al-induced changes of PM H-ATPase activity were not associated with oxalate secretion in two tomato cultivars differing in the ability to secrete oxalate under Al stress. These results indicate that Al independently regulates oxalate secretion and PM H-ATPase activity in tomato roots. Analysis of expression levels of PM H-ATPase genes by real-time reverse transcription-PCR and protein by Western blot and immunodetection revealed that the regulation of PM H-ATPase in response to Al was subjected to transcriptional and posttranscriptional control. However, since neither transcriptional level of genes nor translational level of proteins directly relate to the enzyme activity, posttranslational modification of PM H-ATPase under Al stress likely contributes to changes in activity of this protein. [ABSTRACT FROM AUTHOR]

The present study was undertaken to determine the effect of inoculation with arbuscular mycorrhizal fungi (AMF) from natural and cultivated tea rhizospheres (NTR and CTR, respectively) on growth as well as on quality parameters of tea [ Camellia sinensis (L.) O. Kuntze]. Seeds (after germination) and cuttings were inoculated with AMF consortia from NTR and CTR in non-sterilized acid soil (pH 5.0). Seedlings and cuttings were grown under net-house conditions and the data on growth and quality parameters were recorded up to 2 years. Tea plants were found to be highly colonized by AMF (74–83%) after 1 year. The significant increase in most of the growth parameters (root/shoot length, dry weight; r/s ratio) was recorded in AMF-treated plants, which also showed better tea quality parameters than noninoculated plants. Maximum significant increases up to 31% and 100%, over control, were recorded in amino acids and total protein content, respectively. Similarly, maximum increase in total polyphenols (15%) and caffeine content (34%) over control was also significant. Enhanced sugar content (maximum 16% in total soluble sugars, maximum 45% in reducing sugars, and maximum 69% in non-reducing sugars) was recorded in AMF-inoculated plants. In most cases, better response was observed in tea plants inoculated with AMF consortia from NTR. These results indicate that growth and quality of tea can be improved by AMF inoculations in acid soils. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the changes in the chemical partitioning of Cu, Pb, Cr and Zn within a column of soil incubated with an anaerobic sewage sludge (ANSS) for 2.5 months. The soil was irrigated during the incubation period. A sequential extraction method was used to fractionate these metals into exchangeable, weakly adsorbed, organic, Al oxide, Fe–Mn oxide, and residual, respectively. ANSS was applied at a loading rate of 69 Mg ha−1. The soil is a Dystric Cambisol with low pH (<3.8), low CEC [<10 cmol(+) kg−1 below the first 4 cm depth], and low base saturation (<7%). The addition of the ANSS caused a decrease in concentrations of Cu, Pb, and Cr in the A1 horizon, and an increase in the concentrations with depth. Below the A1 horizon, concentrations of Cu increased uniformly (~1 mg cm−1), and the greatest increases were observed in the residual, Fe–Mn oxides, and weakly adsorbed fractions. Maximum increases in Pb occurred at 4–9 cm of depth (1.6 mg cm−1), and mainly affected the weakly adsorbed fraction. Chromium essentially accumulated at the limit between the A2 and the Bw horizons (1.1–1.5 mg cm−1) as residual and organic bound forms, probably through particulate transport. Zinc mainly accumulated in the A1 horizon (2.9 mg cm−1) as exchangeable Zn. At depth, Zn increments were predominantly observed in the residual fraction. The results of this study thus demonstrate the redistribution of contaminants into different chemical pools and soil layers after sludge amendment. [ABSTRACT FROM AUTHOR]

Background, aims, and scope Increasing soil acidification is a growing concern in southern China. The traditional green manures applied in the fields mostly comprise legumes that tend to accelerate soil acidification. Moreover, acid deposition can act as a source of nitrogen. Hence, we looked for new plant species that would enhance nutrient concentrations when used as green manure and would reduce soil acidity or at least not worsen it. Materials and methods We studied the use of Erigeron annuus (L.) Pers. for ameliorating acid soil in a pot experiment with simulated acid rain (SAR) treatments (pH 5.8 to 3.0) in an open area in Guangzhou City. The pots were divided into two groups named A and B groups. On day 0, pots of A group were filled with soil and planted with Erigeron annuus seedlings. Pots of B group were only filled with soil as the control. On day 40, seedlings of E. annuus were harvested and buried in the corresponding pots. On day 54, two seeds of Phaseolus vulgaris L. were sown in each pot in both groups. The growth and bean yield of P vulgaris seedlings were then used to evaluate the effects of E. annuus on acid soil. Plant and/or soil samples were collected on days 0, 40, 54, and 150; corresponding parameters were measured. Results Results showed that E. annuus could maintain a good growth even on very acid soil. On day 40, the pH decreased significantly (P<0.0001) in the B group pots without E. annuus compared with the A group. On day 54, after E. annuus was buried as a manure, the soil pH of all A group treatments except the pH 4.0 treatment showed a significant increase compared to day 40 (P<0.01). At the same time, the application of E. annuus as a manure produced a significant increase of soil K and P (P<0.001), Ca (P<0.05), and Mg (P<0.001) concentrations of all A group SAR treatments compared to their B group counter-parts (except control pots for Ca). The soil exchangeable K and available P concentration doubled, and Ca and Mg increased by around 25% in the presence of the E. annuus manure application. Discussion The higher soil pH in the A group than B group on the day 40 was due to a great absorption of NO[sub3][sup-] by the roots of E. annuus. The soil pH increase after E. annuus was applied to the soil of A group was attributed to the release of high amount of K, the mineralization of organic N, and the oxidation of organic acid anions. Nutrient increase in the A group after E. annuus application was mostly the result of the nutrient release during the residue decomposition. The amelioration of the soil was effective as demonstrated by the enhanced growth and bean yield of P. vulgaris seedlings on the manured soil compared to the seedlings grown on a control that was not manured. Conclusions E. annuus could maintain a good growth in the acid lateritic field soil. Cultivating this plant and applying it to the soil with a rate of 1.6 ton ha[sup-1] doubled the soil K and P concentrations and increased soil exchangeable Ca and Mg concentrations by around 25%. This species would be a good green manure candidate for growing in the acid soils of southern China. Application of E. annuus also has beneficial effects on crop growth through reduced Al toxicity and cation leaching. Recommendations and perspectives Since E. annuus would improve soil pH and nutrient concentrations with minimum care, it is recommended for treating acid soils with poor yield whenever a low-cost solution is required. [ABSTRACT FROM AUTHOR]

Simple compounds in soil such as organic acids, amino acids and monosaccharides are believed to be important in regulating many aspects of terrestrial ecosystem functioning (e.g. C cycling, nutrient acquisition). Understanding the fate and dynamics of these low molecular weight (MW) compounds is therefore essential for predicting ecosystem responses to disturbance. Our aim was to quantify the amounts of these compounds in two podzolic forest soil profiles (O, E, Bs and C horizons) and to quantify their contribution to total soil respiration. The total concentration of organic acids, amino acids and monosaccharides in soil solution comprised on average 15 ± 10% of the total dissolved organic C (DOC), with declining concentrations in the deeper soil layers. Dissolved organic N (DON) was the dominant form of N in soil solution and free amino acids contributed to 34% of this pool. The mineralization behaviour of glucose and galactose was described by parabolic (Michaelis–Menten) type kinetics with V max and K M values in the range of <1–250 μmol kg−1 h−1 and 15–1,100 μM, respectively. Assuming that (1) microbially mediated substrate turnover follows Michaelis–Menten kinetics, and (2) steady state soil solution concentrations, we calculated the rate of CO2 efflux attributable to the mineralisation of the three classes of low MW compounds. Our results indicated that in the O horizon, the turnover of these substrates could comprise ~100% of the basal, heterotrophic, soil respiration. In contrast, in the deeper mineral soil <20% of total soil respiration could be attributable to the mineralization of these compounds. Our compound-specific approach has identified the main substrates contributing to soil respiration in forest topsoils. However, our results also suggest that soil respiration in subsoils may be attributable to compounds other than organic acids, amino acids and monosaccharides. [ABSTRACT FROM AUTHOR]

Considerable knowledge exists about the effect of aluminium (Al) on root vitality, but whether elevated levels of Al affect soil microorganisms is largely unknown. We thus compared soils from Al-treated and control plots of a field experiment with respect to microbial and chemical parameters, as well as root growth and vitality. The field experiment was established in a 50-year-old Norway spruce ( Picea abies L.) stand where no Al or low concentrations of Al had been added every 7–10 days during the growth season for 7 years. Analysis of soil solutions collected using zero tension lysimeters and porous suction cups showed that Al treatment lead to increased concentrations of Al, Ca and Mg and lower pH and [Ca + Mg + K/Al] molar ratio. Corresponding soil analyses showed that soil pH remained unaffected (pH 3.8), that exchangeable Al increased, while exchangeable Ca and Mg decreased due to the Al treatment. Root in-growth into cores placed in the upper 20 cm of the soil during three growth seasons was not affected by Al additions, neither was nutrient concentration or mortality of these roots. The biomass of some taxonomic groups of soil microorganisms, analyzed using specific membrane components (phospholipid fatty acids; PLFAs), was clearly affected by the imposed Al treatment, both in the organic soil horizon and in the underlying mineral soil. Microbial community structure in both horizons was also clearly modified by the Al treatment. Shifts in PLFA trans/cis ratios indicative of short term physiological stress were not observed. Yet, aluminium stress was indicated both by changes in community structure and in ratios of single PLFAs for treated/untreated plots. Thus, soil microorganisms were more sensitive indicators of subtle chemical changes in soil than chemical composition and vitality of roots. [ABSTRACT FROM AUTHOR]

The double compartment technique has been commonly used in studies on nutrient uptake by mycorrhizas whereas the double pot technique has been used to assess the nutritional stress of plants grown in different soils. A combination of the double pot and the double compartment technique was used as a tool to understand the processes involving mycorrhiza and plant nutrition. Maize (Zea mays) and three species of the arbuscular mycorrhizal fungi in the genus Glomus were used to study phosphorus (P) uptake with and without mycorrhiza from the A and B horizons of an Oxisol. The plants were supplied from the lower pot with a nutrient solution without P. The upper pot had a double compartment with either a fine and coarse mesh screen to control the volume of soil explored by the roots, and thereby, limit the amount of soil P accessible to plants from the test soil. There were significant effects of time for plants grown in both soil horizons, and of mycorrhizas for plants grown in the A soil horizon. No effect of mesh size was observed. There were significant effects of horizon and mycorrhiza, but not of mesh size, on the dry weight and P contents of shoots and roots. The P concentration (P g kg-1 of plant) for shoots and roots was similar in the A and B soil horizons. The results showed that the double pot - double compartment system was suitable for the experimental objectives. No differences in plant growth were observed when root growth was not limited vs root growth limited to the inner compartment because the non-mycorrhizal plants did not take up P. Consequently, responsiveness of the maize cultivar was wholly dependent on mycorrhiza for P uptake under these experimental conditions. [ABSTRACT FROM AUTHOR]

The goals of this work were to understand the dynamics of H+, Al and Ca in the rhizosphere of maize cultivated in tropical acid soils, and to evaluate the contribution of the dissolution kinetics of the Al-hydroxides to Al dynamics. The study of the dissolution kinetics was based on a comparison between experimental and simulated data, using a model of the chemical processes in the rhizosphere. Two Oxisols, pH 5.1 and 4.6, and one Ultisol, pH 5.2, were studied. An Al-tolerant maize variety (Zea mays L.) was grown for 14 days on a 3-mm thick soil layer. The composition of the soil and the soil solution, together with the concentration of Al in the roots, were determined throughout the experiment. The results showed that root growth (i) decreased the soil solution pH, up to one pH unit, (ii) increased Al concentration in the soil solution, (iii) increased exchangeable Al, and (iv) decreased exchangeable Ca. Soil solution pH, exchangeable Al, and exchangeable Ca were closely linked. Exchangeable Al increased 1.5 – 3.0 times, due to the dissolution of easily mobilised Al components. In addition, Al accumulation in roots depended mainly on Al in the soil solution. Modelling the interactions between H+, Al, and Ca proved that the main factor determining Al in the soil solution was the kinetic reactivity of the easily mobilised Al components. These components, probably poorly crystallised Al-hydroxides, are key players in the functioning of the rhizosphere in tropical acid soils. [ABSTRACT FROM AUTHOR]

Effects of the arbuscular mycorrhizal (AM) fungi Gigaspora margarita and Glomus etunicatum on the growth of cowpea (Vigna unguiculata L. Walp.) were assessed at low pH by growing plants, with and without AM inoculation, individually in pots containing a mixture of sand and soil adjusted to pH 4.7, 4.9 or 5.2 at the start of the experiment, and with soluble aluminium (Al) concentrations at a sub-toxic level for the plant. Cowpea grew poorly in the absence of AM colonisation, particularly at pH 4.7. Growth was enhanced both by increasing the pH and by inoculating with the AM fungi, with plant responses greater with inoculation. The relative growth improvement by mycorrhizas (mycorrhizal growth response) was highest at pH 4.7, and decreased as the pH increased, although effects were not always significant. Gi. margarita was much more effective than G. etunicatum. There were differential effects of the two fungi on uptake of mineral elements. Plants inoculated with Gi. margarita took up a range of elements, including P and Zn as well as Al, to a much greater extent than those inoculated with G. etunicatum, regardless of medium pH. The effectiveness of Gi. margarita in increasing plant growth was closely correlated with colonised root length. [ABSTRACT FROM AUTHOR]

Phosphate rock (PR) and organic manure (OM) are promising amendments to acidic soils to correct P deficiency and Al/Mn toxicities. The interaction between PR and OM and consequent effects in acidic soil are not fully understood. The effects of OM on the dissolution of two types of PR (NCPR, North Carolina PR; SYPR, Syrian PR) and dry matter production and nutrient uptake efficiency in an acidic Lily loamy soil from West Virginia were examined in an incubation and plant pot studies. NCPR and SYPR were supplied at a rate of 500 mg P kg-1 and organic manure at a rate of 30 g kg-1. Observations were made over 126 days at 21-day intervals. The dissolution of applied NCPR and SYPR was calculated based on the estimation of ?Pi and ?TP-NaOH method. Dissolution of NCPR and SYPR calculated by ΔTP-NaOH was quick during the initial 21 day (∼20%), and thereafter increased slowly reaching 42 and 40% at 126 day for NCPR and SYPR, respectively. On the other hand, percent dissolution calculated based on ΔPi-NaOH, while fluctuating within ±5% between intervals, were less by 10 and 15% at 126 day for NCPR and SYPR compared to dissolutions estimated based on Δ-TP-NaOH. OM generally reduced PR dissolution, and to a 11–14% lesser extend in the presence of plant roots, presumably due to plant roots depleting P and Ca from the dissolution zone. OM increased dry matter production (DM) of switch grass, increased specific accumulation rates (SAcR, mg or μg g-1 DM) of P and Mg in shoots, decreased SAcRs of Al and Mn in shoots DM, and increased use of P from NCPR and SYPR. Approximately 29% of dissolved P from applied NCPR or SYPR was Bray-1 extractable-Pi and increasing to 45% when OM was also amended to the soil. This increase in dissolved P probably explains the enhanced growth and P concentration in switch grass DM. [ABSTRACT FROM AUTHOR]