Citrate (Cit) and Deferoxamine B (DFOB) are two important organic ligands coexisting in soils with distinct different affinities for metal ions. It has been theorized that siderophores and weak organic ligands play a synergistic role during the transport of micronutrients in the rhizosphere, but the geochemical controls of this process remain unknown. Here we test the hypothesis that gradients in pH and ion strength regulate and enable the cooperation. To this end, first we use potentiometric titrations to identify the dominant Zn(II)\uffe2\uff80\uff93Cit and Zn(II)\uffe2\uff80\uff93DFOB complexes and to determine their ionic strength dependent stability constants between 0 and 1\uffc2\uffa0mol\uffc2\uffa0dm\uffe2\uff88\uff923. We parametrise the Extended Debye-H\uffc3\uffbcckel (EDH) equation and determine accurate intrinsic association constants (log\uffce\uffb20) for the formation of the complexes present. The speciation model developed confirms the presence of [Zn(Cit)]\uffe2\uff88\uff92, [Zn(HCit)], [Zn2(Cit)2(OH)2]4\uffe2\uff88\uff92, and [Zn(Cit)2]4\uffe2\uff88\uff92, with [Zn(Cit)]\uffe2\uff88\uff92 and [Zn2(Cit)2(OH)2]4\uffe2\uff88\uff92 the dominant species in the pH range relevant to rhizosphere. We propose the existence of a\uffc2\uffa0new [Zn(Cit)(OH)3]4\uffe2\uff88\uff92 complex above pH 10. We also verify the existence of two hexadentate Zn(II)\uffe2\uff80\uff93DFOB species, i.e., [Zn(DFOB)]\uffe2\uff88\uff92 and [Zn(HDFOB)], and of one tetradentate species [Zn(H2DFOB)]+. Second, we identify the pH and ionic strength dependent ligand exchange points (LEP) of Zn with citrate and DFOB and the stability windows for Zn(II)\uffe2\uff80\uff93Cit and Zn(II)\uffe2\uff80\uff93DFOB complexes in NaCl and rice soil solutions. We find that the LEPs fall within the pH and ionic strength gradients expected in rhizospheres and that the stability windows for Zn(II)\uffe2\uff80\uff93citrate and Zn(II)\uffe2\uff80\uff93DFOB, i.e., low and high affinity ligands, can be distinctly set off. This suggests that pH and ion strength gradients allow for Zn(II) complexes with citrate and DFOB to dominate in different parts of the rhizosphere and this explains why mixtures of low and high affinity ligands increase leaching of micronutrients in soils. Speciation models of soil solutions using newly determined association constants demonstrate that the presence of dissolved organic matter and inorganic ligands (i.e., bicarbonate, phosphate, sulphate, or chlorides) do neither affect the position of the LEP nor the width of the stability windows significantly. In conclusion, we demonstrate that cooperative and synergistic ligand interaction between low and high affinity ligands is a valid mechanism for\uffc2\uffa0controlling zinc transport in the rhizosphere and possibly in other environmental reservoirs such as in the phycosphere. Multiple production of weak and strong ligands is therefore a valid strategy of plants and other soil organisms to improve access to micronutrients.Plant roots are exposed to hypoxia in waterlogged soils, and they are further challenged by specific phytotoxins produced by microorganisms in such conditions. One such toxin is hexanoic acid (HxA), which, at toxic levels, causes a strong decline in root O2 consumption. However, the mechanism underlying this process is still unknown. We treated pea (Pisum sativum L.) roots with 20\uffe2\uff80\uff89mM HxA at pH\uffe2\uff80\uff895.0 and 6.0 for a short time (1\uffe2\uff80\uff89h) and measured leakage of key electrolytes such as metal cations, malate, citrate and nonstructural carbohydrates (NSC). After treatment, mitochondria were isolated to assess their functionality evaluated as electrical potential and O2 consumption rate. HxA treatment resulted in root tissue extrusion of K+, malate, citrate and NSC, but only the leakage of the organic acids and NSC increased at pH\uffe2\uff80\uff895.0, concomitantly with the inhibition of O2 consumption. The activity of mitochondria isolated from treated roots was almost unaffected, showing just a slight decrease in oxygen consumption after treatment at pH\uffe2\uff80\uff895.0. Similar results were obtained by treating the pea roots with another organic acid with a short carbon chain, that is, butyric acid. Based on these results, we propose a model in which HxA, in its undissociated form prevalent at acidic pH, stimulates the efflux of citrate, malate and NSC, which would, in turn, cause starvation of mitochondrial respiratory substrates of the Krebs cycle and a consequent decline in O2 consumption. Cation extrusion would be a compensatory mechanism in order to restore plasma membrane potential.In Brazilian agriculture, urea is the most commonly used nitrogen (N) source, in spite of having the disadvantage of losing considerable amounts of N by ammonia-N volatilization. The objectives of this study were to evaluate: N lossby ammonia volatilization from: [urea coated with copper sulfate and boric acid], [urea coated with zeolite], [urea+ammonium sulfate], [urea coated with copper sulfate and boric acid+ammonium sulfate], [common urea] and [ammonium nitrate]; and the effect of these N source son the maize yield in terms of amount and quality. The treatments were applied to the surface of a soil under no-tillage maize, in two growing seasons. The first season (2009/2010) was after a maize crop (maize straw left on the soil surface) and the second cycle (2012/2011) after a soybean crop. Due to the weather conditions during the experiments, the volatilization of ammonia-N was highest in the first four days after application of the N sources. Of all urea sources, under volatilization-favorable conditions, the loss of ammonia from urea coated with copper sulfate and boric acid was lowest, while under high rainfall, the losses from the different urea sources was similar, i.e., an adequate rainfall was favorablet o reduce volatilization. The ammonia volatilization losses were greatest in the first four days after application. Maize grain yield differed due to N application and in the treatments, but this was only observed with cultivation of maize crop residues in 2009/2010. The combination of ammonium+urea coated with copper sulfate and boric acid optimized grain yield compared to the other urea treatments. The crude protein concentration in maize was not influenced by the technologies of urea coating.
", "keywords": ["2. Zero hunger", "copper sulfate", "Agriculture (General)", "volatiliza\u00e7\u00e3o", "ureia revestida", "04 agricultural and veterinary sciences", "6. Clean water", "S1-972", "\u00e1cido b\u00f3rico", "0401 agriculture", " forestry", " and fisheries", "coated urea", "zeolite", "volatilization", "boric acid", "sulfato de cobre", "ze\u00f3lita"]}, "links": [{"href": "https://doi.org/10.1590/s0100-06832013000400014"}, {"rel": "related", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/Revista%20Brasileira%20de%20Ci%C3%AAncia%20do%20Solo", "name": "related record", "description": "related record", "type": "application/json"}, {"rel": "self", "type": "application/geo+json", "title": "10.1590/s0100-06832013000400014", "name": "item", "description": "10.1590/s0100-06832013000400014", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.1590/s0100-06832013000400014"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2013-08-01T00:00:00Z"}}, {"id": "10044/1/96781", "type": "Feature", "geometry": null, "properties": {"license": "Open Access", "updated": "2026-04-04T16:25:00Z", "type": "Journal Article", "created": "2022-04-26", "title": "Synergistic use of siderophores and weak organic ligands during zinc transport in the rhizosphere controlled by pH and ion strength gradients", "description": "AbstractCitrate (Cit) and Deferoxamine B (DFOB) are two important organic ligands coexisting in soils with distinct different affinities for metal ions. It has been theorized that siderophores and weak organic ligands play a synergistic role during the transport of micronutrients in the rhizosphere, but the geochemical controls of this process remain unknown. Here we test the hypothesis that gradients in pH and ion strength regulate and enable the cooperation. To this end, first we use potentiometric titrations to identify the dominant Zn(II)\uffe2\uff80\uff93Cit and Zn(II)\uffe2\uff80\uff93DFOB complexes and to determine their ionic strength dependent stability constants between 0 and 1\uffc2\uffa0mol\uffc2\uffa0dm\uffe2\uff88\uff923. We parametrise the Extended Debye-H\uffc3\uffbcckel (EDH) equation and determine accurate intrinsic association constants (log\uffce\uffb20) for the formation of the complexes present. The speciation model developed confirms the presence of [Zn(Cit)]\uffe2\uff88\uff92, [Zn(HCit)], [Zn2(Cit)2(OH)2]4\uffe2\uff88\uff92, and [Zn(Cit)2]4\uffe2\uff88\uff92, with [Zn(Cit)]\uffe2\uff88\uff92 and [Zn2(Cit)2(OH)2]4\uffe2\uff88\uff92 the dominant species in the pH range relevant to rhizosphere. We propose the existence of a\uffc2\uffa0new [Zn(Cit)(OH)3]4\uffe2\uff88\uff92 complex above pH 10. We also verify the existence of two hexadentate Zn(II)\uffe2\uff80\uff93DFOB species, i.e., [Zn(DFOB)]\uffe2\uff88\uff92 and [Zn(HDFOB)], and of one tetradentate species [Zn(H2DFOB)]+. Second, we identify the pH and ionic strength dependent ligand exchange points (LEP) of Zn with citrate and DFOB and the stability windows for Zn(II)\uffe2\uff80\uff93Cit and Zn(II)\uffe2\uff80\uff93DFOB complexes in NaCl and rice soil solutions. We find that the LEPs fall within the pH and ionic strength gradients expected in rhizospheres and that the stability windows for Zn(II)\uffe2\uff80\uff93citrate and Zn(II)\uffe2\uff80\uff93DFOB, i.e., low and high affinity ligands, can be distinctly set off. This suggests that pH and ion strength gradients allow for Zn(II) complexes with citrate and DFOB to dominate in different parts of the rhizosphere and this explains why mixtures of low and high affinity ligands increase leaching of micronutrients in soils. Speciation models of soil solutions using newly determined association constants demonstrate that the presence of dissolved organic matter and inorganic ligands (i.e., bicarbonate, phosphate, sulphate, or chlorides) do neither affect the position of the LEP nor the width of the stability windows significantly. In conclusion, we demonstrate that cooperative and synergistic ligand interaction between low and high affinity ligands is a valid mechanism for\uffc2\uffa0controlling zinc transport in the rhizosphere and possibly in other environmental reservoirs such as in the phycosphere. Multiple production of weak and strong ligands is therefore a valid strategy of plants and other soil organisms to improve access to micronutrients.Plant roots are exposed to hypoxia in waterlogged soils, and they are further challenged by specific phytotoxins produced by microorganisms in such conditions. One such toxin is hexanoic acid (HxA), which, at toxic levels, causes a strong decline in root O2 consumption. However, the mechanism underlying this process is still unknown. We treated pea (Pisum sativum L.) roots with 20\uffe2\uff80\uff89mM HxA at pH\uffe2\uff80\uff895.0 and 6.0 for a short time (1\uffe2\uff80\uff89h) and measured leakage of key electrolytes such as metal cations, malate, citrate and nonstructural carbohydrates (NSC). After treatment, mitochondria were isolated to assess their functionality evaluated as electrical potential and O2 consumption rate. HxA treatment resulted in root tissue extrusion of K+, malate, citrate and NSC, but only the leakage of the organic acids and NSC increased at pH\uffe2\uff80\uff895.0, concomitantly with the inhibition of O2 consumption. The activity of mitochondria isolated from treated roots was almost unaffected, showing just a slight decrease in oxygen consumption after treatment at pH\uffe2\uff80\uff895.0. Similar results were obtained by treating the pea roots with another organic acid with a short carbon chain, that is, butyric acid. Based on these results, we propose a model in which HxA, in its undissociated form prevalent at acidic pH, stimulates the efflux of citrate, malate and NSC, which would, in turn, cause starvation of mitochondrial respiratory substrates of the Krebs cycle and a consequent decline in O2 consumption. Cation extrusion would be a compensatory mechanism in order to restore plasma membrane potential.
Root citrate exudation is thought to be important for phosphate solubilization. Previous research has concluded that cluster\uffe2\uff80\uff90like roots benefit most from this exudation in terms of increased phosphate uptake, suggesting that root structure plays an important role in citrate\uffe2\uff80\uff90enhanced uptake (additional phosphate uptake due to citrate exudation).
Time\uffe2\uff80\uff90resolved computed tomography images of wheat root systems were used as the geometry for 3D citrate\uffe2\uff80\uff90phosphate solubilization models. Citrate\uffe2\uff80\uff90enhanced uptake was correlated with morphological measures of the root systems to determine which had the most benefit.
A large variation of citrate\uffe2\uff80\uff90enhanced uptake over 11 root structures was observed. Root surface area dominated absolute phosphate uptake, but did not explain citrate\uffe2\uff80\uff90enhanced uptake. Number of exuding root tips correlated well with citrate\uffe2\uff80\uff90enhanced uptake. Root tips in close proximity could collectively exude high amounts of citrate, resulting in a delayed spike in citrate\uffe2\uff80\uff90enhanced uptake.
Root system architecture plays an important role in citrate\uffe2\uff80\uff90enhanced uptake. Singular morphological measurements of the root systems cannot entirely explain variations in citrate\uffe2\uff80\uff90enhanced uptake. Root systems with many tips would benefit greatly from citrate exudation. Quantifying citrate\uffe2\uff80\uff90enhanced uptake experimentally is difficult as variations in root surface area would overwhelm citrate benefits.
Root citrate exudation is thought to be important for phosphate solubilization. Previous research has concluded that cluster\uffe2\uff80\uff90like roots benefit most from this exudation in terms of increased phosphate uptake, suggesting that root structure plays an important role in citrate\uffe2\uff80\uff90enhanced uptake (additional phosphate uptake due to citrate exudation).
Time\uffe2\uff80\uff90resolved computed tomography images of wheat root systems were used as the geometry for 3D citrate\uffe2\uff80\uff90phosphate solubilization models. Citrate\uffe2\uff80\uff90enhanced uptake was correlated with morphological measures of the root systems to determine which had the most benefit.
A large variation of citrate\uffe2\uff80\uff90enhanced uptake over 11 root structures was observed. Root surface area dominated absolute phosphate uptake, but did not explain citrate\uffe2\uff80\uff90enhanced uptake. Number of exuding root tips correlated well with citrate\uffe2\uff80\uff90enhanced uptake. Root tips in close proximity could collectively exude high amounts of citrate, resulting in a delayed spike in citrate\uffe2\uff80\uff90enhanced uptake.
Root system architecture plays an important role in citrate\uffe2\uff80\uff90enhanced uptake. Singular morphological measurements of the root systems cannot entirely explain variations in citrate\uffe2\uff80\uff90enhanced uptake. Root systems with many tips would benefit greatly from citrate exudation. Quantifying citrate\uffe2\uff80\uff90enhanced uptake experimentally is difficult as variations in root surface area would overwhelm citrate benefits.