J. J. Jurinak

The role of calcium oxalate in the availability of phosphorus in soils of semiarid regions: a thermodynamic study

Evidence is presented for the presence of Ca-oxalate crystals at the soil-hyphae interface of mycorrhizal Pascopyrum smithii. This prompted the development of a thermodynamic model that uses the ability of oxalate to scavenge Ca2+ ion from the soil solution. The model predicts the increased solubility of Ca-apatite when oxalate is present in both the calcite-apatite (calcareous) system and in the exchangeable Ca-apatite (noncalcareous) system. The result is a marked increase of soluble (available) P in solution relative to the situation where oxalate is absent. The model is formulated on conditions prevalent in semiarid soils and presents a possible mechanism by which phosphorus uptake of plants is enhanced by mycorrhizal infection.

Interactive effects of sodium chloride, sodium sulfate, calcium sulfate, and calcium chloride on snapbean growth, photosynthesis, and ion uptake

Abstract Excessive sodium (Na) accumulation in soil, which can be a problem for production agriculture in arid and semiarid regions, may be ameliorated by calcium (Ca). The mechanisms of Ca amelioration of Na stress in plants have received much more attention than has the effect of the anion of the Ca salt. Our objective was to determine the relative effects of the chloride (Cl‐) and sulfate (SO4 2‐) anions on Ca amelioration of Na stress. We exposed Phaseolus vulgaris L., cv. Contender seedlings growing in 1‐L styrofoam pots under greenhouse conditions to sodum chloride (NaCl) or sodium sulfate (Na2SO4) at concentrations of 0, 15, 30, 45, and 60 mmol/L combined with either 15 and 30 mmol/L of calcium sulfate (CaSO4) or calcium chloride (CaCl2). Plants in each styrofoam pot were irrigated with 300 mL of salt solution (leaching fraction = 0.25) every fourth day for four weeks. Increasing Na concentration decreased shoot dry weight, number and weight of pods, and number of nodules. The photo‐ synthesis rate...

The effects of oxalates produced by Salsola tragus on the phosphorus nutrition of Stipa pulchra

Oxalic acid is produced by some species of plants and mycorrhizal fungi and it may solubilize unavailable soil phosphorus (P) bound by cations (Ca++, Al++, Fe+++). Field and greenhouse experiments were conducted to show whether oxalate produced by the annual Salsola tragus or added oxalic acid would solubilize P from the inorganic-bound soil P pool, making it available for uptake by Stipa pulchra. Oxalate could be leached in the laboratory from the senescent canopy of Salsola, and leaching by rainfall was hypothesized to be a source of potential increased soil P under the Salsola canopy. Both oxalate leached from the canopy of Salsola and added oxalic acid increased the availability of soil P in greenhouse experiments. The source of the increase in available soil P in the greenhouse experiment was shown to be the inorganic-bound P pool, as the total P concentration of the soil decreased with increasing oxalate. There were significant increases in Stipa shoot P in response to Salsola leachates and in response to added oxalate in the greenhouse studies. These results suggest an important role for oxalate in P cycling. On disturbed sites where Salsola invades it may act to facilitate the establishment of later seral species like Stipa by creating a nutrient island of available P.

Calcium amelioration of NaCl effects on plant rowth, chlorophyll, and ion concentration n Phaseolus vulgaris

Abstract This study was conducted to determine whether different forms of Ca amendments ameliorated the effects of NaCl stress on growth, chlorophyll content, and ion concentration of snapbeans, Phaseolus vulgaris L. cv Contender. The plants were grown in a greenhouse and irrigated with solutions containing 0, 44, 88, or 132 mM NaCl combined with 0, 5, and 8 mM of either CaSO4 or CaCl2. Without Ca amendments, shoot and root dry weights, chlorophyll concentration, and leaf K+/ Na+ ratio decreased more as NaCl increased from 0 and 44 mM than when it increased from 44 to 88 mM. Leaf K+, Na+, Ca2+, and Mg2+ increased and the K+/Na+ ratio decreased with each increase in NaCl concentration. The addition of Ca as either CaCl2 or CaSO4 to all levels of NaCl increased shoot and root dry weights and leaf chlorophyll concentration. The addition of CaSO4 or CaCl2 to different levels of NaCl did not affect leaf K+, Na+, or Mg2+ levels of the leaf. Among the ions, leaf Ca2+ increased significantly as concentration of e...

Oxalate effects on solution phosphorus in a calcareous soil

Abstract Thermodynamics predict that in calcareous soils where the equilibrium activity of solution orthophosphate (P so) is controlled by any calcium‐phosphate mineral, calcium oxalate (CaC2O4) precipitation will increase P so by depressing Ca2+ ion activity in soil solution and enhancing dissolution of the P‐controlling mineral. Plants and/or associated microflora capable of imparting effective levels of oxalic acid (H2C2O4) to soil solution, may significantly improve their phosphorus nutrition via this mechanism. In previous work, we presented evidence for calcium oxalate (CaC2O4) formation in the rhizosphere of vesicular‐arbuscular mycorrhizal (VAM) western wheatgrass (Agropyron smithii Rydb.). Herein, we report on further studies conducted to evaluate the production and effects of indigenous oxalate on P so in a calcareous soil. In greenhouse experiments, we measured P so and soluble oxalate (OXs) concentrations in leachate from bare soil columns and soil columns planted to western wheatgrass (Agropy...

Determination of oxalic acid (ethanedioic acid) in soil extracts using high performance liquid chromatograph

Abstract This paper describes a method for quantifying oxalate in soil HC1 extracts using reversed‐phase ion‐pairing high performance liquid chromatography with UV detection at 220 nm. The method was adapted from a procedure for determining urinary oxalate (6). The mobile phase was 10 percent KH2PO4 and 5 mM TBA adjusted to pH 2.0 with H3PO4. The analytical column was a totally porous, reversed‐phase silica based C‐8 column (Hibar Li‐Chrosorb™). An important step in this method was the pre‐ treatment of each soil extract with a reversed‐phase C‐18 column (SPICE™ C‐18). Sample pre‐treatment removed complex, non‐polar and low polarity compounds often present in soil extracts. The method was applied to calcareous, agricultural and organic soils materials. An oxalate accumulating fungus, Endothia Parasitica, was used as a verification of method applicability to plant‐fungal materials. Oxalate extraction was accomplished by placing 1:2 suspensions (soil: 0.1 M HCl) on a reciprocal shaker for two hours and subs...

Effects of CaSO4, CaCl2, and NaCl on leaf nitrogen, nodule weight, and acetylene reduction activity in Phaseolus vulgaris L.

Abstract Two forms of calcium were used to ameliorate the harmful effects of sodium chloride (NaCl) on total leaf nitrogen, nodule weight, and acetylene reduction activity in snapbeans, Phaseolus vulgaris L., cv Contender, Plants were grown in pots under greenhouse conditions and were irrigated with water containing NaCl with a salinity of 0, 44, 88, or 132 mM., In addition, either calcium sulfate (CaSO4)or calcium chloride (CaCl2) was added at concentrations of 0, 4, and 8 mM. When NaCl concentration increased, nodule weight and acetylene reduction activity decreased and total leaf nitrogen increased. Addition of Ca to the NaCl treatments slightly increased the total leaf nitrogen, nodule weight, and acetylene reduction activity of snapbeans. The positive effect on the measured variables in snapbeans by the addition of Ca compounds may be attributed to maintaining the selective permeability of membranes.

Mechanisms of nonbiological pyritic sulfur oxidation under alkaline conditions

Abstract Pyrite oxidation was studied at 25°C in aqueous solutions at several pH levels for periods of 10 days to 2 weeks to determine the distribution of water‐soluble S products in this reaction. The extent of reaction was measured in terms of total oxidized Fe and compared with total SO4 2−. Sulfate measurements underestimate the extent of oxidation, especially above pH 8. This is due to the production of relatively unreactive reduced S compounds such as S2O3 2− and S4O6 2− in intermediate reactions. Excess S2O3 2− inhibits pyrite oxidation by reducing Fe3+, the principal pyrite oxidant. Mixing of pyrite and CaCO3 in columns was used to model different management strategies for burial of pyritic wastes. The production of reduced S compounds should be considered in disposal plans.