Acidiphily in pteridophytes: Assessment of the role of root cation‐exchange properties

The soil preference with respect to soil acidity of Asplenium scolopendrium L., Dryopteris filix‐mas (L.) Schott, Pteridium aquilinum (L.) Kuhn as well as of subspecies of the Asplenium trichomanes L. and Polypodium vulgare L. complexes were studied in relation to root cation‐exchange properties. Data were collected for substrate acidity, soil exchangeable cations, and root cation‐exchange capacity. Acidiphilous pteridophytes were characterized by low cation‐exchange capacities. It is unlikely that cation‐exchange properties protect plants from potentially harmful cations such as aluminium or hydrogen, which are abundant under acid soil conditions, through immobilization. It is postulated that cation‐exchange properties are a secondary adaptation to soil acidity, in addition to major adaptations which determine the apparent soil preference. Possibly, a limited variation in cation‐exchange capacity as a function of soil conditions could prevent harmful interactions of soil exchangeable cations with the cation‐exchange sites, such as displacement of cell wall calcium by aluminium or hydrogen ions in acid soils.     

Participation of silicon in cation‐anion balance as a possible mechanism for aluminum and iron tolerance in some gramineae

Abstract

Silicon (Si) has been suggested as a factor in aluminum (Al) tolerance of some species of the gramineae when grown on acid soils. Silicon concentrations are generally much higher in monocot plants than in dicot plants, and the phenomenon is related to the fact that mineral cation:mineral anion uptake ratio is much higher in dicots than in monocots. When large amounts of anionic Si, supposedly as sulfate (SO₄ ^4‐), participate in cation‐anion balance to add to the excess of anion uptake, equivalent amounts of hydroxyl ions should be expelled from roots which can increase rhizosphere pH and decrease uptake of Al and iron (Fe). The magnitude of OH^? released by roots for a 5000 kg/ha crop with an excess uptake of 1% Si can be equivalent to 357 kg lime per hectare. This could be very significant in decreasing Al and Fe uptake from acid soils when localized in the rhizosphere. Success of agriculture on highly acid soils may be enhanced by use in a rotation of crops and cultivars that have the ability to accumulate Si.     

Effective cation exchange capacity of manure compost of varying maturity stages determined by the saturation‐displacement method

Abstract

The effective cation exchange capacity (ECEC) of manure composts, at the start and during the composting process, were determined. During this study we developed a new saturation‐displacement principle based method for compost samples. It was clearly demonstrated that ECEC of manure compost, as analyzed from three successive composting series, profoundly increased as compost matured. In addition, the ECEC values were highly repeatable, due to the proper mixing of the matrix with the saturation, washing, and displacement solutions, as well as to the preventing of any matrix losses with the separation of the matrix from those solutions with careful centrifugation‐filtration procedure.     

A simple non‐atomic absorption procedure for determining the effective cation exchange capacity of tropical soils

Abstract

A simple non‐atomic absorption procedure for determining the effective cation exchange capacity of tropical soils has been developed. The method involves the shaking of soil samples (10g) with ammonium chloride (3 x 25 cm³, 1 mol/L) to displace the exchangeable cations. The soil is then equilibrated with dilute ammonium chloride (3 x 25 cm³, 0.01 mol/L). After the final equilibration the ammonium ions retained by the soil are determined to facilitate the calculation of the ECEC. Data obtained for 22 tropical soils ranging in ECEC values from 1–50 cmol(+)/kg show a highly significant correlation with values derived using the compulsive exchange or summation procedures. The silver thiourea procedure data gave significantly poorer correlations with that obtained using all three of the above methods.     

The determination of ammonium and chloride by an auto‐analyser for the measurement of cation exchange capacity of soils

Abstract

An auto‐analyser method has been developed for the simultaneous determination of NH₄ ⁺ and Cl^‐ in Ca(NO₃)₂/KNO₃ extracts of NH₄Cl treated soils for cation exchange capacity measurements. The method gives satisfactory agreement with manual titration procedures.     

Effect of aluminum on soybean nodulation and nodule activity in a vertical split‐root system

Soybean plants (Glycine max L. cv Santa Rosa) grown hydroponically in nutrient solutions had reduced nodule mass and numbers in the presence of aluminum (Al). Reduced nodule number was attributed mainly to hydrogen (H) ion toxicity, whereas Al had a stronger effect on nodule growth. Using a vertical split‐root system with Al exclusively in the lower (hydroponic) layer also resulted in a significant reduction of nodulation and nodule growth in the surface compartment (vermiculite). This indirect effect could be attributed mainly to Al rather than H. Subsurface Al had no apparent effect on shoot growth or root growth of the upper compartment, but significantly limited root growth in the lower compartment where it was applied. The indirect effect of Al on nodulation could be a reflection of the abnormal root growth in the lower compartment. Split‐root experiments with a high Al soil, however, produced different effects. High Al in soil used exclusively in the lower compartment did not reduce nodule numbers or mass in the upper compartment despite being more harmful than the Al solutions to nodulation and growth of plants when used in a single compartment. Growth of roots in the subsurface compartment was also much less affected by the high soil Al compared with the Al‐containing nutrient solutions. Nodule activity, as estimated by xylem sap ureide levels, was only reduced after direct exposure of nodules to Al. A pronounced increase in the ratio of asparagine/glutamine occurred in all Al treatments where nodulation was reduced, and in some cases, there was an increase in total amino acid concentration of the xylem sap.     

Mechanisms of aluminum tolerance in triticum aestivum L. (wheat) III. Long‐term pH changes induced in nutrient solutions by winter cultivars differing in tolerance to aluminum

Five winter cultivars of Triticum aestivum L., representing a known range of tolerance to aluminum (Al), were grown in nutrient solutions with and without Al for 41 days to determine long‐term changes in solution pH. Plant‐induced pH of the nutrient solutions declined for 16 to 17 days. Subsequently, the pH induced by Al‐sensitive plants grown without Al and Al‐tolerant plants grown with Al and without Al increased rapidly, presumably reflecting depletion of NH₄ ⁺ from the nutrient solutions. Aluminum‐sensitive plants grown with Al showed a less pronounced pH rise after 16 to 17 days of treatment.

After nutrient solutions were renewed on days 26 and 34, plant‐induced pH patterns were similar to those during days 1 to 26. However, the time required for the onset of the rapid rise in pH decreased. In these subsequent pH cycles, the pH patterns induced by Al‐tolerant plants grown with Al progressively approximated those induced by plants grown without Al. Aluminum‐sensitive plants grown with Al did not induce a rapid rise In pH of nutrient solutions.

Differential tolerance to Al was apparent visually after three to five days growth. Cultivar tolerance to Al was correlated with the initial rate of the pH decline (days 1 to 26) as well as final pH of solutions discarded on days 26, 34, and 41. These results support the hypothesis that differential uptake of NH₄ ⁺ and NO₃ ^‐ causes cultivar differences in plant‐induced pH of nutrient solutions and affects the relative growth of cultivars in Al‐toxic nutrient solutions.     

Effect of sodium‐vinasse application on seed germination and growth of three species differing in salt tolerance

Abstract

The produced vinasse from molasses of sugar beets contains high amounts of nitrogen, potassium, and sodium (Na‐vinasse). In a pot experiment involving plant species of different tolerance to soil salts (cotton, corn, and beans), applications up to 10 t vinasse ha^‐1 did not significantly affect the seed germination, and had a positive effect on plant growth of all species. Increasing the vinasse application to 20 t ha^‐1 had no effect on seed germination of cotton and increased its growth. In contrast, a 20 t ha^‐1 application delayed the time of germination and inhibited corn and bean growth up to one month. Subsequently, plant growth increased and plant height 52 days after sowing was similar to that with the 10 t ha^‐1 treatment. For the bean plants, the negative effect of the 20 t ha^‐1 application continued and resulted in a higher dry matter in leaves, but lower dry matter in stems and fruits compared to the untreated soil. A replacement of potassium by sodium in cotton and corn plants was also observed at this vinasse application. Very high application of vinasse (100 t ha^‐1) resulted in a damage of cotton and bean seeds, while a higher portion of corn seeds germinated (64%). However, corn seeds that germinated collapsed after a few days. Among the three species studied, cotton plants absorbed the highest amount of sodium, corn plants the highest amount of potassium and those of bean the highest amount of nitrogen.     

Cation exchange capacity of two‐component container media predicted from laboratory analysis of components

Abstract

A mathematical equation predicting cation exchange capacity (CEC) of pine bark‐sand container media from CEC of the individual components was formulated. The equation is the weighted sum of milliequivalents contributed by each component and is corrected for shrinkage due to mixing of components. Both measured and predicted CEC increased linearly with increasing percent volumetric bark in pine bark‐sand media. Regression equations describing measured and predicted CEC were not statistically different. The predictive equation was also tested on 6 non‐synthesized 2‐component media prepared from peat moss, perlite, pine bark, vermiculite, and sand. No statistical differences between measured and predicted CEC were obtained.     

Calcium‐induced modification of aluminum toxicity in sorghum genotypes

Effects of calcium (1, 2 and 5 mM) and aluminum (0, 15 and 45 μM) on growth and internal nutrient concentrations were examined with 12 sorghum genotypes (Sorghum bicolor (L.) Moench) in a nutrient solution experiment with a factorial design. At 1 (or 2) mM Ca the severity of root damage induced by Al well reflected the genotypical variation in growth response to Al toxicity. Severity of Al‐induced root damage slightly decreased with increasing Ca level. Moreover, Ca at 5 mM amplified the Mg deficiency induced by Al, as seen from both heavier deficiency symptoms and lower internal Mg concentrations. Under conditions of Al stress at a high Ca supply, induced Mg deficiency apparently predominated the genotypical differentiation in growth response to Al toxicity. An antagonism between Al‐ and Ca ions for uptake was hardly found with the sorghum genotypes. However, the genotypes differed in Ca efficiency, a characteristic which may be relevant in assessing their sensitivity to Mg deficiency.     

Modified procedures for commercial adaptation of root iron‐reducing capacity as a screening technique

Abstract

Genotypic evaluation is critical to development of soybean [Glycine max (L.) Merr.] cultivars with genetic resistance to Fe‐deficiency chlorosis. Root Fe³⁺ reducing activity is correlated with genotypic resistance to Fe chlorosis measured in field nurseries, and thus may be a reliable method for identifying chlorosis‐resistat genotypes. However, to develop methods useful for large‐scale screening, several modifications of the previously published procedure for measuring root Fe³⁺ reducing activity were investigated. Several hydroponic experiments were conducted to test proposed modifications. It was determined that: (a) different genotypes may be grown together in the same nutrient solution without affecting Fe³⁺ reduction, (b) genotype separation is maximized by growth in CaCO₃ buffered solution (37.5 mg L^?1), (c) a labor‐intensive elongation step can be eliminated, and (d) denotype evaluation can be accomplished without introducing Fe into the hydroponic solutions. These refinements to the procedure should allow its adaptation and use in soybean breeding programs.     

The determination of phosphate‐extractable sulphate in soil with an anion‐exchange membrane

Abstract

A method for extracting sulphate from soils using strips of a phosphated anion‐exchange membrane is described. The results obtained by this method are in good agreement with those obtained by extraction with Ca(H₂PO₄)₂solutions and the method has a number of practical advantages over the use of phosphate solutions. No charcoal treatment, centrifuging or filtering is required and the strips are reuseable. No organic interferences are encountered during the turbidimetric measurement of the extracted sulphate.     

Distribution pattern of root‐supplied 59iron in iron‐sufficient and iron‐deficient bean plants

In order to study the iron (Fe) distribution pattern in bean plants with different Fe nutritional status, french bean (Phaseolus vulgaris L.) seedlings were precultured in a complete nutrient solution with 8x10^‐5 M FeEDTA for five days. Thereafter, plants were further supplied with 8x10^‐5 M FeEDTA (Fe‐sufficient) or with only 2x10^‐6 M FeEDTA (Fe‐deficient) for another eight days. At this stage, the Fe‐deficient plants had much lower chlorophyll contents and lower dry weight of the leaves but higher reducing capacity of the roots compared with the Fe‐sufficient plants. For studies on short‐term distribution of Fe, the Fe‐sufficient plants were supplied 8x10^‐5 M ⁵⁹FeEDTA (specific activity 9.9 GBq/mol) and the Fe‐deficient plants 1x10⁶ M ⁵⁹FeEDTA (specific activity 98.8 GBq/mol). The plants were harvested after 4 and 24 hours. Despite a much lower supply of ⁵⁹FeEDTA/(factor 80), the Fe‐deficient plants took up significantly more ⁵⁹Fe but translocated less to the shoots (14.6% after 24 h) compared with the Fe‐sufficient plants (29.4% after 24 h). However, regardless of the Fe nutritional status of the plants, the majority of ⁵⁹Fe was translocated in the primary leaves. Our results demonstrate a similar distribution patterns of root‐derived ⁵⁹Fe in the shoots of Fe‐sufficient and Fe‐deficient plants, and thus, no preferential direct translocation of Fe to the shoot apex in the Fe‐deficient plants.     

AB‐DTPA cation extraction in Spanish soil samples

Abstract

Since only one extraction is required to determine a large number of nutrients, many laboratories employ universal extractants to determine the available nutrients in a soil sample. This paper compares the universal ammonium bicarbonate‐DTPA (AB‐DTPA) method developed by Soltanpour and Schwab (1977) with the traditional methods, ammonium acetate (NH₄OAc) test for exchangeable cations and the Lindsay and Norwell (1969) test for the micronutrients. Results from the analysis of 28 soils by these methods were compared. Most soils were selected from those used by the Spanish Working Group for the Standardization of Analytical Methods. In most cases, statistical correlations between methods presented good agreement for each element, but depending on the soil pH range, some elements needed two correlations. Also, when results for wet and dry soils were compared, variability was lower when the AB‐DTPA extraction method was used. We concluded that, besides being faster, the AB‐DTPA method is valid for Spanish soils, even for calcium (Ca) extraction in calcareous soils, where the ammonium acetate method fails due to excessive Ca solubilization.     

Relationship of soil properties to p‐fixing capacity of soils in northern Idaho

Abstract

Phosphorus sorption studies were conducted on volcanic ash influenced surface horizons of 29 northern Idaho soils. Results show that the amount of P sorbed was significantly correlated with citrate‐dithionite extractable aluminum (r = .64**), but not with Fe. Other significantly correlated soil properties were: percent base saturation (r = ‐.73**), percent clay (r = .42**), and exchangeable acidity (r = .39*).     

Verification of an in‐situ method for measuring denitr1f1cation

Abstract

The most common direct in‐situ method for the measurement of soil denitrification requires many acetylene (C₂H₂) supply probes and airflow lines to measure nitrous oxide (N₂O) flux from the soil under a sealed cover. A modification to this method simplified C₂H₂ supply by placing a single acetylene supply probe 30 cm deep into the soil and measured soil N₂O emission flux over a 0.11 m² area. Acetylene concentrations ranging from 0.1–10.0% were readily and predictably established by radial diffusion from the supply probe. Over 94% of the N₂O released into the enclosed air space of the soil cover was recovered at an air flow rate of 21 L/h. Recovery decreased rapidly with increased flow rates of 31 and 37 L/h.     

Effects of root‐zone acidity on utilization of nitrate and ammonium in tobacco plants

Abstract

Tobacco (Nicotiana tabacum L., cv. ‘Coker 319') plants were grown for 28 days in flowing nutrient culture containing either 1.0 mM NO₃ ^‐ or 1.0 mM NH₄ ⁺ as the nitrogen source in a complete nutrient solution. Acidities of the solutions were controlled at pH 6.0 or 4.0 for each nitrogen source. Plants were sampled at intervals of 6 to 8 days for determination of dry matter and nitrogen accumulation. Specific rates of NO₃ ^‐ or NH₄ ⁺ uptake (rate of uptake per unit root mass) were calculated from these data. Net photosynthetic rates per unit leaf area were measured on attached leaves by infrared gas analysis. When NO^‐ was the sole nitrogen source, root growth and nitrogen uptake rate were unaffected by pH of the solution, and photosynthetic activity of leaves and accumulation of dry matter and nitrogen in the whole plant were similar. When NH₄ ⁺ was the nitrogen source, photosynthetic rate of leaves and accumulation of dry matter and nitrogen in the whole plant were not statistically different from NO₃ ^‐ ‐fed plants when acidity of the solution was controlled at pH 6.0. When acidity for NH₄ ⁺ ‐fed plants was increased to pH 4.0, however, specific rate of NH₄ ⁺ uptake decreased by about 50% within the first 6 days of treatment. The effect of acidity on root function was associated with a decreased rate of accumulation of nitrogen in shoots that was accompanied by a rapid cessation of leaf development between days 6 and 13. The decline in leaf growth rate of NH₄ ⁺ ‐fed plants at pH 4.0 was followed by reductions in photosynthetic rate per unit leaf area. These responses of NH₄ ⁺ ‐fed plants to increased root‐zone acidity are characteristic of the sequence of responses that occur during onset of nitrogen stress.     

Iron‐stress response of inoculated and non‐inoculated roots of an iron inefficient soybean cultivar in a split‐root system

The objective of this study was to establish whether the iron‐stress responses observed in T203 soybean (Fe‐inefficient) with active nodules are products of the nodules or of the entire root system. A split‐root system was used in which half the roots of each plant were inoculated and actively fixing nitrogen and the other half were not. Soybean cultivar T203 is normally Fe‐inefficient and does not exhibit the Fe‐stress responses, however an iron‐stress response did occur during active N₂ fixation in earlier studies. This implies that the active nodules influenced the plant's ability to respond to Fe‐deficiency stress. In this study, the Fe‐stress response (H⁺ and reductant release) observed in T203 soybean was limited to the inoculated side of the split‐root system. The severe Fe chlorosis which developed in these plants was overcome in a manner similar to Fe‐efficient cultivars undergoing normal Fe‐stress response and the T203 plants completely regreened. Exudation of H⁺ ions was similar in both the presence and absence of Fe, and was generally limited to inoculated roots. Reductant release was nearly nonexistent from the non‐inoculated roots and was greater for the Fe‐stressed (‐Fe) plants than for non‐stressed (+Fe) plants. Thus, the response observed, which alleviated Fe chlorosis, appeared to be associated with N₂ fixation of the active nodules.     

Inadaptive changes in pH with Zn‐stress tolerance in some cultivars of cotton and peanut

The effects of Zn‐stress on pH of the nutrient medium and the occurrence of Zn deficiency symptoms were examined in 12 cotton and 10 peanut cultivars widely grown in several parts of India. It was found that many of the cotton cultivars were able to reduce the pH, but however unable to recover from Zn deficiency. In contrast, all the peanut cultivars tested did not develop Zn‐chlorosis when subjected to Zn‐stress, although the pH reduction was less significant. The study with these crop cultivars revealed that Zn‐stress tolerance response was not related to pH changes in general. The mechanism by which the peanut cultivars made Zn available and thus averted the onset of Zn‐chlorosis was therefore not adaptive to the changes in pH. This feature appeared to be different from the pattern of correlative pH reduction and recovery from Fe‐chlorosis observed in several Fe‐stress tolerant crop cultivars.