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Cadmium uptake kinetics and plants factors of shoot Cd concentration
No full textAccumulation of Cd in the shoots of plants grown on Cd contaminated soils shows considerable variation. A previous preliminary experiment established that one major reason for this variation was the rate of Cd influx into the roots (mol Cd cm(-2) root s(-1)). However, this experiment did not distinguish between solubilization of soil Cd on the one hand and difference in Cd uptake kinetics on the other. The main objectives of the present study were thus to characterize Cd uptake kinetics of plants continuously exposed to Cd concentrations similar to those encountered in soils. Furthermore we determined the factors responsible for differences in shoot Cd concentration such as net Cd influx, root area-shoot dry weight ratio, shoot growth rate and proportion of Cd translocated to the shoot. Maize, sunflower, flax and spinach were grown in nutrient solution with five constant Cd concentrations varying from 0 to 1.0 mu mol L-1. Root and shoot parameters as well as Cd uptake were determined at two harvest dates and from these data Cd net influx and shoot growth rates were calculated. Cadmium uptake kinetics, i.e. the net Cd influx vs. Cd solution concentration followed a straight line. Its slope is the root absorbing power, alpha, . The alpha values of spinach and flax were about double that of maize and sunflower (5 x 10(-6) cm s(-1) vs. 2.5 x 10(-6) cm s(-1)). Spinach and flax had a 3-5 times higher shoot Cd concentration than maize and sunflower. The difference in shoot Cd concentration was partly due to the higher Cd influx but also to a higher translocation of Cd from root to shoot and also to a slower shoot growth rate
Cadmium fractions in an acid sandy soil and Cd in soil solution as affected by plant growth
No full textIn a previous experiment, plants were able to immobilize or solubilize Cadmium (Cd) in a sandy acid soil enriched with 40 mu mol Cd kg(-1), because Cd solution concentration was decreased by maize (Zea mays) and sunflower (Helianthus annuus), and increased by flax (Linum usitatissimum L. ssp. usitatissimum) and spinach (Spinacia oleracea). It is assumed that the equilibrium with Cd fractions in the soil solid phase and the chemical form of Cd in the soil solution were affected. In the present study, the effect of the four plant species mentioned above on Cd binding in soil was investigated by means of a fractionation of soil Cd with a sequential extraction of seven steps. The seven fractions of Cd are operationally defined by the extraction sequence that follows the order of increasing acidity with extractants of different complexing and redox properties. In the unplanted soil, Cd was predominantly present in the exchangeable Fraction I (F. I) and easily mobilizable Fraction II (F. II) (64%). Significant concentrations of Cd were found in F. III (occluded in Mn oxides; 22%) and F. IV (organically bound; 10%). Fractions V (occluded in poorly crystalline Fe oxides), F. VI (occluded in well crystallized Fe oxides), and F. VII (residual fraction) amounted to less than 5% of the total soil Cd concentration. The plants changed the binding of Cd in soil in a different manner. All plants decreased F. I, but F. II was increased by maize and spinach, decreased by flax or remained unaffected by sunflower. Fraction III was not affected by maize and flax, but decreased by sunflower and spinach, and F. IV was not affected by sunflower and spinach, but was increased by maize and flax. These changes of Cd fractions were not related to the changes the plants had caused in total Cd or Cd2+ concentration of the soil solution. These results show that plant species differ in how they affect Cd binding to the soil solid phase, but this effect is not related to how they affect Cd in soil solution. The mechanisms by which plants affect the relationship between the soil solid and liquid phase are still unclear.German Research Foundation (DFG
The effect of the function type for describing the soil buffer power on calculated ion transport to roots and nutrient uptake from the soil
No full textThe relationship between amount of a nutrient in soil and its concentration in solution, the buffer curve, is usually non-linear. However. most models that calculate nutrient transport in the soil and nutrient uptake by the plant often assume a linear buffer curve because of simpler programming. In this paper a model is presented that uses the Freundlich function to describe the non-linear buffer curve in the soil. It has been shown that calculated uptake and depletion curves were not influenced by the shape of the buffer curve. In a sensitivity analysis the buffer capacity, soil solution concentration, soil water content, soil impedance factor, maximum influx and the curvature of the Freundlich function were varied and the influence on calculated uptake was studied. The buffer capacity in general had a minor influence and the linearity or non-linearity of the buffer capacity had under no circumstances an influence on calculated uptake. Thus, the use of a linear buffer curve in transport models does not lead to a significant error in the results
Differential mobilization of P in the maize rhizosphere by citric acid and potassium citrate
No full textThe release of organic acid anions from plant roots into soil has been hypothesized to be a mechanism for enhancing phosphorus availability in the rhizosphere. Although these compounds are excreted from the cytoplasm as organic acid anions (e.g. citrate, malate), when the H+-ATPase is also upregulated there is evidence to suggest that they enter the soil as organic acids (e.g. citric acid, malic acid). The aim of this study was to evaluate the role of citric acid (H-citrate) and potassium citrate (K-citrate) in the mobilization and plant uptake of P from two acid soils contrasting in their P availability. Our results indicated that the mobilization of P from a (KH2PO4)-P-33 labelled patch of soil was soil type dependent, was controlled by its intrinsic P status, and that more P was made available by K-citrate than H-citrate. Similarly, the uptake of P-33 from the rhizosphere by Zea mays L. was greatest in the presence of K-citrate in comparison to H-citrate. However, a significant increase in shoot P-33 content was only observed in the more acidic soil with high P sorption potential (Haplic podzol) while no significant increase was observed in the less acidic soil with low P sorption potential (Eutric cambisol). We conclude that the chemical form of organic acid anion excretion may have a significant impact on its P mobilization capability. The contrasting results with the two acid soils indicate that organic acids may not provide a universal mechanism for enhancing P uptake from soil. (c) 2005 Elsevier Ltd. All rights reserved
CADMIUM DYNAMICS IN THE RHIZOSPHERE AND CD UPTAKE OF DIFFERENT PLANT SPECIES EVALUATED BY A MECHANISTIC MODEL
No full textMaize, sunflower, flax, and spinach differed in the accumulation of Cd when grown on a Cd contaminated soil. This was mainly due to the different Cd net influx, I-n , that varied among species by a factor of up to 30. The objective of this study was to find possible reasons for the different Cd I-n by using a mechanistic model. After 14days of Cd uptake the model calculated only a small Cd depletion at the root surface, e.g. from 0.22mol L(-1)down to 0.19mol L(-1)for maize and from 0.48mol L(-1)down to 0.35mol L(-1)for spinach. Even so the model always overestimated the Cd I-n , for spinach by a factor of 1.5 and for maize by a factor of 10. Only simulating a decrease of C-Li or the root absorbing power, , by 40% to 90% gave an agreement of calculated and measured I-n . This may be interpreted as that about 40% in the case of spinach and 90% in the case of maize of the Cd in soil solution were not accessible for plant uptake. The high sensitivity to also shows that not the Cd transport to the root but was limiting the step for Cd uptake
Growth and Phosphorus Uptake of Three Riparian Grass Species
No full textRiparian buffers can significantly reduce sediment-bound P entering surface water, but control of dissolved P inputs is more challenging. Because plant roots remove P from soil solution, it follows that plant uptake can reduce dissolved P losses. We evaluated P uptake of smooth bromegrass (Bromus inermis Leyss.), reed canarygrass (Phalaris arundinacea L.), and switchgrass (Panicum vitgatum L.) grown in a flowing nutrient solution culture system with P concentrations of 1 or 100 mu mol L(-1). Plants were destructively sampled at approximately 0, 26, 40, and 53 days after transplanting (DAT). In a separate, concurrent experiment, we simulated the effect of an inflow of runoff with low or high dissolved P by switching a subset of pots approximately 40 DAT. When grown in 1 mu mol L(-1) P solution, shoot dry matter (DM) yield increased in the order bromegrass < switchgrass < canarygrass. When grown in 100 mu mol L(-1) P solution, shoot DM yield increased in the order bromegrass = canarygrass < switchgrass. Shoot P content was correlated with shoot DM yield; however, switchgrass was the only species that had higher P content in plants grown in 100 mu mol L(-1) P solution than in 1 mu mol L(-1) P solution. When solution P concentration was abruptly increased or decreased, P uptake was affected more than plant growth. Shoot P concentration of canarygrass increased more than 3.5-fold when the plants were switched from 1 mu mol L(-1) P solution to 100 mu mol L(-1) P solution. Shoot P concentration of switchgrass followed the same trend. The results of this solution-culture experiment suggest that canarygrass and switchgrass would more effectively deplete dissolved P than would bromegrass.Alexander von Humboldt Foundation of Bonn, German
Plant availability of isotopically exchangeable and isotopically nonexchangeable phosphate in soils
No full textIsotopically exchangeable P (IEP) is usually considered to be completely plant-available and the major source of P for plant uptake. The aim of the present study is to test whether plants can, besides IEP, also use non-IEP and if part of the IEP has an equilibrium concentration in soil solution which is below the minimum concentration, C-Lmin, and can therefore not be taken up by plants. A pot experiment was carried out with maize for two years on two soils, an acid sandy and a neutral loamy soil, either without P fertilizer or fertilized with ten P sources of different solubility. Throughout both years of the study, pots were kept moist either without plants or planted twice with maize (Zea mays L., cv. Athletico). At the end of the experiment, plant P uptake, P concentration in the soil solution (C-L), and P accessible to isotopic exchange within 5 d (E-5d) were measured. Plant growth decreased the E-5d which was about equal to P uptake by maize for most treatments in the acid soil. But for some treatments, i.e., five in the acid and eight in the neutral soil, P uptake was up to 50% larger than the decrease of E-5d, indicating that plants had, besides IEP, also used P from non-IEP sources. At adequate P supply, both soils had an E-5d of about 100 mg P (kg soil)(-1), but about 30 to 40 mgkg(-1) of this IEP had an equilibrium P concentration in the soil solution below C-Lmin of 0.1 mol L-1 at which P would actually not be plant-available. This study shows that plants take up P mainly from IEP, but not the whole IEP is plant-available. Furthermore, plants may also use P from non-IEP sources
Mechanisms of potassium uptake efficiency and dynamics in the rhizosphere of safflower and sunflower in different soils
No full textShoot cadmium concentration of soil‐grown plants as related to their root properties
No full textCadmium (Cd) is toxic to plants, animals, and humans. However, different plant species growing on the same soil may have very different shoot Cd concentrations depending on properties such as size of the root system, Cd net influx, shoot-growth rate, Cd translocation from root to shoot, and the ability to affect Cd availability in the soil. To investigate possible reasons for different shoot Cd concentrations maize, sunflower, flax, and spinach were grown on an acid sandy soil (pH(CaCl2) 4.5, and Corg 2.8%) in a growth chamber with Cd additions as Cd(NO3)2 of none, 14, and 40 mu mol (kg soil)-1 resulting in Cd soil-solution concentrations of 0.04, 0.68, and 2.5 mu M. Only the high Cd addition caused a significant growth reduction of flax and spinach. The shoot Cd concentration was up to 30 times higher in spinach than in maize; the other species were intermediate. Of the plant properties studied only the variation of the Cd net influx explained the differences in shoot Cd concentrations. This was due to a decreased (maize, sunflower) or increased (flax) Cd concentration in soil solution or more effective uptake kinetics (spinach).German Research Foundation (DFG
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