J. S. Angle

Zinc and Cadmium Uptake by Hyperaccumulator Thlaspi caerulescens and Metal Tolerant Silene vulgaris Grown on Sludge-Amended Soils

Two metal tolerant plants, Thlaspi caerulescens J. and C. Presl. (hyperaccumulator), and Silene vulgaris L. (indicator) were grown with Paris Island Cos Romaine lettuce (Lactuca sativa var. longifolia) on longterm sewage sludge plots. Metal uptake patterns by plants in relation to total soil metal and soil pH were examined. The 2-year study used four treatments and two pH levels. Zinc and Cd uptake were measured. Zinc and Cd for Silene and lettuce were as expected with increasing plant concentration in the more contaminated treatments and lower pH levels. Thlaspi followed the same pattern for Cd but not for Zn. Concentrations of Cd were not significantly different between Thlaspi and the other plants. Zinc concentrations in Thlaspi (2000 and 4000 mg kg -1 ) were 10-fold greater than in Silene. They showed no relation to available soil Zn. Although Thlaspi appears to hyperaccumulate Zn on mildly contaminated soils, Cd uptake follows predictable patterns.

Free metal activity and total metal concentrations as indices of micronutrient availability to barley [Hordeum vulgare (L.) ‘Klages’]

The form in which a micronutrient is found in the rhizosphere affects its availability to plants. We compared the availability to barley of the free hydrated cation form of Fe3+, Cu2+, Zn2+, and Mn2+ versus their total metal concentrations (free ion plus complexes) in chelator-buffered solutions. Free metal ion activities were estimated using the chemical equilibrium program GEOCHEM-PC with the corrected database. In experiment 1, barley was grown in nutrient solutions with different Fe3+ activities using chelators to control Fe levels. Chlorosis occurred at Fe3+ activities of 10−18 and 10−19M for barley grown in HEDTA and EDTA solutions, respectively. In experiment 2, barley was grown in nutrient solutions with the same calculated Fe3+ activity and the same chelator, but different total Fe concentrations. Leaf, root and shoot Fe concentrations were higher from CDTA buffered solutions which had the higher total Fe concentration indicating the importance of the total Fe concentration on Fe uptake. Results from treatments using EDTA or HEDTA, with one exception, were similar to the results from the CDTA treatment. This suggests differences in critical Fe3+ activities found in experiment 1 were due to differences in the total Fe concentration and not errors in chelate formation constants used to estimate the critical activities. Results for Cu, Zn, and Mn were similar to Fe; despite solutions with equal free Cu2+, Zn2+ and Mn2+ activities, plant concentrations of these metals were generally greater when grown in the solutions with the greater total amount of Cu, Zn, or Mn. When the free Zn2+ activity was kept constant while the total amount of Zn was increased from 4.4 to 49 μM, leaf Zn concentration increased from 77 to 146 μg g-1. In order to predict metal availability to barley and other species in chelator-buffered nutrient solutions, both free and total metal concentrations in solution must be considered. The critical Fe3+ activities required by barley in this study are much higher than those from tomato and soybean, 10-28M, which strongly supports the Strategy 2 model of Fe uptake for Poaceae. This is related to the importance of the Fe3+ (barley) and the Fe2+ (tomato and soybean) ions in Fe uptake. Fe-stressed barley is known to release phytosiderophores which compete for Fe3+ in the nutrient solution, while tomato and soybean reduce Fe3+ to Fe2+ at the epidermal cell membranes to allow uptake of Fe2+ from Fe3+ chelates in solution.

Enumeration and N2 fixation potential of Rhizobium leguminosarum biovar trifolii grown in soil with varying pH values and heavy metal concentrations

Abstract The potential risk to Rhizobium leguminosarum bv. trifolii and white clover ( Trifolium repens cv. ‘Regal’) from biosolids-induced heavy metal toxicity is of great concern because of their symbiotic association and capacity for N 2 fixation. A greenhouse experiment was conducted to assess the effects of heavy metals from biosolids on the population and N 2 fixing potential of Rhizobium leguminosarum bv. trifolii under two pH regimes. In 1994, soils (Typic Paleudults) were collected from plots that had previously received 224 Mg ha −1 heat-treated and 100 Mg ha −1 Nu-Earth biosolids (applied in 1976 and 1978, respectively). Six soil treatments were used for the study: a control with low and high pH and two biosolids treatments, each with low and high pH. Soil pH and biosolids application significantly affected uptake of metals with phytotoxicity observed in the low pH soil amended with biosolids. The number of Rhizobium was significantly reduced in all low pH treatments. This resulted in no or ineffective nodulation by plants grown in these treatments. High numbers of Rhizobium were found in all high pH treatments, irrespective of metal content. Heat-treated biosolids-amended soil had higher numbers of Rhizobium than the control, but Nu-Earth biosolids-amended soil had lower numbers than the control. Nitrogen fixation, as measured by acetylene reduction activity, was greater in all high pH treatments compared with low pH treatments. When soil pH from the acidic plots was adjusted above 6.0, most of the isolates remained ineffective. Shoot yield and the number of Rhizobium did not show any significant increase with the increase in soil pH. Adjustment of high pH soil to low soil pH significantly reduced the number of Rhizobium irrespective of whether biosolids were applied. In conclusion, few significant effects of biosolids-borne heavy metals on plants, N 2 fixation, and on numbers of Rhizobium leguminosarum bv. trifolii were observed at concentrations of metals studied, as long as soil pH was maintained near 6.0. Where reductions in rhizobial number and plant parameters were observed, the decrease was primarily attributed to low soil pH and to a lesser extent heavy metal toxicity from biosolids.

Root hairs on chlorotic tomatoes are an effect of chlorosis rather than part of the adaptive Fe‐stress‐response

Abstract Extensive research has been reported from studies of the Fe‐deficiency‐stress responses of chlorotic‐Fe plants, but little has been done to evaluate the more relevant Fe‐stress‐responses of plants that exhibit no chlorosis. The present work examined the stress responses using a novel, chelator‐buffered hydroponic solution able to induce a wide range of Fe‐deficiency and stress response even in green plants. The solution contains DTPA (diethylentriamine‐pentaacetate), a chelator that limits the availability of Fe2+ (formed at the root by reduction of Fe3+DTPA) to plants by catalyzing Fe2+ oxidation back to the substrate Fe3+TPA. This produces Fe stress and induces the adaptive Fe‐stress‐response in tomatoes (Lycopersicon esculentum) and other non‐Poaceae. At 18–31.6 μM FeDTPA (with 100 μM free DTPA), tomatoes had increased rates of Fe3+‐chelate reduction and proton secretion, but remained green because the adaptive Fe‐stress‐response allowed the roots to obtain adequate Fe. Below 18 μM FeDTPA, the...

A reevaluation of the Fe(II), Ca(II), Zn(II), and proton formation constants of 4,7-diphenyl-1,10-phenanthrolinedisulfonate.

The compound 4,7-diphenyl-1,10-phenanthrolinedisulfonic acid (BPDS) has been found to be very useful in studying Fe uptake by plants, because it forms a large charged complex that is not absorbed. The quantity of BPDS, bound to metals in hydroponic solutions can be estimated from calculations using formation constants of BPDS complexes. These formation constants were used in an earlier experiment to predict the availability of Cu to corn plants. In the experiment, bioassays indicated that Cu was not as phytoavailable in the BPDS-added solutions as predicted by chemical equilibrium calculations. To determine sources of error in this prediction, metal and proton BPDS formation constants were reevaluated at 25°C and 0.10M ionic strength. The CaBPDS formation constant was determined by direct measurement of CaBPDS3 formation and was shown to be ∼1.0; a value much less than that reported before. Formation constants for the HBPDS, H(BPDS)2 and H(BPDS)3, β1, β2, and β3 complexes were, respectively, 5.05±0.044, 7.44±0.019, and 9.33±0.28. The BPDS sulfonic acid group pKs were <1.0, not 2.8 as has been reported. The FeBPDS3 complex determined by ligand competition with EDTA (ethylenediaminetetraacetate) was 20.24±0.08. Copper and Zn constants were determined using the method of corresponding solutions. The CuBPDS, CuBPDS2, and CuBPDS3, β1, β2, and β3 constants were, respectively, 9.76±0.08, 15.9, and 20.9. The ZnBPDS, ZnBPDS2, and ZnBPDS3 β1, β2, and β3 constants were, respectively, 6.43±0.07, 10.7±5.4, and 17.3±0.8. Results indicated that, BPDS affinity to metals was similar to that of its parent compound, phenanthroline, and that errors in published formation constants caused erroneous predictions of Cu phytoavailability used in an earlier experiment.