Cadmium accumulation and physiological response of sunflower plants to Cd during the vegetative growing cycle

The effects of soil Cd contamination on Cd accumulation and distribution, growth and physiological responses of sunflower plants were investigated. Plants were subject to six levels of soil contamination (from 2.5 to 15 mg Cd kg/soil) with an untreated control, from the emergence of the cotyledon leaves until the harvest, when plants were at the flower bud stage. An overall increase of Cd concentration was found in all tissues of the plants (roots, stem, young, mature and old leaves) by increasing the Cd contamination in the soil. Regardless of treatments, Cd concentration in roots always exceeded those in the aboveground dry matter with a low translocation from roots to shoots. At early stage of growth, Cd concentration in plants was higher than at the flower bud stage. Soil Cd contamination did not affect plant growth, relative water content and gas exchange parameters. Negative and significant correlation was only found between Cd concentration in the young leaves and chlorophyll concentration at the end of vegetative growing stage. Roots and old leaves are the main metal sinks suggesting a defense or tolerance mechanism of the plants to avoid toxic levels in physiologically most active apical tissues. These results should be tested in open field to verify the suitability of sunflower in the area of phytotechnologies

Root foraging and avoidance in hyperaccumulator and excluder plants: a rhizotron experiment

Aims: Metal hyperaccumulation is a rare phenomenon described for an increasing number of plant taxa. In this study we investigated the root growth responses of the well-known nickel, zinc, cadmium hyperaccumulator Noccaea caerulescens and of the metal tolerant (non-accumulator) Stellaria media, in order to observe root foraging vs avoidance responses to nickel. Methods: To allow for observations of root growth and foraging preferences, two accessions of Noccaea caerulescens and two accessions of Stellaria media orginating from high nickel and low nickel habitats were grown in rhizotrons with localized nickel enrichment. Results: The root density in the control and nickel-enriched soil areas in the rhizotrons with different N. caerulescens accessions had distinct responses: moderate nickel avoidance was recorded for the non-nickel accession, while a clear foraging response was observed in N. caerulescens from the nickel accession. In contrast, nickel rooting avoidance was observed for both S. media accessions and was more pronounced in the non-nickel accession. Conclusions: This study shows that N. caerulescens originating from different accessions responded differently to soil nickel enrichment, with the nickel accession of N. caerulescens actively foraging for nickel, suggesting a physiological adaptation and demand for this metal. In contrast, a clear nickel avoidance response by a metal tolerant species, S. media, was observed in this study, a phenomenon which has not been previously described; this suggests that root avoidance responses might play a role in the adaptation of metal tolerant species to Ni-rich soils

Growth of Populus alba and its influence on soil trace element availability

The use of fast growing trees is a common practice for phytoremediation of contaminated soils. Plant roots can change trace element bioavailability in soils. We studied the effect of Populus alba on trace element bioavailability on two contaminated soils (one with neutral pH and other with acid pH) comparing two methods (0.01M CaCl2-extractable in soil and concentration in soil pore water SPW), trace element accumulation in leaves and plant development over 36months. Results were compared to those obtained with a non-contaminated soil. The experiment was carried out in containers (95L of volume and 1m height). Half of the containers for each soil were planted with P. alba saplings and the others remained without plant. In neutral soils plant growth did not influence soil pH; the greatest effect due to plant growth was found in acid soil. Values of pH obtained by SPW showed a similar trend compared to those obtained after soil KCl extraction. Bioavailability of trace elements determined by both methods followed the same behavior in the three studied soils. Both methods for determining trace element bioavailability in soil were accurate to predict plant uptake. In non-contaminated soil, plants tended to increase micronutrients (Cu, Mn and Zn) availability. However, in case of contaminated soil, the growth of P. alba did not increase trace element availability. Moreover, results on height and diameter of the trunk of the trees, during 36months, demonstrated that the presence of total trace elements in soil did not affect plant development.AGL2008-00985 is a support from the CICYT of the Ministerio de Ciencia e Innovación of Spain and the FEDER (EU). L. Ciadamidaro thanks CSIC for funding his grant (JAE-PreDoc).Peer Reviewe

Effect of organic amendments on trace element availability in contaminated soil by three extraction methods (0.01 M CaCl2, soil pore water and diffusive gradient in thin films)

Presentación Oral PPS‐HM3 en la Session 1: Heavy metals en el International Congress of Phytoremediation of Polluted Soils. July 29- 30, 2014. Vigo, SpainWe studied the effeet of two organic amendments (biosolid compost and alperujo compost) and two plant species (Medicago sativa and Poa annua) on trace element (TE) bioavailability on two contaminated soils (one with neutral pH and other with acid pH) comparing three methods (0.01 M CaCl2-extractable in soil, concentration in soil pore water SPW and extraction by diffusive gradient in thin films DGT). The experiment was carried out in 72 pots (3L of volume each) that were filled with the two soils. Two treatments with amendments for each soil and species and a control without soil amendments for each species were established. In neutral soils no significant differences between treatments were found for TE availability. The behaviour of Cu, Mn y Zn extracted by CaCI2 was similar to that obtained in SPW and DGT, although characterized by higher concentrations. For Cd, the highest mean values were observed in soil in which M. sativa was growing for the three extraction methods. In the acid soil was found the greatest effect due to organic amendment addition, in which an increase in soil pH and the establishment of vegetation into the pots were observed. The presence of the amendments and the rhizosphere reduced the content of Cd and Zn, reaching the lowest values in the DGT extraction method, especially in soil with alperujo compost in presence of M. sativa. The contents of Cu and Mn follow a different tendency, characterized by an increase in amendment treatments, especially with CaCb extraction.Peer Reviewe

Phytoextraction of heavy metal contaminated soils with Thlaspi goesingense and Amaranthus hybridus : Rhizosphere manipulation using EDTA and ammonium sulfate

Selection of appropriate plant species and rhizosphere manipulation to enhance metal uptake are considered key factors in the development of phytoextraction technologies. A pot trial was conducted with two contaminated soils to investigate the effect of EDTA and ammonium sulfate on the accumulation of heavy metals into shoots of the low-biomass hyperaccumlator Thlaspi goesingense Halacsy (Brassicaceae) and the high-biomass non-hyperaccumulating plant Amaranthus hybridus (Amaranthaceae). Upon application of 1 g EDTA (kg soil)(-1) metal extractability with I M NH(4)NO(3) increased substantially, whereas the application of (NH(4))(2)SO(4) was less effective. The EDTA treatment increased the heavy metal concentrations in both plant species, however, the difference to the control was larger for A. hybridus. EDTA enhanced shoot concentrations in A. hybridus grown on soil Arnoldstein from 32.7 mg kg(-1) to 1140 mg kg(-1) for Pb and from 3.80 mg kg(-1) to 10.3 mg kg(-1) for Cd. Cd concentrations in shoots of T. goesingense were also increased by EDTA application, however, a slight decrease was observed for Pb. T. goesingense accumulated 2840 mg Pb kg(-1) without any treatment. This is the first report of Pb hyperacumulation by T goesingense. A decrease of shoot Pb concentration was observed in T. goesingense upon treatment with ammonium sulfate. Although metal concentrations in the shoots were rather large and significantly increased upon application of EDTA, plant growth and heavy metal removal were still too small to obtain reasonable extraction rates in soils heavily polluted by metals. It should be also noted that metal lability largely increased in EDTA-treated soils and this lability persisted for several weeks after the application of the chelating agent, which is likely to be associated with the risk of groundwater contamination

Aluminium-phosphate interactions in the rhizosphere of two bean species: Phaseolus lunatus L. and Phaseolus vulgaris L.

BACKGROUND: Plants differ in their response to high aluminium (Al) concentrations which typically cause toxicity in plants grown on acidic soils. The response depends on plant species and environmental conditions such as substrate and cultivation system. The present study aimed to assess Al-phosphate (P) dynamics in the rhizosphere of two bean species, Phaseolus vulgaris L. var. Red Kidney and Phaseolus lunatus L., in rhizobox experiments. RESULTS: Root activity of the bean species induced up to a 7-fold increase in exchangeable Al and up to a 30-fold decrease of extractable P. High soluble Al concentrations triggered the release of plantspecific carboxylates, which differed between soil type and plant species. The results suggest that P. vulgaris L. mitigates Al stress by an internal defence mechanism and P. lunatus L. by an external one, both mechanisms involving organic acids. CONCLUSION: Rhizosphere mechanisms involved in Al detoxification were found to be different for P. vulgaris L. and P. lunatus L., suggesting that these processes are plant species specific. P. vulgaris L. accumulates Al in the shoots (internal tolerance mechanism) while P. lunatus L. prevents Al uptake by releasing organic acids (exclusion mechanism) into the growth media