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Summary • The influence of phylogeny on shoot heavy metal content in plants was investigated and the hypothesis tested that traits impacting on the accumulation of cadmium, chromium, copper, nickel, lead and zinc in plant shoots are associated. • Data suitable for comparative analyses were generated from a literature survey, using a residual maximum likelihood (REML) procedure. Both pair-wise regressions and principal components analyses (PCA) were performed on independent contrasts of shoot metal content. • Significant variation in shoot metal content occurred at the classification level of order and above, suggesting an ancient evolution of traits. Traits impacting on the accumulation of metals in plant shoots were associated. • This information can be used to improve predictions of soil-to-plant metal transfer, to formulate hypotheses on the origins of metal-accumulating phenotypes and to inform the exploitation of plant genetic resources for nutritional improvement and phytoremediation.

Global food supplies currently depend on producing inorganic P fertilisers from a finite reserve of rock phosphate (RP). P fertilisers are themselves significant pollutants but their production from RP also leaves a phosphogypsum (PG) by-product that is sufficiently radioactive that its reuse is restricted. PG is mostly accumulated in open 'stacks' that make up a significant proportion of all Technologically Enhanced Naturally-Occurring Radioactive Material (TENORM) waste. Using lower and upper estimates of current RP reserves, historic production, and Hubbert's logistic function-based 'peak theory', lower and upper boundaries for possible RP production were predicted to the year 2100. The 'low' boundary scenario had a production peak of c.350 Mt/a RP in c.2050 followed by a steep decline. The 'high' boundary scenario had a production peak of c.1200 Mt/a RP in about 2090. Future trends in P demand for food production were used to predict a possible, demand-driven, RP production scenario until 2100 which peaked at a demand of c.620 Mt/a RP and was within possible production boundaries. An RP:P ratio of 5.62:1 and PG:P fertiliser ratio of 4:1 was used to calculate that this predicted demand-driven scenario would ultimately produce nearly 350 Mt/a of PG and a cumulative total of c.30 Gt by 2100. Average PG activity concentrations of

The effects of ionising radiation (IR) on plants are important for environmental protection but also in agriculture, horticulture, space science, and plant stress biology. Much current understanding of the effects of IR on plants derives from acute high-dose studies but exposure to IR in the environment frequently occurs at chronic low dose rates. Chronic low dose-rate studies have primarily been field based and examined genetic or cytogenetic endpoints. Here we report research that investigated developmental, morphological and physiological effects of IR on Arabidopsis thaliana grown over 7 generations and exposed for five generations to chronic low doses of either 137Cs (at a dose rate of c. 40 μGy/h from β/γ emissions) or 10 μM CdCl2. In some generations there were significant differences between treatments in the timing of key developmental phases and in leaf area or symmetry but there were, on the basis of the chosen endpoints, no long-term effects of the different treatments. Occasional measurements also detected no effects on root growth, seed germination rates or redox poise but in the generation in which it was measured exposure to IR did decrease DNA-methylation significantly. The results are consistent with the suggestion that chronic exposure to c. 40 μGy/h can have some effects on some traits but that this does not affect function across multiple generations at the population level. This is explained by the redundancy and/or degeneracy between biological levels of organization in plants that produces a relatively loose association between genotype and phenotype. The importance of this explanation to understanding plant responses to stressors such as IR is discussed. We suggest that the data reported here provide increased confidence in the Derived Consideration Reference Levels (DCRLs) recommended by the International Commission for Radiological Protection (ICRP) by providing data from controlled conditions and helping to contextualize effects reported from field studies. The differing sensitivity of plants to IR is not well understood and further investigation of it would likely improve the use of DCRLs for radiological protection.

Statement paper following discussions in March 2019 between the TREE (Transfer-Exposure-Effects) project participants and members of the European Radioecology ALLIANCE working group on ‘transgenerational effects and species radiosensitivity'.

During exposure of cells to acute high dose-rate ionizing radiation (IR), oxidants from the radiolysis of water can overwhelm antioxidant systems. Protecting flora from the effects of IR released from a nuclear industry of increasing global significance and managing the growth of plants during space flight both necessitate estimating the effects of chronic low dose-rate exposure to IR. In contrast to effects at acute high-dose rates, under chronic low dose-rate exposure it is subtle, progressive, long-term effects on antioxidant systems that it is important to estimate. Here, we outline a method that combines biochemical measurement and mathematical modeling to predict the effects of chronic low dose-rate IR on redox potential in plant cells over time.

During exposure of cells to acute high dose-rate ionizing radiation (IR), oxidants from the radiolysis of water can overwhelm antioxidant systems. Protecting flora from the effects of IR released from a nuclear industry of increasing global significance and managing the growth of plants during space flight both necessitate estimating the effects of chronic low dose-rate exposure to IR. In contrast to effects at acute high-dose rates, under chronic low dose-rate exposure it is subtle, progressive, long-term effects on antioxidant systems that it is important to estimate. Here, we outline a method that combines biochemical measurement and mathematical modeling to predict the effects of chronic low dose-rate IR on redox potential in plant cells over time.

Predicting soil-to-plant transfer of radionuclides is restricted by the range of species for which concentration ratios (CRs) have been measured. Here the radioecological utility of meta-analyses of phylogenetic effects on alkali earth metals will be explored for applications such as ‘gap-filling’ of CRs, the identification of sentinel biomonitor plants and the selection of taxa for phytoremediation of radionuclide contaminated soils. REML modelling of extensive CR/concentration datasets shows that the concentrations in plants of Ca, Mg and Sr are significantly influenced by phylogeny. Phylogenetic effects of these elements are shown here to be similar. Ratios of Ca/Mg and Ca/Sr are known to be quite stable in plants so, assuming that Sr/Ra ratios are stable, phylogenetic effects and estimated mean CRs are used to predict Ra CRs for groups of plants with few measured data. Overall, there are well quantified plant variables that could contribute significantly to improving predictions of the fate radioisotopes in the soil-plant system.

We will never have data to populate all of the potential radioecological modelling parameters required for wildlife assessments. Therefore, we need robust extrapolation approaches which allow us to make best use of our available knowledge. This paper reviews and, in some cases, develops, tests and validates some of the suggested extrapolation approaches.\ud \ud The concentration ratio (CRproduct-diet or CRwo-diet) is shown to be a generic (trans-species) parameter which should enable the more abundant data for farm animals to be applied to wild species.\ud \ud An allometric model for predicting the biological half-life of radionuclides in vertebrates is further tested and generally shown to perform acceptably. However, to fully exploit allometry we need to understand why some elements do not scale to expected values.\ud \ud For aquatic ecosystems, the relationship between log10(a) (a parameter from the allometric relationship for the organism-water concentration ratio) and log(Kd) presents a potential opportunity to estimate concentration ratios using Kd values.\ud \ud An alternative approach to the CRwo-media model proposed for estimating the transfer of radionuclides to freshwater fish is used to satisfactorily predict activity concentrations in fish of different species from three lakes. We recommend that this approach (REML modelling) be further investigated and developed for other radionuclides and across a wider range of organisms and ecosystems.\ud \ud Ecological stoichiometry shows potential as an extrapolation method in radioecology, either from one element to another or from one species to another.\ud \ud Although some of the approaches considered require further development and testing, we demonstrate the potential to significantly improve predictions of radionuclide transfer to wildlife by making better use of available data.

An investigation into the phylogenetic variation of plant tolerance and the root and shoot uptake of organic contaminants was undertaken. The aim was to determine if particular families or genera were tolerant of or accumulated organic pollutants. Data were collected from sixty-nine studies. The variation between experiments was accounted for using a residual maximum likelihood analysis to approximate means for individual taxa. A nested ANOVA was subsequently used to determine differences at a number of differing phylogenetic levels. Significant differences were observed at a number of phylogenetic levels for the tolerance to TPH, the root concentration factor and the shoot concentration factor. There was no correlation between the uptake of organic pollutants and that of heavy metals. The data indicate that plant phylogeny is an important influence on both the plant tolerance and uptake of organic pollutants. If this study can be expanded, such information can be used when designing plantings for phytoremediation or risk reduction during the restoration of contaminated sites.

Genomic and proteomic techniques provide the opportunity to investigate plant response to ionising radiation in unprecedented detail. Understanding plant molecular responses to ionising radiation might be useful for radioprotection but also for understanding plant stress responses. This is because radioactivity was a primordial stressor to cells and many stress responses are highly conserved through evolution. DNA microarrays for Arabidopsis plants exposed to 40 µGy h -1 through a hydroponic solution revealed that, after 14 days, there are changes in gene expression primarily in roots. The genes that change are not associated with DNA repair, and correlations with responses to other stressors in public databases suggest that there are elements of plant stress response being activated. The number of genes and their fold changes are lower than those reported for many other stressors but have particular overlaps with oxidative stress responses. Proteomic analyses form similar experiments are ongoing but similarly show no change of abundance in proteins associated with DNA repair and more changes in roots than shoots at these exposures.

There is current interest in managing and manipulating 137Cs transfer from soil to plants. We hypothesized that N source might affect Cs uptake by plants and report experiments that confirm this. Uptake experiments using hydroponics with a variety of species in the Poaceae, Asteraceae and Caryophyllid clade grown in a variety of N regimes with excess N and then acutely exposed to Cs showed that N nutrition could affect Cs uptake rates, total amounts of Cs taken up and root:shoot ratios of Cs. In general, the Caryophyllids tested produced significantly less shoot and root biomass but had higher Cs uptake rates when grown on NH4+ rather than NO3−, whilst species from the Poaceae and Asteraceae almost always produced similar shoot and root biomass and had similar Cs uptake on NH4+, NO3− or glycine as N sources. This is the first time that plants grown on an organic-N source have been demonstrated to take up Cs. Physiological experiments using N-starvation and the N-metabolism inhibitor methionine sulfoxamine (MSX) demonstrated that Cs transport into the root was inversely related to NH4+ transport, i.e. NH4+-grown plants had higher Cs uptake rates if there is no NH4+ present during uptake but lower Cs uptake rates if NH4+ is present. It is suggested that taking account of N ecophysiology might help refine predictions of soil-to-plant transfer of 137Cs and, in some instances, be useful for managing or manipulating it. It is noted that there is much recent research into N nutrition in plants that might be useful in achieving this.

A Residual Maximum Likelihood (REML) procedure was used to compile Sr concentrations in 103 plant species from experiments with Sr concentrations in 66 plant species from the literature. There were 14 species in common between experiments and the literature. The REML procedure loge-transformed data and removed absolute differences in Sr concentrations arising from soil factors and exposure times to estimate mean relative Sr concentrations for 155 species. One hundred and forty-two species formed a group with a normal frequency distribution in mean relative Sr concentration. A nested hierarchical analysis of variance (ANOVA) based on the most recent molecular phylogeny of the angiosperms showed that plant species do not behave independently for Sr concentration but that there is a significant phylogenetic effect on mean relative Sr concentrations. Concentrations of Sr in non-Eudicots were significantly less than in Eudicots and there were significant effects on Sr concentrations in the dataset down the phylogenetic hierarchy to the family level. Of the orders in the dataset the Cucurbitales, Lamiales, Saxifragales and Ranunculales had particularly high Sr concentrations and the Liliales, Poales, Myrtales and Fabales particularly low Sr concentrations. Mean relative Sr concentrations in 60 plant species correlated with those reported elsewhere for Ca in the same species, and the frequency distribution and some phylogenetic effects on Sr concentration in plants were similar to those reported for Ca. This analysis of mean relative Sr concentrations in 155 plant species across the angiosperm phylogeny might be helpful for modelling 90Sr in food chains, predicting radiological doses to flora, and selecting species for phytomonitoring and phytoremediation of 90Sr.

Understanding the behavior of sulfur (S) in the soil-plant system is important for crop production, for predicting the movement of the radioisotope 35S in the environment, and for investigating the role of S in plant metabolism of xenobiotics. A database of relative mean S concentrations in 121 species of flowering plants was constructed using a Residual Maximum Likelihood (REML) procedure with new experimental data for 76 species and literature data for 57 species, there being 12 species in common. The relative mean S concentrations in plant species were normally distributed and their range greater than previously reported for S concentrations between plant species. There was a significant phylogenetic effect on S concentrations when they were analyzed using a nested ANOVA coded with a recent phylogeny of flowering plants. About 36% of the variance between species was associated with the rank of Order and above. At the rank of Order, S concentrations were Brassicales > Malphigiales > Lamiales > Rosales > Caryophyllales > Malvales > Poales > Fabales > Fagales > Asterales. Experiments to quantify intervarietal differences within Beta vulgaris, Triticum aestivum, and Cicer arietinum revealed that these reached a maximum in B. vulgaris at about 20% of those found at the species level and above. A comparison of relative mean S concentrations with previously reported relative mean concentrations for heavy metals suggested correlations between S and cadmium (Cd), and S and zinc (Zn). The frequency distributions and phylogenetic effects reported here are useful to understanding soil-plant transfer of stable and radioactive S isotopes in agricultural and natural ecosystems and might aid investigations of plant response to xenobiotics. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.

Ruthenium-106 is of potential radioecological importance but soil-to-plant Transfer Factors for it are available only for few plant species. A Residual Maximum Likelihood (REML) procedure was used to construct a database of relative 103/106 Ru concentrations in 114 species of flowering plants including 106 species from experiments and 12 species from the literature (with 4 species in both). An Analysis of Variance (ANOVA), coded using a recent phylogeny for flowering plants, was used to identify a significant phylogenetic effect on relative mean 103/106 Ru concentrations in flowering plants. There were differences of 2465-fold in the concentration to which plant species took up 103/106 Ru. Thirty-nine percent of the variance in inter-species differences could be ascribed to the taxonomic level of Order or above. Plants in the Orders Geraniales and Asterales had notably high uptake of 103/106 Ru compared to other plant groups. Plants on the Commelinoid monocot clades, and especially the Poaceae, had notably low uptake of 103/106 Ru. These data demonstrate that plant species are not independent units for 103/106 Ru concentrations but are linked through phylogeny. It is concluded that models of soil-to-plant transfer of 103/106 Ru should assume that; neither soil variables alone affect transfer nor plant species are independent units, and taking account of plant phylogeny might aid predictions of soil-to-plant transfer of 103/106 Ru, especially for species for which Transfer Factors are not available.

There is much current interest in managing and manipulating radionuclide transfer from soils to plants, either for 'safe' crops or for phytoextraction of radionuclide contaminated soils. Potentially there is biodiversity in plant uptake that might aid these efforts. We have established the effects of phylogeny (evolutionary history) on the uptake of numerous heavy metal and nutrient elements. Here, using the same Residual Maximum Likelihood techniques, we report phylogenetic effects on radionuclide uptake by plants derived from databases of several hundred species of plants we have collated over recent years. There are differences of at least two orders of magnitude in the concentration to which plants take up isotopes of Cs, Sr, Cl, Ru, S, and I. When analysed using hierarchical Analysis of Variance coded using a recent molecular phylogeny of flowering plants it is clear that for no radionuclide is all the variation inter-specific. Rather, for all radionuclides some of the inter-taxa variation is associated with higher taxonomic levels. In general, therefore, groups of plants with high and low uptake of radionuclides, and that might be useful for managing or manipulating radionuclide uptake, can be delineated. Here we discuss some of these groups and how they might be useful.

Caesium (Cs) is an alkali metal with chemical properties similar to potassium (K). It has no known role in plant nutrition and it is not toxic to plants at the micromolar concentrations occurring naturally in soil solutions. However, two radioisotopes of Cs (134Cs and 137Cs) are of environmental concern due to their relatively long half-lives, emissions of β and γ radiation during decay, and rapid incorporation into biological systems. There is considerable interest in remediating sites contaminated by these isotopes using phytoextraction and, since the produce from radiocaesium-contaminated areas may enter the food chain, the introduction of `safe' crops that do not accumulate Cs. This article reviews the molecular mechanisms of Cs uptake by plants, and provides a perspective on strategies to develop: (1) plants that extract Cs efficiently from soils (for the phytoremediation of land), or (2) `safe' crops that minimise the entry of radiocaesium directly into the human food chain.

This study investigated the uptake of 134Cs by Lactuca sativaL., Silybum marianumGaertn., Centaurea cyanusL., Carthamus tinctorius L. from the Asteraceae, and Beta vulgaris L. var. `Lutiancai' and Beta vulgaris L. var. `Hongtiancai' from the Chenopodiaceae grown in two widely-distributed soils (a paddy soil and a red soil) in South China. The results showed that the plants growing on the paddy soil had a relatively high yield and low [134Cs] while those growing on the red soil showed the opposite trend. The accumulation of 134Cs was dependent on plant species and soil types. For the paddy soil, mean values for [134Cs] were higher for the species of the Asteraceae (ranging from 165 to 185 Bq g−1) than for those of the Chenopodiaceae (less than 140 Bq g−1). For the red soil, S. marianumand C. cyanus of the Asteraceae had high average concentrations of 134Cs ranging from 340 to 400 Bq g−1 but L. sativa and C. tinctorius from the same family had low concentrations of 134Cs ranging from 115 to 200 Bq g−1 on a dry weight basis. B. vulgaris L. var. `Lutiancai' and Beta vulgaris L. var. `Hongtiancai' accumulated from 120 to 231 Bq 134Cs g−1 of plant shoot. The transfer factor values of 134Cs for the studied species were in general higher in red soil than in paddy soil except C. tinctorius. All plant species from the Asteraceae family growing on the paddy soil had higher transfer factors than the B. vulgaris species. S. marianum, and C. cyanus growing on the red soil had TFs >1, being much higher than the B. vulgaris species. The results therefore showed that the plant species from the Asteraceae could accumulate higher concentrations of radiocesium than the Beta vulgaristhat has previously been suggested as a candidate for phytoremediation of radiocesium contaminated soils.

The fission yield of 99Tc from 239Pu and 235U is similar to that of 137Cs or 90Sr and it is therefore an important component of nuclear weapons fall-out, nuclear waste and releases from nuclear facilities. There is particular current interest in 99Tc transfer from soil to plants for: (a) environmental impact assessments for terrestrial nuclear waste repositories, and (b) assessments of the potential for phytoextraction of radionuclides from contaminated effluent and soil. Vascular plants have a high 99Tc uptake capacity, a strong tendency to transport it to shoot material and accumulate it in vegetative rather than reproductive structures. The mechanisms that control 99Tc entry to plants have not been identified and there has been little discussion of the potential for phytoextraction of 99Tc contaminated effluents or soil. Here we review soil availability, plant uptake mechanisms and soil to plant transfer of 99Tc in the light of recent advances in soil science, plant molecular biology and phytoextraction technologies. We conclude that 99Tc might not be highly available in the long term from up to 50% of soils worldwide, and that no single mechanism that might be easily targeted by recombinant DNA technologies controls 99Tc uptake by plants. Overall, we suggest that Tc might be less available in terrestrial ecosystems than is often assumed but that nevertheless the potential of phytoextraction as a decontamination strategy is probably greater for 99Tc than for any other nuclide of radioecological interest.

Our understanding of the evolutionary relationships (phytogenies) between flowering plants has been transformed in the last yen years. As a result, new phylogenies for flowering plants have been developed specifically for comparative biological studies. Researchers have used these new phylogenies to help explain variation in a number of plant characteristics. We have used them to help explain soil to plant transfer of heavy metal ions and have recently finished applying them to studies of soil to plant transfer of radionuclides.

Spinacia oleracea L. cv. ‘Bloomsdale’, Beta vulgaris L. cv. ‘Flavescens’, Brassica juncea L. ‘OB825’, and Helianthus annuus L. cv. ‘Oranges and Lemons’ were grown for 8 weeks at a site contaminated with 137Cs at Bradwell Nuclear Power Station, UK. The site was a trench approximately 1.5 m deep, 2 m wide, and 100 m long in ‘made ground’ consisting of alluvium with traces of illites, kaolinites, and smectites. 137Cs activity concentration was measured in individual plants after 8 weeks growth and the soil in which they grew. The biomass produced and total 137Cs removed to shoots differed significantly between species but 137Cs activity concentrations and Transfer Factors (TFs) did not. B. vulgaris produced the most biomass and removed the greatest amount of 137Cs. For all plants, and within each taxon, plants growing at low soil 137Cs activity concentrations had significantly greater TFs than those growing at high soil 137Cs activity concentrations. It is concluded that selecting plant taxa suited ...

The Michaelis–Menten kinetic parameters ( I max , K m and Cmin) of Cs uptake were estimated using a solution-depletion method, after 0, 1 and 4 d K-starvation in eight mature grass species of different relative growth rates (Bromus sterilis L., Elymus repens (L.) Gould, Poa annua L., Lolium perenne L. var. ‘Taya’, Anthoxanthum odoratum L., Festuca gigantea (L.) Vill., Festuca ovina L. and Nardus stricta L.). There were species differences in Imax and Cmin, a positive relationship between Km and RGR (r2=0.53; p=0.03), and a negative relationship between Cmin and RGR (r2=0.89; p=0.001) in 0 d K starved plants. In general, Imax increased with K starvation, as previously reported for K uptake kinetics. Km increased with K starvation, contrasting with reported studies on K, and Cmin decreased, although all species did not respond similarly.

The application of the concentration ratio (CR) to predict radionuclide activity concentrations in wildlife from those in soil or water has become the widely accepted approach for environmental assessments. Recently both the ICRP and IAEA have produced compilations of CR values for application in environmental assessment. However, the CR approach has many limitations, most notably, that the transfer of most radionuclides is largely determined by site-specific factors (e.g. water or soil chemistry). Furthermore, there are few, if any, CR values for many radionuclide-organism combinations. In this paper, we propose an alternative approach and, as an example, demonstrate and test this for caesium and freshwater fish. Using a Residual Maximum Likelihood (REML) mixed-model regression we analysed a dataset comprising 597 entries for 53 freshwater fish species from 67 sites. The REML analysis generated a mean value for each species on a common scale after REML adjustment taking account of the effect of the inter-site variation. Using an independent dataset, we subsequently test the hypothesis that the REML model outputs can be used to predict radionuclide, in this case radiocaesium, activity concentrations in unknown species from the results of a species which has been sampled at a specific site. The outputs of the REML analysis accurately predicted (137)Cs activity concentrations in different species of fish from 27 Finnish lakes; these data had not been used in our initial analyses. We recommend that this alternative approach be further investigated for other radionuclides and ecosystems.

It has been hypothesized that radiation-induced oxidative stress is the mechanism for a wide range of negative impacts on biota living in radioactively contaminated areas around Chernobyl. The present study tests this hypothesis mechanistically, for the first time, by modelling the impacts of radiolysis products within the cell resulting from radiations (low linear energy transfer β and γ), and dose rates appropriate to current contamination types and densities in the Chernobyl exclusion zone and at Fukushima. At 417 µGy h −1 (illustrative of the most contaminated areas at Chernobyl), generation of radiolysis products did not significantly impact cellular concentrations of reactive oxygen species, or cellular redox potential. This study does not support the hypothesis that direct oxidizing stress is a mechanism for damage to organisms exposed to chronic radiation at dose rates typical of contaminated environments.

Assessments of the behaviour of 99Tc in terrestrial environments necessitate predicting soil-to-plant transfer. An experiment with 116 plant taxa showed that 99Tc transfer to plants was positively related to plant dry weight but negatively related to % dry matter and age at exposure. Activities of 99Tc analysed by hierarchical ANOVA coded with an angiosperm phylogeny revealed significant effects, with 55% of the variance between species explained at the Ordinal level and above. Monocots had significantly lower transfer of 99Tc than Eudicots, within which Caryophyllales > Solanales > Malvales > Brassicales > Asterales > Fabales. There was a significant phylogenetic signal in soil-to-plant transfer of 99Tc. This phylogenetic signal is used to suggest that, for example, a nominal Tc Transfer Factor of 5 could be adjusted to 2.3 for Monocots and 5.3 for Eudicots.

Soil-to-plant transfer of radionuclides can be related to plant evolutionary history (phylogeny). For some species and radionuclides the effect is significant enough to be useful in predicting Transfer Factors (TFs). Here a Residual Maximum Likelihood (REML)-based mixed model and a recent plant phylogeny are used to compile data on soil-to-plant transfer of radionuclides and to show how the phylogeny can be used to fill gaps in TFs. Using published data, generic means for TFs are used to anchor the data from REML modelling and hence predict TFs for important groups of plants. Radionuclides of Cs are used as an example. With a generic soil-to-plant TF of 0.07, TFs of 0.035 and 0.085 are predicted for monocot and eudicot gaps, respectively. Also demonstrated is how the known effects of soil conditions can be predicted across plant groups—predicted Cs TFs for gap-filling across all flowering plants are calculated for sandy loams with and without waterlogging. Predictions of TFs for Sr, Co, Cl and Ru are also given. Overall, the results show that general predictions of TFs based on phylogeny are possible—a significant contribution to gap filling for TFs.

Analyses reported here quantify the contribution of plant phylogeny and plant growth strategy to soil-to-plant transfer of Co. Estimated relative mean (ERM) Co concentrations in shoots of 241 species of flowering plant were derived using a residual maximum likelihood (REML) analysis. There were significant differences in, and a loge-normal frequency distribution of, ERM Co concentrations between species. A significant percentage of interspecies variance could be assigned to taxonomic categories above the species, (Family and above 21.5%; Order and above 12.22%). Time-series analysis of ERM Co concentrations ordered in the species-sequence of the Angiosperm Phylogeny Group (APG II (2003)) revealed significant autocorrelation with an increase from Commelinid Monocot to Asterid Eudicot and a pronounced peak in the Core Eudicots. ERM Co concentrations categorized by plant growth strategy sensu Grime (2001) showed an increase toward stress-tolerant strategies. Plant species are not, therefore, independent units of Co concentration--factors derived from higher levels of biological organization exert significant effects. These effects can provide the basis of new techniques for selecting plant species for biotechnologies and for predicting the exposure of organisms to Co. They show that plant phylogeny and growth strategy might help refine predictions of soil-to-plant transfer of a variety of pollutants, and suggest research that might link molecular and higher level processes in contaminated soil-plant systems.

Publisher Summary This chapter discusses the phytoremediation of soils contaminated with radionuclides. Knowledge of radionuclide behavior in the environment, plant science, and environmental modeling might allow phytoremediation to meet some of the challenges of cleaning up soil contaminated with radionuclides. Focusing on this challenge might provide new directions for radioecology in the 21st century. Phytoremediation is a nascent technology that might eventually be useful for decontaminating soils of radionuclides. It is useful when contaminants are dispersed in the upper layers of soil at sites where plants capable of absorbing them can grow freely, a scenario that already occurs at many locations around the earth. There are challenges to be overcome, but doing so is probably limited as much by resources for research as scientific possibilities. Although the nuclear industry has certainly overcome much greater challenges, resources available for research are probably dependent on the future status of both the nuclear industry and environmental legislation. These are changeable, but the current absence of alternative decontamination methods and the presence of tightening legislation indicate that it is likely to be worth investing further resources into phytoremediation to build on the foundations of the first phase of field trials. Some of the challenges facing phytoremediation also coincide with those facing the 21st century radioecology. The expertise of radioecologists can be indispensable in developing the technology of phytoremediation and this challenge should provide a significant new outlet for their energies.

High concentrations of 35Cl and the radioisotope 36Cl (produced naturally by cosmic radiation and anthropogenically by U fission and the use of neutron sources) can be problematic in soil, but are potentially amenable to phytoremediation if appropriate plants can be found. Here, results are reported that might aid the selection of plants with unusually high or low uptake of 36Cl A residual maximum likelihood analysis was used to estimate, from 13 experiments, relative 36Cl uptake by 106 species across the angiosperm phylogeny. Nested analysis of variance, coded using a recent angiosperm phylogeny, showed that there were significant inter-species differences in 36Cl uptake and that species behavior was not independent; but linked through theirphylogeny. Eudicots had significantly higher 36Cl uptake than Monocots and related clades and, in particular the Orders Caryophyllales, Apiales, and Cucurbitales had high uptake while the Poales, Lillales, Brassicales, and Fabales had low uptake. Overall, 35% of the inter-taxa variation in 36Cl was attributed to the taxonomic ranks of Order and above, a significant phylogenetic effect compared with other elements for which similar analyses have been published. The implications of these findings for selecting plants for phytoremediation of soil contaminated with 35/36Cl are discussed.