Exposure to Cr(VI) induces organ dependent MSI in two loci related with photophosphorylation and with glutamine metabolism

Chromium (Cr), as a mutagenic agent in plants, has received less attention than other metal pollutants. To understand if Cr induces microsatellite instability (MSI), Pisum sativum seedlings were exposed for 28 days to different concentrations of Cr(VI) up to 2000 mg L⁻¹, and the genetic instability of ten microsatellites (SSRs) was analyzed. In plants exposed to Cr(VI) up to 1000 mg  L⁻¹, MSI was never observed. However, roots exposed to 2000 mg L⁻¹ displayed MSI in two of the loci analyzed, corresponding to a mutation rate of 8.3%. SSR2 (inserted in the locus for plastid photosystem I 24 kDa light harvesting protein) and SSR6 (inserted in the locus for P. sativum glutamine synthetase) from Cr(VI)-treated roots presented alleles with, respectively, less 6 bp and more 3 bp than the corresponding controls. This report demonstrates that: (a) SSRs technique is sensitive to detect Cr-induced mutagenicity in plants, being Cr-induced-MSI dose and organ dependent (roots are more sensitive); (b) two Cr-sensitive loci are related with thylakoid photophosphorylation and with glutamine synthetase, respectively; (c) despite MSI is induced by Cr(VI), it only occurs in plants exposed to concentrations higher than 1000 mg L⁻¹ (values rarely found in real scenarios). Considering these data, we also discuss the known functional changes induced by Cr(VI) in photosynthesis and in glutamine synthetase activity.     

Salinity increases the triterpenoid content of a salt secretor and a non-salt secretor mangrove

The present study describes the effect of salinity on the triterpenoid content of the salt secretor mangrove Avicennia marina and the non-secretor Rhizophora stylosa. Mangrove seedlings were grown for eight months in 0%, 0.5%, 1.5%, 2.0% and 3.0% salt concentration. The growth of both species was increased by salt with maximal stimulation at 1.5%, and this elevation appeared to be attenuated by increasing the salt concentration above 1.5%. The triterpenoid compositions of three types of chemical structures, lupane (lupeol, lupenone), oleanane (β-amyrin, taraxerol, germanicol), and ursane (α-amyrin), were studied. In addition, the phytosterol components campesterol, stigmasterol and β-sitosterol were analyzed. The total triterpenoid contents in the roots and leaves of A. marina for the 0% group were 87.0 and 66.2 μg g⁻¹, respectively, and increased significantly to 173.1 and 142.6 μg g⁻¹ with 3% salinity. The higher salinity also significantly increased the total concentration of phytosterols in the leaves and roots of this species. A similar increase in the concentration of both triterpenoids and phytosterols was observed in the roots and leaves of R. stylosa with increasing salt concentration. Thus, the triterpenoid concentration was increased by salinity in the roots and leaves of both A. marina and R. stylosa irrespective of their differences in salt management by salt excretion or by a non-excretion mechanism. Comparison of the triterpenoid concentration in four species of growing mangrove seedlings revealed a correlation between the total triterpenoid content and the salt tolerance based on the habitat zonation on Iriomote Island. A. marina thrives closest to sea and had the highest content of triterpenoids (173.1 μg g⁻¹ in 3% salt group). Therefore, it is likely that the triterpenoid content play an important role in mangrove plants for protection from salinity in both salt-secretors and non-secretors.     

Phagocytic activity,respiratory burst,cytoplasmic free-Ca concentration and apoptotic cell ratio of haemocytes from the black tiger shrimp, Penaeus monodon under acute copper stress

The aim of this study was to investigate the cellular toxicity of copper-induced injury to the black tiger shrimp Penaeus monodon. The 24 h, 48 h, 72 h and 96 h LC₅₀ (median lethal concentration) of Cu²⁺ on P. monodon (11.63 ± 1.14 g) were found to be 3.49, 1.54, 0.73 and 0.40 mg L^− 1, respectively. Total haemocyte count (THC), phagocytic activity, respiratory burst (RB), cytoplasmic free-Ca²⁺ (cf-Ca²⁺) concentration and apoptotic cell ratio of shrimp were determined after exposure to different concentrations of Cu²⁺ (0, 0.05, 0.5, 1.5 and 3.5 mg L^− 1) for 0, 6, 12, 24 and 48 h. There was no significant effect on the analytic indicator of shrimp exposed to 0.05 mg L^− 1 Cu²⁺. THC decreased after Cu-exposure to 0.5 mg L^− 1 for 48 h, 1.5 mg L^− 1 for 24 h and 3.5 mg L^− 1 for 12 h. Phagocytic activity decreased in P. monodon following 48 h exposure to 3.5 mg L^− 1 Cu²⁺. RB was induced after 6 h exposure to 0.5, 1.5 and 3.5 mg L^− 1 Cu²⁺. cf-Ca²⁺ concentration increased after 48 h exposure to 0.5 mg L^− 1 Cu²⁺, and 12 h exposure to 1.5 and 3.5 mg L^− 1 Cu²⁺. The percentage of apoptotic cells increased to 9.5%, 16.3% and 18.6% respectively following 48 h exposure to 0.5, 1.5 and 3.5 mg L^− 1 Cu²⁺. These results indicate that Cu can induce oxidative stress, elevation of cf-Ca²⁺ and cell apoptosis, and inhibit phagocytic activity in the shrimp P. monodon, and the lethal injury of Cu²⁺ to P. monodon may be mainly due to the sharp reduction of THC caused by ROS-induced apoptosis.     

Effects of light regime and oxygen profile on transformation of oxolinic acid in pond sediment

This study investigated the effects of light (visible light - 5800 lux, 24 h) or dark regime and aerobic or anaerobic condition on the decay of added oxolinic acid (OA) at 5, 10 and 20 mg L⁻¹ in eel pond sediment. An asymptotic decaying exponential model C_t = C_min + C_o × exp (−k × t) was used to facilitate quantitative approach to OA transformation, where C_t is the concentration of OA after t days, C_min the estimated level-off concentration of OA residue, C_o the concentration of added OA and k the decaying coefficient. OA decayed faster under light (C_min = 4.6 mg L⁻¹) than under dark (C_min = 7.8 mg L⁻¹) and also decayed faster under aerobic (C_min = 4.0 mg L⁻¹) than under anaerobic condition (C_min = 8.5 mg L⁻¹). C_min increased with C_o. Sundrying and tilling eel pond bottom should be able to reduce OA residue significantly.     

Ecophysiological responses of the mangrove Avicennia marina to trace metal contamination

Growth responses of Avicennia marina seedlings to contamination by different concentrations of two essential (Cu, Zn) and two non-essential (Pb, Hg) trace metals were studied under glasshouse conditions. We tested the hypothesis that soil retention and root ultrafiltration would exclude most of the trace metals, and that those that are absorbed and translocated to the shoots would interfere with plant performance and be excreted via leaf salt glands. One-month-old seedlings were subjected to Cu, Zn, Pb and Hg at concentrations of 0, 40, 80, 120 and 160 μg g⁻¹ sediment for 12 months in a randomized complete block design (n = 6). Photosynthesis was measured at the end of 12 months of trace metal exposure with a portable gas exchange system and chlorophyll fluorescence with a pulse-modulated fluorometer. After morphometric measurements, plants were harvested and analyzed for Cu, Zn, Pb and Hg by atomic absorption spectroscopy. Total dry biomass decreased with increasing trace metal concentration for all metals. In the 160 μg g⁻¹ Cu, Zn, Hg and Pb treatments, total biomass was significantly lower than the control value by 43%, 37%, 42% and 40%, respectively. Decreases in plant height and number of leaves followed trends similar to those for total biomass and ranged from 37% to 60%, compared to the controls. Decreases in chlorophyll content in the trace metal treatments ranged from 50% to 58% compared to the control. Carbon dioxide exchange, quantum yield of photosystem II (PSII), electron transport rate (ETR) through PSII and photosynthetic efficiency of PSII (F_v/F_m) were highest in the control treatment and decreased with increasing trace metal concentrations. Decreases in CO₂ exchange in the 160 μg g⁻¹ treatments for all trace metals ranged from 50% to 60%. Concentrations of all trace metals in plant organs increased with increasing metal concentrations and were higher in roots than in shoots, with concentrations of Cu and Zn being considerably higher than those of Hg and Pb. Qualitative elemental analyses and X-ray mapping of crystalline deposits over the glands at the leaf surfaces indicated that Cu and Zn were excreted from the salt glands, while Hg and Pb were absent, at least being below the limits of detection. These results demonstrate that growth processes are sensitive to trace metals and therefore can be considered as a cost of metal tolerance, but salt glands of this mangrove species do contribute eliminating at least part of physiologically essential trace metals if taken up in excess.     

Biomass production and nitrogen and phosphorus removal by the green alga Neochloris oleoabundans in simulated wastewater and secondary municipal wastewater effluent

Biomass productivity of 350 mg DCW L⁻¹ day⁻¹ with a final biomass concentration of 3.15 g DCW L⁻¹ was obtained with Neochloris oleoabundans grown in artificial wastewater at sodium nitrate and phosphate concentrations of 140 and 47 mg L⁻¹, respectively, with undetectable levels of residual N and P in effluents. In secondary municipal wastewater effluents enriched with 70 mg N L⁻¹, the alga achieved a final biomass concentration of 2.1 g DCW L⁻¹ and a biomass productivity of 233.3 mg DCW L⁻¹ day⁻¹. While N removal was very sensitive to N:P ratio, P removal was independent of N:P ratio in the tested range. These results indicate that N. oleoabundans could potentially be employed for combined biofuel production and wastewater treatment.     

Accumulation of lead by free and immobilized cyanobacteria with special reference to accumulation factor and recovery

Lead accumulation by free and immobilized cyanobacteria, Lyngbya majuscula and Spirulina subsalsa was studied. Exponentially growing biomass was exposed to 1-20 mg L⁻¹ of Pb(II) solution at pH 6, 7 and 8 for time periods ranging from 10 min to 48 h. L. majuscula accumulated 10 times more Pb (13.5 mg g⁻¹) than S. subsalsa (1.32 mg g⁻¹) at pH 6 within 3 h of exposure to 20 mg L⁻¹ Pb(II) solution and 76% of the Pb could be recovered using 0.1 M EDTA. This chelator (2 μM) did not influence Pb accumulation whereas 100 μM citrate increased that of S. subsalsa 6- to 8-fold. L. majuscula filaments enmeshed in a glass wool packed in a column removed 95.8% of the Pb from a 5 mg L⁻¹ Pb solution compared to free and dead biomass which removed 64 and 33.6% Pb respectively. A 92.5% recovery of accumulated Pb from the immobilized biomass suggests that repeated absorption-desorption is possible.     

Phytotoxic and genotoxic effects of silver nanoparticles exposure on germinating wheat seedlings

We investigated the effects of 1 and 10 mg L⁻¹ AgNPs on germinating Triticum aestivum L. seedlings. The exposure to 10 mg L⁻¹ AgNPs adversely affected the seedling growth and induced morphological modifications in root tip cells. TEM analysis suggests that the observed effects were due primarily to the release of Ag ions from AgNPs.     

Ecology of aquatic Ranunculus communities under the Mediterranean climate

The Iberian Peninsula encompasses more than 80% of the species richness of European aquatic ranunculi. The floristic diversity of the phytocoenosis characterised by aquatic Ranunculus and the main physical–chemical factors of the water were studied in 43 localities of the central Iberian Peninsula. Four aquatic Ranunculus communities are found in most of the aquatic environments. These are species-poor and have an uneven distribution: three species of Batrachium are heterophyllous and their communities are distributed in different aquatic ecosystems on silicated substrates; one species is homophyllous and its community occurs in various aquatic ecosystems with carbonated waters. In the Mediterranean climate, Ranunculus species are present in different habitats, as shown by the results of all the statistical analyses. Ranunculus trichophyllus communities occur in base-rich waters with a high buffering capacity (2273.44 ± 794.57 mg CaCO₃ L⁻¹) and a high concentration of cations (Ca²⁺, 121 ± 33.12 mg L⁻¹; Mg²⁺, 71.64 ± 82.77 mg L⁻¹), nitrates (2.89 ± 4.80 mg L⁻¹), ammonium (2.19 ± 1.36 mg L⁻¹) and sulphates (216.25 ± 218.54 mg L⁻¹). Ranunculus penicillatus communities are found in flowing waters with a high concentration of phosphates (0.48 ± 0.6 mg L⁻¹) and intermediate buffering capacity (683.66 ± 446.76 mg CaCO₃ L⁻¹). Both Ranunculus pseudofluitans and Ranunculus peltatus communities grow in waters with low buffering capacity (R. pseudofluitans, 385.91 ± 209.2 mg CaCO₃ L⁻¹; R. peltatus, 263.3 ± 180.36 mg CaCO₃ L⁻¹), and a low concentration of cations (R. pseudofluitans: Ca²⁺, 12.57 ± 9.42 mg L⁻¹; Mg²⁺, 3.42 ± 1.67 mg L⁻¹; R. peltatus: Ca²⁺, 15 ± 18.26 mg L⁻¹; Mg²⁺, 6.26 ± 8.89 mg L⁻¹) and nutrients (R. pseudofluitans: nitrates, 0.23 ± 0.2 mg L⁻¹; phosphates, 0.09 ± 0.1 mg L⁻¹; R. peltatus: nitrates, 0.19 ± 0.21 mg L⁻¹; phosphates, 0.09 ± 0.12 mg L⁻¹); the first in flowing waters, the latter in still waters.     

Accumulation, speciation, and coordination of arsenic in an inbred line and a wild type cultivar of the desert plant species Chilopsis linearis (Desert willow)

This study investigated the absorption of arsenic (As), sulfur (S), and phosphorus (P) in the desert plant Chilopsis linearis (Desert willow). A comparison between an inbred line (red flowered) and wild type (white flowered) plants was performed to look for differential responses to As treatment. One month old seedlings were treated for 7 days with arsenate (As₂O₅, As^V) at 0, 20, and 40 mg As^V L⁻¹. Results from the ICP-OES analysis showed that at 20 mg As^V L⁻¹, red flowered plants had 280 ± 11 and 98 ± 7 mg As kg⁻¹ dry wt in roots and stems, respectively, while white flowered plants had 196 ± 30 and 103 ± 13 mg As kg⁻¹ dry wt for roots and stems. At this treatment level, the concentration of As in leaves was below detection limits for both plants. In red flowered plants treated with 40 mg As^V L⁻¹, As was at 290 ± 77 and 151 ± 60 mg As kg⁻¹ in roots and stems, respectively, and not detected in leaves, whereas white flowered plants had 406 ± 36, 213 ± 12, and 177 ± 40 mg As kg⁻¹ in roots, stems, and leaves. The concentration of S increased in all As treated plants, while the concentration of P decreased in roots and stems of both types of plants and in leaves of red flowered plants. X-ray absorption spectroscopy analyses demonstrated partial reduction of arsenate to arsenite in the form of As-(SX)₃ species in both types of plants.     

Short term signaling responses in roots of young soybean seedlings exposed to cadmium stress

In the present study, the expression of fourteen genes involved in various signal transduction pathways was examined in young soybean (Glycine max) seedlings exposed to cadmium at two concentrations (10 mg L⁻¹ and 25 mg L⁻¹) for short time periods (3, 6 and 24 h). The results show that cadmium causes induction of genes encoding proteins involved in ethylene and polyamines metabolism, nitric oxide generation, MAPK cascades and regulation of other genes’ expression. The bioinformatic analysis of promoter sequences of Cd-inducible genes revealed that their promoters possess several regulative motifs associated with the plant response to stress factors and abscisic acid and ethylene signaling. The involvement of ethylene in the response of soybean seedlings to cadmium stress was further confirmed by the real-time analysis of ethylene production during 24 h of CdCl₂ treatment. The role of the described signaling elements in transduction of the cadmium signal in young soybean seedlings is discussed.     

Aerobic granulation with low strength wastewater at low aeration rate in A/O/A SBR reactor

The formation of aerobic granules with low organic loading synthetic wastewater (150-200 mg L⁻¹ of influent COD, acetate/propionate = 1/3) at low aeration rate (0.6 cm s⁻¹ of superficial gas velocity) had been investigated in the anaerobic/oxic/anoxic SBR. Aerobic granules with smooth surface and compact structure were successfully obtained after 50 days. However, these aerobic granules were unstable when the d(0.9) of granules increased to more than 1 mm. The results suggested that the aerobic granules with small diameter (smaller than 1000 μm) were more favorable for treating the low substrate loading wastewater at the low aeration rate. The cycle test revealed that most of the influent COD was removed at the anaerobic stage. The effluent concentrations of N-NH₄⁺ and P-PO₄³⁻ were lower than 1 mg L⁻¹, and the effluent concentration of nitrate gradually decreased with the granulation. Phosphate accumulating organisms were found to utilize O₂ or NO_x⁻ as electron acceptor for phosphorus removal in the study. Simultaneous nitrogen and phosphorus removal occurred inside the granules.     

Toxicity of lead and zinc to developing mussel and sea urchin embryos: Critical tissue residues and effects of dissolved organic matter and salinity

Lead (Pb) EC50 values in the very sensitive early development phases (48–72 h post-fertilization) of the mussels Mytilus galloprovincialis and Mytilus trossolus and sea urchin Strongylocentrotus purpuratus in 100% sea water were: M. trossolus — 45 (95% C.I. = 22–72) μg L^− 1; M. galloprovincialis — 63 (36–94) μg L^− 1; S. purpuratus — 74 (50–101) μg L^− 1. Salinity thresholds for normal development varied: M. trossolus > 21 ppt; M. galloprovincialis > 28 ppt; S. purpuratus ≥ 30 ppt. Addition of two spectroscopically distinct dissolved organic matters (DOM) from fresh water (Nordic Reservoir) and sea water (Inshore) moderately decreased the toxicity of Pb to both mussels, but not in a concentration-dependent fashion, with only an approximate doubling of EC50 over the range of 1.4–11.2 mg C L^− 1. Independent Pb binding capacity determinations for DOC explained the lack of a relationship between DOM concentration and toxicity. Salinity had no effect on Pb toxicity down to 21 ppt in M. trossolus, and low salinity (21 ppt) did not enhance the protective effect of DOC. Both DOMs increased the toxicity of Pb in developing sea urchin embryos, in contrast to mussels. Relative to Pb, the organisms were 6–9 fold less sensitive to Zn on a molar basis in 100% seawater with the following Zn EC50s: M. trossolus — 135 (103–170) μg L^− 1; M. galloprovincialis — 172 (126–227) μg L^− 1, S. purpuratus — 151 (129–177) μg L^− 1. Nordic Reservoir and Inshore DOM (2–12 mg C L^− 1) had no significant effect on Zn toxicity to mussels, in accord with voltammetry data showing an absence of any strong ligand binding for Zn by DOMs. As with Pb, DOMs increased Zn toxicity to urchin larvae. Critical Tissue Residues (CTR) based on whole body concentrations of Pb and Zn were determined for M. galloprovincialis at 48 h and S. purpuratus at 72 h. The median lethal CTR values (LA50s), useful parameters for development of saltwater Biotic Ligand Models (BLMs), were approximately 4-fold higher on a molar basis for Zn than for Pb. The latter were not altered by DOM exposure, despite increased EC50 values, in accord with the tenets of the BLM.     

Effects of vegetation and fertilizer on metal and Sb plant uptake in a calcareous shooting range soil

Shooting range soils frequently contain anomalous concentrations of metals (e.g. Pb, Zn, Mn) and Sb coming from bullets which may be released into the environment. In a pot experiment, we investigated metal and Sb uptake by three plant species (Plantago lanceolata, Lolium perenne and Triticum aestivum) growing on a calcareous shooting range soil (pH 7.8; 500 mg kg⁻¹ Pb, 21 mg kg⁻¹ Sb) and the uptake changes when an acidic fertilizer solution was applied to the soil. Metal and Sb solubility in the soil was determined by extraction with 0.1 M NaNO₃. In addition, we measured pH, electrical conductivity and dissolved organic carbon in drainage samples. The results showed significant increase over time of pH (from 7.8 to 8.3) and decrease of electrical conductivity and dissolved organic carbon (from 230 to ∼130 mg L⁻¹). Fertilizer application increased NaNO₃-extractable Pb and Sb and root:shoot biomass ratio but not plant metal uptake. In T. aestivum spikes accumulated more Zn, Ni and Cu than shoots and grains. Mn and Zb uptake was correlated in L. perenne shoots. P. lanceolata, a Sb-bioindicator, did not accumulate high amounts of Sb (<1 mg kg⁻¹).     

Bio-kinetic analysis on treatment of textile dye wastewater using anaerobic batch reactor

An anaerobic digestion technique was applied to textile dye wastewater aiming at the colour and COD removal. Pet bottles of 5 L capacity were used as reactor which contains methanogenic sludge of half a liter capacity which was used for the treatment of combined synthetic textile dye and starch wastewater at different mixing ratios of 20:80, 30:70, 40:60, 50:50 and 60:40 with initial COD concentrations as 3520, 3440, 3360, 3264 and 3144 mg L⁻¹, respectively. The reactor was maintained at room temperature (30 ± 3 °C) with initial pH of 7. The maximum COD and colour removal were 81.0% and 87.3% at an optimum mixing ratio of 30:70 of textile dye and starch wastewaters. Both Monod’s and Haldane’s models were adopted in this study. The kinetic constants of cell growth under Haldane’s model were satisfactory when compared to Monod’s model. The kinetic constants obtained by Haldane’s model were found to be in the range of μ_max = 0.037-0.146 h⁻¹, K_s = 651.04-1372.88 mg L⁻¹ and K_i = 5681.81-18727.59 mg L⁻¹.     

Survival,osmoregulation and ammonia-N excretion of blue swimmer crab, Portunus pelagicus, juveniles exposed to different ammonia-N and salinity combinations

Ammonia-N toxicity to early Portunus pelagicus juveniles at different salinities was investigated along with changes to haemolymph osmolality, Na⁺, K⁺, Ca²⁺ and ammonia-N levels, ammonia-N excretion and gill Na⁺/K⁺-ATPase activity. Experimental crabs were acclimated to salinities 15, 30 and 45‰ for one week and 25 replicate crabs were subsequently exposed to 0, 20, 40, 60, 80, 100 and 120 mg L^− 1 ammonia-N for 96-h, respectively. High ammonia-N concentrations were used to determine LC₅₀ values while physiological measurements were conducted at lower concentrations. When crabs were exposed to ammonia-N, anterior gill Na⁺/K⁺-ATPase activity significantly increased (p < 0.05) at all salinities, while this only occurred on the posterior gills at 30‰. For crabs exposed to 20 and 40 mg L^− 1 ammonia-N, both posterior gill Na⁺/K⁺-ATPase activity and ammonia-N excretion were significantly higher at 15‰ than those at 45‰. Despite this trend, the 96-h LC₅₀ value at 15‰ (43.4 mg L^− 1) was significantly lower (p < 0.05) than at both 30‰ and 45‰ (65.8 and 75.2 mg L^− 1, respectively). This may be due to significantly higher (p < 0.05) haemolymph ammonia-N levels of crabs at low salinities and may similarly explain the general ammonia-N toxicity pattern to other crustacean species.     

The response of freshwater plants to salinity pulses

To test whether a pulse of saline water affects the growth and survival of aquatic plants, the response of four common freshwater macrophytes; Triglochin procerum, Myriophyllum simulans, Cotula coronopifolia and Baumea arthrophylla was examined. Plants established in freshwater were exposed to a pulse of diluted sea water of <1000, 4000, or 8000 mg L⁻¹ for either three or six weeks followed by four weeks in water of <1000 mg L⁻¹. All four species survived exposure to salinity pulses. At the end of the recovery period all species had a positive relative growth rate of between 0.01 and 0.06 g g⁻¹ day⁻¹. It can be concluded that all four species can tolerate short periods of exposure to saline conditions and this gives some flexibility to managers when deciding the best way to utilise and dispose of saline groundwater.     

Laboratory experiments on the effects of variable suspended sediment concentrations on the ecophysiology of the porcelain crab Petrolisthes elongatus (Milne Edwards, 1837)

The porcelain crab Petrolisthes elongatus is a particulate suspension feeding species common to coastal areas of New Zealand (NZ). Consistent with the responses of other suspension feeding species, it is likely to be negatively influenced by elevated suspended sediment concentrations. Laboratory experiments were conducted to quantify the effect of temperature (12 °C, 15 °C and 18 °C) and suspended sediment concentration (total particulate matter (TPM): low < 100 mg L^− 1; medium 100-1000 mg L^− 1; high > 1000 mg L^− 1) on the clearance rate (CR in L h^− 1), oxygen uptake rate (VO₂ in mL h⁻¹), net absorption efficiency (AE), and net energy budget (NEB in J h^− 1) of P. elongatus across a range of sizes. Variation in CR and AE was independent of temperature and of body size, but were significantly different (P < 0.05) at low and medium suspended sediment concentrations compared with high suspended sediment concentrations. CR responded in a non-linear manner to changes in TPM, increasing with TPM up to a maximum value at medium-low concentrations (approximately 250 mg L^− 1) and then decreasing thereafter. CR had almost completely shut down at TPM concentrations of > 1000 mg L^− 1 and at particulate organic matter (POM) concentrations of > 250 mg L^− 1. AE was zero at approximate TPM and POM values of 1200 mg L^− 1 and 300 mg L^− 1, respectively. VO₂ was positively correlated with body size and with temperature, but was independent of TPM. NEB values for P. elongatus were low (approx 110 J g^− 1 h^− 1) at low sediment concentrations, were high (approx 320 J g^− 1 h^− 1) at medium sediment concentrations, and were negative (approx − 114 J g^− 1 h^− 1) at high sediment concentrations. These findings indicate that P. elongatus is likely to be food-limited at sediment concentrations of < 100 mg L^− 1, and severely negatively affected at sediment concentrations of > 1000 mg L^− 1, at least for the duration of such events which may persist for 2-3 days in coastal environments where this crab occurs.     

Effects of eutrophic water flooding on nitrate concentrations in mine wastes

Salt marshes near urban, industrial and mining areas are often affected both by heavy metals and by eutrophic water. The aim of this study was to assess and evaluate the main processes involved in the decrease of nitrate concentration in pore water of mine wastes flooded with eutrophic water, considering the presence or absence of plant rhizhosphere. Basic (pH ∼ 7.8) carbonated loam mine wastes and free-carbonated acidic (pH ∼ 6.2) sandy-loam mine wastes were collected from polluted coastal salt marshes of SE Spain which regularly receive nutrient-enriched water. The wastes were put in pots and flooded for 15 weeks with eutrophic water (dissolved organic carbon ∼26 mg L⁻¹, PO₄³⁻ ∼23 mg L⁻¹, NO₃⁻ ∼180 mg L⁻¹). Three treatments were assayed for each type of waste: pots with Sarcocornia fruticosa, pots with Phragmites australis and unvegetated pots. Soluble organic carbon, nitrate, soluble Cd, Pb and Zn, pH and Eh were monitored. But the 2nd day of flooding, nitrate concentrations had decreased between 70% and 90% (equivalent to 1.01-1.12 g N-NO₃⁻ m⁻² day⁻¹) with respect to the content in the water used for flooding, except in unvegetated pots with acidic wastes. Denitrification was the main mechanism associated with the removal of nitrate. The role of vegetation in improving the rhizospheric environment was relevant in the acidic wastes because higher sand content, lower pH and higher soluble metal concentrations might strongly hinder microbial activity Hence, revegetation of salt marshes polluted by acidic sandy mining wastes might improve the capacity of this type of environment to act as a green filter against excessive nitrate contents flowing through them.     

Bicarbonate blocks iron translocation from cotyledons inducing iron stress responses in Citrus roots

The effect of bicarbonate ion (HCO₃⁻) on the mobilization of iron (Fe) reserves from cotyledons to roots during early growth of citrus seedlings and its influence on the components of the iron acquisition system were studied. Monoembryonic seeds of Citrus limon (L.) were germinated “in vitro” on two iron-deprived media, supplemented or not with 10 mM HCO₃⁻ (−Fe+Bic and −Fe, respectively). After 21 d of culture, Fe concentration in seedling organs was measured, as well as gene expression and enzymatic activities. Finally, the effect of Fe resupply on the above responses was tested in the presence and absence of HCO₃⁻ (+Fe+Bic or +Fe, respectively). −Fe+Bic seedlings exhibited lower Fe concentration in shoots and roots than −Fe ones but higher in cotyledons, associated to a significative inhibition of NRAMP3 expression. HCO₃⁻ upregulated Strategy I related genes (FRO1, FRO2, HA1 and IRT1) and FC-R and H⁺-ATPase activities in roots of Fe-starved seedlings. PEPC1 expression and PEPCase activity were also increased. When −Fe+Bic pre-treated seedlings were transferred to Fe-containing media for 15 d, Fe content in shoots and roots increased, although to a lower extent in the +Fe+Bic medium. Consequently, the above-described root responses became markedly repressed, however, this effect was less pronounced in +Fe+Bic seedlings. In conclusion, it appears that HCO₃⁻ prevents Fe translocation from cotyledons to shoot and root, therefore reducing their Fe levels. This triggers Fe-stress responses in the root, enhancing the expression of genes related with Fe uptake and the corresponding enzymatic activities.