L. Andrades-Moreno

Silicon alleviates deleterious effects of high salinity on the halophytic grass Spartina densiflora.

The non-essential element silicon is known to improve plant fitness by alleviating the effects of biotic and abiotic stresses, particularly in crops. However, its possible role in the exceptional tolerance of halophytes to salinity has not been investigated. This study reports the effect of Si supply on the salinity tolerance of the halophytic grass Spartina densiflora; plants were treated with NaCl (0-680 mM), with or without silicon addition of 500 μM, in a glasshouse experiment. Plant responses were examined using growth analysis, combined with measurements of gas exchange, chlorophyll fluorescence and photosynthetic pigment concentrations. In addition, tissue concentrations of aluminium, calcium, copper, iron, potassium, magnesium, sodium, phosphorus and silicon were determined. Although high salinity decreased growth, this effect was alleviated by treatment with Si. Improved growth was associated with higher net photosynthetic rate (A), and greater water-use efficiency (WUE). Enhanced A at high salinity could be explained by beneficial effects of Si on the photochemical apparatus, and on chlorophyll concentrations. Ameliorative effects of Si were correlated with reduced sodium uptake, which was unrelated to a reduction in the transpiration rate, since Si-supplemented plants had higher stomatal conductances (G(s)). These plants also had higher tissue concentrations of essential nutrients, suggesting that Si had a positive effect on the mineral nutrient balance in salt-stressed plants. Si appears to play a significant role in salinity tolerance even in a halophyte, which has other, specific salt-tolerance mechanisms, through diverse protective effects on the photosynthetic apparatus, water-use efficiency and mineral nutrient balance.

Accumulation and tolerance characteristics of cadmium in a halophytic Cd-hyperaccumulator, Arthrocnemum macrostachyum.

The potential of the extreme halophyte Arthrocnemum macrostachyum was examined to determine its tolerance and ability to accumulate cadmium for phytoremediation purposes. A glasshouse experiment was designed to investigate the effect of cadmium from 0 to 1.35 mmol l(-1) on the growth and the photosynthetic apparatus of A. macrostachyum by measuring chlorophyll fluorescence parameters, gas exchange and photosynthetic pigment concentrations. We also determined ash, cadmium, calcium, copper, iron, manganese, magnesium, phosphorous, sodium, and zinc concentrations, and C/N ratio. A. macrostachyum demonstrated hypertolerance to cadmium stress; it did not show phytotoxicity at shoot concentration as high as 70 mg kg(-1). The bioaccumulator factors exceeded the critical value (1.0) for all Cd treatments, and the transport factors indicated that this species has higher ability to transfer Cd from roots to shoots at lower Cd concentrations. At 1.35 mmol l(-1) Cd A. macrostachyum showed 25% biomass reduction after a month of treatment. Long-term effects of cadmium on the growth were mainly determined by variations in net photosynthetic rate (P(N)). Reductions in P(N) could be accounted by higher dark respiration and lower pigment concentrations. Finally, A. macrostachyum has the basic characteristics of a Cd-hyperaccumulator and may be useful for restoring Cd-contaminated sites.

Synergic effect of salinity and zinc stress on growth and photosynthetic responses of the cordgrass, Spartina densiflora

Spartina densiflora is a C4 halophytic species that has proved to have a high invasive potential which derives from its physiological plasticity to environmental factors, such as salinity. It is found in coastal marshes of south-west Spain, growing over sediments with between 1 mmol l−1 and 70 mmol l−1 zinc. A glasshouse experiment was designed to investigate the synergic effect of zinc from 0 mmol l−1 to 60 mmol l−1 at 0, 1, and 3% NaCl on the growth and the photosynthetic apparatus of S. densiflora by measuring chlorophyll fluorescence parameters and gas exchange, and its recovery after removing zinc. Antioxidant enzyme activities and total zinc, sodium, calcium, iron, magnesium, manganese, phosphorus, potassium, and nitrogen concentrations were also determined. Spartina densiflora showed the highest growth at 1 mmol l−1 zinc and 1% NaCl after 90 d of treatment; this enhanced growth was supported by the measurements of net photosynthetic rate (A). Furthermore, there was a stimulatory effect of salinity on accumulation of zinc in tillers of this species. Zinc concentrations >1 mmol l−1 reduced growth of S. densiflora, regardless of salinity treatments. This declining growth may be attributed to a decrease in A caused by diffusional limitation of photosynthesis, owing to the modification of the potassium/calcium ratio. Also, zinc and salinity had a marked overall effect on the photochemical (photosystem II) apparatus, partially mediated by the accumulation of H2O2 and subsequent oxidative damage. However, salinity favoured the recovery of the photosynthetic apparatus to the toxic action of zinc, and enhanced the nutrient uptake.

Assessing the effect of copper on growth, copper accumulation and physiological responses of grazing species Atriplex halimus: Ecotoxicological implications

Tolerance of plants to elevated concentrations of heavy metals in growth media and in its tissues leads to high degrees of metal bioaccumulation, which may pose a risk for humans and animals alike. Therefore, bio-accumulating plants need thorough evaluation from an environmental health point of view. A glasshouse experiment concerning the xerohalophyte Atriplex halimus was carried out to determine its tolerance and capacity to accumulate copper. We investigated the effect of Cu from 0 to 30 mmol l(-1) on the growth, photosynthetic apparatus and nutrient uptake of A. halimus by measuring gas exchange, chlorophyll fluorescence and photoinhibition. We also determined total Cu, sodium, potassium, magnesium, phosphorous, and nitrogen content in the plant. Our results indicated that A. halimus presented a high resistance to Cu-induced stress, since the plants were able to survive at concentrations higher than 15 mmol l(-1) Cu. However, this capacity was not reflected in its ability to accumulate and tolerate greater amounts of Cu in its tissues, since clear phytotoxicity symptoms were detected at tissue concentrations greater than 38 mg kg(-1) Cu. Thus, Cu increment caused a reduction in A. halimus growth, which was related to a decrease in net photosynthetic rate. This reduction was associated with the adverse effect of Cu on the photochemical apparatus and the reduction in the absorption of essential nutrients. The high resistance of A. halimus was largely related with the capacity of this species to avoid the absorption of great amounts of Cu. For all the above reasons, A. halimus could have the characteristics of a Cu-exclusion plant.

Comparison of germination, growth, photosynthetic responses and metal uptake between three populations of Spartina densiflora under different soil pollution conditions.

Spartina densiflora has demonstrated a high tolerance to heavy metal contamination and a high capacity for accumulating metal in its tissues. In the Gulf of Cadiz this species has colonized habitats with different degrees of metal pollution. The aim of this study is to analyse the responses of populations of Spartina densiflora to this pollution. Germination, growth, photosynthesis and metal uptake of two populations of Spartina densiflora collected from contaminated sites (Odiel and Tinto marshes) and of one population from a clean site (Piedras marshes) were examined through two reciprocal experiments, in which seeds and adult plants were exposed to metal-contaminated and uncontaminated soil under greenhouse conditions. The seeds of Spartina densiflora were able to germinate in all sediments with little differences between populations, even in more contaminated soils. However, these conditions decreased the growth and survival of the seedlings to a similar degree for all populations. Likewise, no differences were recorded in relation to physiological and metal uptake. Contrarily, in the adult experiment, we found that the Odiel population differed from the other populations in growth and metal uptake, with overall greater values. These differences in growth were strongly supported by lower photosynthetic rates and stomatal conductance in the Piedras and Tinto populations. The reduction in photosynthetic performance was largely due to the reduction in photosynthetic pigment concentration in both populations. Despite these differences, there was insufficient evidence to support that Spartina has evolved to heavy-tolerant ecotypes, since all Spartina densiflora populations proved to have a great capacity for accumulating heavy metals in its roots. Nonetheless, this finding suggests that the Odiel population could have a greater phytoremediation potential.

Growth and photosynthetic responses of the cordgrass Spartina maritima to CO2 enrichment and salinity.

Future climatic scenarios combine increasing concentrations of atmospheric CO(2) and rising sea levels. Spartina maritima is a C(4) halophyte that is an important pioneer and ecosystem engineer in salt marshes of the Atlantic coast of southern Europe. A glasshouse experiment investigated the combined effects on its growth and photosynthetic apparatus of approximately doubling CO(2) concentration (from 380 to 700 μmol mol(-1)) at a range of salinity (0, 171 and 510 mM NaCl). We measured relative growth rates, gas exchange, chlorophyll fluorescence parameters, photosynthetic pigment concentrations, and total ash, Na(+), K(2+), Ca(2+) and N concentrations. Elevated CO(2) stimulated growth of S. maritima by c. 65% at all external salinities; this growth enhancement was associated with greater net photosynthetic rate (A) and improved leaf water relations. A increased despite a drop in stomatal conductance in response to 700 μmol mol(-1) CO(2). CO(2) and salinity had a marked overall effect on the photochemical (PSII) apparatus and the synthesis of photosynthetic pigments. Φ(PSII) values at midday decreased significantly with external salinity in plants grown at 380 μmol mol(-1) CO(2); and F(v)/F(m) and Φ(PSII) values were higher at 700 μmol mol(-1) CO(2) in presence of NaCl. Plant nutrient concentrations declined under elevated CO(2), which can be ascribed to the dilution effect caused by an increase in biomass. The results suggest that the productivity S. maritima and the ecosystem services it provides will increase in likely future climatic scenarios.

Prospecting metal-resistant plant-growth promoting rhizobacteria for rhizoremediation of metal contaminated estuaries using Spartina densiflora

In the salt marshes of the joint estuary of Tinto and Odiel rivers (SW Spain), one of the most polluted areas by heavy metals in the world, Spartina densiflora grows on sediments with high concentrations of heavy metals. Furthermore, this species has shown to be useful for phytoremediation. The total bacterial population of the rhizosphere of S. densiflora grown in two estuaries with different levels of metal contamination was analyzed by PCR denaturing gradient gel electrophoresis. Results suggested that soil contamination influences bacterial population in a greater extent than the presence of the plant. Twenty-two different cultivable bacterial strains were isolated from the rhizosphere of S. densiflora grown in the Tinto river estuary. Seventy percent of the strains showed one or more plant growth-promoting (PGP) properties, including phosphate solubilization and siderophores or indolacetic acid production, besides a high resistance towards Cu. A bacterial consortium with PGP properties and very high multiresistance to heavy metals, composed by Aeromonas aquariorum SDT13, Pseudomonas composti SDT3, and Bacillus sp. SDT14, was selected for further experiments. This consortium was able to two-fold increase seed germination and to protect seeds against fungal contamination, suggesting that it could facilitate the establishment of the plant in polluted estuaries.

Tolerance to and accumulation of arsenic in the cordgrass Spartina densiflora Brongn

A glasshouse study concerning the halophyte Spartina densiflora was carried out to determine its tolerance and capacity to accumulate As. S. densiflora presented a high tolerance to As-induced stress, since all plants were able to survive at concentrations higher than 6.7 mmol l(-1) As. However, As increment caused a reduction in S. densiflora growth, owing to a decrease in net photosynthetic rate. This reduction was prompted by the adverse effect on the photochemical apparatus and the reduction in the absorption of essential nutrients, which was linked with the reduction in G(s), caused by the alteration of the K/Ca ratio, and with the reduction of photosynthetic pigment and Rubisco carboxilation. Arsenic tolerance was associated with the capacity to accumulate As in its roots (with values up to 2 mg g(-1)) and largely avoid its transport to the leaves, this fact indicating that this species could be useful for arsenic phytostabilization purposes.

Spartina densiflora demonstrates high tolerance to phenanthrene in soil and reduces it concentration

The present study was conducted to investigate the tolerance of Spartina densiflora to phenanthrene, and to test its ability in phenanthrene dissipation. A glasshouse experiment was designed to investigate the effect of phenanthrene from 0 to 1000 mg kg(-1) on growth and photosynthetic apparatus of S. densiflora by measuring chlorophyll fluorescence parameters, gas exchange and photosynthetic pigments. We also performed chemical analysis of plant samples, and determined the concentration of phenanthrene remaining in soil. S. densiflora survived to concentrations as high as 1000 mg kg(-1) phenanthrene in soil; in fact, there was no significant difference in RGR among the treatments after 30 days. Otherwise, phenanthrene affected photosynthetic apparatus at 100 and 1000 mg kg(-1); thus, the lower ΦPSII could be explained by the declined photosynthetic pigment concentrations. Soil extraction indicated a more marked rate of phenanthrene disappearance in the soil in the presence of S. densiflora.

Growth and survival of Halimione portulacoides stem cuttings in heavy metal contaminated soils

The halophytic shrub Halimione portulacoides demonstrates a high tolerance to heavy metal contamination and a capacity for accumulating metals within its tissues. On the Iberian Peninsula, this species has colonized habitats with high levels of metal pollution. The aim of this study is to analyze the response of H. portulacoides stem cuttings to this pollution. Growth, photosynthesis and metal uptake were examined in H. portulacoides through an experiment in which stem cuttings were replanted in metal-contaminated soil. This condition decreased growth and lowered both photosynthetic rate and stomatal conductance. Reduced photosynthetic performance was largely due to the reduced concentration of photosynthetic pigments. Despite these responses, there was some important evidence suggesting the phytoremediatory potential of Halimione stem cuttings. The results of our study indicate that this salt-marsh shrub may represent a biotool of value in the restoration of polluted areas.