Susana Redondo-Gómez

Growth and photosynthetic responses to copper stress of an invasive cordgrass, Spartina densiflora.

Spartina densiflora Brongn. is found in coastal marshes of south-west Spain, growing in sediments with between 300 and 3000mg Cu kg(-1) total soil DW (450-4500mg Cu kg(-1) supposing that the soil porosity is 0.5). An experiment was designed to investigate the effect of copper from 0 to 5000mgkg(-1) (64mmoll(-1)) on the photosynthetic apparatus and the growth of S. densiflora. We also determined total ash, copper, calcium, magnesium and phosphorous concentrations, as well as C/N ratio. S. densiflora survived to concentrations as high as 320mg Cukg(-1) DW in leaves, although excess of Cu diminished water use efficiency and Ca-, Mg- and P-uptake. Also, quantum efficiency of PSII, net photosynthetic rate, stomatal conductance and pigment concentrations declined with increasing external Cu. Finally, the decline in the photosynthetic function resulted in a biomass reduction of between 50 and 80% (for 600 and 5000mg Cu kg(-1), respectively).

Salt stimulation of growth and photosynthesis in an extreme halophyte, Arthrocnemum macrostachyum

Halophytes that are capable of tolerating a wide range of salinity may grow best at intermediate salinities, but the physiological mechanisms underlying positive growth responses to salinity are not clear. This work investigated the growth of Arthrocnemum macrostachyum (Moric) C. Koch (a halophytic C3 shrub) over a wide range of salinities, and the extent to which its responses can be explained by photosynthetic physiology. Growth, gas exchange and chlorophyll fluorescence characteristics of plants were examined in a glasshouse experiment; tissue concentrations of photosynthetic pigments, ash, sodium, potassium, calcium and nitrogen were also determined. Plants showed marked stimulation of growth by salt, with a broad optimum of 171-510 mm NaCl for relative growth rate (RGR). Stimulation of RGR appeared to depend mainly on an increase in specific shoot area, whereas reduced RGR at high salinity (1030 mm) could be attributed to a combination of lower unit shoot (leaf) rate and lower shoot mass fraction. The non-saline treatment plants had the greatest fraction of non-photosynthetic, atrophied surface area. However, net photosynthesis (A) was also stimulated by NaCl, with an optimum of c. 510 mm NaCl. The responses of A to salinity could be accounted for largely by limitation by stomatal conductance (Gs) and intercellular CO(2) concentration (Ci). Even the most hypersaline treatment apparently had no effect on photosystem II (PSII) function, and this resistance could be an important strategy for this halophyte in saline soils. In contrast, Fv/Fm indicated that absence of salt represents an environmental stress for A. macrostachyum and this could be a contributory factor to salt stimulation of A. Notwithstanding the importance of the ability to develop and maintain assimilatory surface area under saline conditions, stimulatory effects on A also appear to be part of a suite of halophytic adaptations in this plant.

Accumulation and tolerance characteristics of chromium in a cordgrass Cr-hyperaccumulator, Spartina argentinensis.

The cordgrass Spartina argentinensis, which occurs in inland marshes of the Chaco-Pampean regions of Argentina, has been found to be a new chromium hyperaccumulator. A glasshouse experiment was designed to investigate the effect of Cr(6+) from 0 to 20 mmol l(-1) on growth and photosynthetic apparatus of S. argentinensis by measuring chlorophyll fluorescence parameters, gas exchange and photosynthetic pigment concentrations. Boron, calcium, chromium, copper, iron, manganese, magnesium, potassium and phosphorous concentrations were also determined. S. argentinensis showed phytotoxicity at tiller concentration of 4 mg g(-1) Cr, and symptoms of stress at tiller concentration of 1.5 mg g(-1) Cr, as well as reductions in leaf gas exchange, in chlorophyll a fluorescence parameters, in photosynthetic pigment contents and in the uptake of essential nutrients. Reductions in net photosynthetic rate could be accounted for by non-stomatal limitations. Moreover, the bioaccumulator factors exceeded greatly the critical value (1.0) for all Cr treatments, and the transport factors indicated that this species has a higher ability to transfer Cr from roots to tillers at higher Cr concentrations. These results confirmed that S. argentinensis is a chromium hyperaccumulator and that it may be useful for restoring Cr-contaminated sites.

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.

Carry-over of Differential Salt Tolerance in Plants Grown from Dimorphic Seeds of Suaeda splendens

BACKGROUND AND AIMS Halophytic species often show seed dimorphism, where seed morphs produced by a single individual may differ in germination characteristics. Particular morphs are adapted to different windows of opportunity for germination in the seasonally fluctuating and heterogeneous salt-marsh environment. The possibility that plants derived from the two morphs may also differ physiologically has not been investigated previously. METHODS Experiments were designed to investigate the germination characteristics of black and brown seed morphs of Suaeda splendens, an annual, C(4) shrub of non-tidal, saline steppes. The resulting seedlings were transferred to hydroponic culture to investigate their growth and photosynthetic (PSII photochemistry and gas exchange) responses to salinity. KEY RESULTS Black seeds germinated at low salinity but were particularly sensitive to increasing salt concentrations, and strongly inhibited by light. Brown seeds were unaffected by light, able to germinate at higher salinities and generally germinated more rapidly. Ungerminated black seeds maintained viability for longer than brown ones, particularly at high salinity. Seedlings derived from both seed morphs grew well at high salinity (400 mol m(-3) NaCl). However, seedlings derived from brown seeds performed poorly at low salinity, as reflected in relative growth rate, numbers of branches produced, F(v)/F(m) and net rate of CO(2) assimilation. CONCLUSIONS The seeds most likely to germinate at high salinity in the Mediterranean summer (brown ones) retain a requirement for higher salinity as seedlings that might be of adaptive value. On the other hand, black seeds, which are likely to delay germination until lower salinity prevails, produce seedlings that are less sensitive to salinity. It is not clear why performance at low salinity, later in the life cycle, might have been sacrificed by the brown seeds, to achieve higher fitness at the germination stage under high salinity. Analyses of adaptive syndromes associated with seed dimorphism may need to take account of differences over the entire life cycle, rather than just at the germination stage.

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.

Bioaccumulation of heavy metals in Spartina

The Spartina Schreb. genus is composed of C4 perennial grasses in the family Poaceae. They are native to the coasts of the Atlantic Ocean in western and southern Europe, north-west and southern Africa, the Americas and the southern Atlantic Ocean islands. Most species are salt tolerant and colonise coastal or inland saltmarshes. The available literature on heavy metal bioaccumulation by Spartina sp. was compiled and compared. Spartina alterniflora Loisel. and Spartina maritima (Curtis) Fernald were the most commonly researched species of the genus, whereas many species were not represented at all. In contrast, Cu and Zn are the most intensively researched heavy metals. The few studies dealing with the physiological impacts of heavy metals or the mechanisms of metal accumulation, which involve extracellular and intracellular metal chelation, precipitation, compartmentalisation and translocation in the vascular system, were documented. Bioaccumulation of metals in roots and tillers of some species of the Spartina genus (e.g. S. maritima and Spartina densiflora Brongn.) has been described as a feasible method for remediating waters and soils contaminated with heavy metals. One such example is Spartina argentinensis Parodi, which has been found to be a Cr-hyperaccumulator; it can concentrate chromium in its tissues to levels far exceeding those present in the soil.The Spartina Schreb. genus is composed of C4 perennial grasses in the family Poaceae. They are native to the coasts of the Atlantic Ocean in western and southern Europe, north-west and southern Africa, the Americas and the southern Atlantic Ocean islands. Most species are salt tolerant and colonise coastal or inland saltmarshes. The available literature on heavy metal bioaccumulation by Spartina sp. was compiled and compared. Spartina alterniflora Loisel. and Spartina maritima (Curtis) Fernald were the most commonly researched species of the genus, whereas many species were not represented at all. In contrast, Cu and Zn are the most intensively researched heavy metals. The few studies dealing with the physiological impacts of heavy metals or the mechanisms of metal accumulation, which involve extracellular and intracellular metal chelation, precipitation, compartmentalisation and translocation in the vascular system, were documented. Bioaccumulation of metals in roots and tillers of some species of the Spartina genus (e.g. S. maritima and Spartina densiflora Brongn.) has been described as a feasible method for remediating waters and soils contaminated with heavy metals. One such example is Spartina argentinensis Parodi, which has been found to be a Cr-hyperaccumulator; it can concentrate chromium in its tissues to levels far exceeding those present in the soil.

Synergic effect of salinity and CO2 enrichment on growth and photosynthetic responses of the invasive cordgrass Spartina densiflora

Spartina densiflora is a C4 halophytic species that has proved to have a high invasive potential which derives from its clonal growth and its physiological plasticity to environmental factors, such as salinity. A greenhouse experiment was designed to investigate the synergic effect of 380 and 700 ppm CO2 at 0, 171, and 510 mM NaCl on the growth and the photosynthetic apparatus of S. densiflora by measuring chlorophyll fluorescence parameters, gas exchange and photosynthetic pigment concentrations. PEPC activity and total ash, sodium, potassium, calcium, magnesium, and zinc concentrations were determined, as well as the C/N ratio. Elevated CO2 stimulated growth of S. densiflora at 0 and 171 mM NaCl external salinity after 90 d of treatment. This growth enhancement was associated with a greater leaf area and improved leaf water relations rather than with variations in net photosynthetic rate (A). Despite the fact that stomatal conductance decreased in response to 700 ppm CO2 after 30 d of treatment, A was not affected. This response of A to elevated CO2 concentration might be explained by an enhanced PEPC carboxylation capacity. On the whole, plant nutrient concentrations declined under elevated CO2, which can be ascribed to the dilution effect caused by an increase in biomass and the higher water content found at 700 ppm CO2. Finally, CO2 and salinity had a marked overall effect on the photochemical (PSII) apparatus and the synthesis of photosynthetic pigments.

Effects of Salinity on Germination and Seedling Establishment of Endangered Limonium emarginatum (Willd.) O. Kuntze

Abstract The germination and subsequent seedling establishment of Limonium emarginatum, an endangered and endemic halophyte of the Strait of Gibraltar, was studied under exposure to different NaCl concentrations (0, 2, 4, and 6%) in a laboratory experiment. We assessed final germination percentage, number of days to first and final germination, mean time to germinate (MTG), as well as seed viability and seedling survival. Increasing salinity delayed the beginning and ending of germination and reduced final germination percentage, inhibiting germination completely above 2% salinity. L. emarginatum exhibited the greatest germination in fresh water. When seeds were removed from all saline solutions, between 60% and 70% of final germination was recorded, although at hypersalinity, germination viability diminished. Salinity pretreatments had a stimulatory effect on germination since germination speed was higher for the recovery experiment than for the seed germination experiment. Transition between germination and seedling establishment was a critical phase, given that less than 50% of seedlings of L. emarginatum survived in distilled water and 5% survived at 2% salinity.

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.