J.M. Mancilla-Leytón

Zinc tolerance and accumulation in the salt-marsh shrub Halimione portulacoides.

The halophytic shrub Halimione portulacoides is known to be capable of growth in soils containing extremely high concentrations of Zn. This study evaluated in detail the tolerance and accumulation potential of H. portulacoides under moderate and high external Zn levels. A greenhouse experiment was conducted in order to investigate the effects of a range of Zn concentrations (0-130 mmol L(-1)) on growth and photosynthetic performance by measuring relative growth rate, total leaf area, specific leaf area, gas exchange, chlorophyll fluorescence parameters and photosynthetic pigment concentrations. We also determined the total zinc, nitrogen, phosphorus, calcium, magnesium, sodium, potassium, iron and copper concentrations in the plant tissues. H. portulacoides demonstrated hypertolerance to Zn stress, since it survived with leaf concentrations of up to 2300 mg Zn kg(-1)dry mass, when treated with 130 mmol Zn L(-1). Zinc concentrations greater than 70 mmol L(-1) in the nutrient solution negatively affected plant growth, in all probability due to the recorded decline in net photosynthesis rate. Our results indicate that the Zn-induced decline in the photosynthetic function of H. portulacoides may be attributed to the adverse effect of the high concentration of the metal on photosynthetic electron transport. Growth parameters were virtually unaffected by leaf tissue concentrations as high as 1500 mg Zn kg(-1)dry mass, demonstrating the strong capability of H. portulacoides to protect itself against toxic Zn concentrations. The results of our study indicate that this salt-marsh shrub may represent a valuable tool in the restoration of Zn-polluted areas.

Tolerance and accumulation of copper in the salt-marsh shrub Halimione portulacoides.

The present study evaluated the tolerance and accumulation potential in the salt-marsh shrub Halimione portulacoides under moderate and high external Cu levels. A greenhouse experiment was conducted in order to investigate the effects of a range of external Cu concentrations (0 to 60 mmol l(-1)) on growth and photosynthetic performance by measuring gas exchange, chlorophyll fluorescence parameters and photosynthetic pigments. We also determined total copper, nitrogen, phosphorus and sulfur concentrations in the plant tissues. H. portulacoides survived with external Cu concentrations of up to 35 mmol Cu l(-1), although the excess of metal resulted in a biomass reduction of 48%. The effects of Cu on growth were linked to a drastic reduction in net photosynthesis. However, H. portulacoides tolerated Cu levels of up to 15 mmol Cu l(-1) without suffering adverse physiological effects. Our results indicate that this species could play an important role in the restoration of Cu-contaminated soils.

Effects of soil physicochemical properties on plant performance of Glaucium flavum Crantz

Background and aimsGlaucium flavum is an endangered coastal herb capable of growth in a wide variety of ecosystems. We explore plant-soil relationships in this species by evaluating plant performance and soil physicochemical properties in the different types of ecosystems where it grows.MethodsTen natural populations from southern Spain were chosen for the study. In each experimental site, a number of variables related to the growth, reproduction and nutritional status of G. flavum were studied and an analysis of the soil physicochemical properties (texture, pH, electrical conductivity and total N, P, S and Ca concentration) was conducted. Data were statistically analyzed in order to characterize the habitat of G. flavum and to explore possible relationships between the studied variables.ResultsAt all experimental sites, the soil presented an alkaline pH and high concentrations of Ca. Despite the low levels of soil N, P and S, our data did not indicate nutrient deficiencies in leaf tissues. The percentage of reproductive plants and number of seeds per fruit correlated positively with leaf Ca concentrations.ConclusionsIncreasing Ca concentrations in plant tissues and elevated soil pH have a positive effect on plant performance of G. flavum.

A vegetation management experiment: Goats grazing shrublands in Doñana Natural Park

We have studied the effect of goat grazing on the shrub understory of a pine forest situated in a protected area (Doñana Natural Park). Along three years we have studied the changes in phytovolume, flammability, species richness and diversity in a grazed shrubland and in a control area not grazed by the goats. We studied also food preferences of the goats and the ability of the goats to disperse the seeds of the plants they eat. Goat grazing significantly reduced shrub biomass and flammability, decreasing the risk of forest fire. Goats selected the species they eat, changing the pattern of selection throughout the year. Grazing reduced shrub diversity, but did not affected species richness. The goats can also potentially disperse the seeds of some of the species they eat, since the seeds were able to pass through the goat’s gut and germinated afterwards. Goat grazing on scrub vegetation can be used as an effective tool for the control of shrubs in protected forest areas, without losing biodiversity.

Differential photosynthetic performance of three Mediterranean shrubs under grazing by domestic goats

The impact of grazing by domestic goats, Capra hircus, on the photochemical apparatus of three co-ocurring Mediterranean shrubs, Erica scoparia, Halimium halimifolium, and Myrtus communis was evaluated. Seasonal course of gas exchange, chlorophyll fluorescence and photosynthetic pigment concentrations were measured in the field in grazed and ungrazed plants. Net photosynthetic rate was higher in grazed plants of E. scoparia and H. halimifolium in May, while there were not significant differences in M. communis. Photosynthetic enhancement in grazed plants of E. scoparia could be explained largely by higher stomatal conductance. On the other hand, the lack of differences in stomatal conductance between grazed and ungrazed plants of H. halimifolium could indicate that carboxylation efficiency, and ribulose-1,5-bisphosphate (RuBP) regeneration may have been enhanced by grazing. Overall grazing has little effect on the photochemical (PSII) apparatus, however grazed plants of M. communis showed chronic photoinhibition in the short term. Finally, seasonal variations recorded on photosynthesis, photochemical efficiency and pigment concentrations may be a physiological consequence of environmental factors, such as summer drought and competition for light, rather than an adaptation to grazing.

Handling High Soil Trace Elements Pollution: Case Study of the Odiel and Tinto Rivers Estuary and the Accompanying Salt Marshes (Southwest Iberian Peninsula)

Salt marshes are being increasingly polluted by trace elements, and the design and implementation of management actions adapted to each particular situation are necessary. Salt marshes developed at one of the most heavy metal-polluted systems in the world, the Odiel and Tinto joint estuary, are threatened by high pollution levels, erosion and the invasion of the alien plant species Spartina densiflora, despite the high ecological values recognized by regional to international protection figures. Soft management on these marshes tries to preserve the equilibrium between conservation and decontamination. The ability of key native halophytes in the area to phytoextract or phytostabilizate trace elements has been taking into account. A local restoration project has resulted in a rapid recovery of the native prairies of low tidal marshes, dominated by S. maritima, becoming a promising tool to phytostabilize eroding areas in European marshes. These prairies also seem to stop the advance of the alien S. densiflora invasion and prevent erosion. On the other hand, areas invaded by S. densiflora are difficult to manage due to the acidity and pollution level of sediments preventing the establishment of any other plant species. Despite its invasive character, S. densiflora avoid at present the removal of highly toxic sediments and the trace element release to the food chain in this area.