Effects of heavy metal pollution on germination and early seedling growth in native and invasive Spartina cordgrasses

Seed germination and seedling establishment are the stages most sensitive to abiotic stress in the plant life cycle. We analyzed the effects of copper, zinc and nickel on seed germination and early seedling growth of native Spartina maritima and invasive S. densiflora from polluted and non-polluted estuaries. Germination percentages for either species were not affected by any metal at any tested concentration (up to 2000 μM). However, the increase in metal concentration had negative effects on S. densiflora seedlings. The primary effect was on radicle development, representing initial seedling emergence. Spartina densiflora seedlings emerging from seeds from Tinto Estuary, characterized by high bioavailable metal loads, showed higher tolerance to metals than those from less polluted Odiel and Piedras Estuaries. Comparing our results to metal concentrations in the field, we expect S. densiflora seedling development would be negatively impacted in the most metal-polluted areas in Odiel and Tinto Estuaries.

Bacterial inoculants for enhanced seed germination of Spartina densiflora: Implications for restoration of metal polluted areas

The design of effective phytoremediation programs is severely hindered by poor seed germination on metal polluted soils. The possibility that inoculation with plant growth promoting rhizobacteria (PGPR) could help overcoming this problem is hypothesized. Our aim was investigating the role of PGPR in Spartina densiflora seed germination on sediments with different physicochemical characteristics and metal pollution degrees. Gram negative Pantoea agglomerans RSO6 and RSO7, and gram positive Bacillus aryabhattai RSO25, together with the consortium of the three strains, were used for independent inoculation experiments. The presence of metals (As, Cu, Pb and Zn) in sediments reduced seed germination by 80%. Inoculation with Bacillus aryabhattai RSO25 or Pantoea agglomerans RSO6 and RSO7 enhanced up to 2.5 fold the germination rate of S. densiflora in polluted sediments regarding non-inoculated controls. Moreover, the germination process was accelerated and the germination period was extended. The consortium did not achieve further improvements in seed germination.

May arsenic pollution contribute to limiting Artemia franciscana invasion in southern Spain?

Limited information exists regarding the complex interactions between biological invasions, pollution, and climate change. Most studies indicate that pollution tends to favor invasive species. Here, we provide evidence that arsenic (As) pollution may have a role in limiting the invasion of the exotic brine shrimp Artemia franciscana. We tested As toxicity in natural populations of Artemia parthenogenetica (a native taxon) and A. franciscana from localities in southern Spain with differing degrees of As contamination. Tests were conducted both under current mean temperature conditions (25 °C), and as per a future climate scenario (i.e., an increase in mean temperature of 4 °C). Acute toxicity was estimated on the basis of the median lethal concentration (at 24 h), and chronic toxicity was evaluated by measuring Artemia survival and growth under sublethal exposures (after 26 days). At 25 °C, native A. parthenogenetica from the highly polluted Odiel and Tinto estuary was much more resistant to acute As stress (LC₅₀-24 h, 24.67 mg L⁻¹) than A. franciscana (15.78 mg L⁻¹) and A. parthenogenetica from unpolluted sites (12.04 mg L⁻¹)–suggesting that local adaptation to polluted conditions may occur. At 29 °C, resistance of A. parthenogenetica from Odiel decreased significantly, and there were no statistical differences in sensitivity between the three species/populations, suggesting that climate change may enhance the probability of invasion. Resistance increased with developmental stage from nauplii to adults, and was extremely high in cysts which still hatched at As concentrations of up to 6400 mg L⁻¹. Under sublethal chronic exposure A. franciscana performed better (survival and growth) than A. parthenogenetica, and both species experienced a faster growth when exposed to As, compared with unexposed (control) individuals, probably due to the hormesis. We discuss the ecological implications of our results.