Phragmites australis: How do genotypes of different phylogeographic origins differ from their invasive genotypes in growth, nitrogen allocation and gas exchange?

It has been suggested that in plant invasions, species may develop intrinsically higher gas exchange and growth rates, and greater nitrogen uptake and allocation to shoots, in their invasive range than in their native habitat under excess nutrients. In this study, native populations of two old world Phragmitesaustralis phylogeographic groups (EU and MED) were compared with their invasive populations in North America [NAint (M) and NAint (Delta)] under unlimited nutrient availability and identical environmental conditions in a common garden. We expected that both introduced groups would have higher growth, nitrogen uptake and allocation, and gas exchange rates than their native groups, but that these enhanced traits would have evolved in different ways in the two introduced ranges, because of different evolutionary histories. Biomass, leaf area, leaf nitrogen concentrations (NH4+ and NO3−) and transpiration rates increased in introduced versus native groups, whereas differences in SLA, leaf pigment concentrations and assimilation rates were due to phylogeographic origins. Despite intrinsic differences in the allocation of C and N in leaves, shoots and rhizome due to phylogeographic origin, the introduced groups invested more biomass in above-ground tissues than roots and rhizomes. Our results support the concept that invasive populations develop enhanced morphological, physiological and biomass traits in their new ranges that may assist their competiveness under nutrient-enriched conditions, however the ecophysiological processes leading to these changes can be different and depend on the evolutionary history of the genotypes

Germination capacity and viability of threatened species collections in seed banks

Facing the current biodiversity crisis, the value of ex situ conservation has been increasingly acknowledged in international treaties and legislations. Seed banks are a good way of conserving biodiversity, providing that seeds are of high quality and at maximum viability. However, despite the number of established ex situ facilities, there is little information on seed viability in botanic garden seed banks. This paper analyses the status of the seed collection of the National Botanic Garden of Belgium by determining the germination capacity and viability of seeds that have been stored for 1-26 years. It aims at: (1) ensuring that existing storage conditions provide effective ex situ conservation of threatened species; (2) providing viability data on threatened species; (3) planning future collection and storage efforts for seeds of West European species of conservation value. Results from this study showed that the germination and viability percentages of the 250 tested species reached on average 59 and 79% respectively. Some families typically performed better than others. Within a species, consistent results were not always obtained. Over a quarter of accessions exhibited some degree of dormancy. Considering the current lack of knowledge in seed germination and dormancy of many rare and threatened species, we believe that the quality of a seed collection should be estimated by its viability and not by its germination percentage. This study calls for further research in order to better understand the biology of a range of threatened native species. © Springer Science+Business Media B.V. 2009.SCOPUS: ar.jinfo:eu-repo/semantics/publishe