Print PageThe ability of exotic plant species to deal with biotic and abiotic components of the native community can determine their invasive potential. Survival and stress tolerance at early stages are critical for the colonization of a new habitat. While high levels of stress conducive to mortality will prevent the invasion, at moderate stress levels individual fitness differences can have critical consequences at a population level.
Baccharis halimifolia (Asteraceae) is a shrub native to North America and an aggressive invader of coastal habitats in Southern Europe, where it is replacing the native subhalophytic herbaceous communities in tidal marshes. Previous fieldwork in Europe shows that this is a plastic species that colonizes sea rush communities with phreatic salinity levels of 1-30 gNaCl/L. However, it has been shown that the fitness of adult plants decreases with increased salinity.
Here we explore the role of genetic variation, plasticity and maternal effects in tolerance and plasticity to salinity in B. halimifolia through a salinity gradient (0-20g NaCl/L) in controlled conditions (greenhouse). We grew plants from eight maternal lines derived from two communities (halophytic, non-halophytic), from an estuary of Northern Spain, and we measured fitness, morpho-anatomical and physiological traits during a 5-month growth experiment.
Results/Conclusions
Leaves of mother plants from halophytic areas showed a Na+ concentration two times higher than leaves of plants from non-halophytic areas, suggesting that environmental salinity may affect the physiological state during seed maturation.
A high percent of survival in the greenhouse at the highest Na+ concentration (20g/L) indicates high tolerance to salinity. Growth of all maternal lines decreased at low levels of salinity (5g/L), and maximal reduction is reached at 15g/L. However, growth responses differed significantly among maternal lines at intermediate levels of salinity (5-10g/L), reflecting genetic diversity for plasticity. More importantly, at intermediate levels of salinity, maternal lines from halophytic communities displayed higher reproductive effort and allocation to belowground biomass than maternal lines from non-halophytic communities, suggesting trans-generational plasticity effects.
The patterns observed for fitness traits can be explained by the high plasticity found for different morpho-anatomical and physiological traits. These traits also showed genetic variation for plasticity and differentiated responses to salinity depending on maternal environment.
We conclude that synergetic effects of plasticity, genetic variation and maternal effects drive the invasion of halophytic communities by B. halimifolia and play an important role in the adaptive potential to salinity at the population level.
