Ecophysiological differentiation between two invasive species of Carpobrotus competing under different nutrient conditions

Carbon and nitrogen stable isotope compositions provide new insights into the phenotypic plasticity of the invasive species Carpobrotus sp. pl. in different coastal habitats

The genus Carpobrotus N.E.Br. comprises several aggressive invasive species that threaten biodiversity in coastal areas worldwide. We studied the phenotypic plasticity of Carpobrotus sp. pl. invading four coastal habitats in the north-western Iberian Peninsula (coastal cliffs, disturbed areas, dunes and coastal forests). We measured morphological traits and carbon (δ13C) and nitrogen (δ15N) stable isotope compositions of Carpobrotus sp. pl. individuals collected in each habitat. Our results indicated that leaf carbon content (% C) and dry shoot weight were higher on cliffs and lower in mixed forests. In contrast, leaf hydration was higher in mixed forests and lower on cliffs. Leaf nitrogen content (% N) was higher in forests, which might be due to the presence of Acacia longifolia, an alien tree that accumulates N in the soil through symbiotic associations with N fixing bacteria. Differences in δ15N showed the use of different N sources in each habitat. Values were higher in disturbed areas with greater human activity and lower on cliffs and forests. δ13C was higher in cliffs and dunes, suggesting CAM activity where drought and salinity are more intense. Water use efficiency (iWUE) and δ13C were higher on cliffs and dunes, suggesting an adaptation and high tolerance of Carpobrotus sp. pl. to unfavourable conditions such as drought or salinity in the invaded areas.

A test of native plant adaptation more than one century after introduction of the invasive Carpobrotus edulis to the NW Iberian Peninsula

Background

Although the immediate consequences of biological invasions on ecosystems and conservation have been widely studied, the long-term effects remain unclear. Invaders can either cause the extinction of native species or become integrated in the new ecosystems, thus increasing the diversity of these ecosystems and the services that they provide. The final balance of invasions will depend on how the invaders and native plants co-evolve. For a better understanding of such co-evolution, case studies that consider the changes that occur in both invasive and native species long after the introduction of the invader are especially valuable. In this work, we studied the ecological consequences of the more than one century old invasion of NW Iberia by the African plant Carpobrotus edulis. We conducted a common garden experiment to compare the reciprocal effects of competition between Carpobrotus plants from the invaded area or from the native African range and two native Iberian plant species (Artemisia crithmifolia and Helichrysum picardii) from populations exposed or unexposed to the invader.

Results

Exposure of H. picardii populations to C. edulis increased their capacity to repress the growth of Carpobrotus. The repression specifically affected the Carpobrotus from the invader populations, not those from the African native area. No effects of exposition were detected in the case of A. crithmifolia. C. edulis plants from the invader populations had higher growth than plants from the species' African area of origin.

Conclusions

We found that adaptive responses of natives to invaders can occur in the long term, but we only found evidence for adaptive responses in one of the two species studied. This might be explained by known differences between the two species in the structure of genetic variance and gene flow between subpopulations. The overall changes observed in the invader Carpobrotus are consistent with adaptation after invasion.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-021-01785-x.

A physiological approach to study the competition ability of the grassland species Trifolium pratense and Agrostis capillaris

The response of plant species to external factors depends partly on the interaction with the environment and with the other species that coexist in the same ecosystem. Several studies have investigated the main traits that determine the competitive capacity of plant species, and although the relevance of the traits is not clear, traits both from belowground and aboveground have been observed. In this paper, we grew Trifolium pratense and Agrostis capillaris in intra- and interspecific competition, analyzing the photosynthetic metabolism and nitrogen uptake, among other variables. The results indicated that T. pratense possesses better competition ability due to the higher competitive performance for soil resources compared to A. capillaris, explained by a higher root biomass and a higher nitrogen uptake rate in the former than in the latter. These traits permitted T. pratense to show higher photosynthetic rate than A. capillaris when both species were grown in mixture. Furthermore, the interspecific competition provoked A. capillaris to activate its antioxidant metabolism, through SOD activity, to detoxify the reactive oxygen species generated due to its lower capacity for using the photochemical energy absorbed. In this experiment, we conclude that the competitiveness seems to be more related with soil resources competition than with light competition, and that the photosynthetic rate decline in A. capillaris is more a secondary effect as a consequence of nitrogen limitation.