Functional trait plasticity in globally invasive and non-invasive Rosa sp. in response to different light environments

Background/Question/Methods

Biological invasions pose major threats to natural habitats by reducing native biodiversity, disrupting ecological function, and disturbing plant community dynamics. As a result, understanding the factors that promote the success of a novel species has important implications for conservation and restoration efforts. Theory suggests that the expression of specific functional traits, as well as the plasticity of those traits, may promote the invasiveness of a given species. More specifically, plasticity in functional traits associated with rapid resource capture may result in higher competitive ability and survivorship in globally invasive species.

To determine if functional trait plasticity promotes global invasiveness (i.e. invasive status and distribution reported by the Global Compendium of Weeds) we conducted a greenhouse experiment at John Carroll University (Ohio, USA).  For 7 weeks, replicates of 11 Rosa sp. were exposed to high light (≈1000 μmol m^-2 s^-1 PPFD) or low light (≈315 μmol m^-2 s^-1PPFD) conditions. To quantify functional trait differences, 11 biomass allocation and physiological plant traits were measured. We hypothesized that globally invasive species would express higher trait values and plasticity in traits related to rapid resource capture. Additionally, those species considered non-invasive would demonstrate trait values and plasticity in traits associated with resource conservation.

Results/Conclusions

Based on their relative degree of invasiveness, Rosa sp.differed in their ability to allocate biomass. Globally invasive species expressed biomass partitioning traits promoting their ability to rapidly capture light under limiting conditions (higher leaf mass ratio (LMR), higher leaf area ratio (LAR), and lower stem mass ratio (SMR)).  Contrary to our original hypothesis, globally invasive species also expressed higher water use efficiency (WUE), lower photosynthetic rates, and lower stomatal conductance across light treatments.  However, the plasticity of these functional traits was not significantly associated with global invasiveness.

The simultaneous expression of both resource capture and resource conservation traits by globally invasive Rosa sp. suggests that invasive species may be more tolerant of low resource conditions, as well as better able to exploit resources during high availability. Despite plasticity not playing an immediate role in describing the differences observed between globally invasive and non-invasive Rosa sp., it still may influence local adaptation and overall plant fitness of novel populations.  To gain a full understanding of the interaction between functional trait plasticity, plant performance, and global invasiveness, future studies should be conducted across multiple environmental gradients at the individual, population, and community levels.