Intraspecific variations of adaptive strategies of native and invasive plant species along an elevational gradient

The dispersal of invasive alien plant species (IAPS) into mountains has posed great threats to local native plant species. It has been assumed that high intraspecific trait variability contributes to the spread of invasive plant species, even along mountains. Although intraspecific variability of single trait was more often investigated, Grime's competitor, stress-tolerator, and ruderal (CSR) plant strategies, representing trade-offs among multiple functional characters, provides both theoretical and methodological frameworks to inspect plant species’ adaptation to environments. Thus, considering Grime's CSR plant strategies with its intraspecific variation could improve the understanding of mechanisms of successful invasion by alien plant species. We estimated intraspecific variation of CSR plant strategies of five invasive and three native herb species and environmental characteristics (e.g., soil physiochemical variables) in their habitats along an elevational gradient ranging from 300 m to 1500 m a.s.l. We conducted linear mixed models to assess the variance explained by status (native vs. invasive), species identity and elevation, whereas linear regressions were used to link each of CSR scores of each species to elevation and environmental factors. The C- and R-score decreased, and the S-score increased along the elevational gradient, especially for invasive plant species. Species identity explained more proportion of the variation of CSR plant strategies. In addition, microhabitat variables like canopy cover and the ratio of soil ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N) concentrations (NH4/NO3) rather than elevation better explained the variation of CSR plant strategies of four out of the eight examined species. Our results showed that the species-specific and microhabitat-dependent factors determined the intraspecific variation of CSR plant strategies of the eight species along the elevational gradient. Furthermore, our study stresses the importance of microenvironment, particularly soil characteristics, in shaping intraspecific variation of plant species, which is essential for plant species to survive on large environmental gradient.