Intraspecific variation in invasion traits of the exotic grass Aegilops triuncialis

Abstract

Intraspecific variation is critical for adaptation to novel environments, but is often ignored in studies of invasive species. If intraspecific variation is considered it is most often to compare differences between populations in the home versus invaded ranges, rather than within the invaded range itself. In these works I investigated whether the two most invasive lineages of the exotic grass, Aegilops triuncialis, differed in traits important to invasion-ability. Invasive species can influence nutrient cycling and availability for subsequent generations. Soil nutrient availability is mediated by activity of the soil microbial community, which is influenced by nearby roots. Thus, I tested whether lineages differed in rhizosphere activity that leads to nutrient mineralization in the soil. Additionally, as invasive species are well known to out-compete native species, I tested whether invasive lineages differed in their response to competition by three common grassland species. I found that two lineages ('East' and 'West') differed in rhizosphere community activity, in reproductive traits, as well as in competitive abilities. The East lineage showed increases in rhizospheric enzyme activity throughout and after the growing season, and produced fewer, but larger, seeds. The West lineage showed no change in rhizospheric enzyme activity throughout the growing season, and produced more, but smaller seeds. Additionally, we found a significant negative correlation between rhizospheric enzyme activity early in growth and average seed weight produced, showcasing that plant-soil microbe relationships have the potential to experience selection. In terms of response to competition, the East was most resilient in its competitive response to common grassland species by flowering at the same time and producing the same number of spikelets, regardless of whether it was in competition or grown alone. The West flowered later and produced fewer spikelets with decreased biomass production when in heavy competition with the same grassland species. The results of my work not only highlight the need to incorporate intraspecific variation into studies on invasive species within the invaded range, but demonstrate that these widely distributed lineages can have different impacts on their communities and interact with neighbor species differently. Variations in activity of rhizospheric microbial communities that lead to nutrient mineralization means lineages may differentially affect available nutrients in the soils they invade, and pose different problems for restoration efforts. The variation in response to competition by common grassland species may mean that alternative mechanisms for control and eradication of Ae. triuncialis are warranted depending on the genetic lineage present. I underline the need to include intraspecific variation in future studies, particularly concerning the impact of invasive species in the novel range.