COS 9-5
Microbial nitrogen acquisition as a novel plant trait that impacts fitness among lineages of an invasive grass
The use of functional traits to link species composition and community function is an increasingly popular approach in ecological research, but tends to focus on species means and ignore important variation around those means. Furthermore, most research has emphasized the impact of aboveground traits, despite burgeoning evidence of the importance of belowground interactions on plant fitness. Beneficial associations with the rhizosphere community can arise from interactions with mycorrhizae, nitrogen fixing bacteria, or extracellular enzymes produced by soil microbes which stimulate nutrient turnover- all of which can impact plant fitness and can in turn be impacted by the plant. In our study we investigate plant stimulation of microbial enzyme activity as a functional trait. We developed a novel approach by incorporating both intraspecific and temporal variation in our study, as both time and genotype are known to influence plant-soil interactions but are rarely studied simultaneously. We compared multiple populations of two genetic lineages of the invasive grass, Aegilops triuncialis, to investigate differences in rhizosphere enzyme stimulation, resource acquisition, and reproductive fitness.
Results/Conclusions
Our results show both genetic lineage and harvest stage influenced soil microbial activity. One lineage demonstrated increasing enzyme activity in the rhizosphere from early growth to post-senescence, while the other lineage showed no significant difference between any sampling periods. Additionally, we found that greater stimulation of microbial enzyme activity early in growth was associated with a fitness cost of smaller seed size. Extracellular enzymes release nutrients from plant-unavailable sources, mobilizing them for eventual plant uptake. Differences in temporal stimulation of these enzymes among lineages could translate to differences in resource availability and abundance in the soil surrounding the plant. As this species tends to form monocultures, this could result in changes in temporal resource dynamics in the invaded community. Additionally, the potential for this trait to impact plant fitness through seed size could result in selection on this trait in different environments. This is the first study to show differences in timing and allocation of resources within a species in plant-soil microbe interactions, and to demonstrate this as an important functional trait that may influence distributions of genetic lineages within a species’ range.