Niche partitioning within a dominant plant species to affect ecosystem function: Plant-plant genetic distance promotes trait variance

Background/Question/Methods

Intraspecific diversity can be a strong driver of ecosystem structure and function. However, the factors that drive the strength of this relationship are poorly understood. In particular, it seems probable that relatedness among genotypes within a species should influence the relationship between intraspecific diversity and ecosystem function, but this is rarely mentioned. To explore how intraspecific relatedness influences ecosystem function via niche complementarity, we conducted a mesocosm experiment where we assembled pairs of the dominant prairie grass Schizachyrium scoparium (little bluestem) with varying levels of genetic relatedeness and tracked their above- and belowground functional traits (specific leaf area and specific root length), above-and belowground productivity, and mesocosm-level exchange carbon with the atmosphere. Once the foliar material from the mesocom senesced, we established a plant litter + soil laboratory incubation experiment to track the release of carbon via plant litter decomposition.

Results/Conclusions

We found that increasing genetic relatedness of Schizachyrium scoparium promoted mesocosm carbon fixation via greater productivity and greater net ecosystem CO₂ exchange. In other words, pairs with greater genetic distance between plant genotypes, had 28% greater productivity and 16% greater net mesocosm CO₂ exchange relative to more closely related pairs. We document positive associations between intraspecific relatedness and variance in above- (SLA) (R²=0.14) and belowground (SRL) (R²=0.16) traits (P<0.0001). Our findings indicate that niche partitioning may contribute to greater ecosystem function due to greater trait variance in genetic relatedness between plant genotype pairs. On the other hand, genetic relatedness did not influence carbon release, in the form of plant litter decomposition. Our laboratory incubation study found that genetic relatedness did not influence litter decomposition. This is likely driven by the litter C:N ratio, which did not differ significantly along a genetic distance gradient. Our findings show the importance of genetic relatedness within a dominant prairie species to influence ecosystem function in the form of carbon input without altering release through changes in litter quality.