Conclusions
To return to our initial three questions we set out to address, we conclude that the full L. minor microbiome unequivocally supresses fitness of the host plant. This was the case in all environment treatments for seven of the eight genotypes. The decrease in fitness was accompanied by phenotypic changes, with plants producing smaller fronds and shorter roots with the microbiome present. There was some variation in the magnitude of the effect of microbiome on plant fitness among genotypes perhaps because of differences in microbial composition among sites. Likewise, there was variation among genotypes in the phenotypic response to environment, but this was independent of the microbiome. Although the microbiome clearly includes important symbionts including several nitrogen fixers, it is a mistake to discount the important pathogenic, parasitic, and competitive interactions, whose influence seem to override that of mutualists.
Acknowledgments: We thank Julia Kossakowski, who helped with data collection. This experiment was supported by a Discovery Grant from the Natural Science and Engineering Research Council of Canada to GB and an Alexander Graham Bell Canada Graduate Scholarship from the Natural Science and Engineering Research Council of Canada to MDJ. SJVM was supported by a grant from the Swiss National Science foundation.
Authors’ contributions: The study was conceived together by MDJ and GB. MDJ and SVM performed the experiment. The manuscript was written by MDJ. SVM and GB contributed substantially to revisions.
Competing interests: The authors declare no competing interests.
Data availability: Raw data from which all figures were generated will be stored in the Dryad repository before publication of the article.