Implications and Future Research Directions
Increasingly researchers, using a wide range of experimental systems,
are exploring microbe-mediated adaptation (Kohl et al. 2014;
Weigel & Erwin 2017; Sison-Mangus et al. 2018; Moeller et
al. 2019). If microbes commonly influence adaptation through
microbe-mediated local adaptation or microbe-mediated adaptive
plasticity, then our understanding of the traits and mechanisms
underlying adaptation may be incomplete, therefore making our responses
to environmental and agricultural challenges potentially inappropriate.
Just as Clausen, Keck, and Heisey (1948) realized 70 plus years ago,
plants are excellent study systems to perform reciprocal transplants and
partition the variation of plant phenotypes into genetic and
environmental components (Núñez-Farfán & Schlichting 2001). However,
early pioneers were unaware that microbes can be heavily influenced by
their host’s genotype (Bulgarelli et al. 2012; Lundberg et
al. 2012; Gehring et al. 2017) and have large effects on plant
phenotypes (Friesen et al. 2011; Friesen 2013; Wagner et
al. 2014; Giauque et al. 2019). Consequently, in early studies
many microbial effects may have been erroneously attributed to plant
genotype and at other times erroneously attributed to environment
effects (e.g. Chanway et al. 1989). In many cases, such
bookkeeping may not fundamentally change outcomes. For example, in the
Gehring et al. (2017) case study the mycorrhizal community is so
tightly under plant control, it functions as an extended phenotype of
the plant host. However, even in this case, one must wonder what will
happen to those plant genotypes enriching for drought tolerance
promoting mycorrhizae if the ectomycorrhizal community is eroded by
other forces? Below we discuss how explicitly considering microbial
effects may substantially alter our views of the spatial scales, pace,
and consequences of plant adaptation.