Microbe-mediated adaptation and temporal scale of adaptation
Just as microbes mediate plant adaptation to spatially heterogeneous
environments, microbes may also promote adaptive plant responses to
temporally varying environments, and these effects may allow for more
rapid adaptation to changing environmental conditions than evolution
through genetic differentiation (Hawkes et al. 2020).
Specifically, microbes might respond more rapidly to environmental
change (both in terms of shifts in community composition and
evolutionary changes within key microbial populations) because of
incredibly diverse metabolic strategies, high mutation rates, large
population sizes, diverse communities, short generation times, and the
potential for lateral gene transfer (Gillings & Stokes 2012). These
shifts in microbial form or function can introduce novel pathways of
adaptation (e.g., endophytes producing novel chemical defenses in the
face of increased herbivory) or change/enhance existing traits (Friesen
2013). If only plant genotypes that are locally adapted to those
microbial symbionts can take advantage of these innovations, then
microbe-mediated local adaption would result. If any plant genotype can
benefit from these innovations, then microbe-mediated adaptive
plasticity is possible. For example, in Lau & Lennon’s 2012 experiment,
plant responses to drought were almost entirely mediated by microbes and
occurred over very short times scales (~16 months; Lau
& Lennon 2012), indicating the potential for rapid responses mediated
by microbes to climate change. Microbes affecting response to climate
change might be a wide-spread phenomenon, at least for fungi. Kivlin and
coauthors ( 2013) found that fungal symbionts widely affect plant
responses to global change, and fungal symbionts particularly benefited
plants exposed to drought.