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.