Abstract
Local adaptation of plants to mycorrhizal fungi helps determine the outcome of mycorrhizal interactions. However, there is comparatively little work exploring the potential for evolution in interactions with ectomycorrhizal fungi, and fewer studies have explored the heritability of mycorrhizal responsiveness, which is required for local adaptation to occur. We set up a reciprocal inoculation experiment using seedlings and soil from four populations of Scots pine (Pinus sylvestris) from Scotland, measuring seedling response to mycorrhizal inoculation after 4 months. We estimated heritability for the response traits and tested for genotype × environment interactions. While we found that ectomycorrhizal responsiveness was highly heritable, we found no evidence that pine populations were locally adapted to fungal communities. Instead, we found a complex suite of interactions between pine population and soil inoculum. Our results suggest that, while Scots pine has the potential to evolve in response to mycorrhizal fungi, evolution in Scotland has not resulted in local adaptation. Long generation times and potential for rapid shifts in fungal communities in response to environmental change may preclude the opportunity for such adaptation in this species, and selection for other factors such as resistance to fungal pathogens may explain the pattern of interactions found.
Highlights
Mycorrhizal fungi are near-ubiquitous across the plant kingdom, forming associations with approximately 80% of plant species (Smith & Read, 2008)
Clear evidence of the importance of these adaptive processes has been shown for plants forming arbuscular mycorrhizal (AM) symbioses (Rúa et al, 2016a; Johnson et al, 2010), but there have been comparatively few studies exploring local adaptation in ectomycorrhizal (EM) systems
While there is some evidence suggesting the existence of genotype × genotype interactions in ectomycorrhizal hosts (Piculell et al, 2008; Hoeksema & Thompson, 2007; Hoeksema et al, 2012; Pickles et al, 2015); overall, there appears to be little evidence so far for local adaptation in host populations (Rúa et al, 2018)
Summary
Mycorrhizal fungi are near-ubiquitous across the plant kingdom, forming associations with approximately 80% of plant species (Smith & Read, 2008). Local adaptation (the differential success of a genotype in its home environment compared with a foreign environment) has been explored as a potentially important process in structuring some of the context-dependency in host benefit seen in many mycorrhizal studies (Rúa et al, 2016b; Hoeksema, 2010). Clear evidence of the importance of these adaptive processes has been shown for plants forming arbuscular mycorrhizal (AM) symbioses (Rúa et al, 2016a; Johnson et al, 2010), but there have been comparatively few studies exploring local adaptation in ectomycorrhizal (EM) systems. Theoretical work on coevolution in mycorrhizal interactions has usually considered factors affecting the outcomes of mutualism, such as partner selection, variation in symbiont community composition, and environmental quality as the drivers of selection (Hoeksema, 2010), resulting in pockets of local adaptation or maladaptation depending on the outcomes of these processes (the “geographic mosaic of coevolution”) (Thompson, 2005). While much work has used reciprocal transplants to investigate the potential for genotype
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