Heritable genetic variation but no local adaptation in a pine-ectomycorrhizal interaction

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.

Location, but not defensive genotype, determines ectomycorrhizal community composition in Scots pine (Pinus sylvestris L.) seedlings

“…This generalism is likely to be more pronounced in long-lived species, such as trees, where shifting environmental conditions may change the composition of EM communities, disrupting any adaptation that has taken place. In agreement with this, a previous study in this system found no evidence of local adaptation of Scots pine seedlings to EM fungi (Downie et al, 2020), and overall evidence for local adaptation in EM interactions is lacking (Rúa et al, 2018). Instead, host genotype effects on EM community composition found in other studies (Korkama et al, 2006;Patterson et al, 2018) may reflect differing nutritional requirements due to variation in growth rate, with hosts promoting associations that best meet their needs through preferential allocation (Bever, 2015), rather than reflecting evolution for increased or decreased association with specific fungal species.…”

“…The lack of genetic signature in EM associations found here also highlights the potential importance of the life history of trees in shaping the evolutionary response to EM fungi (Batstone et al, 2018;Downie et al, 2020). High density-dependent mortality due to competition among seedlings for light and space may mean that selectivity, through association only with "high quality" EM partners, may impose significant competitive penalties via opportunity costs.…”

“…The native Scots pine (Pinus sylvestris) forests of Scotland provide a good system within which to test the effects of terpenes on EM fungal colonization (Downie et al, 2020). These pinewoods have a well-documented EM community, which varies in response to the dominant rainfall gradient in Scotland (Jarvis et al, 2013(Jarvis et al, , 2015.…”

“…Additionally, seedlings from different populations have been shown to be genetically differentiated in their response to EM inoculation (Downie et al, 2020). Scots pine populations also show a geographic bias in their terpene chemotype; much of this chemotypic variation is captured in the variation between trees in their issue concentration of Δ 3 -carene (Forrest, 1980;Thoss et al, 2007), which is usually the second-most abundant terpene in Scots pine (O'Reilly-Wapstra et al, 2007).…”

Patterns of genetic diversity vary among shoot and root functional traits in Norway spruce Picea abies along a latitudinal gradient

“…Soil fungi appear to play an important role in belowground adaptation in interior Douglas fir (Pickles et al 2015), and in coastal Douglas fir in British Columbia, population transfers across environmental gradients showed that height growth of trees declined as the difference between the ectomycorrhizal communities of the non‐native populations and those of the native hosts grew larger (Kranabetter et al 2015). Contrastingly, Downie et al (2020) found no indications of local adaptation to belowground fungal communities in a common‐garden trial with Scottish populations of Scots pine.…”