Thuja plicata exclusion in ectomycorrhiza-dominated forests: testing the role of inoculum potential of arbuscular mycorrhizal fungi

Abstract

The ability of trees dependent on arbuscular mycorrhizal (AM) fungi to establish in ectomycorrhizal forests is unknown. On northern Vancouver Island, Canada, there are sharp boundaries between mixed red cedar (Thuja plicata)-hemlock (Tsuga heterophylla) (CH) stands, and stands of hemlock and amabilis fir (Abies amabilis) (HA). We tested differences in AM colonization of red cedar between ectomycorrhiza-dominated (HA) stands and stands containing red cedar (CH), across a range of light levels. We used a soil bioassay approach to determine whether there was sufficient AM fungal inoculum in the HA tree stands to colonize red cedar seedlings. Seeds of hemlock and red cedar were sown in forest floor samples collected from the two types of forests, and shade treatments ranging from < 1 to 53% of full sunlight were imposed. After 6 months, seedling survival and root and shoot biomass were quantified, and red cedar seedlings were sampled for AM fungal colonization. Hemlock survival and growth did not differ between soil types, suggesting there was no substrate-associated limitation to its establishment in either forest type. Red cedar colonization by AM fungi was significantly correlated with light levels in CH soils but arbuscular mycorrhizas were absent in roots of red cedar seedlings grown in HA soil. Red cedar survival and relative growth rate were significantly greater in the CH than in HA soil; higher growth was due primarily to greater shoot growth in CH soils at high light levels. The low soil inoculum potential for red cedar in ectomycorrhiza-dominated stands may account for the virtual exclusion of red cedar seedlings from these forests.

Root-Associated Ectomycorrhizal Fungi Shared by Various Boreal Forest Seedlings Naturally Regenerating after a Fire in Interior Alaska and Correlation of Different Fungi with Host Growth Responses

“…It is known that the presence of particular mycorrhizal species in a given soil can facilitate the establishment of plant species that benefit from that fungus in that soil (4,8,18,25,35,36,51,55,59). There are also many examples of relationships between mycorrhizal fungal infection by specific fungal species and the growth rate and/or competitive dynamics of particular plant species (6,12,36,38,43,54,55) and ECM or plant ability to acquire N and other nutrients (16,21,35).…”

Different soil moisture conditions change the outcome of the ectomycorrhizal symbiosis between Rhizopogon species and Pinus muricata

“…For example, changes in light availability (Zhou and Sharik 1997;Weber et al 2005) and herbivory pressure (Gehring and Whitham 2002) have both been shown to influence how plants and ECM fungi interact. Another environmental factor that has received less attention in this context is water availability.…”

Lack of belowground mutualisms hinders Pinaceae invasions

“…Conversely, facilitation by beneficial soil microbes may directly control biological invasions (Simberloff and Von Holle 1999, Richardson et al 2000, Bruno et al 2003. For example, ectomycorrhizal symbioses can be crucial for plant establishment, as evidence from native ranges suggests , Weber et al 2005, Horton and van der Heijden 2008. However, the role of ectomycorrhizal fungi in plant invasion has rarely been explored.…”