COS 179-6 - Tree seedling survival responses to light availability and soil-borne microbes depend upon mycorrhizal association

Abstract: Plant-soil feedback (PSF), where a plant’s presence alters soil conditions, can exert profound effects on seedling performance and ultimately on community dynamics. There is a growing consensus, that seedings of tree species associated with arbuscular mycorrhizal fungi (AMF) experience negative PSF whereas those associated with ectomycorrhizal fungi (EMF) experience positive PSF. Light availability may influence how species respond to PSF and this might vary by whether a tree species is associated with AMF (decreased light levels increase negative PSF) or EMF (increased light levels increase positive PSF). Our global hypothesis is that soil source (both species and mycorrhizal type) and light availability interact to influence seedling survival. We conducted a greenhouse experiment with seedlings of five temperate tree species in soil collected beneath conspecific (sterilized and non-sterilized) and heterospecific adults and across three light levels. When seedlings were three weeks old, we measured percent mycorrhizal colonization; survival was monitored over 12 weeks.



Seedling survival responses were influenced by both light availability and soil source but were highly dependent upon mycorrhizal association. For AMF associated species (Acer rubrum, Acer saccharum and Prunus serotina), seedling survival decreased with light availability across all soil sources. Survival was highest in sterilized conspecific soil and lowest in non-sterile conspecific soils. Furthermore, survival was lower in conspecific than heterospecific soils, but only in comparison to the heterospecific soils associated with EMF tree species. For EMF associated tree species (Quercus alba and Quercus rubra), there was no significant effect of light availability on survival. There was also no effect of soil sterilization and survival was higher in conspecific than heterospecific soils, but only in comparison to the heterospecific soils associated with AMF tree species. Overall, survival was lower, and differences in survival due to treatments were greater, for AMF than EMF seedlings. Mycorrhizal colonization was highest in soils cultured by adults of the same mycorrhizal type. AMF colonization had a negative effect on survival for A. rubrum and Q. rubra at low light and for P. serotina at both low and medium light. Whereas, across light levels, for EMF associated tree species, EMF colonization had a positive effect on seedling survival. These results suggest that mycorrhizal type, through effects on PSF, could be an important contributor to temperate forest community dynamics.