Are roots and mycorrhizal fungi complementary in nutrient foraging of tree species?

Background/Question/Methods

The roots of the majority of tree species are associated with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi. Well established evidence shows that roots of tree species vary in their morphology with a continuum from very fine to coarse absorptive roots. But it remains unclear whether tree species with coarse roots are more dependent than fine roots on their associated fungi in nutrient acquisition. 

Results/Conclusions

To test for this, we conducted a large litterbag experiment in a Common Garden located in central Pennsylvania. The common garden had 16 tree species with each replicating 8 times. We selected 4 tree species with a 2 × 2 combination of root morphology (coarse verse fine) and mycorrhizal type (AM verse EM). In the summer of 2012, we buried 4 root ingrowth bags (mesh size 1 mm) with different nutrient treatments (control, low and high chemical nitrogen and phosphorus addition, and residue addition) in each plot and incubated for 5 and 15 weeks. We then determined the root and mycorrhizal fungal biomass in each of root-ingrowth bags. We found that trees species with fine roots tended to proliferate more than those with coarse roots in the root-ingrowth bags. Results from fungal biomass measurements showed that both AM and EM biomass in root-ingrowth bags in species plots with coarse roots were higher than those of fine roots. These findings suggest that tree species with different root morphology might select their associated fungi with complementary functions.