The effects of mycorrhizal-associated trees on the belowground food web

Background/Question/Methods

Aboveground and belowground systems are known to link plant and microbial groups; however, their relationship to belowground fauna is less understood. The relationship between fungi and plant roots have increasing become a linkage to the above and belowground world. Ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) fungi form mutualistic relationships with plant roots. These associated plants have different leaf-litter chemistry, microbial communities, and cycle nutrients in distinct ways. Still, we have a limited understanding of whether varying abundances of ECM and AM-associated plants can serve as a predictive trait to describe belowground animal community structure and composition. To assess vegetation’s role on faunal structure, we studied whether tree species and root-associated mycorrhizal symbionts are correlated with soil microarthropod communities. We utilized three natural tree gradients that shift from species of trees associating with AM to trees associated with ECM fungi, which we refer to as the ECM Tree Index. Using amplicon sequencing, we test the predictive capability of the ECM Tree Index for estimating fungal abundances in three forested sites and test its ability to estimate soil microarthropod abundance. We predicted microarthropods would be more abundant in ECM-dominated stands because of an increase in fungal abundance and a higher C: N.

Results/Conclusions

We confirmed the ECM Tree Index hosted different but predictable fungal communities along the gradient. Additionally, we found the ECM Tree Index plays a significant role in predicting most fungivore and predator abundances when paired with litter depth. Fungivore (oribatid mites) and predator (mesostigmatid mites) abundance increased by 2X as plots shifted from AM-dominated systems to ECM-dominated systems. Predator abundances were tightly correlated with fungivores, suggesting substantial bottom-up control for this predatory group. We found oribatids and predacious mesostigmatids linearly increased with the ECM Tree Index, following a presumed change in fungal abundance. Contrary to our prediction, changes in Collembolan (fungivore and microbivore) abundances were not explained by the ECM Tree Index but were explained mainly by litter depth and abiotic site differences. These results suggest basal resources and litter depth drive oribatid and mesostigmatid mites. In contrast, local differences like litter depth and soil habitat properties are more important for structuring Collembolan communities.