The ghosts of glades past: mycorrhizal interactions in degraded and restored dolomite glades

Background/Question/Methods

Successional changes in aboveground plant communities result in changes to obligate mutualists interacting with plants belowground, such as mycorrhizal fungi. Succession may differentially alter interactions depending on the habitat patch size or proximity to habitat edge. Here, we address how succession, habitat size, and proximity to habitat edge affect mycorrhizal interactions in dolomite glades - harsh, dry grassland environments on southwestern slopes of the Ozarks. With the onset of fire suppression, many dolomite glades were invaded by Juniperus virginiana (cedar) and surrounding woodland species. Restoration of the once-present glade community has begun at many of these sites through mechanical woody species removal and fire reintroduction. These restoration efforts mimic successional patterns. In summer 2011, we conducted mycorrhizal surveys at 29 dolomite glades that varied in restoration age (un-restored to 30 years post-restoration) and size. We collected root samples of specific plant species (Rudbeckia missouriensis and Schizachyrium scoparium) and random plant roots from the community at the center and edge of glade sites. Restoration age, habitat size, and proximity to habitat edge were analyzed as potential predictors of inner root forming arbuscular mycorrhizal fungi (AMF) and outer root tip forming ectomycorrhizal fungi (ECM) root colonization.

Results/Conclusions

AMF root colonization was significantly higher than ECM root colonization, and restoration age was a significant predictor of both AMF and ECM colonization. Specifically, AMF colonization increased with restoration age, while ECM colonization decreased. These results suggest that ECM and their plant hosts are partially inhibited from invading glades, even during times of fire suppression.  AMF/plant interactions are abundant in well-restored dolomite glades, and there is a time-lag in establishment of AMF relationships early in restoration. This suggests that cedar invasion and fire suppression may alter the mycorrhizal community, making it difficult for glade plant species to make these connections early in the restoration process, though the mechanism is not clear. Though AMF colonization did not significantly vary between edge and center habitat, ECM colonization was significantly higher in edge habitat, in un-restored cedar-filled glades and well restored sites. This is most likely due to the presence of woodland ECM plant hosts near the edge. R. missouriensis showed significantly higher AMF root colonization than S. scoparium or community root samples. This suggests that transplanting R. missouriensis into glades may be a possible tool to help promote mycorrhizal connections early in the restoration process.