Composition, diversity, and resilience of fungal communities colonizing the roots of native and exotic hosts in an urban environment

Background/Question/Methods

The number of humans in cities is rapidly increasing and now exceeds half of the global population. Consequently, urbanization and its anthropogenically-driven impacts are reconstructing natural ecosystems into fragmented and severely altered novel environments. These novel urban ecosystems are often unique in organismal composition and characterized by decreased biodiversity. The unique characteristics of the urban communities are in part attributable to conscious choices by land management entities. In this study, we aim to better understand the consequences of choosing either a native (Quercus macrocarpa) or non-native (Pinus nigra) ornamental trees for the ectomycorrhizal (ECM) fungi that are necessary for health and growth of most trees. We hypothesize that non-native trees have lower inoculum loads compared to the native hosts. We cast our studies in the conceptual framework of “ecological memory” and predict that choosing the non-native trees will lead to a lesser resilience and therefore to a reduced ability of the urban systems to support fungal communities. Three repeated samplings over the growing season were conducted within the city limits of Manhattan, KS. Three soil coils, one meter from the tree, were collected from each host species and taken back to the lab and frozen at -20 C until further processing. The cores were allowed to thaw and after careful sifting, all root fragments were collected to be examined under microscope for ECM colonization. Total and ECM root tips were counted, total DNA extracted, and total fungal abundance estimated by quantitative PCR (qPCR).

Results/Conclusions

Our results show that although ECM fungi heavily colonize both native and non-native tree species, the trees differ significantly in root and ECM densities based on the simple counts of the root tips:  pines had lower root (F_5,27 = 6.718; P = 0.0152) and ECM densities (F_5,26=5.9943; P=0.214) than oaks. In contrast, our qPCR estimates of the fungal biomass did not differ among the two host tree species suggesting that  although the ECM counts may differ, the inoculum loads are invariable.  However, it remains unanswered whether the compositional attributes of the communities differ. The composition of the ECM communities among the hosts will be evaluated by direct 454-pyrosequencing of the Internal Transcribed Spacer1 (ITS1) PCR amplicons and hypotheses on differences in richness, diversity, and community composition tested.