Open Access Kent State (OAKS)

The Rhododendron genus can be found in many different habitats around the world but scarce in desserts, and dry forests as well as tundra regions. . Rhododendrons are studied from the xylem to the leaves, but we believe the secret is in the roots. Kong et al., found two different dimensions of root trait diameter across 96 subtropical woody species: a diameter related dimension that may integrate root construction, and possibly maintenance and persistence, with a branching density dimension that may express difference in root plastic responses to environment. We would like to address the question of what really goes on in the roots and if the anatomy and morphology of the roots are connected to the temperature tolerance of different rhododendron species. We also believe that Rhododendron with similar cold tolerances have similar fungi on their roots. The study site was the Helen S. Layer Rhododendron garden at Holden Arboretum. We studied the morphology, anatomy of six species of Rhododendron from three sections: Ponticum section (Maximum, Degronianum), Pentanthera section (Austrinum, Molle), and Tsutsuti (Yedoense, Indicum).

Tree species are typically identified using leaf and bark traits but identifying species by roots is extremely challenging and would not be feasible by morphological features. Currently, our lab is in the process of identifying roots from mixed species forests to compare belowground productivity between species. We will be using polymerase chain reaction (PCR) and sequencing to identify tree root presence. Four different genes (Matk, psb-trn, Rbcl, and ITS) have been identified as possible candidates for PCR identification. To test these genes, sequences have been downloaded from NCBI and compared using BioEdit. Not enough sequences were found for psb-trn in NCBI, so tests were unable to be run on this gene. Matk had very poor distinguishing ability and therefore was excluded from further testing.Using a single gene, Rbcl had the best ability to distinguish between species alone. There was one genus, Carya, could not be distinguished. Using a combination of ITS and Rbcl for single tree specimen samples 35/41 species could be identified. Four of the six that were unidentifiable were within the genus Carya. These results will be validated by sequencing our own tree samples with primers Rbcla-F and Rbcla-R, ITS-p5 and ITS-u2, and psbA3 and trnHf_05. Results for psb-trn genes will then be able to be compared with Rbcl and ITS. This information will then be used to test our larger hypothesizes to better understand positive and negative feedback loops within different tree species.

Because of conflicting results in previous studies, it is unclear whether litter diversity has a predictable impact on microbial communities or ecosystem processes. We examined whether effects of litter diversity depend on factors that could confound comparisons among previous studies, including leaf type, habitat type, identity of other leaves in the mixture, and spatial covariance at two scales within habitats. We also examined how litter diversity affects the saprotrophic microbial community using terminal restriction fragment length polymorphism to profile bacterial and fungal community composition, direct microscopy to quantify bacterial biomass, and ergosterol extraction to quantify fungal biomass. We found that leaf mixture diversity was rarely significant as a main effect (only for fungal biomass), but was often significant as an interaction with leaf type (for ash-free dry mass recovered, carbon-to-nitrogen ratio, fungal biomass, and bacterial community composition). Leaf type and habitat were significant as main effects for all response variables. The majority of variance in leaf ash-free dry mass and C/N ratio was explained after accounting for treatment effects and spatial covariation at the meter (block) and centimeter (litterbag) scales. However, a substantial amount of variability in microbial communities was left unexplained and must be driven by factors at other spatial scales or more complex spatiotemporal dynamics. We conclude that litter diversity effects are primarily dependent on leaf type, rather than habitat type or identity of surrounding leaves, which can guide the search for mechanisms underlying effects of litter diversity on ecosystem processes.