Research News and Highlights
News
Holden’s tree collections used in doctoral dissertation research
Arboreta collections are appreciated as living collections of diverse woody plant species from around the globe, but they are often undervalued as a resource for scientific research. However, many arboreta collections represent a controlled environment for asking fundamental questions about the evolution of traits in woody plants. Collection specimens are often grouped by family, adequately spaced, and grown in similar conditions with respect to soil and climate, making it possible to compare individuals from different plant lineages. Oscar Valverde, a doctoral candidate at Kent State University, has been researching the evolution and importance of tree root morphology and function across various tree families that represent major lineages of flowering plants (angiosperms). He believes that many forest species coexist in tree communities by having rooting systems that provide different strategies for acquiring soil resources, thus allowing them to effectively compete with one another in a non-detrimental manner. Valverde, along with his doctoral adviser Christopher Blackwood and Holden scientist Kurt Smemo, has been working in both native Northeast Ohio forests and Holden’s specimen collections to address the evolution and significance of rooting patterns and nutrient acquisition strategies in a variety of tree species common to temperate forests in Northeast Ohio. His basic approach is to study the root morphology patterns in specimens growing in a common garden (Holden’s tree collections) and compare them to those of species growing under natural conditions (native forests).
Valverde has found that root morphology in tree groups that are evolutionarily older, such as magnolids-magnolias and tulip trees, is substantially different from more recently evolved groups like maples or ashes. In general, magnolids showed thicker, less branched roots that those of other groups, and might be more dependent on mycorrhizal fungi for nutrient uptake. He also found large differences in root chemistry between groups, with trees from the Rose family having tough long-lived roots that are low in nitrogen content. When Valverde studied how all these different kinds of roots interact in natural conditions, he found that roots modify their morphology in response to other species competing in the same soil location. Moreover, there was more root biomass and greater coexistence when adjacent root systems were more unrelated (evolutionarily father apart). His overall findings suggest that variations in the evolution of tree rooting patterns actually improve the use of soil resources and productivity of the entire ecosystem. Part of his dissertation has already been submitted for publication. He hopes to defend his dissertation and complete his doctorate in December 2012.
Holden’s ecological research extends to northern wetlands
The vast wetlands that dominate earth’s high latitude landscapes are of great ecological importance. Besides being vital habitat for many migratory animal species, northern wetlands have a unique set of environmental conditions that link them directly to the earth’s climate system. Namely, cold, wet, anaerobic conditions result in plant growth exceeding decomposition of dead plant material. The dead plant material accumulates as peat and can be very deep. These peat deposits represent an important storage unit for carbon dioxide, a greenhouse gas, which came from the atmosphere and would go back to the atmosphere if not stored in peat. However, the same environmental conditions that allow peat to form also allow microorganisms to produce methane, a greenhouse gas ten times more potent than carbon dioxide. For more than a decade, Holden Research Scientist Kurt Smemo has been studying the processes that control carbon dioxide storage and methane production in these northern wetlands. Smemo, along with colleagues Nathan Basiliko (University of Toronto), Joseph Yavitt (Cornell University), and University of Toronto graduate students Michael Preston and Varun Gupta, have recently published several wetland microbiology and ecology papers in the international journals Biogeosciences, Microbial Ecology, and Frontiers in Terrestrial Microbiology. One of those studies (see highlights section) was made possible by a grant from the National Science Foundation that funded a month-long visit to Holden by Michael Preston. Preston used his time at Holden to work with Smemo and learn new techniques for measuring the activity and function of microorganisms in peat and design future experiments for a portion of his doctoral dissertation.
Highlights
Future ecology of northern wetlands depends on vegetation change
The James Bay Lowlands of northern Canada are a vast complex of wetlands and peat deposits that remain largely unstudied. Climate change models predict the region will experience warmer and drier conditions, potentially altering plant communities and soil microbial processes that decompose organic matter. Visiting scientist Michael Preston, along with Holden scientist Kurt Smemo and colleagues, conducted the first study of soil microbial populations in this wetland wilderness and looked at how those populations respond to environmental changes. The results of this study were recently published in Frontiers in Terrestrial Microbiology (doi: 10.3389/fmicb.2012.00070) and showed that the same groups of microbes dominate northern wetlands in this region, regardless of differences in chemistry and vegetation. Although the microbial communities were similar, the processes carried out by these microbes did vary among the sites and were primarily influenced by soil pH and the dominant vegetation. These findings suggest that expected regional climate change and replacement of mosses with shrubs and grasses could increase methane emission from these wetlands and decrease the amount carbon dioxide stored in peat.
Fungal mats are an important component of forest soil respiration
Most people don’t realize that the soil under their feet is actually breathing. Carbon dioxide released from plant roots and soil microorganisms travels through the soil and is released at the soil surface. Scientists study soil respiration because it provides clues as to how carbon and energy moves through ecosystems. The amount of carbon dioxide respired by soil is influenced by a number of factors including moisture, temperature, and the organisms present. Holden scientist Laurel Kluber and collaborators from Lawrence Livermore National Laboratory and Oregon State University recently published a paper in the international journal Biogeosciences Discussions (doi:10.5194/bgd-9-1635-2012) where they examined the contribution of ectomycorrhizal (ECM) fungi to forest soil respiration. Because ECM fungi form a symbiotic relationship with plant roots, determining the individual contributions of roots and fungi to total respiration can be difficult.
Kluber and colleagues took advantage of naturally occurring mats of ECM fungi that form in some soils and were able to determine that soils containing these fungal mats had significantly higher respiration than soils without mats. Furthermore, they found that much of this extra respiration was actually associated with the decomposition of the fungal mats themselves. These fungal mats cover approximately 57 percent of the soil surface in the old-growth Douglas-fir forests where the study took place and accounted for nine percent of the total soil respiration over the course of the year. Thus, mats formed by ECM fungi play a more significant role in the function of forest ecosystems than previously thought and this study highlights our need to better understand the role of fungi in forests of the Great Lakes region.
