226 research outputs found
Disparate responses of above- and belowground properties to soil disturbance by an invasive mammal
No full textIntroduced mammalian herbivores can negatively affect ecosystem structure and function if they introduce a novel disturbance to an ecosystem. For example, belowground foraging herbivores that bioturbate the soil, may alter process rates and community composition in ecosystems that lack native belowground mammalian foragers. Wild boar (Sus scrofa) disturb the soil system and plant community via their rooting behavior in their native range. Given their size and the numbers in their populations, this disturbance can be significant in forested ecosystems. Recently, wild boar were introduced to Patagonian forests lacking native mammalian herbivores that forage belowground. To explore how introduced wild boar might alter forested ecosystems, we conducted a large-scale wild boar exclusion experiment in three different forest types (Austroducedrus chilensis forest, Nothofagus dombeyi forest, and shrublands). Wild boar presence altered plant composition and structure, reducing plant biomass 3.8-fold and decreasing both grass and herb cover relative to areas where wild boar were excluded. Decomposition rates and soil compaction also declined by 5% in areas where boar had access; however, rooting had no effect on soil nutrient stocks and cycling. Interestingly, there were no differences in wild boar impacts on different forest types. We found that after 3-years of exclusion, belowground foraging by wild boar had a larger impact on plant community structure and biomass than it did on soil nutrient processes.Fil: Barrios Garcia Moar, Maria Noelia. Administración de Parques Nacionales. Delegación Regional Patagonia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Classen, Aimee T.. University of Tennessee; Estados UnidosFil: Simberloff, Daniel. University of Tennessee; Estados Unido
Evolutionary histories of soil fungi are reflected in their large‐scale biogeography
No full textAlthough fungal communities are known to vary along latitudinal gradients, mechanisms underlying this pattern are not well-understood. We used high-throughput sequencing to examine the large-scale distributions of soil fungi and their relation to evolutionary history. We tested the Tropical Conservatism Hypothesis, which predicts that ancestral fungal groups should be more restricted to tropical latitudes and conditions than would more recently derived groups. We found support for this hypothesis in that older phyla preferred significantly lower latitudes and warmer, wetter conditions than did younger phyla. Moreover, preferences for higher latitudes and lower precipitation levels were significantly phylogenetically conserved among the six younger phyla, possibly because the older phyla possess a zoospore stage that is vulnerable to drought, whereas the younger phyla retain protective cell walls throughout their life cycle. Our study provides novel evidence that the Tropical Conservatism Hypothesis applies to microbes as well as plants and animals. © 2014 John Wiley & Sons Ltd/CNRS
Does mineralization and pH control the distribution of ammonia-oxidizing archaea in temperate forest soils?
No full textAmmonia-oxidizing archaea (AOA) are a primary contributor to nitrification – a key
process in nutrient cycling that influences the concentration of nitrate in forest ecosystems.
This study addressed (1) how AOA community composition changes across upland forest stands
in Manistee National Forest and (2) how environmental factors such as pH and net N
mineralization may be associated with AOA distribution. From collected soil samples, amoA (a
functional gene involved in ammonia oxidation) was amplified and sequenced to detect AOA.
Sequences were classified based on the known taxonomy of AOA, and the relative abundances
of AOA taxa were compared between stands and along changes in pH and mineralization.
Results of PERMANOVA and Mantel tests show that both pH and net N mineralization
are significantly associated with AOA distribution (p < 0.05). Moreover, pH is a stronger
predictor of AOA distribution than mineralization, contributing to up to 23% of variations in
community composition, while mineralization contributes 8%. Phylogenetic analyses revealed
that two AOA lineages are represented in the stands: Nitrososphaeales and Ca. Nitrosotaleales.
Titan analyses revealed that within these lineages, specific taxa can be negatively correlated or
positively correlated with pH and mineralization. Furthermore, the relative abundance of these
lineages and their clades are markedly different across stands.
These results show that AOA communities can be very distinct within similar ecosystem
types. Furthermore, AOA taxa do not share a single directional response to pH or net
mineralization, emphasizing the diversity of AOA and their interactions with the environment.
In this study, we were able to contribute to an understanding of how a gradient of
environmental factors is associated with the distribution of nitrifying microorganisms, and we
recommend to incorporating AOB abundances into future research on the composition and
relative contributions of ammonia-oxidizing organisms to nitrification.Master of Science (MS)School for Environment and SustainabilityUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/172192/1/Wen_Jennifer_Thesis.pd
Ecosystem Function Along an Elevational Gradient in Vermont
No full textLiving (biotic) and non-living (abiotic) factors drive the function of ecosystems across a variety of scales from the root-soil interface to the watershed. Biotic and abiotic global change pressures such as increasing temperature and invasive species are shifting how ecosystems function. Thus, exploring and understanding how these factors shape function across the landscape is an important research area. For example, climate change both directly and indirectly affects soil microbial functions – such as carbon mineralization and nitrogen transformations – through increasing activity under warming and altering inputs to the soil through species composition changes. Mountains provide a useful tool for studying relationships among biotic and abiotic factors because climate and species diversity shift along gradients. Here, I measured carbon and nitrogen soil processes as well as microbial extracellular enzyme activity along an elevational gradient to explore how changes in climate, edaphic properties, and biotic composition affects ecosystem function. As expected, climate and species composition varied in predictable ways along the gradient – actual evapotranspiration declined, and conifer dominance increased. Soil functions also shifted along the gradient. Potential carbon mineralization increased with elevation and with conifer dominance. Potential nitrogen mineralization rates increased with elevation and with conifer dominance. Surprisingly, there were few predictors for potential soil nitrification, which increased only with soil functional diversity. While temperature and moisture availability drive ecosystem function at broad scales and biotic factors typically drive function at the regional scale, we saw that function of soils at the mountain watershed scale was best explained by a combination of both abiotic and biotic factors.Natural ResourcesMaster of Science (MS
Relationships Among Vision, Visual Attention, and Fitness to Drive in Adults With Multiple Sclerosis
No full textAbstract
Date Presented 4/1/2017
We quantified the relationships among visual abilities, visual attention, and fitness to drive in 30 adults with multiple sclerosis. Visual acuity and visual processing speed correlated with critical driving errors (predictive of crashes) may be useful to identify potential at-risk drivers.
Primary Author and Speaker: Sarah Krasniuk
Contributing Authors: Sherrilene Classen, Sarah A. Morrow</jats:p
Visual Attention Cut Points Predicting Fitness to Drive in People With Parkinson’s Disease
No full textAbstract
Date Presented 4/1/2017
People with Parkinson’s disease (PD) have impaired visual attention affecting driver fitness. This study presents cut points to demonstrate that visual attention is an early and persistent impairment in PD drivers and accurately predicts failing or passing an on-road assessment.
Primary Author and Speaker: Sherrilene Classen
Contributing Authors: Karla Crawford, Sarah Jenniex</jats:p
The missing linkages between mineral soil organic carbon and litter decomposition
No full textMineral soil carbon is an important terrestrial carbon stock, however, the pathway between leaf litter decomposition and mineral soil organic carbon is still undefined. To gain an understanding of this carbon stabilization pathway and the other drivers of mineral soil carbon I addressed the question: (1) is leaf litter decomposition correlated with soil mineral carbon pools within and across forest ecosystems? And more broadly, (2) what are the drivers of mineral soil carbon stabilization at a global and biome specific scale? I answered the first question by conducting a meta-analysis of previously collected litter decomposition data and soil organic carbon (SOC) content in the mineral layer. The data was extracted from data depositories and primary literature. My results showed that mineral SOC was not correlated with litter decomposition rates, or the amount of carbon remaining when the decomposition rate is zero (asymptotic limit value (A)), determined through linear regression. For the second question, I found different drivers of mineral SOC in temperate, tropical, and boreal biomes using structural equation modeling. Including actual evapotranspiration (AET), soil microbial carbon, soil nitrogen, soil clay content, gross primary productivity, litter decomposition rate, and the asymptotic limit value (A), I was able to explain 24.8% of the variation in SOC in the mineral layer globally. This varied in the different biomes; in the temperate biome, 69.2% of the variation in SOC in the mineral layer was explained by the same variables as above, in the boreal system 48.1% of the variation was explained excluding soil N, and in the tropics, 48.5% of the variation was explained excluding AET. Some of the most important drivers of mineral SOC include soil N and AET. However, I found no relationship between mineral SOC and litter decomposition, therefore pushing the scientific community to look at other inputs of stabilized SOC in the mineral layer, such as root inputs.Rubenstein School of Environment and Natural Resource
Driving Intervention for Returning Combat Veterans: Interim Analysis of a Randomized Controlled Trial
No full textAbstract
Date Presented 3/31/2017
Motor vehicle collisions are a leading cause of deaths for combat veterans, and effective occupational therapy driving interventions (OT–DIs) are needed. We conducted an analysis of an efficacy trial comparing an OT–DI with traffic safety education and demonstrated a reduction in driving errors for the OT–DI group.
Primary Author and Speaker: Sherrilene Classen
Additional Authors and Speakers: Sandra Winter
Contributing Authors: Charles Levy, Abraham Yarney, Miriam Monahan</jats:p
Revealing the Direct and Indirect Effects of Climate Change on Soil Nutrient Dynamics and Forage Resources in Mountain Ecosystems
No full textModern climate change is already altering the structure and function ofecosystems around the world in nontrivial ways. Mountain ecosystems in particular will continue to experience a greater magnitude and rate of climatic warming than the global average, threatening the stability of key ecosystem processes like nutrient cycling as well as the supply of benefits from ecosystem services provided by mountains. While significant advancements have been made to address the direct effects of rising temperatures on nutrient cycling dynamics, our understanding of the synergies between the direct effects of warming and the indirect effects of climate change, mediated by the response of plant soil properties, lags behind. This dissertation leverages a global network of climate changeexperiments in mountains to understand the direct and indirect effects of warming on nutrient cycling and forage resource production in alpine ecosystems around the world. First, I use a series of plant removal experiments distributed across an elevational gradient in the Colorado Rocky Mountains to explore how the effects of biodiversity loss on nitrogen cycling vary across a natural temperature gradient. Second, I identify globally consistent climate change effects on nitrogen and phosphorus cycling across seven sites in the warming and (species) removal (WaRM) network of climate change experiments in mountains. Finally, I focus on a single WaRM network site in the Colorado Rocky Mountains to analyze the effects of climate change on the quality and quantity of forage resource production in a federal rangeland. Taken as a whole, this body of research lends insight to the future of alpine nutrient dynamics in a warmer world and describes opportunities to link empirical evidence from global change experiments to management decisions in order to sustain essential ecosystem services in the face of climate change.Natural ResourcesDoctor of Philosophy (PhD
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