Browsing by Author "Hudson, Janice E."
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Item Relevant field data for Phenoseasonal subcanopy light dynamics and the effects of light on the physiological ecology of a common understory shrub, Lindera benzoin - PLOS ONE(Department of Geography, University of Delaware, Newark, DE, 2017) Hudson, Janice E.; Levia, Delphis F.; Hudson, Sean A.; Bais, Harsh P.; Legates, David R.Item Tree-mediated water-nutrient fluxes from the microbial to regional scale: insights from mixed-deciduous forests in the northeastern United States(University of Delaware, 2019) Hudson, Janice E.Most people consider trees in passing. Trees provide necessary ecosystem services, chief among them are the production of oxygen and sequestration of carbon dioxide through photosynthesis, the creation of stable and fertile soils, and reduction of storm run-off. Additionally, humans utilize tree biomass as fuel, consumable products, building material, and foodstuffs. However, trees are rarely thought of as agents of biogeochemical influence and change. In the Northeast region of the United States, knowledge of the ways in which trees influence and change watersheds are key, as the surface waters held within these watersheds are essential for human activities and often the primary source of drinking water. Not only do trees experience changes in their environment at different temporal scales (e.g., individual storm events, periodic disturbances, seasons), they also create a changing environment for chemical and microbial processes within those conditions. Further, trees not only exist in but are themselves, a habitat. This dissertation explores some ways in which trees can influence a watershed. ☐ The decomposition of broadleaved tree leaves can contribute a substantial amount of energy to forested watersheds via dissolved organic matter, nutrients, and biological activity. Less is known about how these inputs may vary within a single tree species that is known to have two genetically distinct and geographically separate populations, or how these inputs may change throughout autumn senescence and abscission. We analyzed the morphological and chemical leaf traits, and leachates from Fagus grandifolia (American beech) leaves during three phenophases: fresh green leaves, senescing leaves, and fallen leaves collected from four sites along a geographic transect stretching from Vermont to North Carolina (over 1400 km). Leachates were analyzed for routine solutes and nutrients, as well as fluorescent and UV-visible absorbance indices. Results suggest significant differences in leached nutrients among sites and optical properties and nutrients among phenophases. These results also suggest that geographically (or genetically) separate populations of the same species do not experience senescence in the same way and that implicit assumptions of intraspecific uniformity of leaf-litter leachate chemistry for a given tree species may be invalid. ☐ Precipitation incident on a forest canopy is partitioned into throughfall, stemflow, and interception loss. Throughfall is the dominant subcanopy water flux and is responsible for numerous nutrient cycles between the atmosphere, canopy, and soil. Events impacting the eastern United States (Maryland, Rhode Island, and Vermont) were sampled, and throughfall chemistry was explored for each site in the lens of large-scale storm events. Season was found to be the strongest driver of base cation flux differences among the study sites. Additionally, strong regional deposition played a key role in the discrimination of throughfall chemistry in the region, overriding the influence of the synoptic scale storm events. ☐ The second subcanopy water flux, stemflow, differs from throughfall in nutrient enrichment and residence time. Stemflow coupled with bark texture and hypothesized bark microclimates could provide a refuge for bark surface bacteria. Additionally, it is expected that microbial communities will differ along an urban to rural gradient. This study found that there were indeed multiple phyla of microbial life on the bark surface, and while their biological functions are not understood at this time, there is a difference in composition and location along the tree bole between the urban and rural sites. Stemflow also acts to translocate microbial biomass during precipitation events creating sources and sinks of microbial diversity on the bark.Item Understory variability of photosynthetically active radiation in a Mid-Atlantic deciduous forest and its effects on Lindera benzoin L. Blume (northern spicebush)(University of Delaware, 2015) Hudson, Janice E.Photosynthetically active radiation (PAR, 400-700 nm) is of critical importance to the physiological ecology of plants, partially governing photosynthesis and the carbon balance of forest ecosystems. The spatiotemporal variability of PAR is particularly critical for understory shrub species which rely on uneven PAR inputs for their survival. Employing a combination of field and laboratory techniques over the seven phenoseasons of deciduous forests, this research sought to better understand the spatial and temporal dynamics of subcanopy PAR and link differences in the length and intensity of PAR to the physiological ecology of Lindera benzoin L. Blume (northern spicebush). Nearly 4,600 individual observations of PAR were made under a Mid-Atlantic deciduous forest canopy to quantify the effect of phenoseason on the spatial and temporal distribution of light reaching the subcanopy and how this distribution of light impacted L. benzoin within the plot. Additionally, laboratory experiments were conducted to assist in the quantification of the effect of various photointensities on the physiological ecology of L. benzoin. Health was determined by monitoring physical growth and biomass, as well as the amount of chlorophyll a, chlorophyll b, and carotenoid by way of UV-vis spectrophotometry. The leafless subcanopy PAR values were almost 10 times higher than leafed season PAR. Sunflecks and sun patches could be three orders of magnitude higher than the subcanopy mean during the leafed season. Phenoseason (i.e. the combination of canopy state and celestial geometry) is responsible for nearly three-quarters of the variation between levels in this mid-Atlantic deciduous forest. Understory PAR is typically less than 40% of open PAR, values of PAR in the shrub canopy are often ~5% lower than the subcanopy. Growth of spicebush in the field is significantly clustered. Locations with spicebush growth are in the top 36% of annual PAR receipt. UV-vis spectrophotometry showed significant differences in Root to shoot ratios, biomass, initial stomatal conductance, and all chemical attributes. Changes in photointensity resulted in significant changes in biomass. Spicebush under lab conditions do significantly alter their individual pigments and pigment ratios in response to high intensity light conditions. Temporal light sequences in the field may be a very important factor in the health of northern spicebush. This work represents a novel approach to measuring photosynthetic photon flux density. By utilizing instruments capable of providing the user with a 15 second spatially integrated one meter linear average of the PPFD, obtaining measurements at multiple locations and elevations in the subcanopy over a full year for all cloud conditions, and coupling our research with detailed laboratory experiments, we are able to synthesize our understanding of PAR and its impact on the ecology and physiology of a common and significant regional understory plant.