Browsing by Subject "lignin"

Now showing 1 - 5 of 5
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    Chemical Characterization Of Soil Organic Matter In A Chesapeake Bay Salt Marsh: Analyzing Microbial And Vegetation Inputs
    (2018-05) Bye, Erik
    Blue carbon ecosystems play an outsized role in the burial and storage of organic matter compared to other ecosystems. Increasing CO2 levels, sea level rise, and increasing temperature have been shown to influence the storage of organic matter in these environments. Changes to the stability of organic carbon stocks in these systems could have potentially significant affects to the current climate. For this reason, the stability of organic carbon stocks in these ecosystems must be understood at a deeper level to be able to predict how different environmental stressors will affect their stability. Through the combination of bulk organic matter analyses and biomarker methods, this project characterized the changes that organic matter underwent in a C3 and C4 plant-dominated marsh in the Chesapeake Bay to understand the degradation and stable soil organic matter formation process. Overall, the results support the MEMS framework that states soil organic matter is formed mainly through microbial degradation products that create stable organo-mineral complexes with the mineral soil fraction that resist degradation. The top section of each core shows a large decrease in labile materials coupled with indicators of microbial processing of organic matter. Overall, the formation of stable soil organic matter in this study was determined by the ecosystem properties instead of the initial input of organic matter.
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    Informing Mechanism through Application: Chemical Mimicry and Comparative Decay Studies of Brown Rot Fungi
    (2015-12) Kaffenberger, Justin
    Biodegradation of wood by fungi offers an example of how lignocellulose can be efficiently converted from a recalcitrant mixture of complex biopolymers into readily metabolized sugars. Representing a diverse group, brown rot fungi utilize a unique, yet incompletely understood cellulolytic decay process, believed to involve the generation of hydroxyl radicals by Fenton chemistry, which rapidly depolymerize cellulose. Thermodynamically driven in the absence of enymzatic catalysis, this process can be chemically mimicked, allowing for accelerated bioconversion as fungal growth and colonization rates often bottleneck biological pretreatment times. Furthemore, brown rot fungi are able to circumvent lignin, leaving behind a potentially value-added byproduct in the form of an oxidized lignin-rich residue. This dissertation expands our understanding of brown rot decay through a set of studies with differing approaches. First, decay residues were compared across phylogenetic groupings of brown rot fungi to explore decay variability. As substrate can dictate decay rates, three distinct and representative substrate types were used. Noting significant differences in the Antrodia clade on corn stover, a separate study was conducted to explore the relationship between membership in this clade and the extent of decay they can cause in Poales grasses. Next, a survey of wood-degrading fungi was conducted to assess their ability to improve saccharification yield, the differences in variability across decay types, and to determine the relationship between chemical changes within the substrate and yield improvement. Lastly, hydroquinone-driven Fenton oxidation was both chemically mimicked and theoretically modeled to discern the efficacy of this mechanism in improving cellulose accessibility, its compatibility with cellulases, and the potential role that other redox active chemical species might have in the brown rot mechanism. Saccharification potential in relation to chemical and compositional changes in various substrates was used as a metric in most studies, allowing for consideration of the applied biotechnological benefit of brown rot, while furthering our fundamental understanding of this remarkable decay mechanism. The progression of substrate chemical component losses on a mass loss basis was found to be consistently identical among all known clades of brown rot fungi in all relevant studies. This contrasted with white rot decay, which displayed notably greater variation among tested species in how decay progressed. Despite this consistency in how brown rot decay progressed, there were notable differences between clades in their ability to initiate decay. Where a Gloeophyllum-clade representative was capable of degradation rates similar to those observed on wood substrates, Antrodia clade brown-rotters were found to have a limited ability to degrade Poales grasses. Meta-analysis indicated that this finding was consistent with previous studies. Lastly, the direct use of the Fenton reaction resulted in chemical composition changes that were consistent with brown rot. Despite this, improvement in saccharification yield was difficult to realize because of the reactivity of hydroxyl radical with the desired monosaccharide product. This suggests that if the mechanism for brown is dependent on Fenton chemistry, the manner in which hydroxyl radicals are produced by this reaction must be highly controlled.
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    Leaf carbon fraction data from tree and grassland species collected at the Cedar Creek Ecosystem Science Reserve in 2015 and 2016
    (2020-08-12) Schweiger, Anna K; Lapadat, Cathleen; Kothari, Shan; Cavender-Bares, Jeannine; cavender@umn.edu; Cavender-Bares, Jeannine
    This data set contains results from carbon fraction analysis (Fiber Analyzer 200, ANKOM Technology), including non-structural carbohydrates, hemicellulose, cellulose, lignin, neutral detergent fiber, and acid detergent fiber contents in percent (%) from tree and grassland species sampled at the Cedar Creek Ecosystem Science Reserve in East Bethel, MN. The data was collected as part of the Dimensions of Biodiversity project “Linking remotely sensed optical diversity to genetic, phylogenetic and functional diversity to predict ecosystem processes”. Samples were collected in or near the old fields chronosequence, the oak savanna, and the Forest and Biodiversity Experiment (FAB 1) plots. We used this data together with leaf-level spectral measurements to build partial least squares regression (PLSR) models for predicting leaf traits from spectra.
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    Lignin reduction in alfalfa (Medicago sativa) does not affect foliar disease resistance
    (2018) Samac, Deborah A; Ao, Samadangla; Dornbusch, Melinda R; Grev, Amanda M; Wells, M Scott; Martinson, Krishona; Sheaffer, Craig C
    Disruptions in the lignin biosynthetic pathway have been shown to reduce disease resistance in a number of crops. Recently, genetically modified alfalfa (Medicago sativa) varieties have been marketed with reduced lignin and improved forage quality traits, including increased digestibility by ruminants at later stages of plant maturity. The objective of this study was to compare foliar disease resistance in three reference alfalfa varieties, 54R02, DKA43-22RR, WL355.RR, and the reduced lignin variety, 54HVX41, to evaluate the effect of the reduced lignin trait on foliar disease resistance. Alfalfa plants in research plots at three locations in Minnesota were evaluated for percent defoliation caused by foliar pathogens at four maturity stages; early bud, bud, early flower, and flowering; with natural inoculum. Spring black stem and leaf spot, Leptosphaerulina leaf spot, and common leaf spot were observed from June through September in all locations on all varieties. Summer black stem and leaf spot was most prevalent in August on all varieties at one location. The amount of defoliation increased with maturity stage for all varieties. When harvest was delayed until the flowering stage, moderate to severe (32 to 64%) leaf loss occurred, depending on location. Alfalfa varieties did not differ in percent defoliation at any maturity stage indicating that the reduced lignin trait did not affect foliar disease resistance.
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    Tree species effects on decomposition and forest floor dynamics in a common garden
    (Ecological Society of America, 2006) Hobbie, Sarah E; Reich, Peter B; Oleksyn, Jacek; Ogdahl, Megan; Zytkowiak, Roma; Hale, Cynthia; Karolewski, Piotr
    We studied the effects of tree species on leaf litter decomposition and forest floor dynamics in a common garden experiment of 14 tree species (Abies alba, Acer platanoides, Acer pseudoplatanus, Betula pendula, Carpinus betulus, Fagus sylvatica, Larix decidua, Picea abies, Pinus nigra, Pinus sylvestris, Pseudotsuga menziesii, Quercus robur, Quercus rubra, and Tilia cordata) in southwestern Poland. We used three simultaneous litter bag experiments to tease apart species effects on decomposition via leaf litter chemistry vs. effects on the decomposition environment. Decomposition rates of litter in its plot of origin were negatively correlated with litter lignin and positively correlated with mean annual soil temperature (MATsoil) across species. Likewise, decomposition of a common litter type across all plots was positively associated with MATsoil, and decomposition of litter from all plots in a common plot was negatively related to litter lignin but positively related to litter Ca. Taken together, these results indicate that tree species influenced microbial decomposition primarily via differences in litter lignin (and secondarily, via differences in litter Ca), with high-lignin (and low-Ca) species decomposing most slowly, and by affecting MATsoil, with warmer plots exhibiting more rapid decomposition. In addition to litter bag experiments, we examined forest floor dynamics in each plot by mass balance, since earthworms were a known component of these forest stands and their access to litter in litter bags was limited. Forest floor removal rates estimated from mass balance were positively related to leaf litter Ca (and unrelated to decay rates obtained using litter bags). Litter Ca, in turn, was positively related to the abundance of earthworms, particularly Lumbricus terrestris. Thus, while species influence microbially mediated decomposition primarily through differences in litter lignin, differences among species in litter Ca are most important in determining species effects on forest floor leaf litter dynamics among these 14 tree species, apparently because of the influence of litter Ca on earthworm activity. The overall influence of these tree species on leaf litter decomposition via effects on both microbial and faunal processing will only become clear when we can quantify the decay dynamics of litter that is translocated belowground by earthworms.