Browsing by Subject "mineralization"

Now showing 1 - 7 of 7
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    Do evergreen and deciduous tree differ in their effects on soil nitrogen availability
    (Ecological Society of America, 2012) Mueller, Kevin E; Hobbie, Sarah E; Oleksyn, Jacek; Reich, Peter B; Eissenstat, David M
    Evergreen and deciduous plants are widely expected to have different impacts on soil nitrogen (N) availability because of differences in leaf litter chemistry and ensuing effects on net N mineralization (Nmin). We evaluated this hypothesis by compiling published data on net Nmin rates beneath co-occurring stands of evergreen and deciduous trees. The compiled data included 35 sets of co-occurring stands in temperate and boreal forests. Evergreen and deciduous stands did not have consistently divergent effects on net Nmin rates; net Nmin beneath deciduous trees was higher when comparing natural stands (19 contrasts), but equivalent to evergreens in plantations (16 contrasts). We also compared net Nmin rates beneath pairs of co-occurring genera. Most pairs of genera did not differ consistently, i.e., tree species from one genus had higher net Nmin at some sites and lower net Nmin at other sites. Moreover, several common deciduous genera (Acer, Betula, Populus) and deciduous Quercus spp. did not typically have higher net Nmin rates than common evergreen genera (Pinus, Picea). There are several reasons why tree effects on net Nmin are poorly predicted by leaf habit and phylogeny. For example, the amount of N mineralized from decomposing leaves might be less than the amount of N mineralized from organic matter pools that are less affected by leaf litter traits, such as dead roots and soil organic matter. Also, effects of plant traits and plant groups on net Nmin probably depend on site-specific factors such as stand age and soil type.
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    Fire and vegetation effects on productivity and nitrogen cycling across a forest-grassland continuum
    (Ecological Society of America, 2001) Reich, Peter B; Peterson, David W; Wedin, David A; Wrage, Keith
    Mixed tree–grass vegetation is important globally at ecotones between grasslands and forests. To address uncertainties vis-à-vis productivity and nitrogen (N) cycling in such systems we studied 20 mature oak savanna stands, ranging from 90% woody dominated to 80% herbaceous dominated, growing on comparable soils in a 32-yr-old fire frequency experiment in Minnesota, USA. Fire frequencies ranged from almost annual burning to complete fire protection. Across all stands, aboveground net primary productivity (ANPP) ranged from 2 to 12 Mg·ha−1·yr−1, decreased with fire frequency (r2 = 0.59), increased with woody canopy dominance (r2 = 0.83), and increased with soil net N mineralization rates (r2 = 0.79), which varied from 25 to 150 kg·ha−1·yr−1. ANPP was positively related to total biomass (r2 = 0.95), total canopy leaf N content (r2 = 0.88), leaf area index (LAI; r2 = 0.87), annual litterfall N cycling (r2 = 0.70), foliage N concentration (r2 = 0.62), and fine root N concentration (r2 = 0.35), all of which also increased with increasing tree canopy cover. ANPP, soil N mineralization, and estimated root turnover rates increased with woody canopy cover even for stands with similar fire frequency. ANPP and N mineralization both decreased with fire frequency for stands having a comparable percentage of woody canopy cover. Fine root standing biomass increased with increasing grass dominance. However, fine root turnover rate estimated with a nitrogen budget technique decreased proportionally more with increasing grass dominance, and hence fine root productivity decreased along the same gradient. Via several direct and indirect and mutually reinforcing (feedback) effects, the combination of low fire frequency and high tree dominance leads to high rates of N cycling, LAI, and productivity; while the opposite, high fire frequency and high grass dominance, leads to low rates of N cycling, LAI, and productivity. Carbon and N cycling were tightly coupled across the fire frequency and vegetation type gradients.
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    Information Circular 30. Workshop on the Applicability of Gold and Platinum-Group-Element Models in Minnesota
    (Minnesota Geological Survey, 1989) Morey, G.B.
    The geology of Minnesota is highly varied and contains combinations of lithologic and structural factors that are known to be associated with important deposits of metallic minerals elsewhere in the world. Despite this broadly favorable potential for a diverse array of deposit types, however, only the world-class deposits of iron ore have yet been discovered. This suggests that we know too little about the geology, too little about the criteria for recognizing nonferrous mineral deposits, or, as is probably the case, too little about both. As a step toward remedying these deficiencies, a mineral deposit workshop was convened in April 1989 with support from the Minnesota Legislature through the Mineral Diversification Program, as administered by the Minnesota Minerals Coordinating Committee (W.C. Brice, Minnesota Department of Natural Resources, Division of Minerals; P.C. Grew, Minnesota Geological Survey; K.J. Reid, Mineral Resources Research Center; T.B. Johnson, Natural Resources Research Institute). The topic of the workshop was a discussion of mineral deposit models applicable to gold and the platinum group of elements (PGE) in Minnesota. Co-convenors of the workshop were Priscilla C. Grew (Minnesota Geological Survey), Michael P. Foose (U.S. Geological Survey), and Steven A. Hauck (Natural Resources Research Institute, University of Minnesota, Duluth). Professor Samuel S. Adams (Colorado School of Mines) provided special assistance in planning the workshop program. Industry participation was coordinated by Keith Laskowski (Newmont Exploration, Ltd.) and William C. Ulland (American Shield), both of the Minnesota Exploration Association. The body of this report consists of two parts-an overview of Minnesota's geologic framework, by D.L. Southwick, and a summary of the workshop discussions.
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    Information Circular 44. Geochemical Evaluation of Platinum Group Element (PGE) Mineralization in the Sonju Lake Intrusion, Finland, Minnesota
    (Minnesota Geological Survey, 1999) Miller, James D., Jr.
    This study was undertaken to evaluate the potential for stratiform platinum group element (PGE) mineralization in the Sonju Lake intrusion (SLI). The SLI is a well differentiated, tholeiitic, mafic layered intrusion that is part of the multiple intrusive Beaver Bay Complex, and is exposed near Finland, Minnesota. Geochemical analyses of outcrop and drill-core samples that span the 1200-m-thick SLI were interpreted in the context of (1) data from PGE reefs in other tholeiitic layered intrusions (most notably the Skaergaard intrusion of East Greenland), and (2) models of PGE and sulfide mineralization in tholeiitic intrusions. The geochemical data show that a PGE-mineralized horizon is present approximately two-thirds of the way up from the base of the moderately south-dipping, sheet-like SLI. PGE mineralization was apparently related to initial sulfide saturation and subsequent exsolution of sulfide melt from the SLI magma. The data also indicate that as it settled, the sulfide melt efficiently scavenged PGEs from the SLI magma, and concentrated them into a relatively narrow interval of gabbroic cumulates. The geochemical signature of the SLI is remarkably similar to that of the PGE-bearing Platinova reef in the Skaergaard intrusion. The highest Pd, Pt and Au concentrations in SLI outcrop samples are far from economic grade (360, 66, and 85 ppb respectively); but a more precise evaluation of peak grade, thickness, and lateral continuity requires drilling and analysis of the entire interval. When the results of the study reported here are combined with evidence for similar mineralization in the Layered Series at Duluth, they indicate that tholeiitic layered intrusions of the Duluth and Beaver Bay complexes are favorable exploration targets for reef-type PGE mineralization.
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    Invasive species’ leaf traits and dissimilarity from natives shape their impact on nitrogen cycling: A meta‐analysis
    (Wiley, 2017) Lee, Marissa R; Bernhardt, Emily S; Bodegom, Peter M; Cornelissen, J. Hans C; Kattge, Jens; Laughlin, Daniel C; Niinemets, Ülo; Peñuelas, Josep; Reich, Peter B; Yguel, Benjamin; Wright, Justin P
    Many exotic species have little apparent impact on ecosystem processes, whereas others have dramatic consequences for human and ecosystem health. There is growing evidence that invasions foster eutrophication. We need to identify species that are harmful and systems that are vulnerable to anticipate these consequences. Species’ traits may provide the necessary insights. We conducted a global meta-analysis to determine whether plant leaf and litter functional traits, and particularly leaf and litter nitrogen (N) content and carbon: nitrogen (C : N) ratio, explain variation in invasive species’ impacts on soil N cycling. Dissimilarity in leaf and litter traits among invaded and noninvaded plant communities control the magnitude and direction of invasion impacts on N cycling. Invasions that caused the greatest increases in soil inorganic N and mineralization rates had a much greater litter N content and lower litter C : N in the invaded than the reference community. Trait dissimilarities were better predictors than the trait values of invasive species alone. Quantifying baseline community tissue traits, in addition to those of the invasive species, is critical to understanding the impacts of invasion on soil N cycling.
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    A Multi-functional st-ELR Scaffold for Dentin Regeneration
    (2018-12) LAN, CAIXIA
    Pulpitis is one of the most widespread diseases in the world. Current advances in dental tissue engineering have provided an interesting alternative therapeutic approach in the field of regenerative endodontics. However, there remains a strong need to develop an optimized scaffold for supporting dentin regeneration. The objective of this PhD project is to develop a dental scaffold using elastin-like recombinamers(ELRs) to stimulate dentin regeneration while exhibiting antimicrobial ability to control potential re-infection of the pulp cavity. To provide a biomimetic scaffold that resembles the extracellular matrix in dentin tissue, we fabricated fibrous scaffold of ELRs using electrospinning technique and analyzed its ability in inducing biomimetic mineralization using the polymer-induced liquid precursor (PILP) process. The ELR scaffolds exhibited intra- and extra-fibrous mineralization, which highly mimicked the structure of mineralized native collagen in dentin. The scaffold is expected to be applied in the pulp cavity with direct contact with the pulp tissue. Therefore, we investigated the interaction between the mineralized ELR scaffold that contains statherin-derived peptide (st-ELR) and human dental pulp stem cells (hDPSCs). Proliferation and odontogenic differentiation of hDPSCs were analyzed and the study indicated that biomimetically mineralized st-ELR scaffold supported the proliferation and odontogenic differentiation of hDPSCs. Bacterial infection is considered as the major reason for the failure of implanted materials. Therefore, we functionalized st-ELR scaffold with antimicrobial peptides to prevent the potential infection caused by oral bacteria. A cysteine modified antimicrobial peptide GL13K(Cys-GL13K) was used in this study to achieve site-specific modification on the developed scaffold. First, we tethered Cys-GL13K peptides on titanium surface to analyze the properties and antimicrobial ability of immobilized peptides. A homogenous and strong coating of peptides was obtained. The tethered peptides exhibited promising antimicrobial ability against S. mutans, S. gordonii and E. faecalis. Furthermore, we bio-conjugated the peptides to st-ELR membranes using the same modification technique. Successful peptide modification was achieved, and the peptide functionalized st-ELR membrane exerted antimicrobial ability against S. mutans and S. gordonii. This research sheds light on the development and functionalization of scaffolds for the application of regenerating hard tissues such as dentin and bone. It allows the scaffold to highly resemble the architecture and physical properties of extracellular matrix in mineralized tissues. In addition, this research provides a new approach to modify the scaffold with diverse bioactive molecules to obtain multiple functions, while maintaining good interaction with native tissues.
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    Nitrogen mineralization and productivity in 50 hardwood and conifer stands on diverse soils
    (Ecological Society of America, 1997) Reich, Peter B; Grigal, David F; Aber, John D; Gower, Stith T
    The generality of relationships between soil net nitrogen (N) mineralization, aboveground N cycling, and aboveground net primary production (ANPP) for temperate forest ecosystems is unclear. It is also not known whether these variables and their relationships differ between evergreen and deciduous forests, or across soil types. To address these questions we compiled data on annual rates of in situ net N mineralization and ANPP for 16 conifer and 34 hardwood forests, including plantations and natural stands on a range of soils at six locations in Wisconsin and Minnesota, USA. For 31 natural stands, 48 stands with native species (including plantations), and all data, ANPP increased linearly with annual net N mineralization rates. Native evergreen conifer and two deciduous hardwood types (oaks and mesic hardwoods) followed similar patterns in this regression, indicating common functional relationships at the ecosystem level. The relationship of N mineralization and ANPP differed between finer textured Alfisol soils and sandier Entisols, with higher ANPP at any given N mineralization level in Alfisols. A multiple regression of N mineralization on soil texture (percentage silt plus clay), litterfall N, and mean annual temperature explained 81% of the variance in annual N mineralization for natural stands, and a multiple regression of ANPP on soil texture and annual N mineralization rate explained 83% of the variance in ANPP. Naturally regenerated forest types differed in mean annual net N mineralization, litterfall N, and ANPP, and all were greater in oaks than in mesic hardwoods or conifers, respectively. However, differences among the 50 stands and six locations were largely a result of differences in soils and stand origin. For all natural hardwood stands, ANPP and N mineralization were greater on fine-textured Alfisols than on sandy Entisols. For evergreen conifers, ANPP and N mineralization were greater in plantations on Alfisols than in natural stands on Histosols, Entisols, or Spodosols. Hardwood and evergreen conifer stands did not differ significantly in ANPP or N mineralization on comparable soils and stand origin: they differed neither as plantations on Alfisols nor as natural stands on Entisols. This suggests that observed average differences among natural forest types in ANPP and N mineralization resulted largely from variation in their distribution on differing soils, and not from feedback effects on N mineralization or differing productivity per available N. These data suggest that, at a regional scale, at least half of the variation in ANPP can be attributed to variation in annual N mineralization. Both ANPP and N mineralization differ more strongly with soil type/parent material than with forest type; ANPP at any given level of N mineralization is higher on silty/loamy Alfisols than on sandy Entisols, Histosols, or Spodosols, but not different for coniferous and broad-leaved deciduous species. There is no indication of N saturation of ANPP within the range of natural N availability in these forests.