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27 results for “light penetration”
Percent light penetration: BioCON : Biodiversity, Elevated CO2, and N Enrichment
BioCON (Biodiversity, CO2, and Nitrogen) is an ecological experiment started in 1997 at the University of Minnesota's Cedar Creek Ecosystem Science Reserve. BioCON's goal is to explore the ways in which plant communities will respond to three environmental changes that are known to be occurring on a global scale: increasing nitrogen deposition, increasing atmospheric CO2, and decreasing biodiversity. Why Biodiversity, CO2, and Nitrogen? While there are many uncertainties in global change biology, there are also some well documented facts. Some of these are: 1. The amount of carbon dioxide (CO2) in the atmosphere is rising. Since the industrial revolution, the CO2 concentration in the atmosphere has increased from approximately 275 parts per million (ppm) to about 378 ppm today. This has been largely the result of fossil fuel burning. It is expected that CO2 levels will continue to rise, and that by the year 2050 these levels will be approximately 550 ppm. CO2 is the raw material for photosynthesis and is known to affect plant growth and development. 2. The amount of nitrogen moving through terrestrial ecosystems has increased in the recent past. While natural "background" levels of nitrogen fixation have remained constant, human additions to the system through fertilizer production and fossil fuel use have increased dramatically. Nitrogen is a key nutrient for plant growth and plays a critical role in plant community structure and composition in many environments. 3. Biodiversity levels are falling. While the research and data are not as complete as they are for CO2 and nitrogen, data indicate that the number of species globally, is being reduced. Perhaps more important for ecosystem function, diversity levels on local to regional scales have fallen due to land use change, biotic invasion and many other drivers. While much is known about how each of these factors affects ecosystem functioning, many questions remain. There is also little data on how these issues affe
Cirrus HD-OCT Measurement of Area of Increased Light Penetration Under the Retinal Pigment Epithelium (RPE)
ClinicalTrials.gov study NCT01272076. IPD Sharing: Not stated. Countries: 1. Publications: 6.
Percent light penetration: Long-Term Nitrogen Deposition: Population, Community, and Ecosystem Consequences
The purpose of this experiment is to measure how adding nitrogen over a long time will affect the number of species, the type of species present, the amount of annual growth, and the change from year to year in the growth of each species in a plant community which is also relieved of grazing by large and small mammals. The experiment is being conducted within fields (A, B, C, and D) which were initially low in soil nutrients. There are 8 different levels of nitrogen addition with other nutrients added to ensure that nitrogen remains the limiting nutrient, and a control which receives no nutrients. There are 6 replicates of the 9 treatments in fields A, B, and C and 5 replicates in field D. The treatments were randomly assigned to the plots. In fields A, B, and C the plots are in 6 by 9 grids and are 4 by 4 meters in size with 1 meter aisles between plots. In field D the plots are 1.5 by 4 meters and are placed in a 3 by 17 grid. The plots are enclosed by a fence to keep out mammalian herbivores. Gophers are trapped and removed as they appear. Nitrogenfertilizer (NH4NO3) is applied twice per year, once in early May and once in late June. This experiment was begun in 1982 by David Tilman.
Percent light penetration: The Effect of Nitrogen Addition and Different pH Levels on Microorganism Populations
The purpose of this experiment was to measure the effect of NH4NO3 addition and different levels of pH on microorganism populations. The experiment was located in field B. This experiment was laid out as a full factorial design with 3 nitrogen levels and 4 pH levels. The pH levels strived for are 4.0, 5.5, 6.5, and controls. The nitrogen levels are E, G, and I are defined in fertilization details. The experiment had 4 replicates. The treatments were randomly assigned to the 48 plots. The plots were 4 by 4 meters and were laid out in a 6 by 8 grid. On May 5, 1995, a wildfire burned all of the plots in experiment 24 in field B.
Percent light penetration and maximum plant height: Traits: Competition and Resource Reduction for Five Grass Species Grown in Monoculture and Competition in Soils with Different Nitrogen Availabilities
This experiment was designed to determine the relationships between plant traits, successional status, and resource reduction for five grass species that were grown for three years in monoculture in replicated field plots on soils prepared to have different availabilities of nitrogen. It also determines the results of competition experiments among various combinations of these species as well as the differing feedback effects of each species on soil nitrogen mineralization rates. All of this work has motivated the desire to more fully understand the mechanisms of interactions among plants and their resources, in the belief that this might eventually allow predictions of the dynamics, diversity, and composition of plant communities.
Percent light penetration: Interactive Effects of Fertility and Distribution on Plant Community Diversity and Structure
There are four levels of nitrogen, corresponding to treatments A, C, F and G in E001, applied at the same time as in that experiment. For a description of fertilizer added to E052, see file fertilization details. There are four levels of soil disturbance designated 1, 2, 3 and 4. Level 1: undisturbed Level 2: 1 pass with a 7 HP Honda rear-tined rototiller with the elevator set to till to a depth of 9 inches Level 3: 2 passes or however many required to produce about 50% bare ground Level 4: 3 passes or however many required to produce 100% bare ground. This requires 3 passes in some plots but 5 or 6 in others. In addition, all woody vegetation not destroyed by tilling is cut at the base. Rototilling is applied in late April. Each fertilization treatment receives each disturbance treatment, for a total of sixteen treatments. There are four replicates of each of the sixteen treatments. In addition, the four extreme ends (lowest N, lowest disturbance; highest N, lowest disturbance, etc. ) are replicated an additional ten times. Treatments are applied in a completely randomized design. Each of the 104 plots is 5m x 5m. Measurements taken at E052 will include: 1) species abundances, 2) community biomass allocation to leaves/roots/stems/flowers, 3) above and below ground net primary production and 4) rates of nitrogen mineralization. For a list of treatments, see the treatment layouts in file trmte52. The plots in E052 are enclosed by a fence to exclude mammalian herbivores. Galvanized welded-wire hardware cloth with 6mm x 6mm openings was buried to a depth of 50cm. Additional hardware cloth extends 60cm above the ground and poultry netting extends to 2m above the ground. In 1990, ten plots of each of four treatments (N1D1, N1D4, N4D1, N4D4, where N is the level of nitrogen added and D is the disturbance treatment) were randomly selected for the competition experiment. The above and belowground effects of neighbors on transplanted grass seedlings were measured using three
Percent light penetration: Components of Plant Competition Along an Experimental Gradient of Nitrogen Availability
This experiment was set up in Field C, on top of the already existing experiment C011. For a description of the plot layout, see E011. For a list of fertilizer treatments for each plot, see file trmte11 and fertilization details. The object of this research was to measure the intensity of above and below-ground competition along a gradient of soil resource availability. Neighbor effects were quantified by measuring the biomass, growth, morphology and survivorship of three species transplanted into vegetation along a gradient of soil nitrogen availability. Transplants were used to test for an inverse relationship between above and below-ground competition, variation in the intensity of competition at different levels of nutrient availability, and reversal of competitive hierarchies. Eight plots of each nitrogen treatment were randomly selected and used for competition experiments. Three competition treatments were used to measure the above and below-ground effects of neighbors on transplanted seedlings at each rate of nitrogen supply. Transplants were grown in subplots with no neighbors, or in subplots with the roots but not shoots of neighbors, or in subplots with all above- and below-ground parts of neighbors present. No neighbor treatments were imposed by driving a ring of galvanized sheet steel (50cm in diameter, 15cm tall) into the ground until the top of it was at the soil surface and then killing all the plants in the enclosed circle with a systemic, rapidly decomposing herbicide (Roundup). Transplants were grown with only the roots of neighbors using white plastic garden net (50x50cm; mesh:1x2cm) to tie back the shoots and leaves of neighbors so that a transplant in the center of the net was not shaded by neighbors but was surrounded by neighbor roots. The all neighbors treatment consisted of a transplant grown in the center of a 50cm x 50cm subplot of undisturbed vegetation. Treatments were replicated five times for each of three transplanted species in each
Percent light penetration: Plant Competition Under Different Nitrogen Levels:A Garden Experiment
This garden plot experiment is located next to the E026 gardens in Field E (Old Field 44). This garden contained monocultures of major grass species from across the grassland biome of North America, and also 3 legume species (E070). The design and purpose were similar to E026, except the plots were larger. The basic experimental design consisted of growing plants in monoculture and in various competitive combinations on each of 14 different soil mixtures. In 1988 a bulldozer was used to remove 30 inches of top soil at the site. To each plot a certain amount of black dirt, ranging from 0.3 inches to 10 inches, was added. Total carbon ranged from 0.1928% to 5.63134% and total nitrogen ranged from 0.0158% to 0.4591%. The exact amounts of black soil added to each plot are described in the field operations. Equal amounts of MgSO4, CaCO3, P2O5 \
Percent light penetration: Long-Term Nitrogen Deposition During Grassland Succession
The purpose of this experiment is to measure how initially disturbing an area and adding nitrogen over a long time will affect the number of species, the type of species present, the amount of annual growth, and the change from year to year in the growth of each species in a plant community which is also relieved of grazing by large and small mammals. This experiment is conducted within fields (A, B, and C) which were initially low in soil nutrients. The ground was disturbed by thoroughly disking the area prior to establishment of the experiment. There are 8 different levels of nitrogen addition with other nutrients added to ensure that nitrogen remains the limiting nutrient, and a control which receives no nutrients. Nitrogen fertilizer (NH4NO3) is applied twice per year, once in early May and once in late June. There are six replicates of each treatment per field. The treatments were randomly assigned to plots of size 4 by 4 meters. The plots are in 6 plot by 9 plot grids with 1 meter aisles between plots. The plot grids are enclosed by a fence to keep out mammalian herbivores. Gophers are trapped and removed as they appear. In the spring of 1992, subexperiments E097 and E098 were established. E097 is in fields A and C where randomly selected plots within each treatment no longer receive fertilizer. E098 is in field B where randomly selected plots within each treatment are burned. Note that the design of E002 is similar to E001 except E002 was thoroughly disked prior to establishment.
Percent light penetration: The Diversity and Abundance of Prairie Plant Communties
This study is divided into six experiments that test the influence of many factors on the diversity and abundance of prairie plant communities. Each "community" is a 2.25 meter square plot seeded with the same amount of seeds from 59 different species of plants. The first experiment is a nitrogen-fire-water factorial. The second experiment is a nitrogen-pH factorial. The third experiment is a nitrogen gradient and the fourth experiment is a nitrogen gradient with a diversity of seeds added each year. The fifth experiment is a disturbance gradient and the last experiment has three levels of soil heterogeneity (variance from the mean) for both nitrogen and pH. See trmte86, trmte103, trmte104, trmte105, trmte106, trmte107 for plot layout.
Percent light penetration: Soil Heterogeneity and Plant Diversity in an Oak Savanna
This experiment was established in field D in August of 1991. There are 30, 2m x 2m plots. These plots are in prairie openings in unmanipulated natural vegetation. They were placed in a haphazard manner, being about 20m apart within an opening. Each plot was divided into 16, 0.5m x 0.5m subplots. Percent cover estimates of vegetation are done in September for each of the sixteen subplots in each of the 30 plots.
Percent light penetration: Soil Disturbance Gradient
This study is one of six experiments (E086, E103, E104, E105, E106, E107, E108) that test the influence of many factors on the diversity and abundance of prairie plant communities. Each community is a 2.25 meter square plot seeded with the same amount of seeds from 59 different species of plants. The first experiment is a nitrogen-fire-water factorial. The second experiment is a nitrogen-pH factorial. The third experiment is a nitrogen gradient and the fourth experiment is a nitrogen gradient with a diversity of seeds added each year. This experiment (E108) is a disturbance gradient and the last experiment has three levels of soil heterogeneity (variance from the mean) for both nitrogen and pH.
Percent light penetration: Seedling Addition Experimant in Field D
The purpose of this experiment is to determine the extent to which species not normally present in a small plot are able to survive and potentially reproduce if added to the plot as seedlings. In the area of Field D in which this experiment is to be done, the average 4 x 4 meter area contains approximately 30 species of vascular plants. Into replicate 4 x 4 meter areas we will either add no species or we will add the seedlings of 50 native prairie species. These were grown by Prairie Restoration, Inc. and were planted on May 27-28, 1993. In adding the seedlings of a variety of species to these plots we will, for all cases, add three seedlings per species into a given plot. These will be fairly uniformally spaced throughout each plot. Thus, the average distance between seedlings will be approximately 28cm apart.
Percent light penetration: Biodiversity II: Effects of Plant Biodiversity on Population and Ecosystem Processes
Biodiversity II (E120) is designed to determine how the number of plant species affects the dynamics of ecological processes at the population, community, and ecosystem levels. By experimentally manipulating the number of species and the kinds of species, the amount of plant growth and the change from year to year, that result can be examined. Plots are large (9m x 9m actively maintained) and well-replicated, allowing responses of plant pathogens, insect herbivores, seed predators, soil parameters, invasive plant species and other variables to also be studied. Plots were seeded in May 1994 to have 1, 2, 4, 8, or 16 species, with roughly 30 replicates of each diversity level. The species composition of each plot was chosen by random draw from a pool of 18 grassland perennials that included four warm-season (C4) grasses, four cool-season (C3) grasses, four legumes, four non-legume forbs, and two woody species. All species occur in monoculture allowing comparison of responses of each species in monoculture to combinations of these same species. The experiment was established in 1994 by the lead investigators David Tilman, Peter Reich, Johannes Knops, and David Wedin. Experiment 120 is similar to Experiment 123, but it uses larger plots to provide a large capacity for long-term subexperiments.
Percent light penetration: The Small Biodiversity Experiment
Biodiversity I (E123), also called the ?small biodiversity experiment,? was designed to determine how the number of species affects the dynamics of ecological processes at the population, community, and ecosystem levels. By experimentally manipulating the number of species and the kinds of species, the amount of plant growth and the change from year to year that result can be examined. Also, the effects of number of species on carbon and nitrogen in the soil and on the ability of other species to invade can be studied. The experiment contains 147 3 x 3m plots that were randomly allocated 1, 2, 4, 6, 8, 12 or 24 plant species. The particular species in a plot were randomly selected from a set of 24 prairie-grassland species which included seven warm-season (C4) grasses, four cool-season (C3) grasses, four legumes, nine non-legume forbs. Each level of number of species has 20 to 24 replicates. In this experiment not all of the species are in monocultures. The study was established in 1994 by lead investigators David Tilman, David Wedin, Peter Reich, and Johannes Knops. Experiment 123 is similar to Experiment 120, but it uses smaller plots and did not categorize by type of plant species prior to randomizing species to plots. This size of plot in Experiment 123 means that the soils are relatively more homogeneous and the desired number of species can be more easily maintained by frequent hand weeding than with larger plots. However, the small size of plots limits sampling and the nesting of other studies within the plots.
Percent light penetration: Effect of Burning Patterns on Vegetation in the Fish Lake Burn Compartments
This study examines the effects of long-term prescribed burning treatments on vegetation structure and composition, productivity, and nutrient cycling in upland oak savanna and woodland vegetation. The basis for the study is an ongoing, experimental prescribed burning program begun in 1964 at Cedar Creek, and a similar program operating since 1962 on the adjacent Helen Allison Savanna property (owned by The Nature Conservancy). These prescribed burning programs are designed to subject upland oak communities (and some old fields) to different burn frequencies and patterns of burning, with the ultimate objectives of 1) restoring and maintaining the historically important savanna and open woodland vegetation, and 2) providing information about the effects of different burning patterns on vegetation structure and composition. This study addresses the latter of these two purposes and expands on it by also investigating possible influences of fire on resource availability (nutrients, water, and light) and net primary productivity. This study represents a continuation and expansion of experiments 015 and 094.
Percent light penetration: Effects of Various Nutrients and Water on Vegetation
This experiment was conducted within the fenced areas of fields A, B, C, and D. The purpose of this experiment was to determine the effect of various nutrients on vegetation. There were eight different nutrients and a control. The different nutrients were N, P, K, Ca, Mg, Na, H2O, and a combination of trace metals. There were 36 plots in each field, 4 replicates of the 9 treatment levels. The plots were 1 meter by 4 meters and were laid out in a 4 by 9 grid. The grid was divided into 4 quarters and treatments were assigned with a randomized block design.
Percent light penetration: Effect of Herbivores on Vegetation Treated with Different N Levels and the Effect of N Addition on Herbivore Populations.
The purpose of this experiment is to study the effect of NH4NO3 addition on vegetation and herbivore populations and the effects of various herbivores on vegetation treated with different nitrogen levels. This experiment is being conducted in fields A, B, and C and is nested within the macroplots of E004. There are 4 fence exclosures each designed to exclude a specific group of herbivores, a fence exclosure to exclude all 4 groups, a fence that should exclude no herbivores to measure fence effects, and a plot with no fence as a control. Exclosures are 2 by 4 meters and are located in macroplot subsections 3 and 8. Herbivore treatments are randomly placed in the grid. For a description of fertilizer added to E005, see file fertilization details. For a list of treatments, see the treatment layouts in file trmte05.
Percent light penetration: Nitrogen Addition and Dynamics of Recovery from Cessation of N Addition
This experiment was established on top of E002 in fields A and C. In the spring of 1992, 3 randomly chosen replicates of each nutrient treatment of experiment E002 were chosen to receive no more fertilizer. For a description of these plots, see E002. For a description of fertilizer added to E097, see file fertilization details. For a list of treatments, see the treatment layouts in file trmte97.
Percent light penetration: Fire X Nitrogen: Interactive Effects in a Prairie-Like Grassland
This experiment was established on top of E002 in field B. In the spring of 1992, 3 randomly chosen replicates of each nutrient treatment of experiment E002 were chosen to be burned each spring. For a description of these plots, see E002. For a list of treatments, see the treatment layouts in file trmte98.
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