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Articles 1561 - 1590 of 1698

Full-Text Articles in Botany

A Review Of Plant Introductions To The Kimberley 1955 To 1987, R Mccartney Nov 1991

A Review Of Plant Introductions To The Kimberley 1955 To 1987, R Mccartney

Grain and other field crops published reports

This report summarizes the work done by the Department of Agriculture, Western Australia, in the west and north Kimberley in introducing plant species during 1955-1987.

For the purposes of this repor1the following areas are defined thus:

• West Kimberley- lies between latitude 17°5 and 19°5 and longitude 121°E and 127°E, with an extension to the north of 1° between 121°E and I 24°20'E. The area is 118,000 km".

• North Kimberley - lies north of latitude 17°5 and between longitude 124°20'E and 127°30'E. The area is 85,000 km'.

• East Kimberley-lies north of latitude 19°5 and between longitude 127°30'E and …


Inheritance Of Acid-Soil Tolerance In Sorghum (Sorghum Bicolor) Grown On An Ultisol, C. I. Flores, L. M. Gourley, Jeffrey F. Pedersen, R. B. Clark Jan 1991

Inheritance Of Acid-Soil Tolerance In Sorghum (Sorghum Bicolor) Grown On An Ultisol, C. I. Flores, L. M. Gourley, Jeffrey F. Pedersen, R. B. Clark

Department of Agronomy and Horticulture: Faculty Publications

Inheritance of acid-soil tolerance (generally considered AI-toxicity tolerance) i.n sorghum [Sorghum bicolor (L.) Moench] is not clear. Forty F1 sorghum hybrids and their 14 parents were grown two seasons in the field at relatively high (67 and 71%) and low (43 and 42%) Al saturations on an acid Ultisol in Colombia, South America to evaluate the effects of acid soil on agronomic component traits and to better understand inheritance of acid-soil tolerance of sorghum. For plants grown at the high Al saturation levels, hybrids from acid-soil tolerant [AS-T] x acid soil-sensitive [AS-S] crosses were as tolerant as hybrids from …


Fertility And Forage Yield Of Sorghum X Sudangrass Hybrids In A1 And A3 Cytoplasm, J. J. Toy, Jeffrey F. Pedersen, K. J. Moore Jan 1991

Fertility And Forage Yield Of Sorghum X Sudangrass Hybrids In A1 And A3 Cytoplasm, J. J. Toy, Jeffrey F. Pedersen, K. J. Moore

Department of Agronomy and Horticulture: Faculty Publications

Most sorghum x sudangrass hybrids are currently produced in Al male-sterile cytoplasm. Availability of alternative cytoplasmic sterility systems allows production of sorghum x sudangrass hybrids that may have superior forage characteristics. A study was conducted to compare the agronomic performance of Al and A3 sorghum x sudangrass hybrids. A bulk of eight sudangrass populations was used to pollinate four grain sorghum inbreds normally used as females that had been sterilized in both Al and A3 cytoplasm, and two inbreds normally used as males that had been sterilized in A3 cytoplasm. The hybrids were evaluated in 1990. Results indicate that male-sterile …


Notes: Interpretive Analysis For Forage Yield Trial Data, Jeffrey F. Pedersen, K. J. Moore, Edzard Van Santen Jan 1991

Notes: Interpretive Analysis For Forage Yield Trial Data, Jeffrey F. Pedersen, K. J. Moore, Edzard Van Santen

Department of Agronomy and Horticulture: Faculty Publications

Forage cultivar evaluation is often done in small plots with multiple harvests throughout the growing season. Data is often summarized by presenting a yearly total yield for each cultivar in addition to the mean for each harvest date. Data summarization often becomes burdensome and difficult to interpret. Regressing yield against a growth index associated with harvest dates can be utilized to describe forage performance in a concise and easily interpreted format. Subsets of data from tall fescue (Festuca amndinacea Schreb.) yield trials conducted in Alabama and Kentucky were used to demonstrate the technique. The analysis involves regressing yield of a …


Nitrogen And Methyl Jasmonate Induction Of Soybean Vegetative Storage Protein Genes, Paul E. Staswick, Jing-Feng Huang, Yoon Rhee Jan 1991

Nitrogen And Methyl Jasmonate Induction Of Soybean Vegetative Storage Protein Genes, Paul E. Staswick, Jing-Feng Huang, Yoon Rhee

Department of Agronomy and Horticulture: Faculty Publications

Vegetative storage protein (VSP) and VSP mRNA levels in soybean (Glycine max) leaves correlated with the amount of NH4NO3 provided to nonnodulated plants. The mRNA level declined as leaves matured, but high levels of N delayed the decline. This is consistent with the proposed role for VSP in the temporary storage of N. Wounding, petiole girdling, and treatment with methyijasmonate (MeJA) increased VSP mRNA in leaves 24 hours after treatment. The magnitude of the response depended on leaf age and N availability. N deficiency essentially eliminated the response to wounding and petiole girdling. MeJA was …


Notes On Neotropical Amanoa (Euphorbiaceae), W. John Hayden Oct 1990

Notes On Neotropical Amanoa (Euphorbiaceae), W. John Hayden

Biology Faculty Publications

Lectotypes are designated for Amanoa caribaea Krug & Urban and A. guianensis Aublet; presumed syntypes of the latter taxon are shown to be heterogeneous by inclusion of a previously unrecognized species. Four new species of Amanoa are described: A. congesta from French Guiana and northeastern Brazil; A. gracillima from Manaus, Brazil; A. nanayensis from Amazonian Peru and adjacent Colombia and Brazil; and A. neglecta from French Guiana and Surinam. Amanoa sinuosa is proposed as a new name for the later homonym A. robusta Leal. A key to the 13 neotropical species is presented.


Methyl Salicylate Secretory Cells In Roots Of Viola Arvensis And V. Rafinesquii (Violaceae), W. John Hayden, John Clough Mar 1990

Methyl Salicylate Secretory Cells In Roots Of Viola Arvensis And V. Rafinesquii (Violaceae), W. John Hayden, John Clough

Biology Faculty Publications

The aromatic roots of Viola arvensis and V. rafinesquii were studied in order to determine the chemical nature and anatomical localization of their volatile compounds. Gas chromatography and mass spectroscopy revealed a single detectable volatile compound, methyl salicylate. Light microscopy and differential staining with Sudan III indicates the source of this compound to be enlarged secretory cells located in the endodermis, an unusual position for such cells in roots of angiosperms. The secretory endodermal cells are sporadic, but are more frequent in primary roots than in secondary roots and the lower portion of the hypocotyl. It is hypothesized that …


Distribution Of Polyploid Variation In Big Bluestem (Andropogon Gerardii, Poaceae) Across The Tallgrass Prairie Region, Kathleen H. Keeler Feb 1990

Distribution Of Polyploid Variation In Big Bluestem (Andropogon Gerardii, Poaceae) Across The Tallgrass Prairie Region, Kathleen H. Keeler

Kathleen H. Keeler Publications

The objective of this research was to describe the distribution of polyploid cytotypes of the grass big bluestem (Andropogon gerardii Vitman) along an east-west transect across the tallgrass prairie region, as an integral part of understanding the function of intraspecific polyploid polymorphism. Andropogon gerardii shows intraspecific variation in amount of nuclear DNA as a result of intraspecific poly-ploidy. Nearly 600 plants from 15 prairies in 5 states were collected and nuclear DNA was determined by flow cytometry. In the eastern part of the tallgrass prairie region, higher polyploids were rarely found. However, at the western edge of the tallgrass …


Maine's Endangered And Threatened Plants, Maine State Planning Office Jan 1990

Maine's Endangered And Threatened Plants, Maine State Planning Office

Maine Collection

Maine's Endangered and Threatened Plants

Executive Department, Maine State Planning Office, Critical Areas Program, 1990.


Evaluation Of Seeding Rates Of Au Triumph And Endophyte-Infected Kentucky 31 Tall Fescue, Jeffrey F. Pedersen, D. M. Ball Jan 1990

Evaluation Of Seeding Rates Of Au Triumph And Endophyte-Infected Kentucky 31 Tall Fescue, Jeffrey F. Pedersen, D. M. Ball

Department of Agronomy and Horticulture: Faculty Publications

Increased difficulty in stand establishment of tall fescue (Festuca arundinacea Schreb.) has been reported by producers since the introduction of endophyte (Acremonium coenophialum Morgan Jones and Gams)-free tall fescue seed into the market place. This has encouraged the use of higher seeding rates for endophyte-free tall fescue without scientific basis. The objective of this study was to determine whether ‘AU Triumph’, and endophyte-free cultivar, and endophyte-infected ‘Kentucky 31’ differ in minimum seeding rates for successful establishment. Experiments were established at two locations in each of two years, using a randomized complete block with four replications. Soils at the two locations …


Heritability Of Root Characteristics Affecting Mineral Uptake In Tall Fescue, J. H. Edwards, Jeffrey F. Pedersen, R. C. Kingery Jan 1990

Heritability Of Root Characteristics Affecting Mineral Uptake In Tall Fescue, J. H. Edwards, Jeffrey F. Pedersen, R. C. Kingery

Department of Agronomy and Horticulture: Faculty Publications

Modification of plant roots can potentially increase the area. of adaptation of tall fescue (Festuca arundinacea Schreb.). Limited information is available on the heritability of root diameter and root volume in tall fescue. A greenhouse experiment was conducted with'50 random 'Kentucky 31' (Ky-31) tall fescue parents and their progeny grown in aerated nutrient solution during four separate time intervals. Measurements of root volume, root diameter, shoot Mg concentration, and shoot K/(Mg + Ca) ratio were made six weeks after clonal material was transplanted in nutrient solution. Heritability estimates for root volume, root diameter, shoot Mg concentration, and shoot K/(Mg …


A Review Of The Agronomic Characteristics Of Endophyte-Free And Endophyte-Infected Tall Fescue, Jeffrey F. Pedersen, G. D. Lacefield, D. M. Ball Jan 1990

A Review Of The Agronomic Characteristics Of Endophyte-Free And Endophyte-Infected Tall Fescue, Jeffrey F. Pedersen, G. D. Lacefield, D. M. Ball

Department of Agronomy and Horticulture: Faculty Publications

Agronomic differences between endophyte- (Acremonium coenophialum Morgan Jones and Gams) free and endophyte-infected tall fescue (Festuca arundinacea Schreb.) exist, and should be considered when implementing a management strategy. Although dry matter yield of tall fescue does not generally appear to be influenced by endophyte infection status, endophyte infection has been shown to improve seedling performance and survival, is associated with insect and nematode resistance, drought resistance, improved nitrogen assimilation, and higher seed set. Considering all biologically valuable characters of the endophyte-tall fescue relationship, survival of endophyte-infected tall fescue is probably better than that of endophyte-free tall fescue, especially in drought- …


Fescues With Large Roots Are Drought Tolerant, H. A. Torbert, J. H. Edwards, Jeffrey F. Pedersen Jan 1990

Fescues With Large Roots Are Drought Tolerant, H. A. Torbert, J. H. Edwards, Jeffrey F. Pedersen

Department of Agronomy and Horticulture: Faculty Publications

Consideration of root/soil interactions is essential in, adapting tall fescue (Festuca arundinacea Schreb.) to soil and climatic conditions of the Coastal Plain region of the southeast. Sandy soils of the region are very susceptible to the formation of hardpans. These compacted layers often restrict plant root development to the plow layer (0 to 6 in.) and prevent plant roots from reaching available moisture and nutrients in the subsoil horizons. Plants grown under these conditions are shallow rooted and will be subjected to water stress up to 50% of the time during the growing season. Although implements are available to penetrate …


Noteworthy Collections: Virginia, W. John Hayden Sep 1989

Noteworthy Collections: Virginia, W. John Hayden

Biology Faculty Publications

The above collections represent the second record for the state of Virginia, and may well establish the northernmost station for the species in the eastern United States. According to B.L. Lipscomb (Sida 8:320-327. 1980), this Old World weed is spreading throughout the warmer regions of North America. The only previous record of the species from the state is a Fernald specimen from Owl Creek in Virginia Beach. R.W. Tyndall, who found the species in northeastern North Carolina, was unable in 1978 to locate the plant at Fernald's Virginia Beach locality (Castanea 48:277-280. 1983). The Amelia County plants occur in two …


Flora Of Richmond National Battlefield Park, Virginia, W. John Hayden, Melanie Lynn Haskins, Miles F. Johnson, James M. Gardner Jun 1989

Flora Of Richmond National Battlefield Park, Virginia, W. John Hayden, Melanie Lynn Haskins, Miles F. Johnson, James M. Gardner

Biology Faculty Publications

An inventory of the vascular flora of nine of eleven units of Richmond National Battlefield Park was compiled from 1985 to 1987. Each site was visited during the growing season in two to four week intervals; plant species were identified and recorded in the field and/or collected for later study. A total of 761 different species were identified in the surveyed units, and 2487 individual records of species per particular park unit were noted. Twenty-three percent of the flora consists of exotic species, largely from Eurasia. Voucher specimens are housed in the herbaria of the University of Richmond and Virginia …


Tissue Culture In Rice (Oryza Sativa L. Subsp. Japonica Var. Lemont), Young M. Woo Jan 1989

Tissue Culture In Rice (Oryza Sativa L. Subsp. Japonica Var. Lemont), Young M. Woo

Masters Theses

The purpose of this study was to obtain callus induction and subsequent plantlet regeneration from various explants of rice (Oryza sativa L. subsp. japonica var. Lemont). Callus induction occurred from the somatic cells of ovary wall, immature and mature embryos, immature endosperm, stem nodes, and seedlings. Plantlets were regenerated from embryo-, endosperm-, and stem node-derived calli on differentiation media. Stem nodes were the most responsive to callus induction. Requirements for optimal callus formation and plantlet regeneration differed from each culture. The study investigated the effects of cold treatment of explants, initial culture in darkness, media, and subculture for individual explant …


Concetta Tm (Papconc) C.V. (Rose Plant), Ellen T. Paparozzi Jan 1989

Concetta Tm (Papconc) C.V. (Rose Plant), Ellen T. Paparozzi

Department of Agronomy and Horticulture: Faculty Publications

A new and distinct variety of rose plant of the hybrid tea rose class, which was originated as a sport of the rose Gabriella; characterized by its bright orange red, well-formed hybrid tea type blooms with dark velvet overtones on the outer edges of the open flower; disease resistant with everblooming habit and outstanding pot forcing characteristics.


Ontogeny Of The Cotyledonary Region Of Chamaesyce Maculata (Euphorbiaceae), W. John Hayden Nov 1988

Ontogeny Of The Cotyledonary Region Of Chamaesyce Maculata (Euphorbiaceae), W. John Hayden

Biology Faculty Publications

Development of the cotyledonary region in Chamaesyce maculata is described from germination of the seed through formation of the dense mat of branches which characterize this common weed. The cotyledonary node is trilacunar with split-lateral traces. Epicotyl development is limited to a pair ofleaves ("V-leaves") inserted directly above and decussate to the cotyledons. The two V-leaves are also vascularized by three traces and insertion of these traces relative to the vasculature at the immediately subjacent cotyledonary node is asymmetrical; four of the six V-leaf traces arise on one side of the intercotyledonary plane and two arise on the opposite side. …


Considerations In Breeding Endophyte-Free Tall Fescue Forage Cultivars, Jeffrey F. Pedersen, D. A. Sleper Jan 1988

Considerations In Breeding Endophyte-Free Tall Fescue Forage Cultivars, Jeffrey F. Pedersen, D. A. Sleper

Department of Agronomy and Horticulture: Faculty Publications

Breeding tall fescue (Festuca arundinacea Schreb.) cultivars that are free of the endophytic fungus Acremonium coenophialum Morgan-Jones and Gams [previously identified and referred to as Epichloe typhina (Fries) Tulasne] is necessary to improve animal performance. The techniques used in developing new cultivars are not greatly different from those used previously, with one exception. Prior to the evaluation of new tall fescue lines or populations, the endophyte needs to be eliminated from the seed or the plants. Several techniques utilizing aging, heat, or chemical treatment are being used to effectively accomplish this in the seed. Methods for permanently eliminating the endophyte …


Levels And Timing Of Nitrogen Fertilizer Applications For Tall Fescue In Central Alabama, J. W. Odom, Jeffrey F. Pedersen Jan 1988

Levels And Timing Of Nitrogen Fertilizer Applications For Tall Fescue In Central Alabama, J. W. Odom, Jeffrey F. Pedersen

Department of Agronomy and Horticulture: Faculty Publications

Tall fescue (Festuca arundinacea Schreb.), the most important cool season perennial pasture grass in the United States, is generally well adapted to the northern two-thirds of Alabama. Unfortunately, the most commonly grown tall fescue cultivar, Kentucky 31, is of northern origin and is dormant during the winter. To reduce this problem, AU Triumph was selected from Mediterranean germplasm. The Alabama Agricultural Experiment Station released this cultivar to growers in 1981. Compared to Kentucky 31, AU Triumph produces about 80 percent more forage during the winter and produces mature seed about 2 weeks earlier in the spring. Total annual forage production …


The Identity Of The Genus Neowawraea (Euphorbiaceae), W. John Hayden Apr 1987

The Identity Of The Genus Neowawraea (Euphorbiaceae), W. John Hayden

Biology Faculty Publications

On the basis of newly acquired morphological evidence gathered in the course of floristic studies, the monotypic genus Neowawraea Rock is now recognized as a species of Flueggea Willd. and is renamed F. neowawraea W. J. Hayden. Taxonomic documentation presented for F. neowawraea includes an expanded morphological description, a map showing its widely scattered distribution in the Hawaiian Islands to which the species is endemic, and discussions of type specimens, common names, and its extreme rarity. The combination of flowers in pedicellate axillary clusters, the lobed staminate disk, pistillode, extrorse anthers, hemitropous ovules, and, especially, the smoothish dry seeds with …


Anatomy And Affinities Of Penthorum, Melanie Lynn Haskins, W. John Hayden Feb 1987

Anatomy And Affinities Of Penthorum, Melanie Lynn Haskins, W. John Hayden

Biology Faculty Publications

The genus Penthorum L. consists of two species of perennial herbs, P. sedoides of eastern North America and P. chinense of eastern Asia. Penthorum has long been considered intermediate between Crassulaceae and Saxifragaceae. An anatomical study of both species was undertaken to contribute to a better understanding of the relationships of these plants. Prominent anatomical features of Penthorum include: an aerenchymatous cortex and closely-spaced collateral vascular bundles of stems; one-trace unilacunar nodes; brochidodromous venation, rosoid teeth bearing hydathodes, and anomocytic stomata of leaves; angular vessel elements with many-barred scalariform perforation plates and alternate to scattered intervascular pits; thin-walled nonseptate fiber-tracheids; …


Evaluation Of Repellent Seed Treatments And Effects On Early Corn Performance, Ann E. Koehler, Ron J. Johnson, Orvin C. Burnside, Stephen R. Lowry Jan 1987

Evaluation Of Repellent Seed Treatments And Effects On Early Corn Performance, Ann E. Koehler, Ron J. Johnson, Orvin C. Burnside, Stephen R. Lowry

Department of Agronomy and Horticulture: Faculty Publications

A combination of field, field enclosure, and germination chamber studies was used to evaluate the effects of methiocarb [3,5-dimethyl-4-(methylthio)phenol methylcarbamate] and thiram (tetramethylthiuram disulfide) repellent seed treatments on early corn performance. The thiram treatments used (0.08, 0.4,0.8,0.5,1.25, and 2.5% active ingredient by corn seed weight) had negligible effects on germination/emergence time or on com plant heights. The thiram treatments never reduced stand counts in comparison to controls, but apparently increased stand counts in some trials, particularly under wet conditions. The methiocarb treatments evaluated (0.5, 1.25, 2.5, and 5.0% active ingredient by corn seed weight) had only occasional effects on early …


The Effect Of Pre-Sterile Medium Ph Photoperiod And N6-(2-Isopentenyl)-Adenine (2ip) On Shoot Production During Stage Ii Micropropagation Of Rhododendrons, Lori Longo Smith Oct 1986

The Effect Of Pre-Sterile Medium Ph Photoperiod And N6-(2-Isopentenyl)-Adenine (2ip) On Shoot Production During Stage Ii Micropropagation Of Rhododendrons, Lori Longo Smith

Biological Sciences Theses & Dissertations

The number of shoots produced during a six week subculture of two Rhododendron sp., cultivars Rocket and Gibraltar was the same for both 16 and 24 hour photoperiods under cool white fluorescent lights, whereas significantly fewer shoots were produced under a 10 hour photoperiod for ‘Rocket.' Increasing concentrations of N6- (2-isopentenyl)- adenine (2iP) from 0 to 32 μMin Anderson's medium resulted in proportional increases in shoot number. When shoots were cultured in the presence of indole-3-acetic acid (IAA) and 2iP, shoot multiplication was increased significantly over shoots cultured with 2iF alone. No interaction affecting shoot multiplication was …


Organic Matter Budgets And Models For Four Plant Communities In The Great Dismal Swamp, J. Patrick Megonigal Apr 1986

Organic Matter Budgets And Models For Four Plant Communities In The Great Dismal Swamp, J. Patrick Megonigal

Biological Sciences Theses & Dissertations

Budgets and models of organic matter dynamics were developed for one mesic and three seasonally flooded plant communities in the Dismal Swamp. Components included aboveground parts, belowground parts, litter and soil organic matter (SOM).

Net primary- production was significantly greater on them flooded sites. Comparisons show that the Dismal Swamp is highly productive despite relatively low nutrient inputs.

Budget calculations showed that over 65% of the total input to SOM comes from roots. Leaves contributed about 70% of the aboveground inputs.

The model predicted that species composition, aboveground biomass and turnover rates on the cedar site will become quite similar …


Nebraska Plant Distribution, David M. Sutherland, Robert B. Kaul Jan 1986

Nebraska Plant Distribution, David M. Sutherland, Robert B. Kaul

Biology Faculty Publications

Distribution notes based on recent collections and herbarium work are provided for 46 Nebraska plant taxa, including 43 flowering plants, two ferns, and one liverwort. The list includes several plants that are new to the State and provides range extensions within the State for many others. Several previously- published distribution records believed to be erroneous are also discussed.


Growth And Magnesium Uptake Of Tall Fescue Lines At High And Low Potassium Levels, J. H. Edwards, Jeffrey F. Pedersen Jan 1986

Growth And Magnesium Uptake Of Tall Fescue Lines At High And Low Potassium Levels, J. H. Edwards, Jeffrey F. Pedersen

Department of Agronomy and Horticulture: Faculty Publications

Five tall fescue (Festuca arundinacea Schreb.) clonal lines with diverse root and xylem diameters were grown in nutrient solutions with magnesium (Mg) concentrations of 42, 125 and 250 µm and potassium K concentrations of 133 and 333 µm. Leaf Mg concentrations increased with increasing Mg rates at both low and high K concentrations. The tall fescue line with the largest root and xylem diameters had low leaf Mg concentrations, indicating a possible increased Mg tetany potential when consumed by cattle. The response of the K/(Mg+Ca) ratio in the plant, an indicator of tetany potential, to varying solution Mg at low …


Eryngium Prostratum In Central Virginia, W. John Hayden Dec 1985

Eryngium Prostratum In Central Virginia, W. John Hayden

Biology Faculty Publications

While visiting Pocahontas State Park in Chesterfield County, Virginia during the fall of 1984, an unfamiliar blue-flowered plant was observed growing near the upper reaches of Swift Creek Lake. This proved to be Eryngium prostratum Nuttall ex DC., a species common near bodies of water in the southeast U.S. While several standard floras include Virginia in the distribution of this plant (Fernald 1950, Gleason 1952, Gleason & Cronquist 1963, Radford et al 1968, Godfrey & Wooten 1981), the only counties for which it is recorded in Harvill et al (1981) are along the extreme southern border of the state, i.e., …


Extrafloral Nectaries On Plants In Communities Without Ants: Hawaii, Kathleen H. Keeler Jan 1985

Extrafloral Nectaries On Plants In Communities Without Ants: Hawaii, Kathleen H. Keeler

School of Biological Sciences: Faculty Publications

Since the Hawaiian Islands lack native ants, it was hypothesized that extrafloral nectaries, an ant-related mutualistic trait, should be lacking on native species. Presence of extrafloral nectaries (EFNs) on plants was determined by direct observation and related to vegetation structure and floral composition. Frequency of plants with EFNs was low by all possible comparisons. However, several endemic species had functional EFNs. The hypotheses to explain these anomalies are (1) phylogenetic inertia or (2) mutualism with some other organism than ants.


Benthic Diatom Community Dynamics In The Colorado River: Interactive Effects Of Periodic Dessication And Current Regime, Christopher Gerard Peterson Dec 1984

Benthic Diatom Community Dynamics In The Colorado River: Interactive Effects Of Periodic Dessication And Current Regime, Christopher Gerard Peterson

Publications (WR)

The response to periodic desiccation of periphyton communities developed in eddy environments or in areas exposed to variable, direct current was examined. Algal communities were incubated on clay tiles for between 2 and 12 weeks in the Colorado River, directly below Hoover Dam from October, 1983 - January, 1984. Mean daily discharge from the dam decreased over this period. To assess the influence of these discharge changes on community dynamics, samples collected over the first 12 weeks of the investigation were compared to samples of the same age collected over the final 8 weeks.

The small diatom taxon Achnahthes spp …