Yr Of Growth Research Articles

Characterization and Flowering Behavior of Eleven Philippine Native Phalaenopsis Species and Gamma Irradiation Effects on Phalaenopsis aphrodite

Eleven species of Phalaenopsis or butterfly orchids collected from different places in the country were characterized for flower traits, leaf characters, growth habit, and capsule maturity, length, and width; evaluated for flowering behavior; and tested for self-compatibility and capsule setting under ambient conditions in Los Baños, Laguna, Philippines. Also, Phalaenopsis aphrodite was used for mutation breeding via gamma irradiation. Subjecting self-fertilized progenies to irradiation will generate mutants with potential for breeding and selection. The eleven Phalaenopsis species studied flowered consistently under ambient conditions for two years with degrees of self-compatibility and capsule setting varying from 3.8 to 50%. P. aphrodite and P. hieroglyphica embryos cultured in vitro germinated successfully at 80–90% within 3–4 wk after explanting. Germinating embryos of P. aphrodite subjected to different levels of gamma irradiation at 10, 15, 20, and 25 Gy responded differently to the treatments. The number of complete regenerants, and those regenerants with shoot only, also differed significantly among the treatments. In addition, leaf length, width, and thickness differed significantly among the treatments after 2 yr of growth. Early flowering was observed in two plants of P. aphrodite irradiated using 15 Gy. Normally, tissue culture-derived P. aphrodite seedlings flower 3 yr after potting out, but one plant flowered at 1 yr and 8 mo while the other did at 2 yr after potting out.

Thirty-year history of Irish (Rossmore) Ostrea edulis selectively bred for disease resistance to Bonamia ostreae.

The protistan pathogen Bonamia ostreae was first detected in Ostrea edulis at Rossmore, Cork Harbour, on the south coast of Ireland in 1987. A selective breeding programme commenced in 1988 by Atlantic Shellfish Ltd. to produce B. ostreae-resistant oysters using 3 to 4 yr old survivors as broodstock for controlled spawning in land-based spatting ponds. On-growing of oyster spat settled on mussel cultch was carried out on designated beds within Cork Harbour. Oyster production subsequently increased successfully, resulting in 3 yr old Rossmore O. edulis being marketed from 1993 onwards and a record tonnage of 4 yr old oysters being produced in 1995 and 1996. O. edulis production, B. ostreae prevalence and oyster mortalities have been monitored and recorded at Rossmore for over 30 yr. The collation and analysis of this data from 52 samples and 3190 oysters demonstrate the introduction and progression of bonamiosis and subsequent interventions to ameliorate disease effects during this period at Rossmore. Results suggest that O. edulis mortalities are now negligible during the first 4 yr of growth, prevalence of B. ostreae infection is low, and no correlation exists between prevalence of infection and oyster mortalities. This study, when compared to other studies of bonamiosis-infected oyster populations, suggests that an intervention in the form of a selective breeding programme is required to reduce the impact of the disease.

Anticholinesterase and mutagenic evaluation of in vitro-regenerated Agapanthus praecox grown ex vitro

Beyond establishing micropropagation protocols for medicinal plants, it is important that the efficacy and safety of propagated plants be ascertained for these plants to be accepted for use in traditional medicine. The use of propagated plants could alleviate/reduce over-exploitation of wild populations. The present study evaluated the anticholinesterase and mutagenic properties of 1-yr-old tissue culture-derived Agapanthus praecox grown ex vitro and naturally grown mother plants. The tissue culture-derived plants were regenerated using different plant growth regulators. A dose-dependent inhibition of acetylcholinesterase (AChE) enzyme was observed in all the tissue culture-derived and naturally grown mother plants. The leaf extract of tissue culture-derived plants regenerated with a combination of benzyladenine (BA) and thidiazuron (TDZ) demonstrated a significantly low AChE-inhibitory activity. Conversely, the root extract of plants regenerated with BA alone demonstrated the highest AChE-inhibition activity (IC50 = 0.20 mg/mL) when compared to extracts from other treatments and the naturally grown mother plants. None of the samples were found to be mutagenic in the absence of metabolic activation. The present study indicated that regenerated plants could be used as potent substitutes for naturally grown plants in traditional medicine. However, the choice of treatment used during micropropagation operation may significantly influence the therapeutic potential of regenerated plants, even after 1 yr of growth.

Interactions in tropical reforestation – how plant defence and polycultures can reduce growth‐limiting herbivory

AbstractQuestionsCan the growth of saplings be improved by limiting herbivory during reforestation? Can chemical ecology and diverse planting designs be applied to decrease herbivory in tropical reforestation?LocationReforestation plantings in Heredia, Costa Rica.MethodsThis study directly evaluates the effects of herbivory on seedling growth and the role of two putative plant defences, saponins and leaf toughness, in limiting herbivory in reforestation. Four planting treatments were studied in a replicated block design in cattle pastures in Costa Rica: (1) a monoculture of a fast‐growing species low in saponins (Dipteryx panamensis); (2) a monoculture of a slower‐growing, saponin‐rich species (Cojoba arborea); (3) a polyculture consisting of half D. panamensis and half three other defended species; and (4) a polyculture of half C. arborea and half the same other defended species. Growth and herbivory were measured every 6 mo during the first 2 yr of plot development and again after 5 yr of growth.ResultsDipteryx panamensis was the fastest‐growing species, and individuals planted in polycultures grew faster in terms of height than individuals in monoculture. Herbivory was negatively related to sapling growth, and damage during the first 6 mo of plot establishment decreased growth even after 5 yr. Patterns of herbivory varied through time, resulting in changes in the importance of plant defences. For example, leaf toughness, which is an effective defence against many herbivores, was negatively related to herbivory at multiple time periods. In contrast, saponins were not a deterrent to all herbivores, so they were not consistently effective as a defence; however saponins were negatively related to Atta cephalotes (leaf‐cutter ant) damage. Saponins are therefore a promising defence against leaf‐cutter ants but not against all herbivores.ConclusionsPlant–insect interactions influence reforestation through growth‐limiting herbivore pressure on seedlings, and this herbivory is likely facilitated by reforestation methods that favour monocultures of fast‐growing species that lack strong antiherbivore defences. This study demonstrates the potential for reducing herbivory and improving sapling growth by reforesting with polycultures of fast‐growing and well‐defended species.

Early Permian seasonality from bivalve δ18O and implications for the oxygen isotopic composition of seawater

Research Article| November 01, 2010 Early Permian seasonality from bivalve δ18O and implications for the oxygen isotopic composition of seawater L.C. Ivany; L.C. Ivany * 1Department of Earth Sciences, Syracuse University, Syracuse, New York 13244-1070, USA *E-mail: lcivany@syr.edu. Search for other works by this author on: GSW Google Scholar B. Runnegar B. Runnegar 2Department of Earth and Space Sciences, and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, California 90094-1567, USA Search for other works by this author on: GSW Google Scholar Author and Article Information L.C. Ivany * 1Department of Earth Sciences, Syracuse University, Syracuse, New York 13244-1070, USA B. Runnegar 2Department of Earth and Space Sciences, and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, California 90094-1567, USA *E-mail: lcivany@syr.edu. Publisher: Geological Society of America Received: 24 Apr 2010 Revision Received: 20 Jun 2010 Accepted: 22 Jun 2010 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2010 Geological Society of America Geology (2010) 38 (11): 1027–1030. https://doi.org/10.1130/G31330.1 Article history Received: 24 Apr 2010 Revision Received: 20 Jun 2010 Accepted: 22 Jun 2010 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation L.C. Ivany, B. Runnegar; Early Permian seasonality from bivalve δ18O and implications for the oxygen isotopic composition of seawater. Geology 2010;; 38 (11): 1027–1030. doi: https://doi.org/10.1130/G31330.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Oxygen isotope values of sequentially microsampled accretionary carbonate from the thick-shelled calcitic bivalve Eurydesma from the Early Permian of southeastern Australia vary seasonally over 6 yr of growth. Paleotemperature constraints derived from coeval glendonite and ice-rafted clasts, in combination with published biome data, indicate near-freezing winter conditions. However, paleotemperatures calculated from oxygen isotope data are too warm unless the δ18O value of seawater approached −4‰. Associated stenohaline brachiopods and lack of covariance with δ13C argue against significantly reduced salinity, and published δ18O data from across Australia suggest that conditions recorded by this bivalve were typical of the Gondwanan high latitudes. The negative δ18O value of seawater implied by these data reflects in part the expected meridional gradient in marine seawater composition related to latitudinal variation in evaporation and precipitation in Permian oceans, but is also consistent with previous suggestions of a secular increase in the oxygen isotopic composition of ocean water through the Phanerozoic. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Winning the Battle Against Childhood Physical Inactivity: The Key to Bone Strength?

Winning the Battle Against Childhood Physical Inactivity: The Key to Bone Strength?

Cloning of Russian sturgeon (Acipenser gueldenstaedtii) growth hormone and insulin-like growth factor I and their expression in male and female fish during the first period of growth

In this study, the GH and IGF-I of the Russian sturgeon (rs), Acipenser gueldenstaedtii, were cloned and sequenced, and their mRNA gene expression determined. In addition, to improve our understanding of the GH function, the expression of this hormone was assessed in young males and females. Moreover, IGF-I expression was quantified in young males and compared to that in older ones. The nucleotide sequence of the rsGH cDNA was 980 bp long and had an open reading frame of 642 bp, beginning with the first ATG codon at position 39 and ending with the stop codon at position 683. A putative polyadenylation signal, AATAAA, was recognized 42 bp upstream of the poly (A) tail. The position of the signal- peptide cleavage site was predicted to be at position 111, yielding a signal peptide of 24 amino-acids (aa) and a mature peptide of 190 aa. When the rsGH aa sequence was compared with other species, the highest degree of identity was found to be with mammalians (66-70% identity), followed by anguilliformes and amphibia (61%) and other fish (39-47%). The level of rsGH mRNA was discovered to be similar in pituitaries of females and males of 5 age groups (1, 2, 3, 4, and 5- yr-old). In females and males, the levels did not change dramatically during the first 5 yr of growth. The partial nucleotide sequence of the rsIGF-I was 445 bp long and had an open reading frame of 396 bp, beginning with the ATG codon at position 50. The position of the signal-peptide cleavage site was predicted to be at position 187, yielding a signal peptide of 44 aa. The highest level of IGF-I mRNA expression was recorded in the kidney of adult sturgeons. The IGF-I mRNA expression levels in the intestine, pituitary gland, and liver were not significantly different. Low levels of expression were found in the brain, heart, and muscle. In most tissues, there was no significant difference between mRNA levels of one and 5-yr-old fish. In conclusion, based on the GH-sequence analysis, A. gueldenstaedtii is genetically distant from other teleosts. The expression of the GH mRNA was similar in males and females, and its level remained constant during the first 5 yr of growth. While the IGF-I mRNA expression differed amongst various tissues, the level in each tissue was similar in 1 and 5-yr-old fish.

Stable genetic transformation of embryogenic cultures of Abies nordmanniana (nordmann fir) and regeneration of transgenic plants

Stable genetic transformation of embryogenic cultures of Abies nordmanniana (Nordmann fir or Caucasian fir) was achieved using the Biolistic® transformation technology, followed by regeneration of transgenic plants. Selection of the transgenic tissue was based on the antibiotic resistance induced by the neomycin phosphotransferase II gene (npt II), in combination with the antibiotic geneticin. Six transclones were recovered from a total of 215 bombardments. Expression of the β-glucuronidase gene (uidA) was confirmed by histochemical analysis, and expression of npt II was verified by quantification of NPTII protein by enzyme linked immunosorbent assay (ELISA). Both genes were still expressed in the embryogenic tissue after 5 yr of in vitro culture and in mature somatic embryos and plants produced from these cultures. The integration of npt II was confirmed by Southern hybridization in embryogenic tissue after 5 yr of culture. After 5 yr of growth, uidA was still expressed in needles from the transformed trees.

Formation of embryogenic callus in hairy roots of pumpkin (Cucurbita pepo L.)

Excised cotyledons from 8-d-old pumpkin (Cucurbita pepo L.) seedlings were inoculated with Agrobacterium rhizogenes and cultured on hormone-free Murashige and Skoog medium. At the site of inoculation, transformed hairy roots were successfully induced by using wild strains 8196 (mannopine-type) and 15834 (agropine-type). After a subsequent transfer on a solid MS medium without hormones, roots obtained by transformation with strain 15834 failed to form stable hairy root cultures, while several hairy root lines were established with strain 8196. Three hairy root lines, Cp1, Cp2, and Cp31, have spontaneously generated callus with embryo-like structures after more than 3 yr of growth on the solid medium. The callus proliferation was more frequent when the autoclaving of nutrient medium, pH 5.7, was prolonged to 30 min. Separated calluses continued to proliferate and generated embryos with abnormal morphology. The combination of indole-3-acetic acid and benzyladenine had a favorable influence on embryogenesis and organogenesis in the Cp31 callus line. The Southern analysis of Cp31 root and embryo DNA confirmed the presence of the T-DNA of Agrobacterium rhizogenes.

Response of Densely Stocked Loblolly Pine (Pinus taeda L.) to Applied Nitrogen and Phosphorus

Abstract Forest productivity may be enhanced by satisfying the nutrient requirement of trees through fertilization. A field experiment was designed to study the response of densely stocked 1-yr-old loblolly pine to nitrogen and phosphorus in the presence of applied K on a Beauregard silt loam soil (fine-silty, siliceous, thermic Plinthaquic Paleudults) of the Gulf Coastal Plain. The continuous function design with three replications was used. Fertilizer P rate was based on the P adsorption characteristics of the soil. After 1 yr of growth, the response variables: height; total aboveground dry matter; foliage and wood dry matter; diameter at ground level; and N, P, and K contents were related to the rate of N and P applied by quadratic models with response surface methodology. The lack-of-fit test showed that the quadratic model was adequate in explaining the relationship between N and P applied and all the response variables except height. Fertilization with N alone on this soil had a depressing effect on yield. Growth and nutrient uptake were enhanced when both N and P were applied. The predicted N and P levels that would give maximum growth were beyond the rates of N and P tested, indicating that more time should be given to observe the full response. South. J. Appl. For. 27(3):180–189.

Ponderosa Pine and Lodgepole Pine Growth Response to One-Time Application of Herbicide During Seedling Establishment in Western Montana

Abstract This study examined long-term diameter and height response of ponderosa pine (Pinus ponderosa) and lodgepole pine (Pinus contorta var. latifolia) to a one-time application of herbicide during seedling establishment in western Montana. Two herbicide trials initiated in 1981 and 1983 by Champion International Corporation were resurrected during the summer of 1997. Analysis of variance (ANOVA) F-tests along with Duncan's Multiple Range tests (DMR) were performed on mean tree dbh, tree height, and competing vegetation percent cover estimates. In addition, a graphical analysis of mean annual height growth over time was performed. Significant increases (alpha = 0.05) in ponderosa pine dbh (25 to 44%) and height (11 to 28%) were found after 16 yr of growth on Velpar L. (hexazinone) treated plots, while lodgepole pine had significant increases in dbh (70 to 118%) and height (41 to 82%) after 15 yr of growth on Velpar L. treated plots. Graphical analyses indicated a positive height growth effect for a period of 11 to 13 yr following treatment for ponderosa pine; however, total height gains had decreased in recent years. Positive increases in height growth for lodgepole pine were continuing after 15 yr of growth. These results indicate that a one-time application of herbicide applied during seedling establishment will promote faster tree growth in western Montana. We also note that proper density management will be necessary early in the life of the stand to maintain height gains. West. J. Appl. For. 18(3):149–154.

Impact of Pruning Eastern Redcedar (Juniperus virginiana)

Abstract In recent years, eastern redcedar has been the most rapidly expanding tree resource in the Great Plains from Oklahoma to South Dakota, primarily in rangelands and pastures. Based on these increases and potential management-related problems, eastern redcedar is perceived as a threat to the rangeland resource. Pruning eastern redcedar can allow for increased herbaceous growth under the eastern redcedar's crown, improve livestock handling, maintain the species for diversity and habitat contributions, and improve wood quality for potential future utilization by forest industries. To determine the effect of pruning to different heights on tree growth, we compared unpruned trees' total height and diameter to trees pruned from ground level to heights of 60, 90, 120, and 150 cm. No significant differences in the total height were found for all pruning treatments over all time periods. After more than 10 yr, trees pruned to 60, 90, and 120 cm had smaller diameters at ground level than unpruned trees. There were no differences in ground diameters for trees pruned to 150 cm compared to unpruned trees after 4 yr of growth. There were no significant differences in dbh for eastern redcedar trees pruned to all heights. Management of eastern redcedar, including pruning, is recommended as an alternative to control measures. West. J. Appl. For. 17(4):189–193.

Below-ground carbon input to soil is controlled by nutrient availability and fine root dynamics in loblolly pine.

• Availability of growth limiting resources may alter root dynamics in forest ecosystems, possibly affecting the land-atmosphere exchange of carbon. This was evaluated for a commercially important southern timber species by installing a factorial experiment of fertilization and irrigation treatments in an 8-yr-old loblolly pine (Pinus taeda) plantation. • After 3yr of growth, production and turnover of fine, coarse and mycorrhizal root length was observed using minirhizotrons, and compared with stem growth and foliage development. • Fertilization increased net production of fine roots and mycorrhizal roots, but did not affect coarse roots. Fine roots had average lifespans of 166d, coarse roots 294d and mycorrhizal roots 507d. Foliage growth rate peaked in late spring and declined over the remainder of the growing season, whereas fine roots experienced multiple growth flushes in the spring, summer and fall. • We conclude that increased nutrient availability might increase carbon input to soils through enhanced fine root turnover. However, this will depend on the extent to which mycorrhizal root formation is affected, as these mycorrhizal roots have much longer average lifespans than fine and coarse roots.

Inbreeding, outbreeding, and heterosis in the yellow pitcher plant,Sarracenia flava(Sarraceniaceae), in Virginia

The yellow pitcher plant, Sarracenia flava, is an insectivorous plant restricted to fire-maintained wetland ecosystems in southeastern Virginia. Only four natural sites remain in the state totaling fewer than 100 clumps. Plants from sites located in Dinwiddie, Greensville, Prince George, Sussex counties, and the city of Suffolk were tested for the effects of self-pollination, intrasite outcrossing, and intersite outcrossing on offspring quantity (total seed number and total seed mass) and offspring quality (avarage seed mass, germination, and growth).Self-pollination resulted in significantly lower offspring quantity and quality. Total seed number and total seed mass for self-pollinated capsules were approximately one-fourth that of outcrossed capsules. Germination, survivorship, and growth over 5 yr were also significantly lower for offspring from self-pollinated capsules. Together, these results suggest strong inbreeding depression in this species.Relative to offspring from intrasite crosses, offspring from intersite crosses were significantly larger after 5 yr of growth. This suggests that restoration efforts for Virginia S. flava will be most successful when plants from multiple sites are used.

Radiocesium Uptake by One‐Year‐Old Willows Planted as Short Rotation Coppice

AbstractHigh radioactivity concentrations in foodcrops grown in areas contaminated by the Chernobyl accident continue to justify the consideration of a change in land use. Production of biofuel may be one of the alternatives to food production. However, present knowledge about radionuclide cycling in such systems is limited. In the present study, radiocesium uptake and distribution were measured in a willow (Salix viminalis L. var. Orm) short rotation coppice (SRC) stand. This system allows production of energy from the harvested biomass. Experimental plots were established on two soil types of contrasting texture (loamy versus sandy), and contaminated with 8 × 106 Bq 134Cs m−2. Concentrations of 134Cs were measured in wood, litter, roots, and cuttings after 1 yr of growth. At the end of the growing season, only 0.0012% (loamy soil) and 0.0065% (sandy soil) of the initial radiocesium was transferred to the plant biomass (including belowground plant parts). Stem wood contained the lowest concentration of 134Cs among all plant parts analyzed. Wood radiocesium concentrations were 82 Bq kg−1 for the loamy soil and 192 Bq kg−1 for the sandy soil. These values are well below the exemption limit for fuel wood put forward in the Commonwealth of Independent States (CIS) (740 Bq kg−1). Even at this high soil contamination level, radiocesium concentrations in wood do not exceed appreciably the naturally occuring 40K content in the wood (135 Bq kg−1).

Frequency of somaclonal variation in plants of black spruce (Picea mariana, Pinaceae) and white spruce (P. glauca, Pinaceae) derived from somatic embryogenesis and identification of some factors involved in genetic instability

Plants of black spruce (Picea mariana, N = 7047 individuals) and white spruce (P. glauca, N = 3995 individuals) were regenerated from a total of 87 clones over a 5-yr period by somatic embryogenesis to study factors that might be associated with the appearance of variant phenotypes. Morphological evaluation of the plants showed several types of variation. These variations were grouped into nine types: dwarfism (type A), reduced height with various form anomalies (types B, C, and D), needle fasciation (type E), abnormality in tree architecture (type F), variegata phenotype (type G), and plants with an overall regular morphology but smaller than normal plants (type H). Plagiotropic plants were also observed (type I). Each plant from types A to H (except type C where no plants survived more than 6 mo) had retained its phenotype over 4-5 yr of growth. Some of the variant types could be related to chromosomic instability: chromosome counts showed aneuploid cells for type-A and type-D plants. The type I (plagiotropism) was not related to genetic instability but rather to physiological disorders. In total, spruce variants of types A-H were obtained at relatively low frequencies, i.e., 1.0% (39/3995) for white spruce and 1.6% (110/7047) for black spruce. Statistical analyses, conducted with family, clone, and time in maintenance as variables, showed that clone was the most important source of genetic instability followed by time in maintenance.

Annual and Biennial Flowering Habit of Kentucky Bluegrass Tillers

A stand of Kentucky bluegrass (Poa pratensis L.) consists of a collection of leafy tillers at various stages of development. Tiller morphology over 2 yr of growth was studied by sampling 3‐yr‐old dryland fields to determine tiller ages and to test whether burned and nonburned fields show different proportions of tiller types. Three classes of tillers were identified and named (i) small newly emerging nonleafy D tillers, (ii) leafy F tillers that grow directly from D tillers, and (6) leafy C tillers that have persisted for at least a year before flowering. On the basis of measurable floral features, C tillers are larger, more robust, can be induced sooner in the fall, and produce panicles of greater production potential than F tillers. Our results show that bluegrass tillers can be annual or biennial in flowering habit. Dense populations in burned fields produce higher proportions of D tillers in mid‐fall than non‐burned fields, but similar proportions of C and F tillers throughout the growing season. Fall regrowth may thus influence stand composition over a 2‐yr growth cycle. Assessment of tiller density should be a useful tool for grass seed growers when they are designing new management strategies, since annual F and biennial C tillers are found in all of the cultivars examined. Given pressures to avoid open‐field burning, alternative methods can be tested by determining changing proportions of C to F tillers. Manipulation of the balance between annual and biennial tillers may contribute to improving yield in the absence of open‐field burning.

Fifteen-Year Provenance Tests of Lodgepole Pine (Pinus contorta) in North Dakota

Abstract To determine the usefulness of lodgepole pine in windbreak plantings in the Northern Great Plains, seeds were collected from 25 locations in the western United States and Canada and planted at the Northern Great Plains Research Laboratory ( USDA-ARS) in Mandan, North Dakota. Survival, height, crown diameter, crown density, and Petrova damage were recorded over a 15 yr period. Once established, lodgepole pines were hardy and drought resistant, and there was no mortality after the first 6 yr. Average annual growth was 29 cm. Our results suggest that lodgepole pines may be selected for survival after 2 yr of growth in the field and selected for height after 5 yr. Seed sources from southwestern Montana, northern Idaho, and southern Canada had the best overall performance as measured by good survival, superior height, and narrow crowns. West. J. Appl. For. 13(1):5-11.

Soil Structural Form and Stability, and Organic Matter under Cool‐Season Perennial Grasses

AbstractTemperate grasses conserve soil by providing vegetative cover and by favoring soil aggregation. A field study was conducted on a Charlottetown fine sandy loam (a coarse‐loamy, mixed, frigid Typic Haplorthod) to determine the effect of cultivars of orchardgrass (Dactylis glomerata L.) and tall fescue (Festuca arundinacea Schreb.), in comparison to timothy (Phleum pratense L.), on soil structure and organic matter fractions after 4 yr of growth. Timothy is one of the main grasses grown in the cool humid climate of eastern Canada. Bulk density (1.27–1.32 Mg m−3), pore‐size distribution, and shear strength (12.5–15.6 kPa), as a measure of soil structural form, were within the optimum range for this soil type under each grass species. Dry‐aggregate mean weight diameter (MWD) was similar (3.66–4.30 mm) among grass species. Wet‐aggregate MWD was greater under tall fescue cultivars and ‘Farol’ timothy (2.81–3.22 mm) compared with the orchardgrass and ‘Champ’ timothy (2.08–2.36 mm). These differences were also reflected by the difference or ratio of MWD between dry and wet sieving. Aggregate‐size distribution indicated that wet‐aggregate MWD differences were associated with greater levels of macroaggregates (>2 mm). Differences in water‐stable aggregate stability were not related to differences in plant parameters, organic matter, or organic matter fractions (i.e., microbial biomass C, carbohydrates, and particulate organic matter). These data suggest that organic matter parameters, commonly used to characterize soil stability in cropping systems, are less useful for soils under perennial grass with stable microaggregate structures.

Ontogeny of hepatic bovine growth hormone receptors in cattle2

A series of studies examined the binding characteristics and ontogeny of hepatic growth hormone binding sites in dairy bulls on d 2, 30, 180, and 365 of age. Binding of iodinated recombinant bovine growth hormone ([125I]rbGH) to liver membrane receptors was membrane protein-dependent. Receptors were considered growth hormone-specific, because physiological concentrations of bovine prolactin (bPRL) failed to displace [125I]rbGH from bovine hepatocyte membranes. Only 50% of [125I]rbGH was bound reversibly to hepatic microsomes. Addition of dithiothreitol (DTT) to the receptor-assay buffer increased the binding of [125I]rbGH to hepatic membranes in a time-dependent manner. Moderate concentrations of Ca++ and Mg++ in the receptor-assay buffer had no detectable effects on binding of [125I]rbGH to hepatic microsomes. In growing dairy bulls, specific binding of [125I]rbGH per milligram of membrane protein increased from 1.9 +/- 1.8% at d 2 to 14.1 +/- 1.8% at d 180 and then declined to 5.2 +/- 1.6% at d 365. Likewise, concentration of insulin-like growth factor (IGF)-I in serum was low during the 1st mo of age (d 2, 13.3 +/- 8.8 ng/ml; d 30, 9.7 +/- 8.8 ng/ml), but it became maximal at d 180 (151.0 +/- 8.8 ng/ml). Circulating concentrations of IGF-II increased linearly during the 1st yr of growth. Serum concentrations of GH, triiodothyronine, and thyroxine declined from 39.9 +/- 6.5, 2.7 +/- .2, and 75.4 +/- 4.6 ng/ml at d 2 to 16.5 +/- 6.5, 1.3 +/- .2, and 53.4 +/- 4.6 ng/ml at d 30, respectively, and remained low through 1 yr of age. Insulin concentration in serum did not change significantly with development. Results indicated that increasing concentrations of specific bGH receptors in the bovine liver may play a key role in regulating postnatal growth in cattle.