Levels Of Nutrient Availability Research Articles

Nucleic acid synthesis in oceanic microplankton from the drake passage, antarctica: Evaluation of steady-state growth

Differential uptake of [3H]adenine and [3H]thymidine, and incorporation of tritium label into proteins, RNA and DNA as a function of depth, indicate that surface microplankton incorporated most of the assimilated radioisotopes into nucleic acids. Growth processes for deep-sea microplankton were shifted towards higher rates of [3H]-adenine incorporation into RNA compared to rates of thymidine incorporation into DNA. Deep-sea microplankton also diverted a larger portion (up to 80%) of the assimilated tritium into biosynthetic pathways for amino acid and eventual incorporation into proteins. These results imply that protein synthesis is vital for deep-sea microplankton where populations may be stressed by low levels of available nutrients. The rates at which microplankton incorporated [3H]adenine into RNA and DNA, and [3H]thymidine into DNA, suggest that oceanic microplankton are in a transient state of balanced growth, i.e. between two steady-state growth conditions, irrespective of potential growth rates. Our results support the hypothesis that oceanic microplankton are in various growth states.

Variables Affecting Ultrasound Repellency in Philippine Rats

Three ultrasonic devices (20, 20-30, and 40 kHz) were tested for effectiveness in repelling Philippine rats (Rattus rattus mindanensis) under 3 sets of test conditions (i.e., plentiful vs. restricted food supply, native vs. immigrant rats, and continuous vs. discontinuous ultrasound). Food consumption was significantly reduced for all devices under the plentiful-food condition. With restricted food, only the 20-30and 40-kHz devices reduced feeding. Immigrant rats (animals preadapted to living adjacent to the ultrasound test chambers) showed a high avoidance of the new sound-chamber areas including the control (no ultrasound), making the test insensitive. Native rats (animals preadapted [confined] to the chambers before exposure to the ultrasound devices) showed significant avoidance of food in 3 test chambers containing the ultrasound devices, especially the 20-kHz unit. A 2nd repellency measure (rat photocell breaks per day) yielded a similar index of efficacy for the 3 devices. The 20-kHz device produced the lowest photocell-break activity during the native-rat condition. A 30-dB reduced-intensity trial yielded no rat activity effects for any of the devices. Efficacy of the devices was therefore highly dependent upon ultrasonic frequency, intensity, and the preexisting rodent-infestation condition. J. WILDL. MANAGE. 46(1):148-155 Since the first demonstration that rodents were capable of emitting ultrasound (Anderson 1954), many studies have indicated that ultrasonic frequencies may be used for communication in Rodentia (Sales and Pye 1974). Ultrasonic cries can be elicited in Norway rats (Rattus norvegicus) by cold stress or electric shock (Noirot 1972, Bell et al. 1974), isolation of rat pups (Allin and Banks 1972), or handling (Anderson 1954). High-frequency sounds in the range of 20-50 kilohertz (kHz) are also produced by Norway rats during courtship (Sales 1972b), after mating (Barfield and Geyer 1972), and during aggressive encounters (Sales 1972a). High-intensity sound at 120-150 decibels (dB) has been used to produce audiogenic seizures and death in both laboratory and wild Norway rats (Morgan and Gould 1941), but such sound levels may damage the human ear, and wild rats are not as susceptible as laboratory strains (Sprock et al. 1967). Although ultrasound can elicit alarm response in rats in certain situations, there is no firm evidence that ultrasound is noxious to rats. Only 1 report (Belluzzi and Grossman 1969) indicates that ultrasound may sometimes be as effective as electric shock in producing avoidance in rats. This report indicated that albino rats would reliably avoid the onset of 20-30kHz ultrasound by making an escape response in the presence of a cue light. Several commercial ultrasonic devices for repelling rats and mice have been marketed for food-storage warehouses, grain elevators, and other facilities where the use of rodenticides may be impractical. These devices are not ordinarily used in combination with lethal rodent control, but manufacturers often recommend that materials that attract rats (harborage, spilled food, and water) be removed when the units are installed. The conditions under which these devices produce their maximum effects have not been investigated. For example, we can hypothesize that food-deprived, resident rats that have been continuously 148 J. Wildl. Manage. 46(1):1982 This content downloaded from 207.46.13.129 on Wed, 29 Jun 2016 04:23:10 UTC All use subject to http://about.jstor.org/terms ULTRASOUND REPELLENCY IN RATS* Shumake et al. 149 exposed to ultrasound should be extremely difficult to repel. In this report, we evaluate the repellent efficacy of 3 devices (20, 20-30, and 40 kHz) under each of 2 levels of food availability, living-space familiarity, and ultrasound continuity. Comparisons of repellent efficacy for each set of conditions allow acceptance or rejection of the above hypothe-

Selecting for nutrient use efficiency within forage grass species: I. Development of a screening system

Abstract One means of achieving increased forage grass production on infertile soils is to select plant genotypes which grow efficiently at low levels of available nutrients. This requires methods to identify variability in individual plant nutrient response from among large populations of plants grown under controlled environmental conditions. A compact, containerized system, partially developed for growing large numbers of forage grass seedlings for use in automatic machine transplanter research, was adapted as the basis for such a screening technique. Three trials were made with 100‐plant samples of a kleingrass‐75 (Panicum coloratum L.) population to test the utility of the system. Results of these trials showed that differences in nutrient use efficiency (= reciprocal of nutrient concentration in the plant tissue, or milligrams dry matter produced per milligram nutrient absorbed) among the grass plants could be effectively identified by using the system in conjunction with laboratory analysis of the ...

Some effects of orchard soil management on sward composition, levels of available nutrients in the soil, and leaf nutrient content of mature ‘Golden Delicious’ apple trees

The effects of soil management practice on sward composition, the levels of available nutrients in the soil and leaf nutrient content of 11-year-old ‘Golden Delicious’ apple trees were examined over a 3-year period. The treatments consisted of: (a) grass sward mown at either 9 cm or 18 cm high, or controlled with the use of grass suppressant maleic hydrazide; (b) total herbicide coverage using simazine/paraquat or terbacil; (c) clean cultivation. Within the tree rows, beneath the tree canopies, the sward was composed of a higher percentage of weeds and grass and a lower percentage of clover than the sward in the alleys. In both areas, the magnitude of the clover component in the sward was in the order: grass suppressant > short grass > long grass. Over the 3 years, the mean dry-matter yield of herbage clippings returned was 11 938 kg ha −1 year −1 in the long-grass treatment, and 9089 kg ha −1 year −1 in the short-grass treatment. This was reflected in the higher amounts of mineral nutrients returned in the herbage clippings from the former treatment. In general, the surface soil (0–10 cm) from grassed plots contained more exchangeable Ca and Mg and less NO 3-N than that from the non-grassed plots. Available P accumulated in the surface layer of the herbicide-treated plots. No significant differences in available nutrients were detected below 10 cm soil depth. Over the 3 years, soil management practice had no measurable effect on tree growth or crop yield. However, in the second and third seasons, trees from grassed plots tended to have lower leaf total N contents than those from non-grassed treatments, while trees from cultivated plots tended to have lower leaf K levels than trees from other plots.

Seasonal levels of available nutrients under grassed down, Cultivated and zero tilled orchard soil management practices

The effects of zero-tillage, clean cultivation or the maintenance of a sward on the seasonal levels of available nutrients in a silt loam were examined during the third season of an orchard soil management trial. Total nitrogen and sulfur and oxidizable carbon were highest in the surface soil of grassed plots, intermediate in untilled plots and lowest in cultivated plots. The seasonal pattern in levels of nitrate nitrogen and sulfate sulfur showed similar trends in both the surface soil down the profile. Levels of both nitrate nitrogen and sulfate sulfur in the top 5 cm of soil remained high for a longer period into autumn under zero-tillage than under cultivation. During the summer and autumn period, concentrations of nitrate nitrogen in the surface soil from non-grassed treatments were notably higher than those from grassed plots. There was an accumulation of sodium bicarbonate extractable phosphorus and total phosphorus in the surface soil of untilled plots and a phosphorus fractionation indicated the accumulation of phosphorus in the aluminium and iron phosphate fractions. To a lesser extent exchangeable phosphate also accumulated at the surface of the untilled soil. Levels of exchangeable calcium and magnesium in the surface soil under the grassed treatment were markedly higher than those from the non-grassed treatments, indicating less leaching of cations in the former treatment. The possible relevance of the results is discussed in terms of orchard nutrition and maintenance of soil fertility.

Potential of predation byMetaseiulus occidentalis in compensating for increased, nutritionally induced, power of increase ofTetranychus urticae

This study was conducted to ascertain if the predatory phytoseiidMetaseiulus occidentalis (Nesbitt) could contain and regulate a prey population of the two-spotted mite,Tetranychus urticaeKoch, on strawberries at both high and low levels of reproductive increase of the prey species, by use of high and low levels of nitrogen fertilization of the strawberry plants which were grown in 2 hydroponic tanks, 1 with full nutrients, 1 with 1/40 full nutrients. A 14-h day length was provided. Temperatures averaged 21°C with R.H. averaging about 75. After inoculation prey and predator counts were made weekly. Fecundity tests were conducted throughout the experiment as were leaf analyses to determine the levels of available nutrients.

FUNGISTASIS IN SOILS

SUMMARY1. Fungistasis in soil is a widespread phenomenon affecting most fungal propagules, though some are insensitive. In most instances, it is coexistent with the presence of living microorganisms, and is annulled by energy‐yielding nutrients. Fungistasis with characteristics similar to that in soil may also occur on leaves of plants.2. Germination and growth of bacteria and actinomycetes is also restricted in soils. The characteristics of their inhibition appear to be the same as those for fungi. Therefore, the concept of a widespread microbial inhibition in soil can be applied to all three groups of microorganisms.3. Fungistasis can be detected by various direct methods, or indirectly by methods involving the use of porous or permeable carriers. It may be expressed as a restriction on the final amount of germination (the usual parameter), germination rate (with time), and rate of germ‐tube or hyphal growth. Since the expression of fungistasis is often complete in soil, titration with nutrients may be required to distinguish between the sensitivities of different fungi.4. Fungistasis generally is expressed most strongly at soil moisture contents somewhat less than saturation. Its expression usually is maximal in neutral or slightly alkaline soils. In acidic conditions fungistasis may be lessened because of suppression of bacterial and actinomycete activity. Increased sensitivity of some fungi in soils of pH > 7.0 may be caused by a directly unfavourable effect of pH on the fungus.5. Fungal species with small spores tend to be highly sensitive to fungistasis. These spores tend to germinate slowly and to require exogenous nutrients for germination. By contrast, species with larger spores and sclerotia often do not require exogenous nutrients for germination. The larger spores tend to germinate rapidly and to exhibit low sensitivity, as compared with small spores. A few nutrient‐independent spores are insensitive to fungistasis. At least a part of the difference in sensitivity is related to germination time; spores which germinate slowly compete poorly with the soil micro‐flora for their nutrients.6. Fungistasis is often temporarily annulled by enriching the soil with energy‐yielding nutrients. Usually, complex materials such as plant residues are most effective. A few weeks after such treatment, the level of fungistasis may, however, be increased. Annulment of fungistasis by compounds not utilized as energy sources has not yet been demonstrated.7. Several soils naturally suppressive to Fusarium wilt diseases were more fungistatic to Fusarium than soils conducive to wilt. Potential means by which fungistasis may be manipulated to control root‐infecting fungi are (a) through stimulation of germination with nutrients, thus exposing the germ tube to lysis, and (b) by increasing the fungistatic level of soil through appropriate amendments.8. Volatile substances identified in soils, some of which are potentially inhibitory to fungi include (a) ammonia, which apparently is evolved from ammonium salts in some arid soils of high pH, (b) ethylene, which has been identified in some soils of pH < 7.0 (though high levels of this gas seem to be tolerated by most fungi), (c) allyl alcohol, and (d) other unidentified substances. Non‐volatile inhibitors include high molecular weight substances revealed by molecular sieve chromatography of soil extracts. Microbial metabolites such as those present in staled fungal cultures also have been proposed to account for fungistasis. In a few soils fungistasis persists after sterilization because of the presence of inhibitory concentrations of calcium carbonate, iron or aluminium. Inherent in the proposition that inhibitory substances provide the primary mechanism of fungistasis is the concept of a highly complex phenomenon, involving various highly specific inhibitory and counteracting stimulatory substances, with the outcome for the fungus depending on the kinds and relative amounts of each present.9. By the nutrient‐deficiency hypothesis, the level of available nutrients in soil is insufficient to support germination of nutrient‐dependent propagules, except in nutrient‐rich microsites. Inhibition of nutrient‐independent propagules is explained by loss of endogenous nutrients required for germination, through microbial nutrient competition. Evidence for this hypothesis is (a) the imposition of fungistasis on numerous nutrient‐independent propagules during incubation on leaching model systems designed to simulate microbial nutrient competition in soil, (b) similar losses of endogenous nutrients occurring on soil and the leaching system, and (c) the fact that soils are chronically deficient in energy in relation to the microbial populations present, with the consequence that enforced inactivity is imposed upon most of the population at any given time for this reason alone, regardless of the presence or absence of fungistatic substances.Journal series article no. 7747 from the Michigan Agricultural Experiment Station.

The Autecology of Sawgrass in the Florida Everglades

Investigations were conducted in 1971 and 1972 to characterize typical stands of sawgrass (Cladium jamaicense Crantz) in the southern Everglades. Estimates were obtained of standing crop, plant density, stem length, leaf numbers, growth rate, and nutrient relationships in plant tissue, soil, and water. Measurements were also made of daily rainfall and water depths. These various parameters were estimated monthly over a 12—18 mo period in mature stands, as well as in stands regrowing after wild fires. The mature stands showed little seasonal variation in standing crop, plant density, and concentration of most inorganic nutrients. Plant nutrient requirements were estimated to be low, because tissue levels of nutrients were low as compared to those of other species of Everglades macrophytes. Copper (Cu) and phosphorus (P) were particularly low. Levels of available nutrients in soil varied, with no seasonal pattern. Most nutrients were in adequate supply, except that available nitrogen (N), P, potassium (K) and Cu were generally very low. Reserve soil supplies of N and P were plentiful, but not of K. Accumulation of K in sawgrass leaves was more closely related to reserve supplies in soil than to available soil supplies. Waters in the marsh contained on an average 3%, 10%, and 8%, respectively, of the N, P, and K contained in a comparable area of sawgrass standing crop. Concentration of most nutrients in culms regrowing after fires was high during early growth stages, but decreased to levels found in older culms after 3—5 mo. Conenctrations of calcium (Ca), iron (Fe), and zinc (Zn) were exceptions, however. During the 1st year's growth after fires, 1 ha of sawgrass had accumulated 48 kg N, 1.8 kg P, and 38 kg K. After 18 mo growth, burned stands of sawgrass had produced only 38% of the standing crop contained in unburned mature stands. The apparent low nutrient requirements of sawgrass may partially explain the dominance of this plant in the marsh community.

Contents of Eight Nutrients in Central Stem Leaf Segments of Ten Peanut Cultivars and Lines1

Abstract Petioles and blades of central stem leaves of 10 peanut (Arachis bypogaea L.) cultivars or lines grown in fertilized field plots in 1972 and 1973 and the last of four consecutive crops grown in pots during 1971 to 1973 were analyzed for evidence of relative differences in nutritional requirements. Runner-types included were Florigiant, Florunner, Va. 72R, NC 5, Avoca 11, and Va. 61R and bunch-types were NC 17, NC-Fla. 14, Va. 68 Composite, and Va. 70 Composite. The peanuts were grown in Woodstown (Aquic Hapludult) loamy fine sand. Significant (5% level) differences among cultivars or lines occurred in the K, Ca, and Mg contents and not in the P, B, Mn, Zn, and Cu contents of leaf portions of peanuts grown in the field. However, none of the cultivars or lines contained markedly higher or lower contents of any nutrient-considered. Lines Va. 68 Composite and Va. 70 Composite and the cultivar Avoca 11 had not been evaluated in similar previous research. These generally were intermediate or higher in contents of the nutrients, except the Mg content of Va. 70 Composite petioles was lower than in most cultivars or lines but equivalent to NC 5 and Va. 72R. Petioles were higher in K and Mg contents, whereas the blades were higher in P, Ca, B, Mn, Zn, and Cu contents. Continuous cropping of soil in the pots did not develop any apparent restrictive levels of nutrient availability. Hence, the fourth crop was not subjected to nutritional conditions for elucidation of abnormal nutrient-uptake capabilities among cultivars or lines. Florigiant, Va. 72R, and NC-Fla. 14 cultivars were labeled as superior in yield potential in Virginia in previous research. Portions of these cultivars were highest 25%, intermediate 50% and lowest 25% of the cases, in contents of one or more of the eight nutrients of both field and pot-grown plants. The average contents of the nutrients in leaf portions of the bunch or runner type cultivars or lines were similar.

Brood Reduction in the Curve-Billed Thrasher

Lack (1954; 40-41) has pointed out that in species of birds which have asynchronous hatching, brood size may be adjusted to temporal fluctuations in food availability. Parents generally feed the most active of their brood, that is, the largest (oldest) and the strongest. When such nestlings are replete, they become inactive and food is then passed on to the smaller members of the brood. When food availability is high, the parents are capable of satisfying all of the brood; when low, only the largest or first hatched are satisfied and the others starve to death. Thus, because of size differences due to asynchronous hatching, the parents are able to distinguish their young and can distribute limited food resources to the best advantage. If differentiation were not possible, food would be distributed randomly with each nestling having equal probability of being fed. During a poor year, all of the young would be underfed, a condition presumably less advantageous than having fewer well-fed young. Brood reduction is generally thought of as being prevalent in the hawks and owls and in some sea birds. It is the purpose of this paper to demonstrate the phenomenon in a passerine, the Curve-billed Thrasher (Toxostoma curvirostre). Up to a point, the parent can increase its rate of food delivery to the young by increasing its own effort. When food availability is low, it presumably takes a greater effort to deliver food at a given rate than during a more favorable period. It is convenient to think of the rate as being constant for any given level of food availability. Although probably unrealistic, this assumption is not impractical if we consider that regardless of the food availability there is an optimum effort which the parent can devote to gathering food. For different resource levels, this optimum effort will yield different rates of food delivery to the young. The energy requirement for the growth of the nestling increases with age up to a certain point after which it decreases (fig. 1). Thus, the parents are increasingly taxed not only with the addition of more young to the brood, but also with time. In a good year, the parents are able to keep up with the increasing demands and can deliver food at the maximum rate required by a full brood of nestlings. In a poor year, the requirement of the entire brood may exceed the delivery capacity of the parents long before the peak requirement is reached. When this happens, the smallest receives no food and dies. If, several days later, the requirement of the reduced brood again exceeds the delivery capacity of the parents, the smallest of the remaining birds has already been starved to death. It is theoretically possible that not one nestling would end up well fed in extremely hard times, but the birds would not be likely to breed under such conditions.

The john innes composts: Some effects of increasing the base-fertiliser concentration on the growth and composition of the tomato

The effects of increasing the strength of the base fertiliser in John Innes composts on the rates of growth, development, and the chemical composition of tomato ‘Potentate’, and also on the levels of available nutrients within the composts, has been examined. Comparison has also been made between plants grown in the JIP1, JIP2, and JIP3, composts and those grown in sand cultures receiving Hoagland's nutrient solution at each irrigation.