Showing papers by "Swedish University of Agricultural Sciences published in 1992"

The expression of a rab-related gene, rab18, is induced by abscisic acid during the cold acclimation process of Arabidopsis thaliana (L.) Heynh

Abstract: We have isolated a rab-related (responsive to ABA) gene, rab18 from Arabidopsis thaliana. The gene encodes a hydrophilic, glycine-rich protein (18.5 kDa), which contains the conserved serine- and lysine-rich domains characteristic of similar RAB proteins in other plant species. The rab18 mRNA accumulates in plants exposed to low temperature, water stress or exogenous ABA but not in plants subjected to heat shock. This stress-related accumulation of the rab18 mRNA is markedly decreased in the ABA-synthesis mutant aba-1, the ABA-response mutant abi-1 or in wild-type plants treated with the carotenoid synthesis inhibitor, fluridone. Exogenous ABA treatment can induce the rab18 mRNA in the aba-1 mutant but not in the abi-1 mutant. These results provide direct genetic evidence for the ABA-dependent regulation of the rab18 gene in A. thaliana.

Three-dimensional structure of transketolase, a thiamine diphosphate dependent enzyme, at 2.5 A resolution.

Abstract: The crystal structure of Saccharomyces cerevisiae transketolase, a thiamine diphosphate dependent enzyme, has been determined to 2.5 A resolution. The enzyme is a dimer with the active sites located at the interface between the two identical subunits. The cofactor, vitamin B1 derived thiamine diphosphate, is bound at the interface between the two subunits. The enzyme subunit is built up of three domains of the alpha/beta type. The diphosphate moiety of thiamine diphosphate is bound to the enzyme at the carboxyl end of the parallel beta-sheet of the N-terminal domain and interacts with the protein through a Ca2+ ion. The thiazolium ring interacts with residues from both subunits, whereas the pyrimidine ring is buried in a hydrophobic pocket of the enzyme, formed by the loops at the carboxyl end of the beta-sheet in the middle domain in the second subunit. The structure analysis identifies amino acids critical for cofactor binding and provides mechanistic insights into thiamine catalysis.

Reconsideration of the term ‘vitrification’ as used in micropropagation

Abstract: The term vitrification is currently used to describe two types of processes related to tissue-cultured plant material. The first is used to describe organs and tissues having an abnormal morphological appearance and physiological function. The second is used to describe the transition from liquid to solid state, i.e. the formation of ice during low temperature storage of in vitro cultured cells, tissues and organs. Use of the same term to define two greatly different processes in the same research area can only lead to confusion, especially for key words. Thus it is appropriate to reconsider the usage of vitrification in the first sense mentioned above. It is recommended that the term vitrification should no longer be used to indicate plant material with an abnormal morphological appearance and physiological function, and should be substituted by the term ‘hyperhydricity’.

A single mutation affects both N-acetylglucosaminyltransferase and glucuronosyltransferase activities in a Chinese hamster ovary cell mutant defective in heparan sulfate biosynthesis.

Abstract: Mutants of Chinese hamster ovary cells have been found that no longer produce heparan sulfate. Characterization of one of the mutants, pgsD-677, showed that it lacks both N-acetylglucosaminyl- and glucuronosyltransferase, enzymes required for the polymerization of heparan sulfate chains. pgsD-677 also accumulates 3- to 4-fold more chondroitin sulfate than the wild type. Cell hybrids derived from pgsD-677 and wild type regained both transferase activities and the capacity to synthesize heparan sulfate. Two segregants from one of the hybrids reexpressed the dual enzyme deficiency, the lack of heparan sulfate synthesis, and the enhanced accumulation of chondroitin sulfate, suggesting that all of the traits were genetically linked. These findings indicate that the pgsD locus may represent a gene involved in the coordinate control of glycosaminoglycan formation.

5 Ergosterol Analysis as a Means of Quantifying Mycorrhizal Biomass

Abstract: Publisher Summary This chapter describes the ergosterol analysis as a means of quantifying mycorrhizal biomass. A fundamental problem concerns the concept of fungal biomass: while the chitin content may be assumed to be roughly proportional to the total amount of cell wall, the amount of cell wall is certainly not proportional to the amount of cytoplasm, which is normally concentrated at the tips, leaving the bulk of the hyphae highly vacuolated. Another fungus-specific compound, ergosterol, is a principal component of membranes, and should therefore provide a better correlation with the metabolically active biomass of a fungus. The chapter briefly discusses development and current procedure technique. The chapter also evaluates the methods—namely, sensitivity and replicability, variation in ergosterol levels within the same species, and applications in mycorrhiza research. The basic shortcomings of the method are those of variation in the ergosterol content depending on growing conditions, and interspecies variation.

Boreal Forests—The Focal Habitats of Fennoscandia

Abstract: This chapter deals with the question of maintaining biological diversity in the boreal forests of Fennoscandia, i.e. the Scandinavian Peninsula and Finland. The boreal coniferous forest, or taiga, is the dominant biome, with a latitudinal extension from 56°N to 69°N (Fig. 7.1). The total area of the Fennoscandian forest amounts to more than 50 million ha, of which 13% occurs in Norway, 40% in Finland and 47% in Sweden (Nordic Statistical Secretariat, 1990). Man has utilized the boreal forest, for various purposes, during a very long period of time (Tenow, 1974). However, the most intense utilization has occurred during the last 300 years in connection with the development of the forest industry. At present, Fennoscandian forestry is amongst the most mechanized and efficient in the world. The result is that almost all forest land is now used for production of saw-timber and wood pulp. This has a tremendous impact on the structure and function of the boreal ecosystem. Cutting of old-growth forest and other consequences of forestry have a destructive impact on a large number of boreal organisms, despite the fact that some species are favoured by forest management. The result is decreasing populations for many hundreds of plants and animals, as reflected in recent Red Data lists (Andersson et al., 1987; Ahlen & Tjernberg, 1988; Databanken for hotarer och Naturvardsverket, 1991).

Effects of excess nitrogen and phosphorus starvation on the extramatrical mycelium of ectomycorrhizas of Pinus sylvestris L.

Abstract: summary The effect of excess nitrogen alone, and in combination with phosphorus and magnesium starvation, on the production of extramatrical mycelium was studied in Scots pine seedlings ectomycorrhizal with Laccaria bicolor (R. Mre.) Orton, Hebeloma crustuliniforme (Bull, ex St-Amans) Quel. and Suillus bovinus (L. ex Fr.) O. Kuntze. Seedlings were grown in a semi-hydroponic cultivation system and the ergosterol assay was used to estimate fungal biomass. The mycelial biomass increased rapidly when N was kept low (10–20 mg l−1) and in balance with other nutrients, but no extramatrical mycelium was produced when the N concentration was raised to 200 mg l−1. The growth of the extramatrical mycelium resumed when the excess N treatment was terminated and the seedlings were returned to a low nutrient regime, Laccaria showing more complete resumption of growth than Suillus, while Hebeloma had a low production of extramatrical mycelium in all treatments. Compared with the external mycelium, the amount of fungal tissue on the mycorrhizal roots (mantle and Hartig net) was much less affected by the high N treatment. P starvation increased the production of extramatrical mycelium tenfold, with almost no difference between high and low N nutrient regimes, while Mg starvation had no effect on the fungal biomass. The high N treatment lowered P and particularly Mg concentration of the needles, regardless of the mycorrhizal status of the plant. It is suggested that nitrogen deposition from the atmosphere may damage the function of mycorrhiza even before root tip studies reveal any decline in the symbiotic state. On the other hand, moderate nitrogen fertilization of forest land unaffected by nitrogen pollution is likely to have only passing effects on mycorrhizal development.

Polymerase-Chain-Reaction (PCR) Analysis of Microsatellites: A New Approach to Studies of Genetic Relationships in Birds

Abstract: ABSTRAcr.-Genomic DNA libraries of the Barn Swallow (Hirundo rustica) and the Pied Flycatcher (Ficedula hypoleuca) were screened for the presence of dinucleotide microsatellite repeats. Two thymine-guanine repeats, "(TG),," and two thymine-cytosine repeats, "(TC)n," were isolated and sequenced from the two species, respectively. Polymerase-chain-reaction (PCR) analysis of 25 unrelated Barn Swallows and 10 unrelated Pied Flycatchers revealed 3 to 15 alleles per locus and heterozygosities in the range of 0.46 to 0.89. Mendelian inheritance was confirmed for all four loci in 10 Pied Flycatcher and 2 Barn Swallow families comprising a total of 240 meioses. The occurrence of nonparental alleles in offspring from two Barn Swallow families was consistent with extrapair fertilization as revealed by a parallel DNAfingerprinting analysis. A DNA amount approximately corresponding to 0.01 ;Il blood was used for PCR analysis. DNA was also prepared from feathers and approximately 1% of a preparation from a single remex or rectrix was sufficient for PCR amplification. One of the primer pairs from the Barn Swallow also amplified a polymorphic locus in the House Martin (Delichon urbica) and in the Bank Swallow (R. riparia). Received 3 October 1991, accepted 16 June 1992.

Theories and methods on plant nutrition and growth

Abstract: A theory comprising two basic concepts relating nutrition and growth is presented The first concept is a nutrient flux model and is based upon studies of plants at constant internal nutrient concentrations, where a formal mathematical derivation shows that the relative uptake rate (RU) and the relative growth rate (RG) are equal Deviations from equality are results of experimental insufficiencies and errors The second concept is based on the observation that RG is linearly related to the internal nutrient concentration The slope represents nutrient productivity (Pn), an important parameter expressing growth rate per unit of nutrient Light and the plant genome, for example, influence the value of the proportionality factor, Pn, but not the formal relationship between the internal nutrient concentration and RG Not only the theory itself but many results and conclusions are very different from those obtained with traditional methods In experiments where RU was controlled during the exponential period of growth, the relationships between treatment (the relative addition rate, RA), nutrient uptake (RU) and growth (RG) were reproduced with extremely low variability In agreement with theory, internal nutrient concentration and RG remained stable over time (steady-state) An extension of the theory is based upon the empirical assumption that after exponential growth, self-shading and ageing reduce Pn in proportion to biomass This assumption has been successfully applied in predicting growth of forest stands, but the nature of the growth reduction is little understood The generalized model has few parameters and can easily be rewritten to suit different experimental aims, for example to establish reference values and to model changes in soil fertility Further extension and understanding of the model and different interpretations of the parameters are discussed

Transgenic Tobacco Plants Coexpressing the Agrobacterium tumefaciens iaaM and iaaH Genes Display Altered Growth and Indoleacetic Acid Metabolism.

Abstract: Transgenic tobacco (Nicotiana tabacum) SR1 plants expressing the Agrobacterium tumefaciens nopaline transferred DNA iaaH gene were transformed with a 35S-iaaM construct The transformants displayed several morphological aberrations, such as adventitious root formation on stem and leaves, dwarfism, epinastic leaf growth, increased apical dominance, and an overall retardation in development In addition, xylem lignification was higher than in wild type Free and conjugated indoleacetic acid (IAA) levels were quantified by gas chromatography-multiple ion monitoring-mass spectrometry in leaves and internodes of wild-type plants and two transformed lines with different phenotypes Both transformed lines contained elevated levels of free and conjugated IAA, which was associated with increased transcription of the iaaM gene The line with the highest IAA level also had the most altered pattern of growth and development These IAA-overproducing plants will provide a model system for studies on IAA metabolism, IAA interactions with other phytohormones, and IAA roles in regulating plant growth and development

Spatial pattern of cauliflower mosaic virus 35S promoter-luciferase expression in transgenic hybrid aspen trees monitored by enzymatic assay and non-destructive imaging

Abstract: A protocol has been developed for efficiently transforming and regenerating the hybrid aspenPopulus tremula x P. tremuloides. Stem segments were co-cultivated with a strain ofAgrobacterium tumefaciens carrying a disarmed binary vector conferring resistance to kanamycin or hygromycin. The respective vectors also carried a fused bacterialluxF2 gene expressed from the cauliflower mosaic virus 35S promoter. All transformants had a normal phenotype. Genetic tranformation and stable integration of the heterologous DNA was confirmed by Southern hybridization and luciferase expression. The latter was measured by destructive enzymatic assay throughout the transformatnt and by non-destructive image analysis in leaves left attached to intact plants. Both measurement techniques detected marked within- and between-organ variation in luciferase expression. However, the spatial patterns detected by each technique in the leaves were similar. The results indicate thatin vivo imaging of light emission can be used to measure repeatedly the expression of a promoter-luciferase gene fusion in a particular leaf over an extended time period. It was also demonstrated that enzymatically assayed luciferase activity in leaves was notably lowere in transgenic hybrid aspen plants than in tobacco plants transformed with the same vector. This was not due to a difference in luciferase enzyme activity between the two species, and therefore indicated that the 35S promoter is not as active in hybrid aspen as in tobacco.

Chronic valvular disease in the cavalier King Charles spaniel in Sweden.

Abstract: The prevalence of chronic valvular disease was studied in 494 cavalier King Charles spaniels with a mean (+/- sd) age of 3.0 +/- 2.7 years. Cardiac murmurs were detected in 65 (13.2 per cent) of the dogs. Among 61 cavalier King Charles spaniels with a mean age of 6.4 +/- 2.8 years, cardiac murmurs were detected in 32 (52 per cent). In both groups of dogs the prevalence of cardiac murmurs was low among dogs younger than three years (1.9 per cent) but increased with age (P < 0.001). The estimated ages at which 50 per cent of the dogs had developed murmurs were 7.5 and 6.2 years, respectively. When 39 of the 61 dogs were re-examined three years later, cardiac murmurs were detected in 28 (72 per cent), and the intensities of the murmurs had generally increased (P < 0.05). Nine (28 per cent) of the dogs which had previously had murmurs had been euthanased for signs of congestive heart failure whereas none of the dogs which had been free of murmurs had died from congestive heart failure. Animal insurance statistics from 1982 to 1990 (1983 excluded) for dogs less than 10 years old showed that claims for veterinary care or death or euthanasia were five times more common in the cavalier King Charles spaniel than in dachshunds (P < 0.001) and eight times more common than the mean for all other insured breeds (P < 0.001).

Radial velocity profiles of water flow in trunks of Norway spruce and oak and the response of spruce to severing.

Abstract: Trunk-tissue heat balance, volumetric and staining methods were used to study xylem water flow rates and pathways in mature Norway spruce (Picea abies (L.) Karst.) and pedunculate oak (Quercus robur L.) trees. The radial profile of flow velocity was confirmed to be symmetrical in spruce, i.e., maximum flow velocity was in the center of the conducting xylem and tailed with low amplitude (about 30 cm h(-1)) in the direction of the cambium and heartwood. Variability around the trunk was high. In contrast, in oak, the radial profile of flow velocity was highly asymmetrical, reaching a peak of about 45 m h(-1) in the youngest growth ring and tailing centripetally for about 10 rings, but variability around the trunk was less, under non-limiting soil water conditions, than in spruce. In spruce, the flow rate increased abruptly within seconds when the tree was severed while immersed in water, and then decreased gradually, showing significant root resistance. We conclude that water flow through an absorbing cut surface differs from the flow higher in a tree trunk because of the presence of hydraulic capacitances in the conductive pathways. The staining technique always yielded higher estimates of flow velocity than the non-destructive tree-trunk heat balance method.

Carbon and nitrogen mineralization and ammonia volatilization from fresh, aerobically and anaerobically treated pig manure during incubation with soil

Abstract: We studied the decomposition of aerobically and anaerobically treated pig manure during a 2-month incubation with soil. The manure samples had not been in contact with straw or with animal urine. The aerobically decomposed manure proved to be the most stable (23% C mineralization), followed by fresh (75%) and anaerobically treated manure (105%, priming effect). The course of mineralization fitted combined first- and zeroorder kinetics. In the anaerobically treated manure, 76% of NH4+-N was immobilized during the initial incubation phase, followed by a slow linear mineralization. In the aerobically treated manure there was a slow linear mineralization after 5 days, and in the fresh material, a slightly faster linear mineralization after 6 days. Total mineralized N was very similar after 2 months (12%) in all treatments. Total NH3 losses were highest from the anaerobically treated manure (14%), reflecting a higher NH4+content with N mineralization following first-order kinetics. Relating NH3 losses to the initial NH4+content showed that all NH3 in the aerobically treated manure was volatilized, whereas only 28% was volatilized from the fresh and the anaerobically treated manure.

Environmental variation for outcrossing rate in rapeseed (Brassica napus).

Abstract: Rapeseed (Brassica napus) is a predominantly selfpollinated crop with about one-third outcrossing. The outcrossing rate may be influenced by environmental factors, and hence changes in the heterozygosity level of a variety may occur during multiplication. In an investigation on environmental variation in outcrossing, we estimated the outcrossing rate in the Swedish spring rapeseed cv 'Topas' by isozyme analysis and found that outcrossing varied from 12% to 47% over five locations in Sweden, Denmark and Germany. Among flowers at different positions on the same plant, average outcrossing varied from 11% at the top to 39% at the bottom of the plant. In conclusion, environmental factors can greatly influence the outcrossing rate in rapeseed, and an investigation therefore merit further studies.

RUBISCO: structure and mechanism.

Abstract: CONTENTS PERSPECTIVES AND OVERVIEW 1 1 9 PHYSIOLOGICAL AND GENETIC ASPECTS 120 Photosynthesis and Photorespiration 120 Synthesis and Assembly . . . . . ..... ... . . ... . . . . . . . . . . .. .. 121 CHEMICAL MECHANISM 122 Activation-the Ternary Complex of Enzyme, CO" and Mg( II) 122 Overall Carboxylation Reaction . . . ... . . . . . . . . . . . . . . . ... . ..... . . . . . . . . . . . . . . 123 Partial Reactions and Reaction Intermediates 124 THREE·DIMENSIONAL STRUCTURE 126 Overall Structure of Rubisco as Revealed by Protein Crystallography 126 Structural Diff erences Between the L2and LsSs-Type Rubisco: a Function of the Small Subunit 129 The Active Site . . . . . . . . ....... . . . . . . . . . . . ...... ...... . . . . ... . . . . . . . . . . . . . . . . . . 130 Binding of Phosphorylated Compounds to Rubisco 1 32 Conformational Changes During Catalysis 1 3 5 STRUCTURE AND FUNCTION 1 36 Activation .. . .. 1 36 Enolization . . . . . . . . . . ..... . . . . . . . . . . . . . . . . . . . . . . . . . . ..... . . . . . . . . . . . ........ ........ 137 Carboxylation 138

Diet, fecundity and egg size in some polyphagous predatory carabid beetles.

Abstract: Egg size was measured at different rates of egg laying in three polyphagous carabid species, known to be useful predators of cereal aphids; the small Bembidion lampros Herbst and the medium-sized Pterostichus cupreus L. and P. melanarius Illiger. Variations in fecundity, as well as the ability of the medium-sized species to also build up fat reserves, were obtained when beetles were subjected to different dietary regimes consisting of aphids, or foods with a lower or higher protein content. Egg size was found to be dependent on the rate of egg laying within a species. A diet of cereal aphids appeared to be adequate for egg production in these polyphagous carabids, but female P. cupreus were unable to build up fat reserves when they ingested aphids contaminated with the aphicide pirimicarb. Beetles were able to devote resources to more and larger eggs (B. lampros), or to larger eggs and/or fat reserves (P. melanarius/P. cupreus) when given access to a carbohydrate-rich food with low protein content. The highest rate of egg laying was obtained when female P. cupreus and P. melanarius were given a more varied diet at frequent intervals; including regular shifts between unsprayed aphids, carbohydrate-rich food and protein-rich maggots. Within the varied diet treatment a negative relationship was obtained between egg size and egg number among similar-sized individuals of P. cupreus and P. melanarius; females producing the largest number also laid the smallest eggs. Egg size affected larval survival, since first instars hatching from large eggs were found to survive longer than those hatching from small eggs. The influence of differences in food intake on reproduction, maintenance metabolism, and survival of field-inhabiting carabids is discussed.

Errors in Net Radiometry: Comparison and Evaluation of Six Radiometer Designs

Abstract: Net radiation is a fundamental variable in meteorology, but net radiometers have not been used extensively since the 1960s because of what is commonly considered as unreliable function. This study was conducted to determine whether this problem was caused by design, by calibration, or if some more fundamental problem was associated with net radiometry. Comparative measurements between six different types of net radiometers, calibrated in two wares were carried out under different climatic conditions. Calibration factors obtained from shadowing varied between 75% and 129% of the manufacturer's. The range was 85%–161% for calibrations relative to reference measurements of individual radiation components. Differences between the reference and individual meters were between 6% and 20%. After correction for different responsivities for longwave and shortwave radiation, the differences decreased markedly, especially in nighttime, except for two meters that had bad cosine responses. Three meters showed ...

Influence of nutrient and water stress on Norway spruce production in south Sweden : the role of air pollutants

Abstract: A field experiment primarily designed for simulating the indirect effects of air pollutants for a 25-year-old Norway spruce stand in SW Sweden is presented (The Skogaby project). Treatment include irrigation; artificial drought; ammonium sulphate addition; nitrogen-free-fertilization and irrigation with liquid fertilizers including a complete set of nutrients. The experiment has a randomized block design with four replicates per treatment. Growth response on an areal basis of basal area, height and dry mass of stems, branches and needles after up to four years of treatment are presented. Dry mass is estimated using allometric equations based on destructive samplings of trees. The stand suffered from temporary water stress during all four years investigated despite 970– 1160 mm of annual precipitation. Irrigation resulted in improved above-ground dry mass production (stem, bark, branches, needles, litter fall) by 20% during the first 3 years of treatment, whereas 2 years of drought treatment followed by 1 year of recovery led to 10% reduced dry mass growth. During year 2 of recovery, however, basal area growth was only about half of that of the control. Nitrogen, markedly, was a growth limiting nutrient, although the stand got approx. 20 kg N ha-1 y-1 from deposition. Ammonium sulphate addition (100 kg N ha-1 y-1) resulted in 31% improved dry mass production whereas irrigation with liquid fertilization (100 kg N ha-1 y-1) including all important nutrient elements led to 57% increased dry mass growth after 3 years of treatment. Basal area growth of the latter treatment gradually increased and during year 4 of treatment was 123% larger than the control. Nitrogen-free-fertilization resulted in a small improvement of dry mass production (+10%). After 3 years of treatment, the amount of needles had increased markedly for both treatments including irrigation, whereas drought treated trees instead had decreased their needle amount vs control. The increase in needle amount occurred as a result of both larger formation of needles and higher preservence of old needles, the opposite relations being found for the drought treated trees. At the same point larger needle formation in combination with a higher shedding of older needles was found for trees treated with ammonium sulphate and nitrogen-free-fertilizer. It is concluded that there is no stage of N saturation in the Skogaby site as there is no leaching of N from the control plots and N fertilization results in both increased tree growth and N uptake.

Effects of agrochemicals and heavy metals on fast-growing rhizobia and their symbiosis with small-seeded legumes

Abstract: The effect of potentially hazardous agrochemicals including fungicides, herbicides and heavy metals on symbiotic nitrogen fixation have been investigated. The substances were tested with eight rhizobial strains from three cross-inoculation groups: Rhizobium leguminosarum b.v. trifolii, R. meliloti and R. loti in pure culture studies. Bacteria were obtained from a culture collection or from soils. Sensitivity of the bacteria to the agrochemicals and heavy metals varied. None of the bacteria were tolerant to all chemicals. No difference in tolerance between cross-inoculation groups existed. Bacteria were able to multiply at concentrations of agrochemicals equal to or higher than recommended field-application rates. Heavy metals concentrations that severely inhibited growth were far lower than the highest amounts allowed under the current Commission of the European Communities' guidelines for environmental protection. Bacterial growth in presence of the agrochemicals and heavy metals, apart from glyphosate and zinc, did not influence nodulation ability of the strains. Development of uninoculated plants was inhibited at increasing concentrations of all compounds, red clover being most sensitive. Herbicides were most harmful, with injuries occurring at levels 1 10 - 1 10,000 of recommended applied concentrations. Uninoculated plants were less tolerant to agrochemicals, but were more tolerant to heavy metals compared to the bacteria. Root hair deformations similar to bacterial-induced root hair deformations were induced by bentazone, chlorsulphuron and monochlorophenoxyacetic acid on uninoculated plants. Symbiotic interactions were adversely affected by several of the agrochemicals. Bacterial-induced root hair deformations necessary for nodulation decreased in the presence of benomyl, bentazone, chlorsulphuron, fenpropimorph, mancozeb and monochlorophenoxyacetic acid. Fenpropimorph and mancozeb did not cause root hair deformations at increasing concentrations, indicating that these may inhibit nodulation under field conditions. Nodule development was inhibited at increased levels of bentazone, chlorsulphuron, glyphosate and mancozeb. Dry matter production of nodulated plants was adversely affected by bentazone and chlorsulphuron, indicating disturbances in nodule function.

Factors affecting the incidence of necrotic enteritis, caecal carriage of Clostridium perfringens and bird performance in broiler chicks.

Abstract: Two trials were conducted to study the effects of a competitive exclusion (CE) product BROILACT and the anticoccidial narasin on the incidence of necrotic enteritis (NE), the numbers of Clostridium perfringens (CP) in the caeca of broiler chicks and the performance of the birds. In trial 1 the effects of type of protein and partial replacement of a narasin containing diet with whole wheat were also studied. All groups of chicks were studied up to the point of slaughter at 43 days of age and after evisceration in a processing plant to determine slaughter yield. In trial 1, statistically significant results included the following: CE-treatment reduced total mortality, and incidence of NE, on diet containing animal but not vegetable protein. Caecal carriage of CP was also reduced, while slaughter yield increased. Narasin reduced caecal carriage of CP and increased both growth rate and slaughter yield in both trials. Whole wheat replacement improved feed conversion but reduced bird growth rate. In trial 2, both CE-treatment and narasin influenced feed intake, CE-treatment significantly only at days 22 and 44. Narasin improved feed conversion until 5 weeks of age and CE-treatment did so until 22 days of age. In both trials, there was also an interaction effect indicating that CE-treatment increased slaughter yield for birds that were not fed narasin.

A method for determining microbially available N and P in an organic soil

Abstract: A bioassay of microbially available soil N and P is described. It is based on the addition of glucose together with N or P to soil, followed by monitoring of the respiration rate. The addition of glucose + N resulted in an immediate increase in the soil respiration rate followed by a short period of exponential increase, reflecting the growth of microorganisms on the added substrate. The exponential phase levelled off, when lack of P prevented further growth of the soil microorganisms. The soil respiration rate then remained constant for several hours before decreasing, when glucose became limiting. The addition of glucose + P resulted in a lower plateau of the soil respiration rate, indicating that microbial growth was more limited by N than P in this forest soil (0.28 and 0.79 mg CO2 g-1 organic matter h-1, respectively). Additions of the limiting nutrient resulted in a proportional increase in the constant level of the soil respiration rate. This was used to calculated the increase in the soil respiration rate per mg N (0.71 mg CO2 h-1) or mg P (4.6 mg CO2 h-1) added to this particular soil. Microbially available N was then calculated in two ways from the regression equation (0.15 or 0.40 mg g-1 organic matter) and P (0.13 or 0.17 mg g-1 organic matter). A comparison with 2 M KCl extraction showed that in nutrient-poor forest soils the microbially available N was 6.3 or 18.5 times higher than the KCl extractable N.

Inhibition of Scots pine seedling establishment byEmpetrum hermaphroditum.

Abstract: Poor establishment and reduced seedling growth of Scots pine (Pinus silvestris L.) in northern Sweden is related to an allelopathic inhibition by the dwarf shrubEmpetrum hermaphroditum Hagerup. Indoor bioassays with green and brown leaves ofEmpetrum have strong negative effects on rooting ability, radicle elongation, and growth of Scots pine seedlings. Bioassays with soil samples show that phytotoxic substances leached fromEmpetrum foliage accumulate in the soil. Field experiments reveal that chemical inhibition byEmpetrum, causing high mortality and slow growth of pine seedlings, can be reduced by adding activated carbon to the soil.