Previous work in animal nutrition has focused on single feeds and assumed additivity in ration systems. In the tropics, farmers are likely to feed mixtures of feeds, including tree fodders, which may not be simply additive in nutritional terms. This study has increased our understanding of the mechanisms that determine the associative effects on the in vitro fermentation of mixtures of fodder tree leaves. Associative effects are governed by a synchronisation in the fermentation rates of the components of the mixture. This is in turn dependent on the fermentability of their chemical constituents. Effects were demonstrated by changes in the fermentation kinetics of gas production curves. The chemical components of fodder tree leaves that affect the fermentation, and the time at which the effect occurs, were identified, using two media of different nitrogen contents. The fermentation of mixtures of pure chemical entities in various combinations was then examined. The greatest associative effects were found when the mixture had components of similar fermentability. It is proposed that associative effects are a function of the synchronisation of fermentation of the different components and was shown to occur at the point when the rate was maximal. With two types of protein (casein and bovine serum albumin (BSA)), utilisation of a protein by rumen microbes was shown to be a function of its fermentability and not of its solubility. This is also influenced by the type of associated carbohydrate. Fodder tree leaves were then combined with different pure chemical entities. Associative effects between fodder tree leaves and carbohydrates were shown to occur and the responses were similar to those obtained with mixtures of pure carbohydrates and proteins. The effect of tannins and phenolic compounds was studied using quebracho tannin as a model, and in five of the tree species. They were shown to affect the fermentability of both carbohydrates and proteins. The effect was greater with carbohydrates of medium to low fermentability. They also reacted with both soluble and insoluble protein. Forages with phenolic compounds showed both positive and negative effects. The effects were possible due to a synchrony or asynchrony in the release of protein. In mixtures of leaves from different species, associative effects were related to their fermentability. Again, this appeared to be the result of the synchronisation of the release of nutrients. Associative effects with fodder tree leaves were of a composite nature and can be both positive and negative. The implications of these findings in relation to in vivo digestion and animal production are discussed. Due to the diversity of fodder trees, there is the potential to develop feeding systems based on mixtures which make better use of available resources. This will also contribute to improved efficiency in the management and use of natural resources, and take advantage of natural plant diversity in the tropics.

Abstract not available

Mature field-grown apple trees were used to gain a better understanding of the influences of light and fruit on leaf physiology. Light effects on net photosynthesis (Pn), specific leaf weight (SLW), leaf N content (Weight/area) (Nw), and leaf N concentration (% dry weight) (Np) of spur leaves from two canopy locations were evaluated on four dates in 1987. Interior leaves had lower Pn, SLW, Nw, and Np than exterior leaves. In 1988 the influence of %available photosynthetic photon flux (PPF) on the same parameters was examined throughout the season. On most measurement dates both Pn and SLW increased quadratically while Nw increased linearly with increasing PPF. In both years positive linear relationships existed between Pn and Nw, SLW and Nw, and Pn and SLW. / Ph. D.

Microbial respiration on sticks and leaves, measured as oxygen uptake rate, was compared among four (2nd-4th order) sites along an elevational gradient at Coweeta Hydrologic Laboratory, North Carolina. Rhododendron and birch leaves were placed in mesh bags in the stream at each site on 21 Oct 90. Oxygen uptake rates were measured for both leaf species beginning 15 Dec 90 and continuing monthly until leaves were no longer intact (birch-2 months, rhododendron-7 months). Microbial oxygen uptake rates were also measured monthly for one year on qualitative collections of sticks (1-3 cm diameter) found in the stream at each site. Oxygen uptake rates (mg O₂/hr) were calculated on both a surface area and AFDM basis. Overall mean respiration rate per unit surface area was highest for sticks, followed by rhododendron, and birch. When expressed on an AFDM basis, respiration rates were highest for birch, followed by rhododendron, and sticks. Based on continuous measurements, mean monthly stream temperatures were significantly different among sites, but mean incubation temperatures were not significantly different among sites, Respiration rates were significantly correlated with temperature for both rhododendron leaves and sticks on both an AFDM and surface area basis. Respiration rates on rhododendron also increased with exposure time. Results indicate that differences in respiration rates among sites, for both rhododendron leaves and sticks, can be explained primarily by changes in temperature. Additionally, the high respiration rates per unit surface area on sticks indicate that small woody debris may play a significant role as a substrate for microbial metabolism. / Master of Science

The purpose of this investigation is to determine the possible presence and the extent of nutritional material in the extracts of the green leaves of a selected group of common trees in an effort to devise simpler and more economical, yet useful and satisfactory, culture media for the use in bacteriological laboratories, particularly those on the secondary level.

Venturia inaequalis, the causal agent of apple scab, overwinters in apple leaves on the orchard floor. To develop a control strategy based on the prevention of the maturation of overwintering pseudothecia, a sampling of fungi colonizing dead apple leaves was conducted from different orchard floors in Quebec during the spring and fall of 1993. A total of 345 different isolates were obtained, from which fifteen genera have never been previously recorded as colonizers of apple leaves in North America. Small differences were detected in genera richness among orchards but the fungal composition of each orchard was fairly unique. Different tests on growth on amended media and leaf decomposition demonstrated that leaf degradation is not a reliable parameter alone to screen antagonist against V. inaequalis. No significant relation between growth on amended media, leaf rheology and ascospore inhibition was detected. However, 40 fungi reduced significantly ascospore production more than 87% compared to the control (V. inaequalis only). Of these antagonists, 30% decomposed apple leaves, suggesting that competition for the substrate is involved in the mode of action of at least one third of the antagonits detected. Other possible modes of antagonism are discussed.

No description available.

Success in evaluating effects of a 75% oxygen atmosphere, containing an ambient concentration of carbon dioxide, on levels of protein and oxidative enzymes in cotton, Gossypium herbaceum L. C.B. 1697, leaf tissue was dependent upon generation of genetically uniform and physiologically similar leaves. Sufficient quantities of 2-4 week old leaves for experimental procedures were obtained from plants grown in a 1:1 perlite:vermiculite potting medium supplied with 20% Hoagland's nutrient and maintained in a controlled environment growth chamber under the following conditions: 16 hr day/8 hr night cycle, irradiances of 200-300 µE m⁻² sec⁻¹, 70% humidity, and 30°. Maximum yields of soluble protein (10-12 mg/g tissue) and active enzymes were obtained when freshly harvested leaves were crushed in liquid nitrogen and then homogenized in 0.1 M Tris-Cl, pH 6.9, containing 0.01 M isoascorbate and polyvinylpyrrolidone [2% (w/v) PVP-10 and 0.5 g dry Polyclar AT/g tissue]. Routinely 90% of the solubilized protein was obtained following centrifugation and chromatography on Sephadex G-50. Introduction of cotton plants into vinyl chambers of 95% humidity resulted in foliar symptoms of physiological stress, including chlorosis, cellular edema, leaf curling, and loss of turgidity. Of the oxidative enzymes analyzed, catalase activity decreased 30%, glycolate oxidase activity decreased 42%, and peroxidase. increased 89% while soluble protein decreased 27% in plants maintained in the high humidity for 5 days. Exposure of plants to 75% oxygen, 350 ppm carbon dioxide for 48 hr under these conditions resulted in a 70% increase in glutathione reductase and a 25% increase in malate dehydrogenase. Other enzymes, superoxide dismutase, catalase, peroxidase, glyoxylate reductase, and acid phosphatase, appeared to be independent of the oxygen treatment. When humidity was carefully controlled at 70%, treatment with 75% oxygen, 350 ppm carbon dioxide resulted in a 180% increase in glutathione reductase, an 85% increase in acid phosphatase, and a 22% increase in peroxidase. In the same experiment, catalase decreased by 32% and total soluble protein decreased by 15%. Activities of glyoxylate reductase and both cyanide-sensitive and insensitive superoxide dismutases appeared to be unaffected by the 75% oxygen treatment after 48 hr. Obviously the impact of humidity as a component of the regulation of metabolism in leaf tissue must be considered. It is concluded that oxidoreductase activities located in the chloroplast, peroxisome, and cytosol are not equally sensitive to high oxygen tensions, and effects of environmental oxygen are not restricted to oxidative enzymes. / Ph. D.