Two different types of rhizomorphs were produced by A. luteobubalina in vitro conditions - aerial and submerged. They differed in growth rate, amount of mucilage, extent of peripheral hyphae, degree of pigmentation and in the structure of inner cortex. Otherwise they had a similar internal structure comprising 4 radial zones, namely, peripheral hyphae, outer cortex, inner cortex and medulla. Two membrane permeant symplastic fluorescent tracers, carboxy-DFFDA and CMAC which ultimately sequestered in vacuoles, behaved in a similar fashion in aerial and submerged rhizomorphs regardless of whether pigment was present in the outer cortical cell walls or in the extracellular material. Rhizomorphs appeared to be mostly impermeable to these probes with exception of a few fluorescent patches that potentially connected peripheral hyphae to inner cortical cells. In contrast, the apoplastic tracer HPTS which was applied to fresh material and its localisation determined in semi-thin (dry) sections following anhydrous freeze substitution appeared to be impeded by the pigmentation in cell walls and/or the extracellular material in the outer cortical zone. Structures identified as air pores arose directly from the mycelium and grew upwards into the air. A cluster of rhizomorph apices is initiated immediately beneath the air pores. As air pores elongated they differentiated into a cylindrical structure. Mature air pores became pigmented as did also the surface mycelium of the colony. The pigmented surface layer extended into the base of air pores, where it was elevated into a mound by tissue inside the base of the air pore. Beneath the pigmented surface layer there was a region of loose hyphae with extensive gas space between them. This gas space extended into the base of the air pore and was continuous with the central gas canal of rhizomorphs. Oxygen is conducted through the air pores and their associated rhizomorph gas canals into the oxygen electrode chamber with a conductivity averaging 679??68x10-12 m3s-1. The time averaged oxygen concentration data from the oxygen electrode chamber were used to compare three different air pore diffusion models. It was found that the widely used pseudo-steady-state model overestimated the oxygen conductivity. Finally, a model developed on the basis of fundamental transport equations was used to calculate oxygen diffusivities. This model gave a better comparison with the experimental data.

Two different types of rhizomorphs were produced by A. luteobubalina in vitro conditions - aerial and submerged. They differed in growth rate, amount of mucilage, extent of peripheral hyphae, degree of pigmentation and in the structure of inner cortex. Otherwise they had a similar internal structure comprising 4 radial zones, namely, peripheral hyphae, outer cortex, inner cortex and medulla. Two membrane permeant symplastic fluorescent tracers, carboxy-DFFDA and CMAC which ultimately sequestered in vacuoles, behaved in a similar fashion in aerial and submerged rhizomorphs regardless of whether pigment was present in the outer cortical cell walls or in the extracellular material. Rhizomorphs appeared to be mostly impermeable to these probes with exception of a few fluorescent patches that potentially connected peripheral hyphae to inner cortical cells. In contrast, the apoplastic tracer HPTS which was applied to fresh material and its localisation determined in semi-thin (dry) sections following anhydrous freeze substitution appeared to be impeded by the pigmentation in cell walls and/or the extracellular material in the outer cortical zone. Structures identified as air pores arose directly from the mycelium and grew upwards into the air. A cluster of rhizomorph apices is initiated immediately beneath the air pores. As air pores elongated they differentiated into a cylindrical structure. Mature air pores became pigmented as did also the surface mycelium of the colony. The pigmented surface layer extended into the base of air pores, where it was elevated into a mound by tissue inside the base of the air pore. Beneath the pigmented surface layer there was a region of loose hyphae with extensive gas space between them. This gas space extended into the base of the air pore and was continuous with the central gas canal of rhizomorphs. Oxygen is conducted through the air pores and their associated rhizomorph gas canals into the oxygen electrode chamber with a conductivity averaging 679??68x10-12 m3s-1. The time averaged oxygen concentration data from the oxygen electrode chamber were used to compare three different air pore diffusion models. It was found that the widely used pseudo-steady-state model overestimated the oxygen conductivity. Finally, a model developed on the basis of fundamental transport equations was used to calculate oxygen diffusivities. This model gave a better comparison with the experimental data.

Although evidence is mounting that asphalt binder oxidizes in pavements, and that oxidation and subsequent hardening of asphalt binder has a profound effect on pavement durability, important implementation issues remain to be better understood. Quantitative assessment of asphalt binder oxidation for a given pavement is a very important, but complex issue. In this dissertation, a fundamentals-based oxygen transport and reaction model was developed to assess quantitative asphalt binder oxidation in pavements. In this model, oxygen transport and reaction were described mathematically as two interlinked steps: 1) diffusion and/or flow of oxygen from the atmosphere above the pavement into the interconnected air voids in the pavement; and 2) diffusion of oxygen from those air voids into the adjoining asphalt-aggregate matrix where it reacts with the asphalt binder. Because such a model calculation depends extensively on accurately representing pavement temperature, understanding oxygen diffusivity in asphalt binders and mastics, and characterizing air voids in pavements, these key model elements were studied in turn. Hourly pavement temperatures were calculated with an improved one-dimensional heat transfer model, coupled with methods to obtain model-required climate data from available databases and optimization of site-specific pavement parameters nationwide; oxygen diffusivity in binders was determined based on laboratory oxidation experiments in binder films of known reaction kinetics by comparing the oxidation rates at the binder surface and at a solid-binder interface at the film depth. The effect of aggregate filler on oxygen diffusivity also was quantified, and air voids in pavements were characterized using X-ray computed tomography (X-ray CT) and image processing techniques. From these imaging techniques, three pavement air void properties, radius of each air void (r), number of air voids (N), and average shell distance between two air voids (rNFB) were obtained to use as model inputs in the asphalt binder oxidation model. Then, by incorporating these model element improvements into the oxygen transport and reaction model, asphalt binder oxidation rates for a number of Texas and Minnesota pavements were calculated. In parallel, field oxidation rates were measured for these corresponding pavement sites and compared to the model calculations. In general, there was a close match between the model calculations and field measurements, suggesting that the model captures the most critical elements that affect asphalt binder oxidation in pavements. This model will be used to estimate the rate of asphalt binder oxidation in pavements as a first step to predicting pavement performance, and ultimately, to improve pavement design protocols and pavement maintenance scheduling.