Thesis (Ph. D.)--University of Washington, 1993. / Vita. Includes bibliographical references (leaves [208]-235).

Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (MScAgric)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Thesis (M.Sc.)--York University, 2005. Graduate Programme in Earth and Space Science. / Typescript. Includes bibliographical references (leaves 180-191). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url%5Fver=Z39.88-2004&res%5Fdat=xri:pqdiss &rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR11896

Several experiments were conducted to determine: the influence of canopy position, girdling, and defoliation on nectar production; whether instantaneous light measurements yield reliable estimates of cumulative seasonal light levels within the canopy; and the effect of the canopy light environment on spur leaf physiology and fruit quality. Defoliation of nongirdled flowering spurs had no effect on nectar production or composition, while defoliation of girdled spurs induced nectar sugar concentration by 24%. Canopy position had no influence on nectar production or composition. At full bloom there were differences in photosynthetic potential of spur leaves from different canopy positions. Exterior leaves had a greater maximum photosynthetic rate and an unique photosynthetic light response curve compared to the intermediate and interior leaves. Differences among positions persisted throughout the season. Stomatal conductance, specific leaf weight, dark respiration, and light levels were greater for the exterior leaves throughout the season. Instantaneous light measurements made on a single uniformly overcast day after the canopy was fully-developed (average of four times during the day) provided reliable estimates (predictive R2 > 0.90, n = 30) of total cumulative seasonal photosynthetic photon density (PPD). There was a I-to-l relationship between instantaneous and cumulative PPD after canopy development was complete providing both measures were expressed as a percentage. The relationships were equal over multiple dates for two consecutive years. Cloudless conditions provided poor estimates (predictive R2 = 0.49 to 0.80, n = 30). Light environment and harvest date influenced fruit quality characteristics within the canopy. Fruit red color, intensity of red color, and soluble solids concentration were all positively related to light level, with the highest R 2 on the early harvest dates. Fruit weight, firmness, length/ diameter ratio, starch index, and seed number were not consistently influenced by the light environment. The number of hours above an average photosynthetic photon flux density threshold of 250 I-£mol. m-2• sec'! explained slightly more of the variation in fruit quality characteristics than any other expressions of light. / Ph. D.

Several experiments were conducted to determine the influence of modifying the grapevine microclimate on the incidence of fruit rot and selected rot metabolites of Virginia grown White Riesling (<i>Vitis vinifera</i> L.) grapes. Due to the relatively high incidence of rot observed in these studies, an evaluation of the effects of rot on the sensory evaluation of juice and on selected aroma components was also undertaken. The effect of shoot topping to 10 or 20 nodes or the application of ethephon on the incidence of grape rot was measured for three seasons. Canopy modification by both topping and ethephon treatment increased sunlight penetration into the fruiting zone. Fruit rot incidence and the concentrations of rot-associated metabolites were significantly and mutually correlated. Fruit rots and rot metabolites were greatest with control and ethephon-treated vines and were least with vines whose shoots were topped to 10 nodes. In a separate three-year study, two to four leaves were removed from the fruiting zone of grapes grown on two training systems. Selective leaf removal generally increased sunlight penetration into the grapevine canopy. The incidence of Botrytis and sour rot as well as the concentrations of rot organism metabolites in harvested fruit were reduced by leaf removal. The effect of grape sour rot on general fruit chemistry, free volatile terpenes, potentially free volatile terpenes, selected polyols and rot metabolites was undertaken. Grape sour rot increased °Brix, glucose to fructose ratio, titratable acidity, tartaric acid, glycerol and gluconic acid. Grape sour rot reduced the concentrations of geraniol, nerol and linalool, while increasing oxidation products, aromatic alcohols and long chained alcohols. Grape juice sensory analysis appeared to be influenced by the severe fruit rot which occurred in both the control and to a lesser extent in canopy manipulated vines in both studies. The importance of fruit rot was demonstrated by both the production of odors, metabolites, and the destruction of native grape aroma constituents. Reductions in the incidence of fruit rot by selective leaf removal and shoot topping were demonstrated and were probably due to several microclimate factors that collectively increased evaporative potential and spray penetration into the fruit zone. The results illustrate that remedial canopy management practices that improve fruit zone porosity can mitigate the severe disease pressure that exists when rot-prone cultivars are grown in humid grape growing regions. The inability to reduce fruit rots further than noted in these studies may be due to the complex nature of fruit rots observed here, compared to those (principally Botrytis rot) examined in the majority of other canopy management studies. / Master of Science

This thesis examines factors limiting understory herb presence and flowering in young second-growth Douglas-fir (Pseudotsuga menziesii) forests on the west side of the Cascade Mountains, Oregon, USA. I studied the belowground effects of canopy trees on understory herbs and shrubs in old-growth forests using trenched plots from which tree roots were excluded. Effects of tree density and stand age were tested by comparing the understory community composition of old-growth stands and pre-commercially thinned and unthinned young second-growth stands. I also examined the effect of conifer basal area on understory herb presence and flowering within one young second-growth watershed. In young stands, I focused on three groups of understory herb species: disturbance-responsive (release), forest generalist and old-growth associated. The effects of root trenching on vegetation and soil moisture were tested in closed-canopy and gap locations in two old-growth Douglas-fir (Pseudotsuga menziesii) forests. Ten years after installation, trenched plots averaged 92% total understory cover while untrenched plots averaged 47% cover. Trenched plots under closed canopies were moister than control plots throughout the growing season; the trenching effect on soil moisture became apparent in the generally wetter gaps only at the end of the growing season. Vegetation responses to trenching were concomitantly larger under closed canopies than in gaps. Stands that had been pre-commercially thinned 20 years earlier exhibited understory composition more similar to old growth than did unthinned stands. Thinned stands exhibited higher frequencies, abundances and density of flowering of old-growth associated herbs than did unthinned stands, but lower than did old-growth stands. Forest generalist and release species showed mixed responses to thinning. I used both general linear models and classification and regression tree models to explore the association of herb species presence and flowering with conifer basal area and abiotic variables. Both modeling approaches yielded similar biological insights. Flowering was more sensitive than presence to current stand basal area. Flowering of old-growth associated and release species was negatively correlated with conifer basal area. Linear models allowed clearer hypothesis tests, while tree-based models had greater explanatory power and provided information about interactions between variables. / Graduation date: 2004

Biogenic volatile organic compounds (BVOC) are a wide-ranging group of trace gas components in the atmosphere which are emitted naturally from Earth’s surface. It is now recognised that biogenically sourced VOCs are far more significant on a global scale than those from anthropogenic sources, with up to 10 times greater emissions. Very few field-based studies of fluxes from plant canopies have been undertaken, particularly for non-terpenoid compounds. This thesis presents mixing ratio and flux measurements of BVOC from a range of temperate plant canopies: Douglas fir, short-rotation coppice willow, Miscanthus and mixed peatland vegetation. The virtual disjunct eddy covariance technique (vDEC) using a proton transfer reaction mass spectrometer (PTR-MS) as a fast VOC sensor was used for all measurements except for peatlands, where grab samples were collected on adsorbent sampling tubes for later chromatographic analysis. The PTR-MS was also utilised for measuring the rate of degradation of VOCs during laboratory chamber experiments. Mixing ratios and fluxes of VOCs measured within and above a Douglas fir forest were the first canopy-scale measurements for this species. Fluxes of monoterpenes were comparable to previous studies while isoprene was also detected (standard emissions factors up to 1.15 μg gdw -1 h-1 and 0.18 μg gdw -1 h-1, respectively). Emissions of oxygenated VOCs were also found to be significant, highlighting the importance of quantifying a wider variety of VOCs from biogenic sources, other than isoprene and monoterpenes. Results for bioenergy crops Miscanthus and willow showed that willow was a high isoprene emitter (20 μg gdw -1 h-1), but no measureable VOCs were detected from Miscanthus. This indicates that future expansion of bioenergy crops, and hence species selection, should take resultant air quality and human health impacts – due to changing VOC emissions – into account. Fluxes of BVOC from a Scottish peatland are the first reported measurements for this ecosystem in a temperate climate. Additionally, to assess the impact of nitrogen deposition on VOC fluxes, BVOC measurements were taken from sample plots in a pre-existing, long-term field manipulation study to assess impacts of wet nitrate or ammonium deposition on peatland. The peatland was found to be a significant source of isoprene and monoterpenes (590 and 1.5 μg m-2 h-1 respectively) and there was evidence that emissions were affected by wet nitrogen treatment. Isoprene emissions were reduced by both nitrate and ammonium treatment, while nitrate increased β- pinene fluxes. Increasing atmospheric nitrogen concentrations are therefore predicted to have an impact on VOC emission. Chamber studies showed that the rate of loss of α-pinene from the gas-phase during oxidation – and hence potential formation of secondary organic aerosol (SOA) – decreased with increasing isoprene mixing ratio. This was not observed for limonene. These results show that as isoprene mixing ratios increase with increasing global temperatures, negative feedback on radiative forcing from SOA particles may be suppressed. Results from this thesis provide valuable experimental data for a range of temperate plant canopies, which will help constrain modelled predictions of future VOC emissions. Additionally, the importance of understanding the effects of land use and environmental change on VOC emissions was demonstrated.

The spectral distribution of the global radiation from 0.4 to 2.5 microns penetrating deciduous and coniferous canopies were measured during clear days between 10 a.m. and 2 p.m. using a double-quartz monochromator. In the visible region (0.4 to 0.7 micron) the average relative spectral transmissions under both canopies are about one percent beginning at 0.4 micron and decreasing to about half a percent at 0.67 micron. There is only a small peak in the green (0.55 micron) transmission under deciduous stands while there is none under coniferous canopies. The slightly higher transmission in the blue (0.4 micron) is attributed to the direct sky radiation penetrating through the gaps in the canopies. There is a steep increase in the transmission at about 0.7 micron. The increase is relatively higher under deciduous stands compared to coniferous stands. In the infrared region from 0.8 to about 1.4 microns, the average relative spectral transmission under deciduous stands is about 10 percent which is double the transmission under coniferous canopies. The transmission under deciduous stands is about twice that of the coniferous stands throughout the near infrared with very low transmission in the water absorption band at 1.45 and practically no transmission at all in the 1.90 micron-band. The absolute spectral transmission exhibit a somewhat different distribution, especially in the visible region. Since the highest intensity of the solar spectrum in the open is located in the 0.5 micron-band, this is also reflected in the absolute values. The small peak in the green under deciduous stands is now indicated as a slight shift of the peak to the 0.55 micron-band. The water absorption bands at the 0.95 and 1.15 microns are also distinct, with hardly no transmission at all beyond 1.7 microns. The spectral transmittance of forest canopies differ from those reported for single leaves in the proportion of radiation transmitted in the visible and infrared regions. For example, the ratio of the transmission at 0.55 micron to that at 1.10 micron-band is about one to twelve compared to about one to five in single leaves. A deciduous canopy consisting of several layers of leaves wi ll only allow a very small amount of transmission, mostly in the green portion and somewhat more in the infrared region between 0.72 and 1.40 microns. Under natural conditions in the forest, there exists a very weak "green" shadow and a somewhat stronger "infrared" shadow. The altered spectral composition may influence the understory vegetation as regards photosynthesis, seed germination, and the photoperiodic responses in the forest floor.

Because riparian canopy controls most energy inputs to stream ecosystems, it directly affects the structure of aquatic food webs and the ecological processes that govern interactions among trophic levels. This study addresses the interdependence among riparian canopy, benthic community structure, and the carrying capacity of high desert streams for salmonid fishes. In streams in the lower John Day River Basin in eastern Oregon, algal, invertebrate, and fish communities were compared in reaches with varying densities of riparian canopy. Water temperatures varied with the density and upstream extent of canopy. Densely canopied sites were cool, while sites with high irradiances had temperatures exceeding the upper lethal limit for salmonids. Periphyton and grazer biomasses were greater in well-lighted sites, but 90% of grazer biomass consisted of Dicosmoecus gilvipes, a large caddisfly inedible by juvenile trout. Warmer water increased metabolic demands for salmonids, while the overwhelming dominance of Dicosmoecus in open sites shifted energy flow away from trout and shrunk their food base. High water temperatures, however, provided suitable habitat for many warmwater fishes which would otherwise not enter tributaries of this size. At higher elevation study sites in Camp Creek, light levels were higher and less variable than at the lower sites. Periphyton and invertebrate abundances were not correlated with irradiance. Rather, periphyton was maintained at low levels by grazers, particularly Dicosmoecus and snails. Manipulations of fish densities in enclosures showed that trout and dace had no negative impacts on numbers of invertebrate prey, and that grazers played a larger role in regulating lower trophic levels than did fish. Dicosmoecus acted as a keystone species in the benthic food web of Camp Creek by simultaneously influencing the trophic level both below and above its own. When irradiance was experimentally reduced under artificial canopies, periphyton standing crops were not different from those in open control pools after 4 wks. However, grazers were more abundant in open pools. The cropping of periphyton to uniform levels in both sunlight and shade indicated that mobile grazers targeted sites of varying productivities. Comparisons between benthic communities in Camp Creek and in a densely canopied reference stream suggested that benthic community structure shifted to accommodate changes in energy resources that occur when canopy density is altered. / Graduation date: 1998