<p> The net photosynthetic and dark respiration response to moisture, light level and temperature is discussed with reference to the unique Cladonia rangiferina (L.) Wigg.-Shrub association in Cladonia stellaris (Opiz.) Pouz. Spruce Woodland at Hawley Lake, Ontario. Field measurements provide a description of the summer and winter environmental complex. Winter data shows an exceptional thermal insulation afforded by snow cover, protecting lichen thalli from extreme air temperatures. Summer environmental data highlights the need to dissociate periods of thallus hydration (metabolic activity), and thallus dehydration in order that meaningful comparisons may be made with experimentally derived levels of metabolic activity. Experimentally derived physiology of the hydrated thallus showed a broad amplitude of tolerance to light level and temperature correlating with the wide range of temperature and light level experienced during a single thallus drying cycle in the field. Heat stress experiments illustrate this is indeed, a sensitive species restricted to the more ameliorated temperature regime of mature Spruce-Lichen Woodland. Heat sensitivity may also act to restrict C. rangiferina to the cooler micro-site afforded by the elevated shrub-hummocks.</p> <p> A spring to summer series of collections of a Muskoka population of C. rangiferina were coursed through heat stress experiments. Significant heat tolerance acclimation emerged as an essential response to withstand the high summer temperature regime.</p> / Thesis / Master of Science (MSc)

The short-term temperature-response of dark respiration may be altered by climate warming through temperature acclimation; however the role of drought in influencing thermal acclimation is not known. We hypothesized that leaf dark respiration in three dominant species of the southern oak savanna in Central Texas, Schizachyrium scoparium, Juniperus virginiana, and Quercus stellata, would respond differently to the effects of warming and intensified summer drought owing to their contrasting photosynthetic pathways, leaf habits, and drought tolerances. Furthermore, changes in respiration were predicted to be linked to alterations in leaf chemistry and structure, including leaf nitrogen and non-structural carbohydrates in response to warming and drought. Monocultures planted in replicated rainfall exclusion shelters were warmed ( 1.5 �C) and rainfall events were manipulated to intensify summer drought and augment cool season rainfall compared to the long-term mean. Both warming and drought affected the short-term temperature-response functions of dark respiration and species differed in their responses. Evidence of temperature acclimation through adjustment in Q10 (temperature sensitivity) and R10 (base rate at 10 �C) was found in S. scoparium and Q. stellata but not J. virginiana. All three species showed evidence of reduced temperature acclimation of respiration with progressive summer drought. Redistributed rainfall in J. virginiana increased respiration in midsummer compared to plants receiving the long-term mean rainfall, but differences disappeared in late summer when drought intensified. In response to rainfall events during summer drought, rates in S. scoparium increased, and the effect was greater in unwarmed compared to warmed plants. In both S. scoparium and Q. stellata, Q10 was reduced post-watering. Regression analyses of respiration against leaf N, soluble carbohydrates, and SLA revealed that relationships differed between species and temperature treatments. Respiration rates were uncoupled from changes in soluble carbohydrates in response to drought and rainfall pulses, suggesting that thermal acclimation is diminished by increasing drought stress in drying soils in contrasting tree and grass species. These findings suggest that models of respiratory carbon flux that incorporate temporal changes in respiratory temperature responses with drought and warming and unique species responses will be critical in predicting species and ecosystem-scale responses to climate change.

Net photosynthesis, dark respiration, chlorophyll concentrations and growth were determined for Rumex patientia L. exposed to UV-B radiation corresponding to reduced atmospheric ozone concentrations. The hypothesis of whether reciprocity is maintained in the response of R. patientia to polychromatic UV-B radiation was tested. On the basis of the relationships derived from these studies, a simulation model was developed for the prediction of photosynthesis and growth of R. patientia exposed to UV-B radiation corresponding to any atmospheric ozone reduction. Photosynthetic rates were found to be depressed after two hours exposure to UV-B irradiance simulating a 0.18 atm•cm ozone column when the sun is at 30° from the zenith. During this initial exposure period, partial stomatal closure was implicated in the suppression of photosynthesis. However, after one day exposure, substantial increases in photosynthetic resistances apart from stomatal diffusion resistance occurred in the UV-irradiated plants and no differences in stomatal diffusion resistance were apparent between UV-irradiated and control plants. Dark respiration rates were slightly higher in those plants exposed to UV radiation. Leaf expansion of R. patientia was substantially repressed but only during the initial few days of exposure. Thereafter, leaf expansion was similar in the UV-irradiated and control plants. A reduction in total plant dry weight and leaf area of approximately 50 percent occurred after 22 days treatment while chlorophyll concentrations remained unaltered. Time of leaf initiation was shawm to be delayed in those plants exposed to UV-B radiation. Leaf longevity was decreased with increased UV radiation but accelerated whole-plant senescence and death was not observed. Photosynthetic rates determined through the ontogeny of the third leaf of R. patientia exposed to four levels of UV irradiance were found to be depressed as a function of the accumulated biologically effective UV irradiation. Thus, reciprocity was demonstrated between 6350 and 3175 J biologically effective UV irradiation. Results of the simultion model showed that under reduced atmospheric ozone concentrations, suppression of photosynthesis and leaf growth would be more severe during mid-sunnner (i . e. June) than would occur during the March to early May period, This results from smaller solar angles from the zenith and lower prevailing ozone concentrations prevalent during June. A validation test of the model was made with photosynthetic data obtained during a field study with R. patientia exposed to UV-B radiation corresponding to a 38 percent atmospheric ozone reduction (0.18 atm•cm when the sun was at 30° from the zenith). This validation test showed a reasonable correspondence between the measured and predicted photosynthetic rates. R. patientia was selected as the test species for this study because (1) it is reasonably sensitive to UV radiation as determined in preliminary studies evaluating approximately 20 native and agricultural plant species, (2) it is normally exposed to full sunlight in · its natural habitat, and (3) individual leaves are relatively long - lived (about 60 days) and are not normally shaded by other leaves of the same plant. Although this species probably represents one of the more sensitive plants to UV radiation, it would be this group of sensitive plants that would be initially affected under conditions of reduced atmospheric ozone. If more resistant plants with long-lived plant parts also accumulate UV radiation damage as was shown to occur in R. patientia, over sufficient periods of time even these species might be significantly impacted under conditions of reduced atmospheric ozone.

Mit zunehmender Meereshöhe werden die Wachstumsbedingungen in tropischen Bergregionen im Allgemeinen ungünstiger, was sich in einer sinkenden Nährstoffverfügbarkeit, sinkenden Temperaturen und sinkendem CO2-Partialdruck zeigt. In tropischen Bergregenwäldern führen verminderte Abbauraten in größeren Höhen einerseits zu dicken organische Auflageschichten und andererseits in Kombination mit verminderten Mineralisierungs- und Nitrifizierungsraten zu Veränderungen in der Verfügbarkeit der verschiedenen Stickstoffformen, und es gibt Nachweise einer Limitierung der Produktivität dieser Wälder durch Stickstoff. Auf welche Weise sich die Photosynthesekapazität (Amax) tropischer Bäume einerseits und die Stickstoffaufnahmekapazität und Präferenz für einzelne Stickstoffformen andererseits an die veränderten Umweltbedingungen entlang von Höhengradienten adaptieren ist nicht genau bekannt. Die vorliegende Untersuchung wurde in drei tropischen Bergregenwäldern durchgeführt, die entlang eines Höhengradienten auf 1000, 2000 und 3000 m ü. NN in Südequador liegen. Das Ziel war es, (1) die Photosynthesekapazität ausgewachsener tropischer Bäume entlang eines Höhengradienten mit Hilfe von Gaswechselmessungen zu bestimmen und die Effekte von Temperatur, CO2-Partialdruck und Nährstoffverfügbarkeit auf die Photosynthese zu quantifizieren und (2) Veränderungen in der Verwendung von Nitrat, Ammonium und organischen Stickstoffquellen durch tropische Waldbäume mit der Meereshöhe mittels einer Tracer-Untersuchung mit stabilen Isotopen an Jungpflanzen zu untersuchen. Mittelwerte der lichtgesättigten Photosyntheserate (Asat) auf Bestandeseben betrugen 8.8, 11.3 und 7.2 µmol CO2 m-2 s-1, die der Dunkelatmung (RD) 0.8, 0.6 und 0.7 µmol CO2 m-2 s-1 jeweils auf 1000, 2000 and 3000 m Meereshöhe, ohne einen signifikanten Höhentrend. Die Einordnung unserer Daten in den Kontext eines pantropischen Asat-Datensatzes von tropischen Bäumen (c. 170 Arten an 18 Standorten unterschiedlicher Meereshöhe) zeigte, dass das flächenbezogene Asat in tropischen Bergen im Mittel 1.3 µmol CO2 m-2 s-1 pro km Höhenzunahme abnimmt (bzw. 0.2 µmol CO2 m-2 s-1 pro K Temperaturabnahme). Die Abnahme von Asat trat auf, obwohl die Blattmasse je Fläche mit der Höhe zunahm. Eine verminderte Photosyntheserate und eine reduzierte Bestandesblattfläche bewirken gemeinsam eine Verringerung der Kohlenstoffaufnahme des Kronenraums mit der Meereshöhe in tropischen Bergregionen. Der Phosphorgehalt pro Blattmasse war der Faktor, der Amax entlang des Höhengradienten hauptsächlich beeinflusste, während die Effekte von Blattstickstoff, Temperatur und CO2-Partialdruck nicht signifikant waren. Amax erfuhr einen teilweisen und RD einen vollständigen homöostatischen Ausgleich als Reaktion auf die Verminderung von Temperatur und CO2-Partialdruck in größeren Höhen, was hauptsächlich durch eine stark reduzierte spezifische Blattfläche (SLA) und die daraus entstehende Zunahme von Blattstickstoff und -phosphor je Blattfläche bedingt war, während keine Zunahme der Karboxylierungseffizienz festgestellt wurde. Wir schlussfolgern, dass die Verminderung von SLA und Gesamtblattfläche mit der Meereshöhe die Kohlenstoffaufnahme von tropischen Wäldern in großen Meereshöhen deutlich stärker bestimmen als adaptive physiologische Modifizierungen des Photsyntheseapparates. Jungpflanzen von sechs Baumarten unterschieden sich hinsichtlich ihrer Präferenz für verschieden Stickstoffformen, allerdings schienen weder das Amonium- und Nitratvorkommen im Boden noch die Meereshöhe die Präferenz zu beeinflussen. Zwei Arten (jeweils die, mit den höchsten Wachstumsraten) bevorzugten Amonium gegenüber Nitrat, während die restlichen vier Arten Nitrat und Amonium mit ähnlichen Raten aufnahmen, wenn beide Stickstofformen verfügbar waren. Nach der Gabe von 15N13C-Glyzin zeigte sich bei drei Arten eine signifikante Akkumulierung von 13C in der Biomasse (zwei Arten mit arbuskulären Mykorrhiza und eine Art mit Ektomykorrhiza) zusätzlich zu einer signifikanten Akkumulierung von 15N, was darauf hindeutet, dass Bäume in tropischen Bergregenwäldern organische Stickstoffverbindungen unabhängig vom Typ ihrer Mykorrhizierung aufnehmen können.

Sink limitations in plants reduce the potential for photosynthesis and yield, particularly under conditions that favour enhanced source activity such as elevated CO2 (EC). Dark respiration, considered catabolic, has rarely been exploited to enhance sink activity in plants. Arabidopsis thaliana L. lines with partially-suppressed mitochondrial pyruvate dehydrogenase (mtPDH) kinase (mtPDHK), a negative post-translational regulator of the mtPDH complex, was shown previously to have both elevated mtPDH complex activity and increased seed weight and oil content at ambient CO2 (AC), suggesting an enhancement of sink activity. The mtPDH links glycolysis with the tricarboxylic acid (TCA) cycle. It was hypothesized that Arabidopsis having suppressed mtPDHK will display their greatest plant productivity at EC through a combined enhancement of source and sink activities. Control and transgenic Arabidopsis having either constitutive or seed-specific expression of antisense mtPDHK were grown at either AC or EC. Expression of mtPDHK and mtPDH complex activity in rosette leaves and reproductive tissues were measured, which required the development of an assay to quantify mtPDH activity. Vegetative and reproductive growth over time, seed oil parameters, and leaf net C exchange were also quantified. A parabolic relationship was found between mtPDHK expression and mtPDH activity, reflecting a role for mtPDH in balancing photosynthetic and respiratory processes. A number of growth and seed oil parameters were improved in transgenic lines, particularly at EC; many of these parameters showed a significant linear or quadratic correlation with mtPDHK expression and mtPDH activity. The proportion of very long chain fatty acids was increased in transgenic lines. Leaf net C exchange was enhanced at AC and EC, and particularly in lines showing repression of mtPDHK. The greatest enhancement in total seed and oil productivity was found for the constitutive lines 104 and 31 at EC (up to 2.8 times). These two lines exhibited a significant increase in inflorescence size, an increase in leaf water use efficiency, the lowest rate of mtPDH complex inactivation by ATP, and an intermediary enhancement of mtPDH complex activity in seeds. Thus, it is concluded that the mtPDH plays a key role in regulating sink and source activities in plants. / Natural Sciences and Engineering Research Council (NSERC) through the Green Crop Networks Research Network; Ontario Graduate Scholarship; Syngenta Graduate Scholarship; Ball Farm Services and Agrico Canada Ltd. Scholarship; Mrs. Fred Ball Scholarship; Arthur D. Latornell Scholarship; Hoskins Scholarship; Robb Travel Grant; Registrars and the Deans Scholarship and travel awards and bursaries from the University of Guelph, and the Ontario Agricultural College.

農林水産研究情報センターで作成したPDFファイルを使用している。