This thesis consists of three manuscripts describing ecophysiological research on the cyanolichen Lobaria oregana. The first manuscript includes a re-evaluation of the assumptions underlying past estimates of N fixation by this species and provides an estimate of annual N fixation at the Wind River Canopy Crane (WRCC). Based upon litterfall data, canopy biomass data, N content of lichen tissue, and published growth rates, L. oregana fixes 0.4-1.6 kg N₂ ha⁻¹ yr⁻¹. The second manuscript presents a series of physiological response curves and a model of N fixation by L. oregana. Temperature is the most important parameter controlling nitrogenase activity in hydrated thalli. The model is used to predict annual N fixation at the WRCC and at the H.J. Andrews (HJA) Experimental Forest. Lobaria oregana fixes 1.4-1.8 kg N₂ ha⁻¹ yr⁻¹ at the WRCC, and low winter temperatures often inhibit nitrogenase activity. Temperatures at the HJA are slightly warmer during the winter, and L. oregana fixes 2.6-16.5 kg N₂ ha⁻¹ yr⁻¹ depending on its stand-level biomass. The third manuscript investigates the effects of thallus water content, light, and temperature on CO₂ exchange in L. oregana. This species shows a typical photosynthetic response upon rehydration, and like other lichens it becomes light-saturated at low PAR levels. Positive net photosynthesis in L. oregana occurs only between 1-12°C. High respiration rates prevent carbon gain at warmer temperatures. The temperature constraints on carbon gain and nitrogen fixation may explain some of the landscape distribution patterns of L. oregana. / Graduation date: 2002

Thermophysiological traits of two isolated Hoplodactylus maculatus populations were investigated to test adpatations to climate. Geckos were collected from Craigieburn (high altitude, generally cooler site) and Banks Peninsula. If climatic conditions at respective sites influenced physiology, I expected geckos from Craigieburn to exhibit cold-adapted physiological traits, whilst Banks Peninsula geckos would exhibit traits more characteristic of a warmclimate species. To this end I investigated four thermophysiological parameters: metabolism (SMR), preferred body temperature (PBT), locomotory performance and critical thermal minimum (CTMin). I hypothesized that if climate had an effect on SMR, Craigieburn geckos would exhibit higher levels of SMR which typically characterise other coolclimate reptiles. Craigieburn geckos displayed an average relative elevation of SMR over Banks Peninsula geckos of 26%. Furthermore, Craigieburn geckos appeared to be 'geared' towards lower body temperatures and exhibited a greater acclimatory and acclimatizatory ability of SMR. The PBT of Craigieburn geckos was consistently elevated above Banks Peninsula geckos. This finding was somewhat paradoxical in light of previous studies of this parameter. A closer examination of the ecology of the two populations is required to clarify the adaptive significance of a higher PBT in geckos from a cooler climate. With respect to locomotory performance, I hypothesized that if thermal extremes influenced activity, Craigieburn geckos would exhibit activity patterns which help ameliorate the adverse effects of cold temperature. Craigieburn geckos did in fact have greater independence of activity to temperature than Banks Peninsula geckos, especially over lower body temperatures. The final parameter investigated, that of the critical thermal minimum, failed to distinguish the populations decisively. However there was some evidence of a greater acclimatizatory and acclimatory range in Craigieburn geckos, providing somewhat limited support for a population difference. Investigations into all four parameters lead me to conclude that populations of Hoplodactylus maculatus from Craigieburn and Banks Peninsula are physiologically distinct and warrant a revision of nomenclature.

As forests change, tree physiology responds to changes in resource demands. The impact of Pinus taeda (loblolly pine) mortality on physiology of successional hardwoods is unknown. Liquidambar syraciflua (sweetgum) and loblolly pine individuals were measured for resource-use during a simulated southern pine beetle mortality event where several pines underwent a girdling treatment. Sweetgum next to untreated pines had significantly higher sapflow every month, markedly throughout post-mortality months. Sapflow and photosynthetic capacity significantly declined in girdled pines before needle discoloration. Nitrogen concentration of senesced pine and sweetgum leaves significantly increased from pre-mortality to post-mortality. Pine mortality led to increases in sweetgum water use and leaf nitrogen content. A shift in species dominance from loblolly pine to sweetgum would reduce water lost by pine transpiration during sweetgum dormancy by approximately 154 mm. These data indicate significant responses to disturbance and seasonal resource demands in this forest type.

No description available.

Global climate change is predicted to alter the weather patterns around the world, as climatic zones shift, forest carbon sequestration projects (e.g. the UK woodland carbon code) need to take into account the specific requirements of planted species. In the UK, oaks are an important charismatic group of trees favoured in recent planting programmes. The English oak (Quercus robur L.), has poor water conservation, but is a major component of natural forests in lowland UK. On the other hand, Holm oak (Quercus ilex L.) is a Mediterranean oak that has high water conservation and can also tolerate cold despite being restricted by minimum temperatures. At local scales, there may be advantages of planting either evergreen or deciduous oak species for forestry and climate mitigation. Alternatively, a comparative assessment of non native versus native productivity, may give clues to the invasiveness potential of Holm oak and its ability to out compete the deciduous oak along an urban to upland gradient. This thesis documents a series of field based experiments intended to analyse differences in carbon sequestration potential and photosynthetic efficiency between these two species and in relation to their environment within the Southwest UK. 520 one year saplings were planted, half in pots and half in nursery field beds situated on Dart- moor, the east Devon Dartmoor fringe, Totnes, and Plymouth city centre. Originally two sites were chosen for their relative ‘urban’ qualities, two at ‘rural’ localities, one upland and a control site with access to a polytunnel for comparisons with well-watered and non nutrient limited trees. However, data analyses showed that sapling characteristics were site specific with the five sites falling along an urban, rural to upland gradient. The field experiments included monthly height and diameters (ground level diameter or DAG), monthly assimilation rates and analy- sis of chlorophyll fluorescence to aid interpretation of photosystem II functioning and sapling ‘vitality’. Further laboratory experiments analysed specific leaf area (SLA), mass based leaf Nitrogen (Nleaf ) and carbon (Cleaf), with differences between sun and shade leaves included, to aid comparisons between species and sites. The final experiment was a destructive harvest and this was used to find total biomass estimates and carbon allocation to different root shoot fractions. In order to quantify differences between saplings and adult trees a smaller experiment was con- ducted in the canopy using experienced climbers and leaf level productivity analysed. Intrinsic water use (iWUE), stomatal conductance (Gs), means net assimilation rates (An) and chloro- phyll fluorescence parameters; Variable fluorescence over maximum fluorescence (Fv/Fm) and performance index (PI) were measured and relative carbon assimilation rates and productivity assessed and compared between species at one urban , rural and upland site. Results showed that Q. ilex allocated relatively more carbon to branches and leaves as a sapling which in turn increased growth rate and whole tree assimilation rates to larger values than the deciduous oak despite Q. robur being able to increase maximum assimilation rates in response to increasing temperatures. This gives Q. ilex the advantage and overall biomass was higher at all sites than Q. robur apart from the upland site where there were no differences in biomass accumulation between species. However, despite no significant difference in biomass at this site Q. robur had greater survival and photosystem II functioning. In mature trees Q. ilex was under stress and Nleaf and carbon sequestration potential were higher in the deciduous species at the urban site. In contrast, Q. robur was under stress at the upland site at Castle Drogo where thin and nutrient poor soils have made it more vulnerable to drought stress. Here, mature Q. ilex showed reduced photosynthetic efficiency in relation to cold and drought, but was able to recover when milder temperatures occurred. The results were site specific, with a reduction in both SLA and relative allocation to the leaf weight fraction (LWF) in Q.robur the only common urban related effect seen. The potential for Q. ilex to perform well at sapling stage is due to its morphological plasticity and drought tolerance. This species may become more prevalent within the Southwest as local climates continue to push it northwards from its natural Mediterranean range. In contrast, if Q. robur continues to suffer from defoliation and fungal attack and this may leave it more vulnerable to competition throughout less fertile and drier areas of its natural range.

No description available.

The Bromeliaceae is one of the largest and most ecologically diverse angiosperm families in the Neotropics. In recent years, this family has begun to emerge as a model system for the study of plant evolutionary ecology and physiology, and major advances have been made in understanding the factors involved in episodes of rapid diversification and adaptive radiation in specific bromeliad lineages. However, despite a long tradition of ecophysiological research on the Bromeliaceae, an integrative, evolutionarily-contextualised synthesis of the links between anatomical) physiological, and ecological aspects of bromeliad biology has hitherto been lacking. The overarching aim of this research project was therefore to use new quantitative data representing a wide range of bromeliad taxonomic and functional groups to elucidate how variation in leaf traits connected by structure-function relationships influences ecological differentiation among bromeliad taxa. Special emphasis was placed on hydraulic and water relations traits because of fast-paced contemporary developments in these fields. The methodologies employed included an assessment of the diversity of bromeliad hydrological habitat occupancy, quantification of key anatomical and physiological traits and their correlations, investigation of the links between vascular and extra-xylary anatomy and hydraulic efficiency and vulnerability, quantification of stomatal sensitivity to leaf-air vapour pressure deficit and stomatal kinetics, and a case study of trait-mediated niche segregation among congeneric epiphytic bromeliad species on the Caribbean island of Trinidad. The results highlight how divergences in a range of continuous and categorical anatomical traits underpin differences in physiological capacities and sensitivities, which in turn determine environmental relations and ecological distinctiveness. This research project therefore provides critical insights into the mechanistic basis of evolutionary diversification in a highly ecologically important family. It also represents the most comprehensive analysis of the significance of trait variation for ecological differentiation across any major radiation of herbaceous angiosperms.

The colonial, N2 fixing cyanobacterium Trichodesmium is a keystone species in oligotrophic ocean ecosystems. Trichodesmium is responsible for approximately 50% of the total biologically fixed N2 in the ocean, and this “new” nitrogen fuels primary productivity and the amount of carbon sequestered by the ocean. Trichodesmium does not exist in isolation. Colonies occur ubiquitously with an assemblage of epibiotic microorganisms that are distinct from planktonic microbes and modulated across environments, yet the implications of this relationship have not been explored. In this thesis, the ecology, physiology, and potential geochemical impact of interactions within the Trichodesmium host-microbiome system were examined across three different oligotrophic ocean environments. First, to establish the metabolic diversity contributed by the microbiome to Trichodesmium consortia, a whole community metagenomic sequencing approach was used across a transect the western North Atlantic. This study demonstrated that the microbiome contributes a large amount of unique functional potential and is modulated across a geochemical gradient. In the following study, metatranscriptomics was used to show that such metabolic potential in Trichodesmium and the microbiome was expressed and modulated across the environment. Colonies were sampled in the western tropical South Pacific and gene expression dynamics indicated co-limitation by iron and phosphorus, and revealed a mechanism for phosphate reduction by Trichodesmium and subsequent utilization by the microbiome. These activities were verified with phosphate reduction rate measurements and indicated cryptic phosphorus cycling within colonies. Next, the suite of potential physiological interactions between host and microbiome was assessed with metatranscriptome sequencing on high frequency samples of Trichodesmium colonies from the North Pacific subtropical gyre. Synchronized day-night gene expression periodicity between consortia members indicated tightly linked metabolisms. The functional annotations of these synchronous genes indicated intra-consortia cycling of nitrogen, phosphorus and iron, as well as a microbiome dependence on Trichodesmium-derived cobalamin—interactions that could alter the transfer of these resources to the surrounding water column. In the final study, the effect of the microbiome on Trichodesmium N2 fixation was assessed. Using colonies obtained from the North Atlantic, activity in the microbiome was selectively modified using quorum sensing acyl homoserine lactone cell-cell signaling, a mechanism that Trichodesmium itself does not possess. These experiments indicated that the microbiome has the potential to increase or decrease Trichodesmium N2 fixation to a degree that rivals the effects of alterations in nutrient concentration, but at a more rapid rate. In all, the research presented in this thesis demonstrates the integral importance of the microbiome to Trichodesmium physiology and ecology, highlighting the importance of an unexplored facet of marine microbial systems that likely influences the biogeochemistry of the planet.

"June 2002" / Bibliography: leaves 172-198. / viii, 198 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Proposes that the overall outcome of plant interactions along a temporal gradient of resource availability changes from positive during interpulses to negative during pulses. Examines negative interactions between 4 co-dominant chenopod scrubs in arid Acacia papyrocarpa woodlands. Negative interactions were more intense when conditions were least productive. Positive interactions between seedlings also changed over time, depending on the facilitation mechanism. Plant interactions seem to be most intense at the beginning of interpulses when plants are competing for diminishing water, or survivorship is enhanced in the favorable microsites provided by other plants. Later in the interpulse, interactions become less intense as conditions become more stressful and therefore survivorship and growth are affected more by abiotic conditions than plant interactions. / Thesis (Ph.D.)--University of Adelaide, Dept. of Environmental Biology, 2002

Juvenile chinook salmon (Oncorhynchus tshawytscha) were experimentally infected with Renibacterium salmoninarum (Rs), the causative agent of bacterial kidney disease (BKD), to investigate the effects of BKD on three aspects of juvenile salmonid performance: (1) predator avoidance ability; (2) smoltification; and (3) physiological responses to stress. For these experiments, fish with different Rs-infection profiles (created by using an immersion challenge method) were sampled to assess physiological change and subjected to various performance tests during disease progression. When equal numbers of Rs-challenged and unchallenged fish were subjected to predation by northern pikeminnow (Ptychocheilus oregonensis) or smallmouth bass (Micropterus dolomieui), Rs-challenged fish were eaten in significantly greater numbers than controls by nearly two to one. A progressively worsening infection with Rs did not alter the normal changes in gill ATPase and condition factor associated with smoltification in juvenile chinook salmon. A dramatic proliferation of BKD was associated with maximal responses of indicators of smoltification, suggesting that the process of smoltification itself can trigger outbreaks of disease. When Rs-infected fish were subjected to three 60-s bouts of severe handling that were separated by 48-72 h, this experience did not lead to higher infection levels or increased mortality when compared to diseased fish that did not receive the stressors. Furthermore, the kinetics of plasma cortisol, glucose, and lactate over 24-h following each stressor were similar between fish with moderate to high BKD and those that had low or no detectable infection. Fish with moderate to high Rs infections had higher titers of cortisol and lactate prior to each application of the stressor and were also unable to consistently elicit a significant hyperglycemia in response to the stressors when compared to fish with low infection levels. During all experiments, fish consistently developed decreased hematocrits and blood glucose levels and increased levels of cortisol and lactate as the disease worsened, indicating that BKD is stressful, particularly during the later stages. Collectively, these results illustrate the impact of BKD on juvenile salmonids and have also ascribed some ecological significance to this disease beyond that of direct pathogen-related mortality. / Graduation date: 1999