Weed seed contaminants in agricultural products from China in recent years have the potential for introducing new invasive plant species. Seeds of 169 weedy species from 39 families were collected from Chinese farmlands. Fifty-eight of these that are currently absent in Canada were evaluated. Two weed risk assessment (WRA) models (modified WRA+ secondary screen tool and weed elsewhere+ modified WRA+ secondary screen tool) rejected all invasive plant species and showed similar accuracy in non-invasvie plant species prediction based on 140 existing alien plant species in Canada, yet the second WRA model took significantly less time to conduct the evaluation. Fifty-five potential invasive species with various negative impacts in Chinese farmlands were rejected to enter Canada by the “weed elsewhere+ modified WRA+ secondary screen tool” model, including eight species that cause significant damage to Chinese farmlands. However, Anemone rivularis and Silene jenisseensis, which have no negative impacts in China, were also rejected. Seed germination characteristics among 18 Chinese weedy species were found with base temperatures for germination (Tb) varying from -2.5°C to 10.9°C, thermal time requirements to reach 50% germination (θ_50) ranging from 23.7 to 209.2℃*Day, and different optimal temperatures for germination, which may facilitate these species to cause different degrees of negative impacts in Canadian prairie provinces. An alien species would have a higher competitive advantage in resource uptake and space occupation than its congeneric with advantageous seed germination characteristics; otherwise it will be less competitive than its congeneric. In addition, plant functional traits that promote invasiveness would make an alien species more invasive. In conclusion, the “weed elsewhere+ modified WRA+ secondary screen tool” model is a fast and highly accurate way to screen out potential invasive species from Chinese environments, and is applicable to other environments with modification. Seed germination characteristics can be used to predict seasonal dynamics of weed seedling populations. The comparison of seed germination characteristics and other plant functional traits between alien plant and its congeneric weed from native areas provides a new way to evaluate the invasive potential of alien plant species.

River environments are complex and dynamic ecosystems, and provide valuable ecosystem services such as clean water. The species rich riparian vegetation performs many important ecosystem functions such as reducing erosion and filter inputs from upland areas. Regulated flow regimes have decreased riparian plant species richness, cover and plant performance. To restore the integrity of riparian ecosystems, mitigation measures such as re-regulation of water-level regimes toward more natural seasonal fluctuations may be needed. The aim of this study was to assess potential responses of riparian plants to changes in water-level regulation in run-of-river impoundments to better match natural flow regimes. The elevational extent of plant species on riverbanks of two run-of-river impoundments in the Ume River were surveyed and their probability of occurrence along the gradient of inundation duration was modelled and compared to their distribution in the free-flowing Vindel River. Most species showed similar tolerance to flooding in the Ume and Vindel Rivers. Changes in elevational extent in response to three simulated environmental flow regimes were predicted by using the relationship between plant occurrence and inundation duration. A simulated spring flood and low water levels during the latter part of the growing season is predicted to result in the largest increase in elevational extent, with increases of 70-80% for several riparian species. However, only 47% of the riverbanks along run-of-river impoundments in the Ume River is deemed to be suitable for plant establishment, since many riverbanks are steep and devoid of fine-grained substrate as a result of erosion. / Älvmiljöer utgör komplexa och dynamiska ekosystem som tillhandahåller värdefulla ekosystemtjänster så som rent vatten. Den artrika strandvegetation bidrar till många viktiga ekosystemsfunktioner som närings- och giftupptag och till minskad erosion. Vattenregleringen med förändrade flödesregimer har minskat artrikedom, täckningsgrad och tillväxt av strandväxter. För restaurering av strandekosystemen kan omreglering till mer naturliga säsongsvariationer i vattenståndet vara nödvändigt. Den här studien syftade till att förutsäga hur utbredningen av strandväxter längs stränder i vattenkraftsmagasin potentiellt skulle förändras vid användande av miljöanpassade flöden för att mer likna naturliga flödesregimer i outbyggda älvar. Jag undersökte växternas utbredning i höjdled på stranden längs två magasin i Umeälven och beräknade sannolikheten för varje arts förekomst längs strandens översvämningsgradient. Av de arter som förekom i både Umeälven och den närliggande, outbyggda Vindelälven jämfördes växternas utbredningsgränser i respektive älv. De flesta arterna uppvisade liknande översvämningstolerans i Umeälven och Vindelälven. För att förutsäga förändringar i utbredning som respons på tre olika simulerade miljöanpassade vattenståndsregimer, jämfördes arternas översvämningstolerans vid nuvarade vattenstånd med simulerade vattenståndsregimer. En simulerad vårflod och lågt vattenstånd under sensommaren förväntas ge de största responserna i artutbredning med ökningar på 70-80% för ett flertal strandväxter. Endast 47% av älvstränderna i magasinen i Umeälven bedöms vara lämpliga för växtetablering eftersom stora delar av strandsträckorna är branta och saknar finkornigt substrat till följd av erosion.

Atualmente vêm sendo desenvolvidas e utilizadas várias técnicas de modelagem de distribuição geográfica de espécies com os mais variados objetivos. Algumas dessas técnicas envolvem modelagem baseada em análise ambiental, nas quais os algoritmos procuram por condições ambientais semelhantes àquelas onde as espécies foram encontradas, resultando em áreas potenciais onde as condições ambientais seriam propícias ao desenvolvimento dessas espécies. O presente estudo trata do uso da modelagem preditiva de distribuição geográfica, através da utilização de algoritmo genético e algoritmo de distância, de espécies como ferramenta para a conservação de espécies vegetais, em três situações distintas: modelagem da distribuição do bioma cerrado no estado de São Paulo; previsão da ocorrência de espécies arbóreas visando à restauração da cobertura vegetal na bacia do Médio Paranapanema e modelagem da distribuição de espécies ameaçadas de extinção (Byrsonima subterranea). A metodologia empregada e os resultados obtidos foram considerados satisfatórios para a geração de modelos de distribuição geográfica de espécies vegetais, baseados em dados abióticos, para as regiões de estudo. A eficácia do modelo em predizer a ocorrência de espécies do cerrado é maior se forem utilizados apenas pontos de amostragem com fisionomias de cerrado, excluindo-se áreas de transição. Para minimizar problemas decorrentes da falta de convergência do algoritmo utilizado GARP (Genetic Algorithm for Rule Set Production), foram gerados 100 modelos para cada espécie modelada. O uso de modelagem pode auxiliar no entendimento dos padrões de distribuição de um bioma ou ecossistema em uma análise regional e local. / Many different techniques are being used today with different objectives to model the geographic distribution of species. Some of these techniques are based on environmental analysis where algorithms search for environmental conditions similar to those where the species were found, resulting in potential areas where the environmental conditions would be favorable for the development of these species. The present study is based on predictive modeling of the geographic distribution of species using genetic and distance algorithms as a tool for plant conservation in three different situations: modeling the Cerrado biome of the state of São Paulo; predicting the occurrence of tree species, aiming at the recuperation of the Médio Paranapanema watershed; and, modeling the distribution of endangered species (Byrsonima subterranea). The methodology used and the results obtained were considered satisfactory for the generation of geographic distribution models for plant species, based on abiotic data for the regions studied. The accuracy of the model in predicting the occurrence of species in the Cerrado is greater if only points that occur within the Cerrado and not in transition areas are used. In order to minimize problems due to the lack of convergence of the genetic algorithm GARP (Genetic Algorithm for Rule Set Production), 100 models were generated for each specie. The use of modeling tools can help understand the distribution patterns of a biome or ecosystem in a regional or local analysis.

Although water stress is an important selective force in many environments, it is not commonly considered to be of particular importance in tundra areas. Even t hough large portions of tundra may have an abundance of water, other more exposed areas may become quite dry. This microsite variability with respect to moisture stress was reflected in soil water potential measurements obtained from an alpine tundra area on Niwot Ridge in Colorado. Even though soil water potentials were consistently above -5 bars in a relatively low lying Deschampsia meadow, soil water potentials from an exposed fellfield area were often as low as -15 bars. Since moisture stress affects a number of important physiological processes in plants and since moisture stress may develop in at least some tundra areas, this study was undertaken to determine whether the sensitivity of plant physiological processes to water stress may be one important contributing factor in determining the microsite distribution of different tundra species. The alpine tundra species examined in this study were Deschampsia caespitosa which is typically found in wet meadow habitats and Geum rossii, a species which ranges from wet meadow to exposed fellfield habitats. The arctic tundra species investigated were Dupontia fischeri which is restricted mainly to wet meadow areas and Carex aquatilis, a species ranging from wet meadows to drier, more exposed areas. For both the arctic and al pine tundra species, though the photosynthetic capacities of the tundra species restricted mainly to wet meadow areas were higher under conditions of low moisture stress, the wider ranging tundra species were able to maintain greater photosynthetic capacity as soil moisture stress increased. Although the depression of photosynthesis with water stress in these tundra species could be partially attributed to reduced stomatal aperture, with decreased soil water potential most of the decline of photosynthesis was due to a greater non-stomatal or residual resistance, indicating a direct impact of water stress on the photosynthetic apparatus. Dark respiration did not increase with enhanced water stress. Thus, although photorespiration may have increased, increased mitochondrial respiration is unlikely involved in the depression of net photosynthesis. The wet site species typically exhibited higher photosynthesis/transpiration ratios for photosynthesis at low soil moisture stress levels; however, as soil moisture stress increased, the wider ranging species generally maintained higher photosynthesis/transpiration ratios. At high soil water potentials stomata of the species restricted typically to wet meadow tundra areas did not appear to undergo a closing response until the bulk leaf water potential decreased; however, reduced stomatal aperture of the tundra species with a wider distribution was noted before leaf water potential dropped. Although the stomatal mechanism of wet site tundra species exhibited lower degrees of occlusion at high soil water potentials, for the more widely distributed tundra species, Carex and especially Geum, stomatal closure was less pronounced as soil water potential decreased. The ability of Geumto maintain a low liquid phase water transfer resistance from the soil to the leaves as well as to experience relatively small reductions in turgor pressure as moisture stress increased may be important factors in maintaining a favorable leaf water balance over a rather broad range of soil moisture regimes. Differences in turgor pressure response with respect to moisture stress may be associated with differences in cell wall elasticity. Calculations of cell wall elasticity suggest that the wider ranging species have more elastic cell walls as compared with the more rigid, inelastic cell walls in the wet site tundra species. The results of this study show that tundra plants have different gas exchange sensitivities and water relation responses with respect to moisture stress and suggest that these at tributes may be important contributing factors in determining the local distribution of these species.

For this dissertation, I examined the ability of field-grown plants to capture N presented in enriched patches or in whole-plant pulses. I assessed root proliferation in N-enriched patches when Agropyron desertorum plants had been previously fertilized or shaded. All plants responded with increased root growth rates in N-enriched patches. However, root proliferation by shaded plants was 50% less than unshaded plants. Unexpectedly, plants with higher N status had greater root growth rates in enriched patches than plants that had not received N supplement. I concluded that plants already under competitive pressure above ground for light and below ground for nutrients should be less able to respond to opportunities presented in nutrient patches. I then examined plant growth responses and biomass production of six Great Basin species (Bromus tectorum, Taeniatherum medusae, Agropyron desertorum, Pseudoroegneria spicata, Artemisia tridentata, and Chrysothamnus nauseosus) following a pulse ofN applied in the early, mid, or late spring. An equal quantity of N, applied continuously, was a control. Surprisingly, most of the species grown under the continuous supply had lower growth rates and less biomass production than plants recieving an N pulse. The exception was Chrysothamnus, which responded equivalently to all treatments. Generally, the greatest response occurred in early phenological stages. Four of the six species had their greatest response to the early-spring pulse, suggesting that these cold-season species are well-adapted to take advantage of early spring nutrient pulses. This study demonstrated that instead of benefitting from a season-long supply of N, there were times during the growing season when plants were able to use pulses of N for significant gains in biomass. I also investigated the root properties (root biomass, specific root length [the ratio of root length:root mass], and root uptake capacity) that determined plant response to pulses. Despite considerable temperature differences and changes in plant phenological stages, root uptake capacity remained remarkably constant throughout the season. However, this consistency did not explain the differences in productivity during the season. Root biomass also did not explain these growth responses to pulses. Instead, I suggest that the quantity of actively growing fine roots, plus the ability to effectively exploit the soil volume in the early spring, results in capture of early nutrient pulses.

Two hundred and forty three fungal isolates were obtained from roots of four Woollsia pungens (Cav.) F. Muell plants collected from a field site in New South Wales, Australia. 175 sterile isolates were slow growing and dark-coloured on 2 percentage malt agar and were selected for further analysis. Microsatellite-primed PCR using the primers (GACA)4 and (GTG)5 separated these isolates into 50 genets. Isolates representative of 43 genets (including 168 isolates in total) formed typical ericoid mycorrhizal structures when inoculated onto roots of Vaccinium macrocarpon Ait (Ericaceae), confirming their status as mycorrhizal endophytes. It was estimated that a minimum of 43 genetically-distinct mycorrhizal mycelial genets were present in the root systems of the sampled W. pungens population with 7 to 15 distinct endophytic genets identified in each host plant, indicating that considerable genetic diversity exists within the endophyte population. While most genets were represented by less than 8 isolates, 3 genets contained up to 41 isolates, suggesting that root system colonisation by some mycelia may be extensive. While most fungal genets were shown to be confined to individual plants, 2 genets (genets 32 and 33), however, were present within the root systems of 2 adjacent plants (plants C and D), suggesting that the two root systems were interconnected by the endophyte mycelia. The ITS region of 13 mycorrhizal endophytes and a non-mycorrhizal isolate selected from the endophyte population were sequenced and compared to the sequence of Hymenoscyphus ericae as well as sequences from the GenBank database. A phylogenetic tree was generated from the nucleotide sequence data. This analysis revealed that 6 putative taxa were present in the root systems of 4 host plants. No isolates were positively identified to genus or species level. Closest matches with fungal sequences in the database indicated that most isolates probably belonged to the order Leotiales. Cluster analysis on the basis of the ITS sequences indicated that H. ericae was not clustered together with any endophytes from W. pungens, suggesting that endophytes of W. pungens are not identical to the known ericoid mycorrhizal fungus H. ericae. H. ericae had a low degree of sequence similarity with isolates from W. pungens, with similarities ranging from 68.3-80.6%. Cluster analysis based on DNA sequences of the ITS region did not fully support the groupings inferred from microsatellite-based fingerprinting. / Master of Science (Hons)

In the tropics, widespread deforestation and conversion of primary forests to agricultural and pasture lands has resulted in losses of composition, structure, and functions of forest landscapes. Deforestation in the tropics is typically preformed via slash-and-burn practices; the byproducts from combustion have been identified as the second-highest form of anthropogenically derived 'greenhouse-gases' (such as carbon dioxide) to the atmosphere, and have been linked to the warming of the earth. Landscape-scale measures of species composition and biomass structure of primary forests are important for two reasons: (i) they provide accurate, land-based measures to predict what has been lost due to land-uses, and (ii) they aid in the discovery of key factors which explain patterns in compositional and structural diversity that are useful for defining conservation objectives. In this thesis, I enumerate the landscape-level patterns in species composition and biomass and C structure for 20-0.79 ha primary tropical forest stands within the region of "Los Tuxtlas", Veracruz, Mexico. These 20 sites were selected to capture the variability in composition and structure with respect to an array of environmental variables. These variables included a wide elevational range (15-1280 m.a.s.l.), variable slopes (Range: 3-41% slope), 3 soil-types (ash derived, lava flows, and weathered soils), a gradient of mean annual temperatures (~19.5-25.7��C), a broad precipitation range (2500 - 4000 mm year�����), a rainfall frequency range (i.e. max rainfall in 24 hours; ranged 30->100 mm day�����), and 3 Holdridge Life Zones (Tropical Moist Forest, Subtropical Wet Forest, and Subtropical Lower Montane Rain Forest). Species composition was highly correlated with the environmental variables, particularly elevation. In general for plants ���10 cm dbh, site species richness declined at a rate of ~2 species per 100 m rise in elevation. Forest sites located at similar elevations were most similar in their species compositions as compared with sites separated by large elevational differences. Despite the gradual change in species richness and composition, four sub-regions, or forest environments, within Los Tuxtlas were identified that had different species compositions and distinct combinations of elevation, soil-types, and climates. These four sub-regions were described as community-types according to their geographic location: Lowland-Reserve (LR), La Perla Plateau (LP), Volcanic Upslope (VU), and Cloud Forests (CF). The LR, LP, and VU community-types were coarsely described as Tropical Evergreen Forests (TEF's; INEGI 2001). All community-types corresponded with classifications within the Holdridge Life Zone System; the LR community-type was classified as Tropical (transition to Subtropical) Moist Forest; LP and VU community-types were classified as Subtropical Wet Forest, and the Cloud Forest community-type was classified as Subtropical Lower Montane Rain Forest. These community-types and Life Zones are useful tools for conservation, as they represent unique forests that collectively capture much of the variation in the species richness and compositional diversity of the Los Tuxtlas region. Unlike species composition, the variability in forest structure among the 18 TEF sites was not associated with the environmental variables of the Los Tuxtlas landscape. On average, TEF's had a total aboveground biomass (TAGB) of 422 �� 17 Mg ha����� and 205 �� 8 Mg ha����� total aboveground carbon (C). The TAGB and C pools for Cloud Forests was ~18% lower than TEF's, and averaged 346 �� 1 and 168 �� 1 Mg ha�����, respectively. The majority of this biomass difference was due to large trees within the forest structure. Cloud Forests had generally fewer trees ���70 cm dbh, and a more even distribution of trees 30-70 cm dbh than TEF's. The biomass contribution of large trees (���70 cm dbh) accounted for most, if not all, of the variation in TAGB and C for these tropical forests. The relatively high TAGB and C pools implicates Los Tuxtlas forests as a significant pool of aboveground biomass and C within the Neotropics. / Graduation date: 2002

Thesis (M. Environmental Management)--North-West University, Potchefstroom Campus, 2007.

This thesis aims to improve our understanding of how riverine ecosystems respond to dam removal. Riverine and particularly riparian ecosystems are among the most variable and important features of all landscapes. They connect landscape elements both longitudinally and laterally, and are governed by processes such as flooding, erosion and deposition that create dynamic, diverse and heterogeneous habitats. In fact, riparian zones are among the world’s most species-rich habitats. Worldwide there are millions of dams that fragment stream and river systems, regulate flows and degrade ecosystems. Dams impact freshwater, marine and terrestrial ecosystems and threaten biodiversity by disrupting organism movements and energy flows in the landscape. An important upstream effect of dams is inundation of habitats and development of new shorelines around impounded areas. Effects downstream of dams are mainly caused by changed hydrological regimes and retention of organic and inorganic materials in reservoirs, leading to reduced transport and dispersal of for example seeds to reaches downstream. The removal of dams create expectations that biota will eventually recover. We have studied a number of dam removal projects in Sweden. Our experimental results showed that following dam removal, newly exposed soils in former impoundments were rapidly colonized by pre-removal species. Their species richness increased slightly with time and their species composition indicated a slow change towards that in the reference site. In addition, the vegetation in formerly impounded areas showed a direction of change from lentic riparian plants (high proportion of aquatics) towards lotic ones, consisting of native perennials typical of free-flowing streams. We also found that the apprehensions that former impoundments would turn into pools of mud did not come true; in fact, a process towards more pristine channel morphology was observed. After removal there was erosion and downstream transport of sediment. We found only minor effects on macroinvertebrate communities. For example, a few species decreased over the years, suggesting that dam removal in itself might cause a temporary disturbance. This highlights the importance of long-term studies after dam removal, and also the importance of comparisons with pre-removal conditions and stretches unaffected by dams. Thorough documentation of executed dam removal projects and distribution of the results and experiences are tremendously important in the planning process of future decommissioning projects. Also, our experiences have taught us that in order to attain a successful dam removal it is important to involve stakeholders such as non-governmental organizations and local inhabitants in the process.

In order to identify expressologs (orthologs exhibiting the highest expression profile ranking) among a variety of plant species, bioinformatic methods were used in order to first identify sequence orthologs and subsequently to rank these orthologs based on expression profile similarity. Analyses conducted on these data suggested that expressologs exhibited greater functional equivalency. A comparison of drought response in A. thaliana and Populus showed that expressologs exhibited a higher correlation when computed using stress data as opposed to developmental data. This suggested that the use of condition-specific data sets is more appropriate when examining specific conditions. Analysis was conducted in order to investigate the hypothesis that neutral evolution was a predominant factor in gene expression divergence. Some evidence was found for selection acting on expression pattern maintenance. Further analysis will be required in order to confirm the type of selection acting to maintain expression patterns across species.