Dissertations / Theses on the topic 'Seedbanks'

Free radical and aldehydic breakdown product content were determined, by EPR and UV / visible spectroscopy, primarily in intermediate (desiccation tolerant) seeds of Carica papaya L. (Papaya) and recalcitrant (desiccation intolerant) seeds of Aesculus hippocastanum L. (Horse chestnut), but also in other species covering a range of desiccation tolerances, with a view to determining the role of oxidative stress as a diagnostic marker for desiccation tolerance. Axes of non-senescent highly viable recalcitrant seeds of horse chestnut were metabolically active, contained products of lipid peroxidation, displayed low levels of enzymatic protection against activated oxygen and peroxides, and a two-peak free radical EPR signal. During fully hydrated storage at 16 °C for up to 18 months, seeds exhibited, sequentially, an increase in germination rate, a transient increase in intensities of both the low field and high field EPR peaks, a significant increase in membrane leakage and decrease in seed viability, germination rate, and SOD and peroxidase activities. Drying 'unstored' seeds below and embryonic axis moisture content of 40 to 50 % initiated viability loss. At < 25 % moisture content all axes were inviable and displayed a 2- to 4-fold increase in solute leakage, lipid peroxidation products and the low field EPR signal. Seed desiccation sensitivity increased with hydrated storage. The accumulation of lipid peroxidation products and free radicals on drying generally occurred to a greater extent, or at a higher moisture content, than observed with unstored seeds. The results indicate a mediating role for oxidative stress in recalcitrant seed viability loss which is differentially expressed during hydrated, 'natural' ageing and desiccation. Similar trends were seen in other recalcitrant species with the increase in lipid peroxidation products occurring around the point of viability loss. However the study of a more orthodox species (papaya) revealed no such trends.

Fire is a recurrent disturbance that removes above ground vegetation in many locations throughout the world, including the Sydney region. Many species in fire-prone locations, and most species in the Sydney region, form soil seedbanks and regenerate through post-fire germination. However, a germination response is determined by the fire regime acting as a selective pressure over a sufficient period of time, rather than a single fire. The components of the fire-regime are intensity, season, type and frequency. The natural fire regime is dominated by warm-season fire, but management burning is conducted in cooler seasons. Cool season burning produces lower levels of germination than warm season fires in a number of locations with Mediterranean-type climate, but the effects of cool season burning on species composition in the relatively aseasonal Sydney region is unknown. An experimental approach was adopted to address this lack of knowledge. Fire can be simulated using heat shock and smoke (fire cues), and the seasonal factors of temperature and water availability can be reproduced in the laboratory. I have investigated the effect of various combinations of heat shock and smoke, of various pre-and post-fire cue temperatures, of prefire cue hydration status, of various post-fire cue water availabilities, and of accelerated aging before application of fire cues on germination of a number of species forming soil seedbanks in the Sydney region. A degree of primary dormancy was overcome in most species by the combination of heat shock and smoke in the current investigation. Fire intensity is expected to influence germination, as germination of most species was increased by the combination of heat shock and smoke within a narrow heat shock range.The interaction between ambient temperature and the level of heat shock may affect germination. Soil water content, and thus seed moisture content at the time of a fire may interact with the level of heat shock to affect both germination and survival of a seed. The age of a seed may also affect its germination response to fire. The above factors are predicted to affect the germination of species differently, and thus season of fire is expected to alter species composition. Such predictions can be readily field-tested
Doctor of Philosophy (PhD)

Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xx, 147 p.; also includes graphics (some col.) Includes bibliographical references (p. 137-147).

With a growing concern about sustainability of agricultural production systems, interest in integrated weed management systems has increased. Increasing the understanding of weed seedbank dynamics will improve efficiency of management. The objectives of this study were to 1) quantify weed seedbank dynamics in response to seed density and burial depth, 2) determine weed seedbank decay at varying seed densities and burial depths, 3) quantify weed seed predation in wheat and tilled fallow fields, and 4) characterize and compare weed seedbanks in organic and conventional no-tillage production fields. Objective 1 was carried out at Montana State University's Arthur H. Post Agronomy Farm. Seedbanks were established at four densities and two burial depths. Weekly seedling counts were taken for two consecutive growing seasons. Data indicated higher density seedbanks had lower proportions of emergence. Individual species responded differently to depth treatments. We concluded that management affecting seed density and depth will affect seedling emergence. Objective 2 was carried out in the same plots as objective 1. Seedbank samples were used to separate seeds. We found that all studied species declined to low levels over two years with little difference due to depth and density. Wild oat seeds were more germinable in buried treatments. We concluded that seedbanks of these species will decline quickly with lack of seed inputs. Objective 3 was carried out in four spring wheat and four tilled fallow fields at Montana State University's Arthur Post Agronomy Farm. Surface seed predation was measured at six times during the growing season for four weed species. We observed that predation levels did not differ between wheat and fallow fields for three of four species. We conclude that seed predation can represent an important loss in Montana. Objective 4 was carried out in spring wheat production fields near Big Sandy, Montana. Weed seedbanks were sampled along a range of aboveground weed diversity points over two years. Weed seedbank composition and characteristics did not differ between cropping systems, but did between years. We conclude that weed seedbank diversity and richness may vary based more upon yearly environmental factors than the management system.

Aphthona spp. flea beetles were released in the Little Missouri National Grasslands (LMNG) in western North Dakota in 1999 to control leafy spurge (Euphorbia esula L.). The changes in soil seed bank composition and leafy spurge density were evaluated on two ecological sites five (2004) and ten years (2009) after Aphthona spp. release to monitor the effectiveness of the insects on weed control and associated change in plant communities. In 2009, leafy spurge stem density averaged 2 and 9 stems m-2 in the loamy overflow and loamy sites, respectively, compared to 110 and 78 stems m-2, respectively, in 1999 and 7 and 10 stems m-2, respectively, in 2004. Leafy spurge constituted nearly 67% of the loamy overflow seed bank in 1999 compared to 17% in 2004 and 2% in 2009. In the loamy seedbank, the weed represented nearly 70% in 1999 compared to approximately 11% in 2004 and 15% in 2009. As leafy spurge was reduced, native species diversity and seed count increased ten years following Aphthona spp. release. High-seral species represented 17% of the loamy overflow seedbank in 2009, an increase from 5% in 1999. However, Kentucky bluegrass, a non-target weedy species, increased over 250% in the loamy overflow seedbank from 2004 to 2009. The reestablishment of native plant species has often been slow in areas where leafy spurge was controlled using Aphthona spp. A bioassay was completed to evaluate native grass establishment when grown in soil from Aphthona spp. release and non-release sites throughout North Dakota. Native grass production was not affected when grown in soil collected from established Aphthona spp. sites (1.5 g per pot) compared to soil without insects (1.6 g per pot). The cause of reduced native grass production in sites with Aphthono spp. previously observed is unknown but may have been due to a chemical inhibition caused by the insects within the soil that no longer exists. The native warm-season switchgrass (Ponicum virgotum L.) may be an alternative to corn for efficient biofuel production; however, control of cool-season grassy weeds has been a problem in switchgrass production. Various herbicides were evaluated for smooth bromegrass (Bromus inermis Leyss.) and quackgrass [Elymus repens (L.) Gould] control in an established switchgrass stand near Streeter, ND and a weed-infested field in Fargo, ND. Switchgrass yield was higher than the control 14 mo after treatment (MAT) when aminocyclopyrachlor or sulfometuron were applied early in the growing season, but no treatment provided satisfactory long-term grassy weed control. Herbicides were reevaluated at increased rates for smooth bromegrass or quackgrass control in Fargo. Sulfometuron provided 99% smooth bromegrass control when applied at 280 g ha-1 in the fall but injured other grass and forb species as well. Sulfometuron would likely be injurious to switchgrass and could not be used for biofuel production. Aminocyclopyrachlor did not injure other grass species but only reduced smooth bromegrass control by 76% when applied at 280 g ha-1 in the fall. No treatment provided satisfactory long-term quackgrass control.

Accelerated soil erosion affects sustainable food production through the degradation of arable soils resulting in lower crop yields and compromising biodiversity. Over the past 50 years, the weed seedbank has been declining due to farming intensification, increased herbicide use and weed suppression through competitive autumn crop planting. However, there is less recognition of the potential of soil erosion affecting the weed seedbank. This thesis contributes to an improved understanding of the effect of geomorphological processes (soil erosion) on biological systems (weed seedbank) in arable ecosystems. The first investigation assessed whether the management of farm machinery field tramlines would decrease soil erosion rates and effect the movement of weed seeds. Over three winter seasons, eroded material was collected by a network of Gerlach Troughs. The results showed that tramline management with a spiked harrow decreased soil and seed loss by 93.9% and 86.56% respectively, compared to regular tyre tramlines. Analysis of seed data to runoff and sediment load found seeds were transported along with sediment (r²=0.62) rather than runoff (r2=0.2) over the long term. In addition, tramline management significantly affected the number of seed species transported (p<0.001), which was found to relate to seed morphologies. Overall, tramlines cause 0.01% - 0.32% seed fluxes annually depending on management. These findings have implications for farmers to protect tramlines from erosion and displace seeds through management thereby, preventing the loss of biodiversity within the field. The second investigation looked at the movement of weed seeds at the field scale by erosion through the use of a radionuclide (¹³⁷Cs) tracer. A single field was sampled for seedbank and soil cores taken for ¹³⁷Cs analysis in two sub field grids. The results indicated weak relationships between seedbank densities and erosion. The weak relationships in the grids (r² =0.13, p =0.029 in 2011 and r² =0.12, p = 0.036) were due to land management contributing to spatial variability within seedbank abundance and composition. Individual species showed mixed responses to erosion rates. The findings indicate farmers need to consider management strategies at field scale to effectively manage erosion and seedbanks because seedbank losses of between 2 – 2.5 % annually within the field which is linked to field scale sediment budgets. The third investigation looked at specific environmental controls that would affect soil erosion and seedbanks. This was achieved by using a portable rainfall simulator on plots containing either seeds from the natural seedbank or spiked with seeds. The key control was the presence of crop/vegetation cover in affecting erosion rates (p<0.001) and seed movement (p = 0.001). The presence of crop cover resulted in low erosion rates but a greater loss of seeds compared to plots with no crop cover. This was linked to vegetation cover providing a protective environment for weeds to grow and produce additional seeds via seed rain. Ground cover prevents erosion but also highlighted seed movement was higher than on bare soil due to a greater availability. This means that surface wash is more important than rainfall in causing seed transport. For spiked plots, more seeds were displaced in short (3 minute) events compared with long (6 minute) events (p = 0.04). This shows protecting the soil and seedbank from rainfall detachment is crucial to preventing transport of sediment and seeds that could enter other transport pathways (e.g. tramlines, rills, gullies). The fourth investigation looked into the processes and impacts of soil erosion on seedbanks at the catchment scale. This was done by establishing a monitoring station at the outlet of an arable catchment for one year to monitor discharge, suspended solids and seed flux. The results of monitoring in 2012 found seeds numbers were positively related to discharge (observed r² = 0.62, p<0.001; observed plus modelled r²=0.50, p <0.001) and sediment load (observed r² = 0.64, p<0.001; observed plus modelled r2= 0.89, p<0.001). Seed species had poor negative relationships with discharge (observed r² = 0.03, p=0.357; observed plus modelled r²=0.11, p = 0.017) and sediment load (observed r² <0.001, p=0.352; observed plus modelled r²=0.14, p=0.004). An initial estimate of losses from the catchment was around 0.008 – 0.027% of the weed seedbank. Interestingly, there appeared to be a trend in the abundance of seed collected relating to patterns of farming activity within the catchment. This finding has management implications as there is evidence, for the first time, of arable weed seeds being exported from the catchments, which could affect other agricultural land and ecosystems downstream. The findings of these four investigations showed that the effect of soil erosion on the seedbank is connected at different spatial scales. Scope for future work is to improve the understanding of the role of seed morphologies, land management and field scale processes affecting the transportability of seeds by erosion processes.

The Calaveras River is a unique riparian habitat in San Joaquin County, influenced by both tidal water from the San Francisco Bay and impounded rainwater from the New Hogan Dam. The Calaveras River is one of the few river systems in California that does not benefit from snowpack melt. This dynamic system has changed dramatically in both its species composition and hydrodynamic regime due to years of human influences. What was once a thriving population of native plant species has become an environment dominated almost completely by aggressive exotic invasive species. The goal of this project was to remove the nonnative plant habitat by the most cost effective and least labor intensive means. The study area was along a section of river that bisects the University of Pacific campus in Stockton, California. From years of invasive species presence a deep seedbank has developed within the soil which acts to reduce the effectiveness of native plant reintroductions. A technique known as "solarization" was used to eliminate the seedbank and to facilitate the survival of native plants. Tarps were used to eradicate existing plants followed by disturbance of the soil and watering to induce germination of subsoil weed seeds. As the new plant seedlings emerge, tarps are reapplied to eliminate that generation of seedbank plants. After four time series of tarping and watering, a significant difference was found between control plots and treatments utilizing the solarization technique. Treatment 2, which consisted of tarping without weight, was determined to best target the seedbank after four repetitions and resulted in reducing invasive species in the seed bank.

Biological invasions have adverse economic, cultural, and ecological effects worldwide. Among the most impactful in North America is the invasion of Phragmites australis (Phragmites), a large-scale clonal grass that rapidly colonizes wetlands. Phragmites crowds out native plants and alters habitat for native fauna. In doing so, Phragmites also alters human access to water resources and has adverse economic effects, including decreasing property value, inhibiting recreational use, and limiting populations of game species. The efforts described in this dissertation are a component of a large, multidisciplinary effort to better understand the anthropogenic stressors to Chesapeake Bay, Maryland, at the land/water interface. Utah State University worked in collaboration with the Smithsonian Environmental Research Center and other academic and public organizations to address this problem from multiple directions. The diverse and extensive studies ranged from aquatic and avian faunal composition and submerged aquatic vegetation to our work on the invasive wetland grass, Phragmites. Having assessed the existing literature and its shortcomings, we conducted a large-scale, long-term study of the effects of Phragmites removal on the Bay. By removing Phragmites from plots in select sub-estuaries of Chesapeake Bay through herbicide spraying, leaving associated plots intact, and comparing both with native wetland conditions, we sought to better understand herbicidal management of Phragmites and the potential for wetland plant community recovery. Although sprayings decreased the relative cover, stem diameters, and stem densities of Phragmites, we found that herbicide treatment alone was not adequate to restore native plant communities or significantly affect seedbank composition. Our results demonstrate the resilience of Phragmites and call for a diverse range of control measures, including mowing, grazing, burning to expose the seedbank to germination, and—if economics allow—active revegetation to establish the desired plant community composition. This dissertation provides beneficial data for those who seek to manage Phragmites in wetland plant communities, but there is much work still to be done. The literature review, seedbank study, and community analysis included in this volume are components of a larger research program on Phragmites management. Future studies should, in particular, investigate revegetation and nutrient amelioration as means to recover pre-invasion vegetation.

This dissertation grew from an investigation of the farm Doornkloof in Irene, Pretoria. The farm was home to General Jan Smuts and it is here that he wrote his seminal philosophical work “Holism and Evolution” and found his own grass specie Digitaria Smutsii. The theoretical investigation is rooted in the interpretation of Holism, as an architectural theory, which informs the proposed design intervention. This study is informed by an analysis of the area of Irene, its origins and its future growth lead to the development of a holistic framework. This study proposes to inform the future socio-economic and historical importance of the farm as open public space for the citizens of Tshwane and Irene. The research intervention proposes a new architectural programmatic typology that will celebrate the importance of the Bankenveld landscape. The systematic rehabilitation of the grassland landscape will be achieved by introducing small scale interventions. The series of design interventions will rehabilitate the existing historical layers of the site, create new interest in the farm, improve the economic position of the Jan Smuts Foundation (the owners of the farm) and protect the landscape for the future generation users.
Dissertation MArch (Prof)--University of Pretoria, 2012.
Architecture
unrestricted

Native prairie response to aminocyclopyrachlor (AMCP) was evaluated in the Northern Great Plains. AMCP altered plant communities and reduced foliar cover of introduced, high seral, and low seral forb species. After treatment, high and low seral monocots increased at both sites due to reduced competition from susceptible forbs. AMCP reduced richness, evenness, and diversity. Aphthona spp. were released in the Little Missouri National Grasslands in North Dakota in 1999 for leafy spurge biological control. Soil seedbank composition was sampled from two ecological sites to evaluate changes in the plant community. By 2014, leafy spurge abundance decreased 92% on average. Subsequently, Kentucky bluegrass increased, but has also been deterred by a slow reintroduction of native species. High seral forb species richness has doubled in both ecological sites since 1999. Aphthona spp. successfully controlled leafy spurge for over 15 yr without any additional control methods or costs to land managers.

In river ecology the description and understanding of near-natural ecosystem functionality is a difficult task to achieve as the majority of river floodplains have been intensively impacted by human activities. This work addresses ecological functionality of a relatively unimpacted large river system, focussing on the lateral dynamic and connectivity mechanisms driving aquatic vegetation processes. Macrophytes were found to be very patchily distributed at the riverscape scale, being mainly confined to low energy lateral habitats in the floodplain, such as backwaters. Backwaters provided favourable conditions for plants to colonise and recruit and contributed highly to species diversity and productivity at the floodplain scale. Differences between backwaters were attributed to the frequency of connectivity with the main channel during flood events. Nevertheless, the ecological mechanism driving diversity through flooding appears not to be related to flow disturbance. Biomass produced in backwaters was found to remain stable after potentially scouring floods. Therefore the hypothesis that flood disturbances promote species diversity through the removal and destruction of biomass and rejuvenate communities such that species coexistence is increased was rejected. Rather, it appears that diversity in backwaters increases along a temporal gradient as a response to the input of colonists and their accumulation overtime through successive flood inputs. Despite the apparently non-destructive effect of floods on macrophyte biomass, backwaters appear to have a significant role in exporting large amounts of plant propagules from the site of production. Backwaters represented a net source of propagules which highly enriched the main channel pool of potential colonists. However, whereas propagules could be dispersed for long distances in flood flows the probability for them to reach a suitable downstream habitat was extremely low. This work showed that dispersal at baseflow and entry to backwaters through the downstream end after short dispersal drift provided a greater chance of successful colonisation despite the individually much shorter distance moved. Backwaters were demonstrated to be rather isolated aquatic habitats, even though they experience hydrological connectivity, suggesting that primary colonisation of these sites is a limiting step. Instead, colonisation was shown to rely primarily on propagules generated internally by established plants. Whereas colonisation could occur via internal re-organisation of existing plant propagules, the backwater seed bank could also contribute to the macrophytes species established in backwaters. Such contribution was consistently low to medium along a gradient of disturbances and connectivity and showed independence from such river flow processes. Species richness was found to be higher in the established species than in the seed bank, suggesting that asexual reproduction is prioritised by aquatic vegetation in riverine backwaters. The occurrence or persistence of macrophyte species in backwaters depends upon rhizome and plant shoot regeneration. The lack of influence of connectivity revealed that plants may originate from both in situ and externally waterborne vegetative propagules derived from other upstream backwaters. This research demonstrated that the lateral dynamic and associated connectivity are major components of river floodplain ecology which generate a wide spectrum of habitats and have a controlling effect on vegetation processes. Therefore a naturally dynamic ecological state is required to support ecosystem functionality in large river floodplains and especially to maintain a high level of species diversity, productivity and colonisation of backwaters by macrophytes.

In this study three aspects of sexual reproduction in Everglades plants were examined to more clearly understand seed dispersal and the allocation of resources to sexual reproduction— spatial dispersal process, temporal dispersal of seeds (seedbank), and germination patterns in the dominant species, sawgrass (Cladium jamaicense). Community assembly rules for fruit dispersal were deduced by analysis of functional traits associated with this process. Seedbank ecology was investigated by monitoring emergence of germinants from sawgrass soil samples held under varying water depths to determine the fate of dispersed seeds. Fine-scale study of sawgrass fruits yielded information on contributions to variation in sexually produced propagules in this species, which primarily reproduces vegetatively. It was hypothesized that Everglades plants possess a set of functional traits that enhance diaspore dispersal. To test this, 14 traits were evaluated among 51 species by factor analysis. The factorial plot of this analysis generated groups of related traits, with four suites of traits forming dispersal syndromes. Hydrochory traits were categorized by buoyancy and appendages enhancing buoyancy. Anemochory traits were categorized by diaspore size and appendages enhancing air movement. Epizoochory traits were categorized by diaspore size, buoyancy, and appendages allowing for attachment. Endozoochory traits were categorized by diaspore size, buoyancy, and appendages aiding diaspore presentation. These patterns/trends of functional trait organization also represent dispersal community assembly rules. Seeds dispersed by hydrochory were hypothesized to be caught most often in the edge of the north side of sawgrass patches. Patterns of germination and dispersal mode of all hydrochorous macrophytes with propagules in the seedbank were elucidated by germination analysis from 90 soil samples collected from 10 sawgrass patches. Mean site seed density was 486 seeds/m2 from 13 species. Most seeds collected at the north side of patches and significantly in the outer one meter of the patch edge (p = 0.013). Sawgrass seed germination was hypothesized to vary by site, among individual plants, and within different locations of a plant’s infructescence. An analysis of sawgrass fruits with nested ANOVAs found that collection site and interaction of site x individual plant significantly affect germination ability, seed viability, and fruit size (p < 0.050). Fruit location within a plant’s infructescence did not significantly affect germination. As for allocation of resources to sexual reproduction, only 17.9% of sawgrass seeds germinated and only 4.8% of ungerminated seeds with fleshy endosperm were presumed viable, but dormant. Collectively, only 22% of all sawgrass seeds produced were viable.

The aim of this research is to assess various options for the management of topsoil stockpiles on disturbed lands and to evaluate the viability and germinability over time of the seedbanks in these stockpiles for use in rehabilitation. To predict their success, experimental trials were designed and conducted.

Seed loss in canola (Brassica napus, Brassica rapa and Brassica juncea) leads to considerable loss of revenue and dispersal of canola seeds into the soil seedbank. Once canola seeds enter the soil seedbank a portion can become secondarily dormant and persist for many years creating volunteer weed problems in following crops. Reducing canola seed loss and seedbank persistence can be an important strategy to reduce the incidence of volunteer weeds. The primary hypothesis of this research was that canola seedbank addition and dormancy induction in the seed are affected by genotype and harvest method. To test this hypothesis, three studies were conducted with the following objectives: i) to determine canola seedbank addition from windrowing and direct-harvesting operations on commercial farms in western Canada, ii) to determine agronomic- and harvest-related factors that may increase seed loss in canola, iii) to determine the effect of stage of crop maturity at harvest on potential to develop seed dormancy in canola, iv) to evaluate canola genotypes and harvest methods to reduce canola seedbank addition. A total of 66 canola fields were surveyed across Saskatchewan in 2010 and 2011. Shattered seeds from these fields were sampled within 3 weeks of harvest by using a vacuum cleaner. Agronomic- and harvest-related data were collected for each field using questionnaires. In a separate small plot study the effects of harvest methods (windrowing and direct-harvesting) and pod sealant products (Pod-Stik® and Pod Ceal DC®) on seed loss in five canola genotypes (InVigor5440, RR45H26, InVigor5020, RR4362, and CL8571) were evaluated in 2010 and 2011. In both years, 6 harvest samples were collected weekly from InVigor5440 and InVigor5020 genotypes starting at early stage of crop maturity until harvest to assess the effect of seed maturity on dormancy induction. On commercial farms, the average seedbank addition was 5,821 viable seeds m-2, which was equivalent to 7.3% of the total seed yield. There was no difference in the reported yield and seedbank addition between windrowed and direct-harvested canola on commercial farms. But in the small plot study, windrowing resulted in higher seedbank addition. Higher seedbank addition was observed when the yield of canola was higher and when producers had a larger area seeded to canola. The observed seedbank addition was also higher in Roundup Ready genotypes and when a conventional combine harvester was used to harvest canola. Little primary dormancy and low potential to secondary dormancy induction was observed in InVigor5440 and InVigor5020 seeds at an early stage of crop maturity. But at full maturity seeds of both genotypes had no primary dormancy but showed high potential for secondary dormancy induction. This indicates that windrowing the evaluated genotypes at early stage of crop maturity lowered the potential for secondary dormancy induction. There were appreciable differences in seedbank addition among the evaluated canola genotypes but pod sealant products did not affect seed yield and seed shatter in canola. The results of this study suggest that canola seedbank addition can be minimized by growing genotypes having reduced seed loss and with the adoption of direct-harvesting operations.