Over 300 samples were examined from a wide range of Lower Cretaceous exposures. A total of 26 Circumpolles species were recognised, 7 previously published and 19 newly described in this thesis. Each species is described using optical (O.M.), scanning electron (S.E.M.), and, where possible, transmission electron microscopy (T.E.M.). Several new techniques for combined S.E.M., O.M. and T.E.M. microscopy are discussed. The stratigraphic distribution of these Circumpolles allows the recognition of 8 informal palynostratigraphic zones, 6 of which are recognised in both marine and non-marine basins of deposition. These are; the late Volgian, early Ryazanian, late Ryazanian - early Valanginian, late Valanginian, early Hauterivian, Hauterivian - Barremian, late Barremian - early Aptian and Aptian - Albian. Combined S.E.M. and T.E.M. analyses of the Circumpolles described highlights some important phylogenetic trends seen within the Circumpolles group of pollen grains and their parent plants the Cheirolepidiaceae. There is a progressive evolutionary change from an essentially gymnospermous, Late Triassic group to a more advanced Early Cretaceous group (exhibiting many morphological features similar to those found on more recent angiospermous pollen grains). This includes a change in the intexine from undifferentiated to reticulate and from granulate/columellate to alveolate. A change in the external microsculpture of the Circumpolles group is also evident from smooth, to roughened, to granulate, echinate and eventually microechinate. The range of variation shown by the intexine appears to have phylogenetic importance and useful for both generic and specific identification of Circumpolles. Microsculptural variation, however, may well be controlled by environmental factors such as climate and is more useful for specific and suprageneric classification. Of fundamental importance to the Circumpolles group is the change from distal germination in the Jurassic to rimulate germination in the Late Jurassic, Early Cretaceous and eventually to a colpate style of germination in the Aptian. This latter mode of germination was previously considered to be restricted to, and characteristic of, angiosperm pollen grains.

Subsoil physical characteristics are often limiting to root growth, one of the major reasons being high density soil. However, deeper and more efficient root systems could help to explore a larger soil volume and reduce the input of nitrogen fertilisers if roots make more use of the nitrogen at depth. The first target was to develop a screening method which allowed barley root extension rates to be quantified after four days of growth in loose and compacted soils. Firstly, seed quality (loss of germination ability caused by poor conditions in storage and long storage time) was identified as a potential source of variation for root extension rate in seedlings. The screening showed that roots growing in compacted soil had a slower extension rate than roots growing in loose soil. In addition, there was an interaction between soil conditions and cultivars meaning that not all of them showed the same ability to overcome high soil density. Root architecture was characterized at days eight and 12 after planting for four selected divergent cultivars. Measurements were made using X-ray micro-computed tomography (µCT)-scanning. The differences between the four genotypes in root architecture (number of primary roots, root extension rate, root length, root area, root volume, convex hull, centre of mass, lateral density, lateral length) were significant at eight days after planting but disappeared at 12 days after planting for most of the traits measured (i.e. growth rate of primary roots). Soil density influenced the root system architecture at both two-time points, roots elongated less and explored less soil in the high compaction treatment. A third experiment was conducted to test the hypothesis that the differences in root architecture observed between the genotypes in response to the soil bulk density in the µCT-scanning would lead to different patterns of nutrient uptake from topsoil and subsoil. Layered soil columns of topsoil and subsoil were constructed with different subsoil physical parameters (loose, compacted and compacted with macropores) and a nitrogen tracer to measure nitrogen capture from the subsoil. Root length density and other traits determining root architecture differed between two barley cultivars and oat, but increased root length density in the subsoil did not improve nitrogen uptake from the subsoil. Hence showing that nitrogen uptake from the subsoil was not directly related with a greater presence of roots in the experiment.

Sandy soils are one of the most widely distributed soils in the world. However, crop production on these soils can be problematic especially in terms of water and nutrient retention. In the face of climate change and a projected reduction in water availability, food production is likely to be particularly affected. The aim of this research is to examine if amending soils with clay and organic matter can improve their water and nutrient retention. The research approach employed laboratory column leaching experiments, rainfall simulation, Computed Tomography (CT) scanning and field trials to investigate the potential of two types of clay, Kaolin (K) and Bentonite (B), and peat (Pt), as well different combinations of clay and peat, to act as effective soil amendments. The influence of amendment materials was assessed by examining water retention, nutrient retention, soil organic carbon and changes in soil properties. Laboratory analysis was supported by field trials to examine the productivity of spring wheat. The results showed that the amendment materials increased soil water retention and availability, reduced water infiltration, increased nutrient uptake, increased spring wheat growth and yield, and improved soil carbon storage compared to an unamended control. The findings provide a further understanding of how the addition of clay and OM can affect ecological function of sandy soils and elucidate the mechanisms involved in controlling water retention and availability, as well as nutrient retention in the amended soils.

The primary aims of this project were to: i) provide a survey of selenium and iodine concentrations in the terrestrial environment and locally grown crops of Iraqi-Kurdistan; ii) gain greater understanding of the factors controlling bioavailability of these elements in the calcareous soils of the region; iii) investigate the feasibility of biofortification of selenium and iodine and test the use of isotopically enriched tracers for this purpose; iv) assess iodine and selenium dietary intake and nutritional status of the local population using dietary questionnaires and a survey of a human biomarker. A survey was conducted covering locally grown crops, matched soil samples and irrigation water including 300 plant, 100 soil and 20 water samples. The potential availability of Se and I for plant uptake was examined by quantifying the soluble and adsorbed fractions of both micronutrients and their species. The influences of soil factors on plant Se and I uptake were examined. Results indicated that total soil Se (SeTot = 309 μg kg-1) was lower than the global average (400 μg kg-1). Approximately 2.5% of soil Se was present in the soluble and adsorbed fractions with an equal proportion of selenate and selenite in the soluble fraction and mainly selenite in the adsorbed fraction. The organically-bound Se extractability ranged from 20-89% of SeTot, depending on soil pH. Plant Se content was variable between crop species and different areas within Kurdistan with mean concentration of 113,112, 69 and 49 μg kg-1dw for leafy vegetables, tubers, fruit vegetables and wheat grain respectively. Higher plant Se concentrations were observed in plants grown in soils with pH > 8. The mean concentration of total soil iodine was 4140 μg kg-1. Almost 10% of this value was present in the soluble and adsorbed fractions. Mean plant iodine concentrations were 439, 368, 140, and 12 μg kg-1dw for leafy vegetables, fruit vegetables, tubers and grains respectively. The combined concentrations of soluble and adsorbed iodine were correlated with plant iodine content. The mean concentrations of irrigation water Se and I were 0.495 and 11.9 μg L-1 respectively. The amount (%) of soil CaCO3 was strongly correlated with iodine concentration in groundwater used for irrigation and irrigation water iodine concentration was again strongly correlated with plant iodine concentrations. The feasibility of Se biofortification in calcareous soils using local vegetable genotypes from Kurdistan was examined using 10 g ha-1 77Se as a biofortification treatment (and isotopic tracer). Five commonly used vegetables, including celery, chard, lettuce, radish and spring-onion were planted in soils spiked with the 77Se application and grown for 8 weeks under controlled growth room conditions. Results indicated that, at the end of the growth period approximately 35% of applied 77Se had been transferred to a recalcitrant form in the soil which resisted extraction with 10% TMAH. Only 5% of 77Se was present within the soluble and adsorbed soil fractions combined, at harvest. The amount of 77Se taken up by plant biomass varied according to crop species; 25% for radish and 7-8% for other vegetables from the total 77Se applied. Plant 77Se concentrations varied despite growing in identical soils and, unexpectedly, plants contained more Se originating from the soil rather than the fertilizer. The ratio of Sesoil/Sefertilizer also varied between varieties reflecting different growth patterns and uptake rates against a backdrop of decreasing fertilizer Se availability during the growing season. Biofortification of iodine using a range of vegetable crops grown in calcareous soil was investigated, using soil and vegetable genotypes from Kurdistan, and employing 129I as a tracer. Vegetables were irrigated daily with water containing 5.56 and 6.89 μg L-1 129IO3- and 129I- respectively for 8 weeks. Total and fractionated iodine (127I and 129I) was conducted on moist soil (c. field capacity) and air dried soil at the end of the growing season. Plant analysis was also undertaken for 127I and 129I, using ICP-MS. Results showed that plant iodine concentrations originating from native soil iodine were variable even when grown in identical soils. Generally, iodine concentrations in roots was greater than in shoots for both 127I and 129I. Vegetables irrigated with 129I- (iodide) had considerably lower iodine concentrations (6.2-12 μg kg-1dw) than those irrigated with 129IO3- (iodate) (53.3-479 μg kg-1dw). The majority of plant iodine originated from soil iodine rather than fertilizer iodine and varied depending on 129I species applied (iodate or iodide) and the vegetable plant type grown. For vegetable shoots treated with 129I- (iodide) only 3% of the iodine of the three test plants originated from the 129I treatment. By contrast, for 129IO3- (iodate) applications 11, 22 and 58% of iodine in the shoots of celery, lettuce and chard were from the 129I additions respectively. The recovery rate of 129I from soil extracted with 10% TMAH ranged from 63-95% of total iodine applied and varied depending on vegetable variety. The 129I recoveries from pots irrigated by 129IO3- were less than from 129I- irrigated soils suggesting greater loss of iodine from the iodate irrigated system. To assess the Se and I status of the population in a region of Kurdistan, the food composition data and dietary intake of Se and I was determined for 410 volunteers using a semi- quantitative food questionnaire, including commonly used food items. To directly investigate level of nutritional status of Se and I, urine samples were also collected from each participants as a biomarker. Daily dietary intake and source apportionment of Se and I from each food item was determined using questionnaire survey. The daily intake of I from food excluding salt was 119 μg d-1. Vegetables and fruits supplied 48%, protein sources 25%, cereal and grains 9%, dairy products 8% and water 2% of daily I intake. The majority (>90%) of salt samples collected were iodised with a mean I concentration of 40 mg kg-1 and daily intake of salt was estimated as 13.5g d-1. Accounting for salt intake, average daily iodine intakes increased to 668 μg d-1, with salt supplying 82% of daily I intake. The median urinary iodine (corrected for creatinine) was 379 μg g-1CRT and 424 μg L-1 osmolality corrected. More than 90% of school age children and over 55% all participants had excessive I intake according to WHO classification. The salt I concentration consumed by each family was highly correlated with mean urinary iodine of family members. Urinary Na and I were also correlated. The iodine intake estimated according to salt intake (calculated based on urinary Na) was strongly correlated with iodine intake calculated according to urinary iodine. The daily salt intake estimated by urinary Na was 15.3 g d-1 considerably higher than WHO recommended. Mean total daily intake of Se according to the questionnaire responses was 72.9 μg d-1 with 21% of participants having a daily intake lower than recommended RDA. The mean urinary Se fell in the range of 21.2-24.8 μg L-1 depending on justification methods. The predicted Se intake from urinary Se gave a values of 59 and 42 μg d-1 according to the method used which may imply Se deficiency. To conclude, Kurdistan soils Se content was found insufficient. Despite that, Due to high pH effect in some areas plant Se content seems to be having considerably higher Se content rather than areas with lower pH. Later studies revealed that daily Se intake may not enough to address the Se requirement of population. Biofortification of Se possible but to prevent decreasing availability would be recommend to apply in med season or foliar application. Typically soil and plant of Kurdistan found in a minimum of normal range of iodine and comparable with other areas. Irrigation water was found as a main source of plant iodine uptake. The daily iodine intake from food excluding salt is not enough to meet the recommended iodine level but considering high consumption of iodized salt in that region it can be classified as an excessive iodine intake which could cause high intake iodine consumption disorders such as hyperthyroidism and in turn health issues caused by elevated Na intake such as cardiovascular disease. In current iodine nutritional status of the region plant biofortification would not be recommended.

The aim of this work was to investigate the interactions of anionic radionuclides 129I, 77Se (as a proxy for 79Se) and 99Tc with soil geocolloids under a range of conditions. These anionic fission products are of specific concern to policy makers regarding human and environmental risk assessments. Previous research has demonstrated strong links between soil organic matter (SOM) content and reduced mobility of these radionuclides. Negatively charged humic substances (HS), such as humic acid (HA) and fulvic acid (FA), may constitute 80% of organic matter and the mechanisms that allow anionic radionuclide to interaction with these HSs are not well understood. In the case of all three radionuclides, speciation plays a significant role in controlling their environmental mobility, therefore HPLC and SEC coupled to ICP-MS was used to monitor the speciation changes as the isotopes were progressively incorporated into HA. X-ray absorption spectroscopy was also employed in order to establish the solid phase speciation of Se after reaction with soil geocolloids. Surface charge development of the HA significantly affected reaction with iodate (129IO3-) and iodide (129I-). Iodide added to HA systems demonstrated slow oxidation and formation of organically bound iodine (Org-129I) predominantly at higher pH (pH 6). Conversely IO3-, was rapidly transformed to form both I- and Org-I. As pH decreased, the rate of this reduction reaction increased. Increasing HA concentration also increased the rate of IO3- reduction and formation of Org-I. Previous research has suggested that the most likely mechanism is IO3- reduction to I2 or HOI which then binds with phenolic groups on OM forming Org-I species. However, IO3- was observed to rapidly bind to HA forming Org-I species with no initial evidence of I- formation; I- concentration then increased over time as Org-I decreased. Where Fe2+/Fe3+ was present increased reduction of IO3- to I- was observed, mediated by association with HA, resulting in less Org-I formation overall. Instantaneous reaction of I- with HA was observed in the presence of Fe2+/Fe3+, with bonding via cation bridging. Some I- was subsequently re-released as I- likely due to ongoing Fe hydrolysis. Modelling of the systems alone was successful and will assist the improvement of whole soil assemblage models. Selenite (Se(IV)) reaction with HA was most rapid at low pH, with minimal/no reduction occurring at > pH 6. Reduction of selenate (Se(VI)) also occurred but this was less than for Se(IV), at low pH. No formation of Se(VI) from Se(IV) was observed, suggesting no oxidation took place, however some formation of Se(IV) from Se(VI ) was observed, also the formation of an unknown Se species suspected to be organic in nature. Humic acid concentration had no significant effect on the rate of Se(IV) or Se(VI) reduction, suggesting that HA itself was not responsible for the reduction. X-ray absorption spectroscopy (XAS) demonstrated the potential for significant reduction to Se(0) at pH 4 and bonding through a Se-O-C chain. The role of microbial communities on Se(IV) and Se(VI) reduction in the HA systems was demonstrated through the use of soil inoculum and glucose additions in sterile and non-sterile systems. No reduction of Se(IV) or Se(VI) and bonding to HA was observed in filter and -irradiation systems. Additions of inoculum and glucose increased the rate of reduction. Additions of Fe2+ did not increase reduction of Se(IV) or Se(VI) when compared to non-sterile HA systems, however XAS analysis demonstrated formation of HA-Fe cation bridges. No reaction of pertechnetate (99Tc(VII)) with HA was observed in these aerobic systems. An unknown Tc species was occasionally observed (< 0.005 μ L-1) and it is possible that this is an organic-Tc species. Significant incorporation of Tc into the solid phase was observed in aerobic soils, with most Tc(VII) being retained in soils with high OM contents and low pH. The mechanisms considered here build upon the basic processes considered in current biosphere models for I and Se. Assemblage models must be used in order to reliably model the interactions of elements within soils due to the complexity of the systems. In order to understand the long-term radiological risks associated with geological repositories, the fine-scale mechanisms must be understood geochemically across a range of different soil types and conditions. The effect of I and Se speciation on bioavailability in soils determines both the potential transfer of radioactive isotopes to the food chain from GDF’s and from aerial sources of contamination. Alongside this, the work also has significant implications for advising on cost-effect fertiliser application methods for both I and Se, in order to tackle nutrient deficiencies worldwide.

Conservation Agriculture (CA) has potential benefits to the soil, crop yield, and the environment including reducing runoff, enhancing water retention and preventing soil erosion, in addition to increasing soil carbon sequestration and reducing greenhouse gas (GHG) emissions. Although CA is widely adopted in some areas of the world, it is still not widely adopted by UK farmers. The first overall aim of this project was to investigate the effects of tillage practice and residue retention, on soil physical properties, crop yield and GHG emissions. For this purpose, a split-plot field experiment was established on the University of Nottingham farm between September 2014 and August 2016. The main plot treatment was residue retention while cultivation practices were applied to the sub-plots and included three different tillage systems: no-tillage, minimum-tillage and deep ploughing. We used a novel analytical tool, X-ray Computed Tomography, to characterise the 3-D soil pore network in conjunction with a number of other soil physical properties such as bulk density, penetration resistance and shear strength. A range of portable chambers were used to detect the GHG emissions from soil and from soil-plant systems as influenced by the tillage and residue treatments. Winter wheat yield was not affected by the tillage treatments or residue retention in the first year, but, in the second year, no-tillage caused a 10% reduction in triticale yield compared to minimum-tillage and traditional ploughing. Multiple regression analysis showed that the lower triticale yield was partially explained by higher soil strength in the no-tillage plots, together with lower soil moisture content in summer. Our results show that while there is potential for climate change mitigation from no-tillage when the Net Ecosystem Exchange is considered, this effect could not be observed from soil emissions only. The second aim of this project was to assess the current level of reduced tillage (RT) uptake by UK farmers and the constraints for further adoption. A postal questionnaire was conducted in January 2016. This questionnaire found that only 7.0% of the arable land in England is under no-tillage and 47.6% is under minimum-tillage. The adoption of RT increased with an increase in farm size as it was the most adopted on farms >400 ha. Moreover, RT was adopted most on combinable crop farms. Weed management and slugs were identified as main challenges for RT adopters. Increasing uptake of CA from current levels will probably require policy intervention including financial incentives for growers during the early stages of the transition from ploughing to CA. This will encourage farmers to buy RT equipment and may help them to cover any potential yield reduction, if occurred, before the CA system stabilisation.

Informe de seminario para optar al grado de Licenciado en Lengua y Literatura Inglesa / It is agreed that in order for a stretch of language to constitute a text, it has to form a unified whole (see, for example, Halliday and Hasan, 1976, de Beaugrande and Dressler, 1981, Martins, 1992). Language cannot be seen as mere units in isolation. The components of language, whether grammatical,semantic or pragmatic, have to be interrelated and, in actual language use, they always are. It is at this level that the concept of cohesion becomes of paramount importance because it is a supra-sentential phenomenon (Corval?n and Zenteno, 2009). By supra-sentential, we mean that it is a phenomenon whose boundaries go beyond the sentence and which is related to the meaning conveyed by linguistic units used in combination.

Zugl.: Frankfurt (Main), Univ., Diss., 2006

Sinorhizobium meliloti maintains a complex lifestyle, including saprotrophy, rhizophere colonization and root hair infection leading to the formation of root nodules in which the plant provides sustenance in return for nitrogen fixation. S. meliloti cells use a variety of carbon substrates for growth; this omnivory probably contributes to competitive ability in the soil. Several candidates for contribution to the catabolic capacity are found within the family of short chain dehydrogenases /reductases (SDR), which catalyze NAD(P)(H) dependent oxidation / reduction reactions. The 6.7 Mb genome of S. meliloti contains 78 SDR-encoding genes distributed on all three replicons. In this work each of these genes were disrupted by single crossover mutagenesis. These mutants were screened for growth on 93 different compounds as carbon source, and phenotypes were found for 17 of the mutants, providing suggestions for potential substrates of the corresponding enzymes. Carbon sources for which phenotype was observed include sugar alcohols, leucine, lysine, ornithine, galactitol, rhamnose, arabinose, mono-methyl succinate and ribono-γ-lactone. In addition, one of the mutants was found to be a proline auxotroph. In several cases, the phenotypes were consistent with the phenotypes of deletion mutants in which large sections of pSymB were absent. Eight of the mutants exhibited symbiotic deficiency after inoculation of alfalfa, while viable cells of three of the mutants could not be isolated from the nodules even though nitrogen fixation occurred. The results suggest that the corresponding SDR enzymes are involved in a pathway that is required for maintenance of viability by cells throughout infection and nodule development. This work demonstrates that members of the SDR family contribute to both the catabolic capacity and the symbiotic interactions of S. meliloti. Further experiments will address the details of the biochemical pathways involved. Knowledge of the substrate specificities of these enzymes should also prove informative in the description and annotation of orthologs that are identified in other genome sequences.

No description available.