| 1. |
- Ali, Liaqat
(författare)
-
Pre-harvest factors affecting quality and shelf-life in raspberries and blackberries (Rubus spp. L.)
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fruit including berries have been demonstrated to exhibit a broad spectrum of benefits including protection against cardiovascular, neurological, and lung diseases, as well as having antioxidant, antimicrobial, anti-inflammatory, anti- diabetic and anti-aging properties. These protective effects are reported to be due to their high content of bioactive compounds, such as vitamin C, vitamin E, phenolic acids, ellagitannins, flavonoids and carotenoids. This thesis investigated the effect of pre- and postharvest factors on the concentrations of bioactive compounds in raspberries and blackberries. The factors studied included genetic variability, organic and synthetic fertilizers, seasonal variation (harvest-to-harvest and annual variation) in greenhouse, high tunnel and open field production, and post-harvest storage. Concentrations of bioactive compounds (anthocyanins, vitamin C, ellagic acid, carotenoids) in the berries, or in the leaves, were quantitatively analysed by high-performance liquid chromatography, and total phenolics were analysed by a spectrophotometric method. Generative parameters (yield, fruit size) investigated for the cultivar difference and organic nitrogen, responded differently to the nitrogen level within cultivars and varied significantly in primocane raspberries. Taste compounds, such as total acidity and different sugars, varied during the season and with nutrient regimes. Time of harvest also affected the ellagic acid content, which was high in early season, and the vitamin C content, which was high in late season in primocane raspberries. Significant changes were also found between different years. Vitamin C decreased significantly with high synthetic N and with low K application, but the application of high N with high K showed positive influence in the level of nutrients and bioactive compounds in blackberries except for ellagic acid. Increased level of organic fertilization (12-17 g N/plant) in primocane raspberries caused only minor changes in the analysed compounds. The post-harvest performance of raspberries regarding the levels of bioactive compounds was less dynamic than in blackberries. In addition, raspberries harvested in late season showed comparatively less changes in sugar content during storage as compared to early harvest, indicating less enzymatic activity in the late season.
|
|
| 2. |
- Montelius, Malin
(författare)
-
Chlorine Cycling in Terrestrial Environments
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Chlorinated organic compounds (Clorg) are produced naturally in soil. Formation and degradation of Clorg affect the chlorine (Cl) cycling in terrestrial environments and chlorine can be retained or released from soil. Cl is known to have the same behaviour as radioactive chlorine-36 (36Cl), a long-lived radioisotope with a half-life of 300,000 years. 36Cl attracts interest because of its presence in radioactive waste, making 36Cl a potential risk for humans and animals due to possible biological uptake. This thesis studies the distribution and cycling of chloride (Cl–) and Clorg in terrestrial environments by using laboratory controlled soil incubation studies and a forest field study. The results show higher amounts of Cl– and Clorg and higher chlorination rates in coniferous forest soils than in pasture and agricultural soils. Tree species is the most important factor regulating Cl– and Clorg levels, whereas geographical location, atmospheric deposition, and soil type are less important. The root zone was the most active site of the chlorination process. Moreover, this thesis confirms that bulk Clorg dechlorination rates are similar to, or higher than, chlorination rates and that there are at least two major Clorg pools, one being dechlorinated quickly and one remarkably slower. While chlorination rates were negatively influenced by nitrogen additions, dechlorination rates, seem unaffected by nitrogen. The results implicate that Cl cycling is highly active in soils and Cl– and Clorg levels result from a dynamic equilibrium between chlorination and dechlorination. Influence of tree species and the rapid and slow cycling of some Cl pools, are critical to consider in studies of Cl in terrestrial environments. This information can be used to better understand Cl in risk-assessment modelling including inorganic and organic 36Cl.
|
|
| 3. |
- Oyewole, Olusegun Ayodeji
(författare)
-
Soil nitrogen fluxes and root uptake in the boreal forest : key processes to plant nitrogen nutrition
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nitrogen (N) is essential for growth and net primary production of plants. However, N acquisition by plants is influenced by movement of soil N compounds from bulk soil to plant roots and uptake of N by roots. This thesis is aimed at deepening our knowledge on these key processes involved in plant N acquisition in the N-limited boreal forest. To address this aim, a novel, non-invasive microdialysis technique was employed. Amino acids dominated N fluxes in the boreal forest soils. Further, plant roots were shown to have the capacity to absorb organic and inorganic N present in the measured soil fluxes, but these soil fluxes, rather than root uptake, may limit plant N acquisition. The microdialysis technique was further developed to enable simultaneous estimation of diffusion and mass flow of N in soil. Applying this refinement of the technique in the field showed that mass flow significantly increased flux rates of soil N in the boreal forest ecosystem, and that it also altered the chemical composition of the N fluxes. The results from the studies presented in this thesis highlight the potential of the microdialysis technique to improve our understanding of the intrinsic processes involved in N acquisition by plant roots. They also suggest that amino acids might comprise an important source of N for plants in the boreal forest ecosystem. The results suggest that mass flow plays an important role for plant N acquisition in the boreal forest, and mass flow might increase the share of nitrate, particularly in nutrient-rich ecosystems. This finding opens a discussion on the role of transpiration in plant N nutrition, with implications for our understanding of how plant N nutrition will be affected by, among other things, elevated CO2, increased temperatures, and N fertilization.
|
|
| 4. |
- Lv, Yanrong
(författare)
-
Triterpenes and phenolic compounds in apple fruit (Malus domestica Borkh.) : variation due to cultivar, sun exposure, rootstock, harvest maturity, bruising, fungi inoculation, ozone treatment and storage conditions
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Apple (Malus × domestica Borkh.), a popular and widely cultivated fruit world-wide, contains bioactive triterpenes and phenolic compounds with potentially valuable pharmacological functions. This thesis investigated the effects of pre-harvest and postharvest factors on concentrations of these bioactive compounds in apples. It also studied the effect of ozone treatment, before or during storage, combined with cold storage on triterpene and phenolic compound concentrations in apples and the antifungal activity of triterpene-enriched crude extract. Concentrations of two major triterpenes, oleanolic acid and ursolic acid, in apple peel varied significantly between cultivars, with the late-ripening cultivar ‘Gloster’ having higher concentrations than the earlier ripening ‘Discovery’ and ‘Aroma’. The concentrations were higher in peel from the shaded side than from the sun-exposed side of both ‘Discovery’ and ‘Gloster’ apples. Harvest time and storage methods had minor effects on the concentrations, although some between-cultivar variation was observed. Inoculation with Penicillium expansum decreased oleanolic acid concentration in ‘Discovery’ and ‘Gloster’ at harvest in one study year and decreased ursolic acid concentration in ‘Aroma’ after cold storage. Oleanolic acid and ursolic acid concentrations in apple peel showed non-consistent changes in different cultivars after bruising. On four of six harvest occasions during a two-year study of ‘Aroma’, the concentrations were higher in peel of apples from rootstock ‘MM106’ than from ‘M9’. Total polyphenolics concentration was higher in ‘Amorosa’ peel than in ‘Santana’ peel at harvest and after four months of storage. Ursolic acid concentration in apple peel was almost unaffected by ozone treatment, but oleanolic acid concentration showed differing responses to varying ozone application. The concentrations of different bioactive compounds both increased and decreased after ozone treatment, but the changes were within the range of fluctuations observed in untreated apples during storage. Low-dose ozone treatment (0.5 ppm gaseous ozone one hour per day) during four months of cold storage did not affect total polyphenolics in ‘Amorosa’ and ‘Santana’ flesh, but increased total polyphenolics in ‘Amorosa’ peel and decreased them in ‘Santana’. Short-term ozone treatment (2.5 ppm gaseous ozone and ozonated water, alone or combined) before one month of cold storage reduced total polyphenolics content in apple peel, while inconsistent responses were observed in apple flesh. Triterpene-enriched water significantly inhibited mycelial growth of all pathogens studied, but inhibited conidia production differently in each pathogen.
|
|
| 5. |
- Einarsson, Rasmus, 1988
(författare)
-
Agricultural nutrient budgets in Europe: data, methods, and indicators
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Agricultural production systems feed humanity but also cause a range of adverse environmental effects, including climate change, loss of biodiversity, and pollution of air and water. A main cause of these effects is the emissions of nitrogen (N) and phosphorus (P) that occur as a side effect of nutrient cycling in agriculture. One of the things that is needed to mitigate N and P pollution is a quantitative understanding of N and P flows in agricultural systems. A common tool for this is the nutrient budget. A nutrient budget quantifies inputs and outputs of nutrients in a system and can be used to understand how the system functions as well as to calculate quantitative environmental indicators for farms, regions, or products. This thesis aims to explore and expand the limits of how agricultural N and P budgets can be used to support environmental research and decision-making, focusing on European agriculture. To this end, the thesis looks into two broad research questions: (1) What are the limits to the accuracy and level of detail that can be attained in N and P budgets of European agricultural systems? (2) How are present and proposed uses of agricultural N and P budgets and derived indicators limited by (a) the inherent property that agricultural nutrient budgets do not account for environmental impacts, and (b) by uncertainties and lack of data in the estimation of nutrient budgets? This thesis builds on five appended research papers that explore various aspects of data sources, uncertainties, and possible uses of N and P budgets in Europe. International and national data sources are scrutinized and used to estimate N and P budgets. Novel ways to combine existing data sources are explored. The use of nutrient budgets with various system boundaries, with different degrees of spatial resolution, and in different time periods is discussed, emphasizing that the best approach is not only a question of data supply but also of intended audience and purpose.
|
|
| 6. |
- Abubaker, Jamal
(författare)
-
Effects of fertilisation with biogas residues on crop yield, soil microbiology and greenhouse gas emissions : recycling of plant nutrients from bioenergy production
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The amount of residues generated by biogas production has increased dramatically due to worldwide interest in using renewable energy. Biogas residues (BRs) originate from anaerobic degradation of different types of rural and urban organic wastes and have been proposed as organic fertilisers because of their high content of ammonium and other valuable macro- and micro-nutrients. However, application of BRs to agricultural soils may be accompanied by environmental risks, since they may contain heavy metals and organic pollutants. Therefore the effects of BRs on crop production and on the soil ecosystem and environment urgently need to be investigated before their wider use. This thesis evaluated and compared different types of BRs against cattle slurry, pig slurry, compost and mineral fertiliser with respect to their (1) ability to provide plants with necessary nutrients, (2) impact on the soil microbial ecosystem and (3) effects on emissions of the greenhouse gas nitrous oxide (N₂O). The results from short-term laboratory experiments and a long-term field trial showed that BRs increased crop yield to the same extent or more than conventional mineral fertiliser and compost, but less than pig slurry. BRs generated from source-separated organic household waste had a tendency to give higher crop yield and soil microbial activities than other BRs. BRs had no general negative effect on soil respiration, but substrate-induced respiration decreased significantly in organic soil on addition of BRs. Although all BRs initially inhibited potential ammonium oxidation and potential denitrification activity, no long-term negative effects were detected. BRs stimulated ammonium assimilation, which can temporarily decrease nitrogen availability to the plant. Furthermore, the bacterial community structure in the sandy soil was altered by BRs and cattle slurry, but no significant change was seen in the community structure of clay and organic soil. Application of BRs and animal slurry increased N₂O emissions, but the total losses and flux patterns were affected by fertiliser type and soil type. In conclusion, the fertiliser value of BRs should be regarded as high and they apparently have no long-term adverse effects on soil microbial functions and structures. Thus the problematic amounts of residues associated with expansion of biogas production could be turned to advantage, as these residues seem to be safe and competitive fertilisers.
|
|
| 7. |
- Andersson, Helena
(författare)
-
The role of subsoil properties for phosphorus leaching in agricultural soils
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Phosphorus (P) leaching from agricultural land is a large contributor to eutrophication of many surface waters and the Baltic Sea. Better knowledge of P sorption and release in the subsoil could enable the development of effective mitigation strategies for P leaching. This thesis examined the impact of soil properties on P leaching from four Swedish agricultural soils (two clays, two sands), using intact soil columns extracted with (length 1.05 m) and without (length 0.77 m) topsoil. The role of the subsoil as a source or sink for P leaching was also investigated, and placement of quicklime (CaO) on top of the subsoil as a mitigation strategy for P leaching was evaluated. Leaching of dissolved reactive P (DRP) from subsoil lysimeters was 94% of that from full-length lysimeters in one of the clay soils, and 70% in the other. The higher contribution of the former clay subsoil was probably due to high P content deeper in the soil. Leaching of DRP was low from full-length and subsoil lysimeters (0.12 and 0.08 kg ha-1 yr-1, respectively) in one of the sandy soils, despite high topsoil P content, due to high P sorption capacity and low degree of P saturation in the subsoil. However, leaching of DRP was very high from full-length and subsoil lysimeters (3.33 and 3.29 kg ha-1 yr-1, respectively) from the other sandy soil with moderate topsoil P content, due to high P content and low P sorption capacity in the subsoil. These results indicate that the subsoil can function as both a source and sink for P leaching. Phosphorus leaching increased with increasing P content and DPS in subsoil and decreasing P sorption capacity in topsoil and subsoil, indicating that these parameters could be used for P leaching risk assessments. However, on soils with preferential flow in the subsoil, P leaching may be high despite high subsoil P sorption capacity. Hence, both chemical and physical properties of topsoil and subsoil must be considered in implementation of appropriate, cost-effective mitigation strategies for P loss reductions. Application of lime on top of the subsoil significantly reduced leaching of particulate P (PP) in both clay subsoils by 49 and 51%, respectively, compared with unlimed controls. This suggests that subsoil liming might be an appropriate method to reduce P leaching from clay soils.
|
|
| 8. |
- Bella David, Aneth
(författare)
-
Revisiting push-pull technology: Below and aboveground mechanisms for ecosystem services
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Push-pull technology is an effective and ecological solution to suppressing major Lepidopteran pests of cereals, in particular stem-borers (Busseola fusca, Chilo partellus), the fall armyworm (Spodoptera frugiperda) and the parasitic weed Striga. The technology exploits plant-insect interactions in intercropping practices to manage the pests, increasing productivity while maintaining ecosystem resilience. In this study, we show that long-term (14 – 18 years) push-pull farming cause shifts in soil microbial communities, increasing the diversity of fungal taxa than bacteria. Further, the shift in the structure of soil microbial populations seems to require time to establish as observed by the weak impact of Desmodium species cultivated for just two years on soil microbial structure. However, even under the short-term cultivation period, individual taxa enrichment associated to the Desmodium were observed. On the other hand, whole soil microorganisms as well as rhizobia appeared to have little impact on the constitutive release of volatile emissions by Desmodium. Whether the plants grew on live or autoclaved soil, Desmodium did not release volatiles implicated in repelling lepidopteran pests, which is in stark contrast to previous reports. Upon herbivory of Desmodium by Spodoptera frugiperda larvae, a marginal increase in volatile emissions was observed. In line with this observation and contrary to expectation, intact Desmodium spp. did not deter oviposition by gravid S. frugiperda. In feeding bioassays, neonate S. frugiperda larvae strongly preferred Desmodium spp. to maize diet, but did not grow well nor did they survive on it. Older larvae were frequently immobilised on the stems, often dying in position after a few days. Deeper investigation showed that stems and leaves of Desmodium were covered with a dense web of straight and hooked silicon-rich trichomes of varying lengths that prevented larval movement, piercing their cuticle in the struggle. In this light, we propose that in a push-pull setting, Desmodium acts as a mechanical barrier and trap crop instead of a volatiles-dependent “push” crop as previously purported. In addition, intercropping practices have been shown to reduce insect pest populations through diverse mechanisms such as barrier effect and resource concentration. Push-pull technology shows that ecological approaches to pest management and increasing productivity can be effective. A clear understanding of the mechanisms of action of such approaches is critical for further improvements as well as translation into other agro-ecological practices.
|
|
| 9. |
- Bengtsson, Stefan
(författare)
-
Interception and storage of wet deposited radionuclides in crops : field experiments and modelling
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The emission of radionuclides into the atmosphere from various sources, such as nuclear power plant accidents and nuclear bomb explosions, can result in the interception and uptake of radionuclides by crops in the agricultural ecosystem. These radionuclides e.g. radiocaesium (¹³⁴, ¹³⁷Cs) and radiostrontium (⁸⁵, 90Sr), can be transferred to foodstuffs via seeds or animal feed. Therefore, in this thesis, the goal was to study the amount of ¹³⁴Cs and ⁸⁵Sr that have been intercepted, taken-up and redistributed to different plant parts during wet deposition at different growth stages of spring oilseed rape, spring wheat and ley. For spring oilseed rape and spring wheat, the focus was on the transfer to the seeds after wet deposition of ¹³⁴Cs and ⁸⁵Sr. The dependence between the interception of radionuclides and the growth stage, e.g. the total standing plant biomass and the leaf area index (LAI) were also studied. There was a positive correlation between the interception of ¹³⁴Cs and ⁸⁵Sr and LAI for all three crops. A positive correlation between the standing plant interception and the biomass of ¹³⁴Cs and ⁸⁵Sr was found for spring wheat and ley, but not for spring oilseed rape. The highest interceptions of ¹³⁴Cs and ⁸⁵Sr were at shooting for spring oilseed rape, and at maturity for spring wheat. For ley, the highest interception was at the well-developed stages. Accumulation of ¹³⁴Cs and ⁸⁵Sr in the different plant parts increased when deposition was close to harvest and the crops accumulated more ¹³⁴Cs than ⁸⁵Sr. The concentration of ⁸⁵Sr was lower in spring oilseed rape than in wheat grains. There was an indication that the distribution of radionuclides between the above ground plant parts was independent of the way that they entered into the plant after deposition of ¹³⁴Cs and ⁸⁵Sr. The variation in transfer factors found in this thesis in comparison with results from other studies suggest, that the estimate of the risk of possible uptake to crops in the event of future deposition during the growing season, is still subject to uncertainties.
|
|
| 10. |
- Boye, Kristin
(författare)
-
Sulfur cycling in Swedish arable soils : a chemical perspective
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sulfur (S) is an essential plant nutrient. Decreased S deposition in combination with a switch to high-analysis N/P-fertilizers has increased the need for S fertilization. Thus, soil research directed at understanding soil sulfur properties and processes has intensified. However, the methodology at hand has been insufficient for determining relationships between soil properties, S cycling and S availability to crops. In this thesis, recently developed methods were used to study the effect on soil S by two management systems, livestock production and arable crop production, at five different locations within a Swedish long-term fertility field experimental series. In an open incubation study, and a pot trial, where isotopic labeling (35S) was used to trace S transformations, S cycling rates were higher in the livestock system, especially in one soil (Orup). The S delivering capacity of all soils was too low to avoid S deficiency in ryegrass without mineral S application. Observed differences in S cycling patterns could not be satisfactorily explained by soil properties; however, multivariate analyses indicated net S mineralization was negatively related to C/N-ratios and SO42- content. The extent of organic S stabilization through organomineral association and physical protection within microaggregates was investigated by an extraction/dispersion method. The relative distribution between the pools varied between soils, with the residual (non-extractable) pool always being largest; however, only the physically protected fraction was negatively related to plant S uptake. All soil organic S pools were involved in S transformations, although the residual pool was less active than the other pools. Chemical speciation of S in soils and soil fractions was determined by S K-edge X-Ray Absorption Near-Edge Structure (XANES) spectroscopy. A new method for fitting spectra provided reliable quantification of S species by using internally calibrated spectra of dilute (30mM) model compounds. The response of S speciation to management system differed between soils, but highly oxidized S dominated in the organomineral fractions, and intermediate forms of oxidized S in the residual fraction. In conclusion, soil organic S speciation can be accurately quantified by S K-edge XANES spectroscopy. The speciation differs between organomineral associated S and residual S. Treatment effects are dependent on soil type, but S cycling is stimulated by long-term farmyard manure application, as seen in the livestock system.
|
|
