This study addressed the effects of salinity and pot size on the interaction between leguminous plant hosts and arbuscular mycorrhizal fungi in four pine rockland soils using a shade house trap-plant experiment. Little is known about the belowground diversity of pine rocklands and the interactions between aboveground and belowground biota – an increased understanding of these interactions could lead to improved land management decisions, conservation and restoration efforts. Following twelve weeks of growth, plants were measured for root and shoot dry biomass and percent colonization by arbuscular mycorrhizal fungi. Overall, arbuscular mycorrhizal fungi had positive fitness effects on the four legume species (Cajanus cajan, Chamaecrista fasciculata, Tephrosia angustissima and Abrus precatorius), improving their growth rate, shoot and root biomass; pot size influenced plant-fungal interactions; and percent colonization by arbuscular mycorrhizal fungi was influenced by soil type as well as salinity.

Biodiesel from microalgae is a viable alternative for replacing the global demand for petro-diesel. High biomass and lipid production are key desirable characteristics needed in a species to be used for biodiesel production. It has been demonstrated in literature that the increase in salinity can increase the lipid content of microalgae, but lower the growth rate of a species. Therefore the effect that salinity has on the growth and lipid content of ten microalgal species, isolated from a warm temperate solar saltworks, was investigated. The microalgae were cultivated at a temperature of 22°C and at salinities ranging from 17 to 70 psu. It was found that growth and lipid production for all species were influenced to some degree by the salinity. Growth rates greater than 0.6 d-1 showed a decrease with higher salinity. Most (71 percent) of the growth rates that exceeded 0.6 per day were exhibited by cultures exposed to normal salinity (35 psu). This shift is a good indication that salinity inhibits/slows down growth and that the species in general prefer lower salinity conditions. Growth rates ranged from 0.17 ± 0.05 to 1.19 ± 0.17 d-1. Lipid content for the diatoms (2.78 ± 0.36 to 10.86 ± 4.59 percent DW) were lower than expected, whereas the lipid content for the green flagellates (3.10 ± 1.56 to 22.64 ± 1.19 percent DW) was on par with that reported in literature. To bring results into perspective a production model was developed to simulate a production scenario at the Swartkops Saltworks. Lipid and productivity results obtained in this study were used to estimate how much oil and biomass can be produced within the ponds of the Swartkops Saltworks. The model showed that although microalgae cultivation for biodiesel is technically feasible, at present it is not economically viable to do so.

Irrigated lands generate crop yields that are more than double those of rain-fed lands. Unfortunately, these systems are often heavily reliant on water supplies, which are diminishing globally. Alternative use of impaired quality waters for irrigation can reduce soil quality through secondary salinization, affecting plant health and yields. With salinization of agricultural lands increasing around the world, further understanding the impacts of this on crop production are required. The aim of this research is to assess the influence of soil salinity and nutrient stress on leaf photosynthetic pigments, gas exchange and biochemical photosynthetic parameters in wheat plants. The feasibility of estimating key photosynthetic pigments from in-situ leaf hyperspectral data is examined using vegetation indices, linear regression models and a random forest machine learning technique. Results showed that salinity stress presented a significant increase in the chlorophyll and carotenoid contents per leaf area, although the total pigment contents per plant was reduced as a consequence of lower production of leaf matter. While nutrient application enhanced the photosynthetic pigment content per leaf area, its interaction with salinity stress was found to be significant and varied with salinity level. A strong positive relationship was found between SPAD-502 measurements and leaf chlorophyll content and confirmed that SPAD-based retrieval of photosynthetic pigments can be undertaken with confidence irrespective of any prevailing stress in wheat plants. Photosynthetic parameters directly related to biomass accumulation (such as Vcmax, Jmax and gs) varied considerably with stress levels and growth stages, with high values of these parameters observed at low stress and in periods of more vigorous growth. Employing a random forest machine learning approach with all hyperspectral data as input features significantly improved the predictability and accuracy relative to the univariate linear regression model. However, using vegetation indices as direct predictors further improved the estimation accuracy and robustness of the random forest model. Overall, the findings from this research have implications for large scale estimation of vegetation photosynthetic traits from remotely sensed data, and offer a mechanism by which early detection of stress may be monitored, providing a means for enacting a timely crop management response.

Salinity is a major abiotic stress in plants that causes significant reductions in crop yield. The need for improvement of food production has driven research to understand factors underlying plant responses to salt and mechanisms of salt tolerance. The aim of improving tolerance in traditional crops has been initiated but most crops can only tolerate a limited amount of salt in their systems to survive and produce biomass. Studies of naturally occurring high salt-tolerant plants (halophytes) are now being promoted for economic interests such as food, fodder or ecological reasons. Suaeda fruticosa, a member of the family Chenopodiaceae, belongs to a potential model halophyte genus for studying salt tolerance. However, published reports on the identification of genes, expression patterns and mechanisms of salinity tolerance in succulent halophytes are very limited. Next generation RNA-sequencing techniques are now available to help characterize genes involved in salinity response, along with expression patterns and functions of responsive genes. In this study, we have optimized the assembly of the transcriptome of S. fruticosa. We have annotated the genes based on their gene ontology characteristics and analyzed differential expression to identify genes that are up- and down-regulated in the presence of salt and have grouped the genes based on their putative functions. We also have provided evidence for groups of transcription factors that are involved in salt tolerance of this species and have identified those that may affect the regulation of salt tolerance. This work elucidates the characterization of genes involved in salinity tolerance to increase our understanding of the regulation of salt in a succulent halophyte.

Riparian buffers have been created as a sustainable and effective way to combat the harmful effects of excess nitrogen and soil salinity in riparian settings. The goal of this research was to determine what species will I) germinate in saline environments and II) establish and produce sufficient biomass while being exposed to increased nitrogen. Incubation of eight native riparian graminoid species were evaluated for their ability to germinate in MgSO4-induced salinity. In a greenhouse study, seven riparian graminoid species were evaluated to quantify their ability to survive and take up nitrogen, mimicking buffer strips exposed to high inputs of runoff nitrogen. Slender wheatgrass and green needlegrass were able to germinate successfully when exposed to MgSO4 with EC levels up to 16 dS m-1 and 8 dS m-1, respectively. Of the graminoid species tested, smooth brome yielded sufficient biomass and nitrogen uptake percentages in a controlled setting.

Soil salinity and heat stress are two major abiotic stresses affecting plant growth and yield. Transcription factors (TFs) are key regulators in stress responses. They link stress sensing with many tolerance mechanisms by translating stress signals into changes in gene expression that ultimately contribute to stress tolerance. The NAC (NAM, ATAF and CUC) TF family have been found to be involved in responses to biotic and abiotic stresses. In this PhD project, the role of NAC TFs in response to heat and salt stress was studied in the model system Arabidopsis thaliana (Arabidopsis), and in two agriculturally relevant species, Solanum lycopersicum (tomato) and Chenopodium quinoa (quinoa). Plants have the ability to acquire thermotolerance if they are pre-exposed to a mild, non-lethal high temperature. The maintenance of acquired thermotolerance for several days is known as thermomemory. Here we investigated the role of NAC TFs in thermotolerance. The expression profiles of 104 Arabidopsis NAC TFs were measured and compared between primed and unprimed plants. Some NACs with a distinctive expression pattern in response to thermopriming were selected for further phenotypic analysis. Knock-out (KO) mutants of the ATAF1 gene showed an enhanced thermomemory phenotype compared with wild type plants (WT) and from this work, the functions of the ATAF1 gene were studied further. RNAseq co-expression analyses of ATAF1 overexpressor and ataf1 KO plants found that ANAC055 expression was co-regulated with that of ATAF1. JUBGBRUNNEN1 (JUB1) is another NAC TF involved in responses to heat, drought and salinity. In this study, the role of AtJUB1 overexpression in salinity was investigated in tomato plants. AtJUB1 overexpression resulted in higher proline levels and improved maintenance of water content and biomass in AtJUB1-overexpressing plants grown hydroponically under salinity compared with WT plants. Quinoa has recently gained much attention because of its high nutritional value and high tolerance to several stresses including drought and salinity. NAC TFs are hypothesized to play a major role in quinoa’s tolerance to abiotic stresses. In this study, the NAC TFs family were identified and investigated in the genome of quinoa. 107 NAC TF genes were identified and their transcriptional responses to different stresses including salt, drought and heat were investigated.

Abstract Eutrophication and salinization are both major threats to lake ecosystems and the contaminants can alter the structure of freshwater lake ecosystems, resulting in a loss of biodiversity and ecosystem services. Zooplankton and phytoplankton are key components in all aquatic ecosystems as they maintain a healthy quality of the water and they are also an important part of the food chain. Studies show that eutrophication and salinization have severe negative effects on the zooplankton community. This study compares zooplankton communities in 36 mesocosms of eutrophicated waters with nine treatments of salinity and light exposure. The dataset was provided by Associate Professor Lovisa Lind-Eirell, using a randomized design with three levels salt concentrations (15, 250, and 1000 mg of chloride/L of highly eutrophicated waters, in combination with three levels (10%, 35% and 70%) of ambient sunlight. The hypothesis and expected results were a significant decline in zooplankton species richness and population sizes, in treatments with high salinity and low light exposure. The hypothesis was partly correct as nauplii and copepod populations declined treatments of high salinity, whereas cladocerans and rotifers seem to have a saline tolerance which corresponds with other studies. More research is required regarding the combined effects pollutants have on our environment and our ecosystem services. If we wish to keep freshwater ecosystems healthy, prevent further loss of diversity and keep utilizing ecosystem services such as drinking water of good quality, a change of human actions is necessary. More research of interactive effects is needed to better understand the extent of the damage to freshwater ecosystems. Actions to prevent further loss of biodiversity and ecosystem services are necessary but the threats have been acknowledged and finding solutions is currently a work in progress on a global scale. / Sammanfattning Idag är övergödning och förhöjda kloridnivåer två av de största hoten mot ekosystemen i sötvattensjöar. Föroreningarna kan förändra strukturen i dessa ekosystem, vilket leder till förlust av ekosystemtjänster, såsom drickbart vatten. Zooplankton och växtplankton är nyckelkomponenter i alla akvatiska ekosystem eftersom de upprätthåller vattenkvaliteten och utgör en viktig del av näringskedjan. Studier visar att övergödning och förhöjda kloridnivåer har negativa effekter på zooplankton. Denna studie jämför zooplankton i 36 vattentankar med eutrofa vatten med nio behandlingar av varierande nivåer av salthalt och ljustillgänglighet. Datauppsättningen tillhandahölls av docent Lovisa Lind-Eirell på Karlstad universitet och utgjordes av en randomiserad design som bestod av tre olika saltkoncentrationer (15, 250 och 1000 mg klorid/L) av starkt eutrofierade vatten,  i kombination med tre ljusnivåer (10 %, 35 % och 70 %). Hypotesen och det förväntade resultatet var en signifikant minskning av både arter och populationer av zooplankton i behandlingar med hög salthalt och låg ljustillgänglighet. Hypotesen var delvis korrekt eftersom nauplii och copepoda populationer minskade i behandlingar med höga kloridhalter, medan cladocera och rotifera verkade ha en tolerans mot höga kloridhalter. Mer forskning om interaktiva effekter behövs för att bättre förstå omfattningen av skadorna på ekosystemen i våra sötvatten. Åtgärder för att förhindra ytterligare förlust av biologisk mångfald och ekosystemtjänster är nödvändiga, och att hitta lösningar på dessa problem pågår för närvarande på global skala.

>Magister Scientiae - MSc / Salinity is one of the major limiting factors to crop production, which consequently contributes to the risk of reduced food security. Among other factors, food security depends on availability of sufficient and nutritious food for humans. Livestock such as cattle and sheep are fed with various plant-based feeds; with Medicago sativa (commonly known as alfalfa or lucerne) being a very important forage/feed crop, so much that it is regarded as the queen of forage crops. However, alfalfa is severely affected by high soil salinity and thus its growth and yield are drastically reduced in soils with high NaCl content. Among the various alfalfa genotypes/varieties examined in this study, Agsalfa was identified as salt tolerant because it performed better under salt treatment compared to Magna601.

Coral bleaching, i.e. the loss of photosynthetic algal symbionts, caused by ocean warming is now the main factor driving reef decline, but not all corals are affected equally. Corals from the Arabian Seas have unusually high temperature tolerances, and recently studies implicated salinity as one of the contributing factors. In particular, a recent heat stress experiment at different salinities using the model system Aiptasia and Red Sea corals, showed that cnidaria at large bleach less at heat stress under high salinities and that this is associated with an increase of the osmolyte, floridoside Here we were interested to assess microbial community changes under heat stress at different salinity levels and whether this could help to explain the increase in thermal tolerance of the metaorganism at high salinities. We determined microbial community composition via HiSeq 16S rRNA gene amplicon sequencing of two anemone strains that differ in their associated symbionts, namely H2-SSB01 (type B1) and CC7-SSA01 (type A4), after six days under ambient (25 °C) and heat stress (34 °C) temperatures at salinities of 36, 39, and 42. Both anemones harbored distinct microbial communities, irrespective of temperature or salinity, that were also different from the bacteria in surrounding seawater. Within both host-endosymbiont pairings, the bacterial community composition at low (36) and intermediate (39) salinities did not differ between ambient and heat stress, but was significantly different at high (42) salinities. Subsequent elucidation of bacterial indicator species revealed several taxa that could be associated with a response to temperature and salinity. Our results underline that microbial community composition adjusts under different environmental settings. Importantly, microbial community dynamics of H2-SSB01 aligned with observed differences in bleaching susceptibility and thermal tolerance, whereas the pattern remains unclear for CC7-SSA01, which harbors an intrinsically higher thermal tolerance. Such responses could argue for a contribution of the microbiome to the observed increase in temperature tolerance of the Aiptasia metaorganism at increased salinities. An alternative interpretation is that the microbiome changes denotes a parallel response to changing salinities.

A model was developed to predict the effects of soil salinity on crop growth. The model makes three major assumptions: 1) Relative yield for a growing season is directly related to the ratio of actual and potential transpiration. 2) Water uptake by plants is in response to the water potential gradient between the plant roots and the surrounding soil. 3) The effects of the soil salinity on crop growth is solely due to the affect of osmotic potential in decreasing the water potential. Minor assumptions also included are concerned with the plant growth cover, plant root growth, and the separation of E and T from ET. The model's ability to predict crop growth under various irrigation amounts and frequency of application, irrigation water quality, and initial soil salinity was compared with field measured results. The model predicted reductions of crop yield as irrigation rates were decreased which agreed closely to field measurements where salinity was held constant. Increasing salinity of the irrigation water from the normal (EC=0.5 mmhos/cm) to the rate corresponding to the value estimated for the lower Colorado River in 2000 A.D. (EC=2.0 mmhos/cm), was predicted to have a very slight effect on yield for one years use. This agreed with the field measurements. It was found that the model under predicted the effects of high initial soil salinity (simulating many years of salt buildup) on yield. These results indicated that high initial soil salinity for corn had more effect on crop growth than just the osmotic effect for the field situation studied.