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Questions: Which factors influence the persistence of vascular grassland plants in long-abandoned (at least 50 yr) arable fields and meadows? What might be the implications of current levels of species richness on abandoned arable fields and meadows for future restoration?

Location: Forested highlands of Kilsbergen, south central Sweden.

Methods: The abundance of all vascular plant species was investigated in three habitat types: former arable fields, hay meadows and outlands (pastures) at 27 farms, abandoned for either approximately 50 yr or 90 yr. Time since abandonment, tree cover, soil depth, degree of soil podsol development, size of the infield area and two measures of connectivity were used as predictors for species richness and species composition.

Results: Former outland had denser tree cover, fewer species and fewer grassland species than former arable fields and hay meadows, irrespective of time since abandonment. Former hay meadows and arable fields with a longer time since abandonment were less rich in species, more wooded and had greater podsolization than meadows and fields abandoned at a later stage. Species richness was higher in hay meadows and arable fields at farms with larger infield area and deeper soils compared with farms with smaller infield area and shallower soils. The greatest richness of species and most open habitat were former arable fields at larger farms abandoned 50 yr before the study. Former arable fields had the highest number of grassland species.

Conclusion: After 50 yr of abandonment, former arable fields were the most important remnant habitats for grassland species and may be a more promising target for restoration than formerly managed grasslands.

The thesis combines laboratory experiments and field expeditions to study production, transfer and consumption of non-enzymatic antioxidants and thiamine in an aquatic food web. In particular, I (1) documented spatial and seasonal variation of tocopherols and carotenoids in the Baltic Sea pelagic food web, and (2) examined the effects of abiotic and biotic factors on tocopherol, carotenoid and thiamine concentrations in phytoplankton, zooplankton and fish.

Moderate differences in temperature and salinity affected α-tocopherol, β-carotene and thiamine production in microalgae. Furthermore, the results suggest that acute stress favors the expression of non-enzymatic antioxidants rather than enzymatic antioxidants. Because production of α-tocopherol, β-carotene and thiamine differ markedly between microalgae, the availability of non-enzymatic antioxidants and thiamine is likely to be highly variable in the Baltic Sea and is difficult to predict.

The transfer of non-enzymatic antioxidants from phytoplankton to zooplankton was biomass dependent. The field expeditions revealed that phytoplankton biomass was negatively associated with α-tocopherol concentration in mesozooplankton. Thus, increased eutrophication of the Baltic Sea followed by an increase in phytoplankton biomass could decrease the transfer of essential biochemicals to higher levels in the pelagic food web. This could lead to deficiency syndromes, of the kind already observed in the Baltic Sea. Astaxanthin is synthesized from precursors provided by the phytoplankton community. Thus biomass dependent transfer of astaxanthin precursors from phytoplankton to zooplankton could be responsible for astaxanthin deficiency in zooplanktivorous herring. Astaxanthin in herring consists mostly of all-Z-isomers, which are characterized by low bioavailability. Therefore, astaxanthin deficiency in salmon could be explained by the low concentration of this substance and its isomeric composition in herring.

Vitamin E (a-tocopherol in particular) is one of the major and most potent lipid-soluble antioxidants in vivo. It is produced by autotrophs and is essential in the diet of heterotrophs. In the last decades deficiencies of essential substances such as astaxanthin and vitamin B₁ (thiamine) were discovered in aquatic top predators and underlying causes seem to be food-web related. In the case of vitamin E, there is a lack of studies on the mechanisms of production and transport in aquatic food webs, which is partly related to complicated extraction procedures and high detection limits. This paper presents an improved method for the extraction and detection of a-, g- and d-tocopherol in low-biomass plankton samples. The method uses N,N-dimethylformamide (DMF) and n-hexane as extraction solvents  with sodium dodecyl sulphate (SDS) as  additive. This improves extraction yield and simplifies the extraction procedure because elaborate homogenization and saponification steps are unnecessary and extraction time is  decreased to 1 min. Quantification of vitamin E is performed with high performance liquid chromatography (HPLC) using electrochemical detection (ECD). Detection limits of the new method are 18.5, 16.3 and 8.0 pg injected and 0.74, 0.65 and 0.32 ng mL^-1 extract for a-, g- and d-tocopherol, respectively. Altogether, this is a reliable, fast and sensitive method which will allow more detailed investigations of vitamin E dynamics in aquatic food webs.

Oxidative stress occurs in plant and animal cells in association with oxygen. Therefore non-enzymatic antioxidants, like α-tocopherol and β-carotene, are necessary in to prevent irreversible damages caused by reactive oxygen species. Most antioxidants or their precursors are plant-derived and any fluctuation in the synthesis of these substances will affect consumers directly. To study the effects of environmental factors on antioxidant production by microalgae, cultures of the microalgae Dunaliella tertiolecta (Chlorophyceae),  Nodularia spumigena (Cyanophyceae), Prorocentrum minimum Dinophyceae), Phaeodactylum tricornutum (Bacillariophyceae) , Skeletonema costatum (Mediophyceae) and Rhodomonas salina (Cryptophyceae) were incubated for 48 h at different photon flux densities, temperatures and salinities. The initial concentrations varied widely between the cultures (α-tocopherol: 0.03 – 0.52 mg g C^-1; β-carotene: 0.11 – 2.72 mg g C^-1). D. tertiolecta showed increased α-tocopherol content in response to increased photon flux density. The cultures of P. minimum, P. tricornutum and S. costatum showed an increase and N. spumigena a decrease of α-tocopherol concentration with increasing temperature.  Photon flux  density and temperature in combination were of significant importance only for the R. salina cultures. In N. spumigena and P. tricornutum cultures, α-tocopherol concentrations increased with increasing salinity and temperature, whereas in D. tertiolecta cultures the opposite was found. In P. minimum and S. costatum cultures, salinity did not influence α-tocopherol concentration significantly. β-carotene and α-tocopherol were positively associated with each other except in D. tertiolecta and P. tricornutum. Only in one of twelve cases associations between α-tocopherol / super oxide dismutase and β-carotene / super oxide dismutase were found. It can be concluded that besides species composition of phytoplankton communities, differences in temperature and salinity contribute to the variation in antioxidant synthesis. Thus consumers must be adapted to a varying antioxidant pool.

Nearly all organisms are constantly exposed to oxidative threat, because every reaction where oxygen is involved gives rise to oxidants. Efficient protection is provided by antioxidants. Vitamin E (tocopherol) is an essential plant-derived antioxidant and poorly studied so far in marine food webs. In 2004 and 2005 eight offshore expeditions were conducted in the Baltic Sea to explore the dynamics of α-tocopherol in the pelagic food web. In order to analyze tocopherol production and transition to the next food web level, two plankton size classes were sampled; <100 µm (dominated by phytoplankton) and >200 µm (dominated by calanoid copepods). HPLC analysis revealed lowest values of α-tocopherol per L seawater in March in both size classes and highest in May for <100 µm (31.5 ng L^-1) and August for >200 µm (1.3 ng L^-1). No consistent seasonal pattern could be observed in α-tocopherol per unit biomass for the zooplankton. Concentrations ranged in <100 µm from 0.05 to 0.10 ng µg C^-1 and in >200 µm from 0.05 to 0.11 ng µg C^-1.  Partial least square regression (PLS) revealed nutrional status and species composition of the phytoplankton biomass as driving factors of α-tocopherol production in phytoplankton. Abiotic factors, as depth and temperature were only of significant influence in May. In zooplankton, the α-tocopherol concentration was negatively associated with phytoplankton biomass in May. Therefore we concluded that assimilation efficiency of zooplankton in combination with high phytoplankton biomass is the bottle-neck in tocopherol transport from phytoplankton to higher levels in the food web.

Evolutionary change in response to natural selection will occur only if a trait confers a selective advantage and there is heritable variation. Positive connections between pollen traits and fitness have been found, but few studies of heritability have been conducted, and they have yielded conflicting results. To understand better the evolutionary significance of pollen competition and its potential role in sexual selection, the heritability of pollen tube-growth rate and the relationship between this trait and sporophytic offspring fitness were investigated in Collinsia heterophylla. Because the question being asked was if female function benefited from obtaining genetically superior fathers by enhancing pollen competition, one-donor (per flower) crosses were used in order to exclude confounding effects of post-fertilization competition/allocation caused by multiple paternity. Each recipient plant was crossed with an average of five pollen donors. Pollen-tube growth rate and sporophytic traits were measured in both generations. Pollen-tube growth rate in vitro differed among donors, and the differences were correlated with in vivo growth rate averaged over two to four maternal plants. Pollen-tube growth rate showed significant narrow-sense heritability and evolvability in a father-offspring regression. However, this pollen trait did not correlate significantly with sporophytic-offspring fitness. These results suggest that pollen-tube growth rate can respond to selection via male function. The data presented here do not provide any support for the hypothesis that intense pollen competition enhances maternal plant fitness through increased paternity by higher-quality sporophytic fathers, although this advantage cannot be ruled out. These data are, however, consistent with the hypothesis that pollen competition is itself selectively advantageous, through both male and female function, by reducing the genetic load among successful gametophytic fathers (pollen), and reducing inbreeding depression associated with self-pollination in plants with mix-mating systems.

Halymenia floresii is an edible species consumed in some Asian markets. In the Yucatan peninsula coast of Mexico, H. floresii dominates rocky substrata between 3 and 40 m where it grows up to 50 cm high. After analyzing the seasonal pattern of pigment content on H. floresii, we evaluate if and how the spectral composition of light affects growth and pigment dynamics under laboratory cultivation. Unialgal cultures were exposed to white, blue, red and green light in a 3-week experiment. Green light resulted in the highest algal growth rates. Synthesis of chlorophyll a, alpha-carotene and lutein, but not of beta-carotene, was induced by white or green light. Phycocyanin synthesis was stimulated by blue light and phycoerythrin synthesis by blue or red light. Light quality treatments may be used to manipulate pigment composition in Halymenia floresii cultures.

Among wetlands, rich fens are one of the most species-rich, and also one of the most threatened habitats due to drainage activities. We tested the effects of several restoration measures on vegetation composition and dynamics over 4 years in two rich fens in east central Sweden that had been drained about 50 years ago. The encroaching tree layer was removed, and the restoration measures examined were rewetting by ditch blocking, mowing, and peat disturbance (removing vegetation and mixing the surface peat). At both sites, rewetting alone (without mowing or peat disturbance) led to small changes in species composition. In plots with peat disturbance, several characteristic rich fen species established, probably from a persistent diaspore bank or from refugia nearby. The disturbance treatment also prevented a rapid reestablishment of dominant grasses and mosses that had spread since drainage. Late season mowing alone appeared not to be a very efficient treatment in the initial phase after restoration, but seemed to reinforce the positive effects of peat disturbance. The results indicate the necessity of combining several treatments to recreate an ecologically functional vegetation.

We analyzed astaxanthin concentrations and the composition of geometrical (E/Z) astaxanthin isomers in 631 tissue samples from the four chief fish species in the pelagic zone of the brackish Baltic Sea. Salmon and herring showed signs of astaxanthin deficiency, but cod and sprat did not. The isomers were distributed selectively in fish tissues, with highest proportions of all-E-astaxanthin in salmon gonads (71%) and lowest in herring gonads (19%). We discovered that the clupeids are no ideal prey for salmon and cod with respect to their high whole-body concentrations of astaxanthin Z-isomers, which have low bioavailability for salmon and cod. The salmon in the Baltic Sea is entirely dependent on herring and sprat for food intake while cod feeds on a more diverse diet, including crustaceans. This explains the normal low astaxanthin levels in the salmon in the Baltic Sea. Observed decreases in astaxanthin levels in the Baltic salmon during the last 50 years, which are related to a reproductional disturbance (M74 syndrome), can be explained by the here described poor quality of herring as astaxanthin source in combination with recorded changes in the feeding ecology of the Baltic salmon with less sprat and more herring in the diet today. Herring is inferior to sprat as astaxanthin source, especially in autumn when a salmon or cod obtains four times more bioavailable all-E-astaxanthin (by weight) from sprat than from herring. The Baltic herring is starving more than the sprat as a result of competition between the clupeids though fishing mortality and recruitment problems of the cod, their major predator during the last decades. Therefore, less crustacean astaxanthin (mainly all-E) is transferred directly to piscivorous fish from herring stomachs than from sprat stomachs.

The carotenoid pigments of mesozooplankton communities in the Baltic Sea area were investigated in a large-scale survey. Ninety-nine percent of the zooplankton carotenoid concentrations consisted of astaxanthin and only 1% of canthaxanthin. We recorded large seasonal differences in astaxanthin concentrations, but no apparent patterns in the regional distribution within the Baltic Sea proper. Astaxanthin levels were lowest in summer when zooplankton feeding and growth rates are highest. In the cold season astaxanthin concentrations were three to four times higher than in summer and the proportions of astaxanthin esters were much higher than in summer. This suggests that astaxanthin is necessary especially in winter for the antioxidant protection of storage lipids. The seasonal cycles of astaxanthin was strongly intertwined with seasonal environmental conditions and changes in zooplankton community composition. Large differences between cladoceran- and copepod-dominated communities were were discovered. The abundances of the cladoceran genera Bosmina, Evadne and Podon were strongly negatively correlated with community concentrations of all forms of astaxanthin. Among the copepods, Temora longicornis and Pseudocalanus acuspes had the highest affinities with astaxanthin and Acartia spp. the lowest. The proportion of astaxanthin esters in the mesozooplankton of the Baltic Sea proper was on average 35%, which is lower than normally reported for pelagic crustaceans. This may indicate starvation of zooplankton and low nutritional value as astaxanthin source for predators in the Baltic Sea proper. Climate change scenarios for the area predict developments towards higher water temperature and lower salinity in the near future and this may lower the food quality for planktivorous fish if the abundances of Bosmina spp. and Acartia spp. increase at the cost of more nutritious copepods with higher astaxanthin concentrations. Because of their small size these taxa are normally avoided as prey by the major planktivorous fish, herring and sprat, in the Baltic Sea proper. However, when the abundances of larger zooplankton decrease by the ongoing bottom-up and top-down pressures on the zooplankton community, which already has happened in the case of Pseudocalanus acuspes, this may have consequences for the transport of astaxanthin to higher trophic levels.

Thiamine (vitamin B₁) is produced by plants, algae and bacteria and must be acquired through the food web by higher trophic levels. In this study we investigate the biosynthesis of thiamine in six phytoplankton species belonging to five different phyla under different environmental conditions. The chlorophyte Dunaliella tertiolecta, the dinoflagellate Prorocentrum minimum and the prymnesiophyte Rhodomonas salina were found to be thiamine auxotrophs, while the cyanobacterium Nodularia spumigena and the diatoms Phaeodactylum tricornutum and Skeletonema costatum were capable of thiamine synthesis. Measured net thiamine production in the latter three species varied with temperature, photon density and salinity. These effects were different for the cyanobacterium and the diatoms and strongest for salinity. In N. spumigena, the total thiamine concentration increased threefold with increased salinity. P. tricornutum accumulated seven times more thiamine diphosphate when salinity was decreased. Temperature also had pronounced effects on thiamine concentration, while photon density only affected thiamine levels in combination with temperature. In N. spumigena and P. tricornutum, total thiamine levels increased with higher temperature. We demonstrate a high variability among phytoplankton species in thiamine biosynthesis, as well as in the level of thiamine production in response to environmental factors. Thus, regime shifts in phytoplankton community composition through large-scale environmental change can alter the vitamin B₁ availability for higher trophic levels. This may have serious consequences for the access of zooplankton, fish, birds and mammals to this essential vitamin in changing ecosystems.

In heterogeneous environments, selection on life-history traits and flowering time may vary considerably among populations because of differences in the extent to which mortality is related to age or size, and because of differences in the seasonal patterns of resource availability and intensity of biotic interactions. Spatial variation in optimal reproductive effort and flowering time may result in the evolution of genetic differences in life-history traits, but also in the evolution of adaptive phenotypic plasticity. The perennial herb Primula farinosa occurs at sites that differ widely in soil depth and therefore in water-holding capacity, vegetation cover, and frost-induced soil movement in winter. We used data from eight natural populations and a common-garden experiment to test the predictions that reproductive allocation is negatively correlated with soil depth while age at first reproduction and first flowering date among reproductive individuals are positively correlated with soil depth. In the common-garden experiment, maternal families collected in the field were grown from seed and monitored for 5 years. In the field, reproductive effort (number of flowers in relation to rosette area) varied among populations and was negatively related to soil depth. In the common-garden experiment, among-population differences in age at first reproduction, and reproductive effort were statistically significant, but relatively small and not correlated with soil depth at the site of origin. Flowering time varied considerably among populations, but was not related to soil depth at the site of origin. Taken together, the results suggest that among-population variation in reproductive effort observed in the field largely reflects phenotypic plasticity. They further suggest that among-population differentiation in flowering time cannot be attributed to variation in environmental factors correlated with soil depth.