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  • Kaartokallio, Hermanni (Helsingin yliopisto, 2005)
  • Ainasoja, Miia (Helsingin yliopisto, 2008)
    Plants produce a diversity of secondary metabolites, i.e., low-molecular-weight compounds that have primarily ecological functions in plants. The flavonoid pathway is one of the most studied biosynthetic pathways in plants. In order to understand biosynthetic pathways fully, it is necessary to isolate and purify the enzymes of the pathways to study individual steps and to study the regulatory genes of the pathways. Chalcone synthases are key enzymes in the formation of several groups of flavonoids, including anthocyanins. In this study, a new chalcone synthase enzyme (GCHS4), which may be one of the main contributors to flower colour, was characterised from the ornamental plant Gerbera hybrida. In addition, four chalcone synthase-like genes and enzymes (GCHS17, GCHS17b, GCHS26 and GCHS26b) were studied. Spatial expression of the polyketide synthase gene family in gerbera was also analysed with quantitative RT-PCR from 12 tissues, including several developmental stages and flower types. A previously identified MYB transcription factor from gerbera, GMYB10, which regulates the anthocyanin pathway, was transferred to gerbera and the phenotypes were analysed. Total anthocyanin content and anthocyanidin profiles of control and transgenic samples were compared spectrophotometrically and with HPLC. The overexpression of GMYB10 alone was able to change anthocyanin pigmentation: cyanidin pigmentation was induced and pelargonidin pigmentation was increased. The gerbera 9K cDNA microarray was used to compare the gene expression profiles of transgenic tissues against the corresponding control tissues to reveal putative target genes for GMYB10. GMYB10 overexpression affected the expression of both early and late biosynthetic genes in anthocyanin-accumulating transgenic tissues, including the newly isolated gene GCHS4. Two new MYB domain factors, named as GMYB11 and GMYB12, were also upregulated. Gene transfer is not only a powerful tool for basic research, but also for plant breeding. However, crop improvement by genetic modification (GM) remains controversial, at least in Europe. Many of the concerns relating to both human health and to ecological impacts relate to changes in the secondary metabolites of GM crops. In the second part of this study, qualitative and quantitative differences in cytotoxicity and metabolic fingerprints between 225 genetically modified Gerbera hybrida lines and 42 non-GM Gerbera varieties were compared. There was no evidence for any major qualitative and quantitative changes between the GM lines and non-GM varieties. The developed cell viability assays offer also a model scheme for cell-based cytotoxicity screening of a large variety of GM plants in standardized conditions.
  • Ketola, Mirva (Helsingin yliopisto, 2011)
    To protect and restore lake ecosystems under threats posed by the increasing human population, information on their ecological quality is needed. Lake sediments provide a data rich archive that allows identification of various biological components present prior to anthropogenic alterations as well as a constant record of changes. By providing a longer dimension of time than any ongoing monitoring programme, palaeolimnological methods can help in understanding natural variability and long-term ecological changes in lakes. As zooplankton have a central role in the lake food web, their remains can potentially provide versatile information on past trophic structure. However, various taphonomic processes operating in the lakes still raise questions concerning how subfossil assemblages reflect living communities. This thesis work aimed at improving the use of sedimentary zooplankton remains in the reconstruction of past zooplankton communities and the trophic structure in lakes. To quantify interspecific differences in the accumulation of remains, the subfossils of nine pelagic zooplankton taxa in annually laminated sediments were compared with monitoring results for live zooplankton in Lake Vesijärvi. This lake has a known history of eutrophication and recovery, which resulted from reduced external loading and effective fishing of plankti-benthivorous fish. The response of zooplankton assemblages to these known changes was resolved using annually laminated sediments. The generality of the responses observed in Lake Vesijärvi were further tested with a set of 31 lakes in Southern Finland, relating subfossils in surface sediments to contemporary water quality and fish density, as well as to lake morphometry. The results demonstrated differential preservation and retention of cladoceran species in the sediment. Daphnia, Diaphanosoma and Ceriodaphnia were clearly underrepresented in the sediment samples in comparison to well-preserved Bosmina species, Chydorus, Limnosida and Leptodora. For well-preserved species, the annual net accumulation rate was similar to or above the expected values, reflecting effective sediment focusing and accumulation in the deepest part of the lake. The decreased fish density and improved water quality led to subtle changes in zooplankton community composition. The abundance of Diaphanosoma and Limnosida increased after the reduction in fish density, while Ceriodaphnia and rotifers decreased. The most sensitive indicator of fish density was the mean size of Daphnia ephippia and Bosmina (E.) crassicornis ephippia and carapaces. The concentration of plant-associated species increased, reflecting expanding littoral vegetation along with increasing transparency. Several of the patterns observed in Lake Vesijärvi could also be found within the set of 31 lakes. According to this thesis work, the most useful cladoceran-based indices for nutrient status and planktivorous fish density in Finnish lakes were the relative abundances of certain pelagic taxa, and the mean size of Bosmina spp. carapaces, especially those of Bosmina (E.) cf. coregoni. The abundance of plant-associated species reflected the potential area for aquatic plants. Lake morphometry and sediment organic content, however, explained a relatively high proportion of the variance in the species data, and more studies are needed to quantify lake-specific differences in the accumulation and preservation of remains. Commonly occurring multicollinearity between environmental variables obstructs the cladoceran-based reconstruction of single environmental variables. As taphonomic factors and several direct and indirect structuring forces in lake ecosystems simultaneously affect zooplankton, the subfossil assemblages should be studied in a holistic way before making final conclusions about the trophic structure and the change in lake ecological quality.
  • Niemistö, Juha (Helsingin yliopisto, 2008)
    Sediment resuspension, the return of the bottom material into the water column, is an important process that can have various effects on a lake ecosystem. Resuspension caused by wind-induced wave disturbance, currents, turbulent fluctuations and bioturbation affects water quality characteristics such as turbidity, light conditions, and concentrations of suspended solids (SS) and nutrients. Resuspension-mediated increase in turbidity may favour the dominance of phytoplankton over macrophytes. The predator-prey interactions contributing to the trophic state of a lake may also be influenced by increasing turbidity. Directly, the trophic state of a lake can be influenced by the effect of sediment resuspension on nutrient cycling. Resuspension enhances especially the cycling of phosphorus by bringing the sedimentary nutrients back into the water column and may thereby induce switches between phosphorus and nitrogen limitation. The contribution of sediment resuspension to gross sedimentation, turbidity, and concentration of SS and nutrients was studied in a small, deep lake as well as in a multibasin lake with deep and shallow areas. The effect of ice cover on sediment resuspension and thereby on phosphorus concentrations was also studied. The rates of gross sedimentation and resuspen¬sion were estimated with sediment traps and the associations between SS and nutrients were considered. Sediment resuspension, caused by wind activity, comprised most of the gross sedimenta¬tion and strongly contributed to the concentration of SS and turbidity in the lakes studied. Additionally, via the influence on SS, resuspension affected the concentration of total phosphorus (TP) and soluble reactive phosphorus (SRP), as well as the total nitrogen to total phosphorus (TN:TP) ratio. Although contrasting results concerning the dependence between the SS and SRP concentrations were observed, it could be concluded that sediment resuspension during strong algal blooms (pH > 9) led to aerobic release of P. The main findings of this thesis were that in the course of the growing season, sediment resuspension coupled with phytoplankton succession led to liberation of P from resuspended particles, which in turn resulted in high TP concentrations and low TN:TP ratios. This development was likely a cause of strong cyanobacterial blooms in midsummer.
  • Fatal, Netta (Helsingin yliopisto, 2004)
  • Szilvay, Géza R. (Helsingin yliopisto, 2007)
    Hydrophobins are small surface active proteins that are produced by filamentous fungi. The surface activity of hydrophobin proteins leads to the formation of a film at the air-water interface and adsorption to surfaces. The formation of these hydrophobin films and coatings is important in many stages of fungal development. Furthermore, these properties make hydrophobins interesting for potential use in technical applications. The surfactant-like properties of hydrophobins from Trichoderma reesei were studied at the air-water interface, at solid surfaces, and in solution. The hydrophobin HFBI was observed to spontaneously form a cohesive film on a water drop. The film was imaged using atomic force microscopy from both sides, revealing a monomolecular film with a defined molecular structure. The use of hydrophobins as surface immobilization carriers for enzymes was studied using fusion proteins of HFBI or HFBII and an enzyme. Furthermore, sitespecifically modified variants of HFBI were shown to retain their ability to selfassemble at interfaces and to be able to bind a second layer of proteins by biomolecular recognition. In order to understand the function of hydrophobins at interfaces, an understanding of their overall behavior and self-assembly is needed. HFBI and HFBII were shown to associate in solution into dimers and tetramers in a concentration-dependent manner. The association dynamics and protein-protein interactions of HFBI and HFBII were studied using Förster resonance energy transfer and size exclusion chromatography. It was shown that the surface activity of HFBI is not directly dependent on the formation of multimers in solution.
  • Zohdy, Sarah (Helsingin yliopisto, 2012)
    Mouse lemurs are the world s smallest primates and a model species for ancestral primates that lived 55 million years ago. In captive conditions, mouse lemurs live over six times longer than similarly sized mice and have been found to exhibit many symptoms of human senescence, including Alzheimer s-like neurodegeneration. These traits make captive mouse lemurs an exemplary model for aging. Despite this, to date no study has examined the aging process in wild mouse lemurs. This thesis addresses multidisciplinary questions relating to mouse lemur aging and life history. Through mark-recapture data and a combination of field and laboratory techniques I examine the aging process in wild brown mouse lemurs (Microcebus rufus). To estimate ages of individual wild mouse lemurs a technique was developed using dental wear. I found that in their natural habitat these tiny primates live up to 8 years of age, well past the captive age of senescence (5 yrs). Among old individuals, both males and females are represented, and unlike other polygamous vertebrates age-dependent survival rates do not differ between sexes. With the ages of wild mouse lemurs identified, other age-related factors such as hormone levels and parasite loads were subsequently examined. Contrary to findings in captivity no observable physical symptoms of senescence were found in old mouse lemurs, i.e. over the age of five. Further, new findings highlight mouse lemurs as an exception to many assumptions of mammalian physiology. In this study, testosterone levels were found to be comparable in both males and females, potentially providing an explanation for the lack of difference in survival rates between sexes. Testosterone and DHEA-S, two hormones typically found to decrease with age, did not differ between young and old lemurs. However, cortisol, the stress hormone, did decrease with age in male mouse lemurs, but not in females. Differences in immunity with age were examined indirectly via parasite dynamics. Specifically, I described the ectoparasites found on brown mouse lemurs, and created and implemented a novel method which allows the tracking of the natural flow of parasites between known individuals in a wild. This method revealed that parasite movement between lemurs suggests a much more complex social network than indicated by trapping, provided new insight about how parasites/pathogens move among wild populations, and revealed that only a few individual lemurs could be responsible for population-wide louse-borne epidemic. In addition to shedding light on the social behavior of mouse lemurs, I used the presence of ecto- and endoparasites as an indicator of immune health in young and old individuals, exposing a decline in endoparasites with age, but not in ectoparasites. Hormone measures and parasite loads were also employed to test the immunocompetence handicap hypothesis (ICHH) (which implicates testosterone as a cause for immunosuppression and hence higher parasite intensities) in both sexes. Contrary to the ICHH no correlation between testosterone and parasite intensities was found; however, when cortisol and testosterone positively co-varied higher parasite loads were observed in both sexes. In conclusion, in the search for a better understanding of the aging process in wild brown mouse lemurs I examined the multifaceted physiological transformations (parasitological, endocrinological, and dental wear). This research produced novel, replicable methodologies and findings with wide-reaching implications that extend beyond aging and challenge some of the previously-held assumptions of mammalian biology.
  • Niemi, Katri (Helsingin yliopisto, 2012)
    The immune response is operated by two integrated systems, the adaptive and innate immune responses. Innate immunity includes both cellular and soluble components. The cellular part consists of host cells at the front line of defence - macrophages, monocytes, dendritic cells, neutrophils, endothelial cells and mast cells - that express receptors capable of recognizing common pathogen constituents, hence called pattern-recognition receptors, PRRs. Several cooperating PRR families, for example Toll-like receptors (TLRs) and receptors with nucleotide-binding domain leucine-rich repeats (NLRs), have been identified. They recognize two different classes of structures, pathogen-associated molecular patterns (PAMPs) and non-microbial, danger-associated molecular patterns (DAMPs). The soluble component of the innate immune system includes an arsenal of acute-phase proteins, the expression of which is induced during the acute-phase response (APR), an immediate systemic reaction triggered by a local or systemic abnormal condition such as tissue injury, infection or trauma. In addition, the innate immune response is driven by numerous proinflammatory cytokines and mediators, most notably interleukin (IL-) 1β. The activity of IL-1β is tightly controlled; the induction of gene expression and the activation of pro-IL-1β require separate stimuli. IL-1β maturation takes place in cytosolic protein platforms called inflammasomes, of which NLRP3 is the most characterized. The major acute-phase proteins in human are C-reactive protein (CRP) and serum amyloid A (SAA). In response to inflammatory stimulus, SAA concentration in plasma can increase up to 1000-fold. SAA circulates in association with high-density lipoprotein (HDL) and is, thus, suggested to play a role in lipid metabolism and transport. In addition, SAA possesses strong cytokine-like and proinflammatory properties. A pathogenic role for SAA has most clearly been implicated in AA amyloidosis, a systemic protein misfolding disease that can complicate chronic inflammatory conditions. Current evidence indicates that SAA is also as an active mediator in cardiovascular diseases. The aim of the study was to elucidate the interaction between SAA and two types of innate immune system cells, human mast cells and macrophages, and the consequences of this interaction in the pathogenesis of AA amyloidosis and atherosclerosis, as well as the regulation of SAA in inflammation. It was demonstrated that SAA is a potent activator of mast cells and macrophages, as indicated by a dose-dependent production of key proinflammatory cytokines, IL-1β and tumor necrosis factor (TNF) -α, in both cell types. In mast cells, this activation led to the degradation of SAA by the mast cell-derived protease tryptase and to the formation of amyloid-like structures, suggesting a pathogenic role for mast cells in AA amyloidosis. The secretion of IL-1β was studied in more detail in human macrophages, in which SAA was found to be able to induce both the gene expression of IL1B, via TLR2 and TLR4, and the activation of the NLRP3 inflammasome, resulting in the secretion of mature IL-1β. The activation of NLRP3 involved the ATP-receptor P2X7 and cathepsin B activity. Native serum lipoproteins were shown to inhibit the activity of SAA and this inhibition was further enhanced by lipoprotein oxidation. Besides the expression of IL1B, oxidized LDL inhibited also the activation of the NLRP3 inflammasome. A decrease in the SAA-induced IL-1β production was observed also in vivo, suggesting that oxidized LDL, although possessing many pathological features, may represent a novel and significant regulator of SAA activity in inflamed tissues, including atherosclerotic lesions. All together, the findings of this study stress the significance of SAA in the pathogenesis of inflammatory diseases, such as atherosclerosis, and provide new insights into mechanisms leading to AA amyloidogenesis.
  • Eklund, Johanna (Helsingin yliopisto, 2016)
    Protected areas are a key tool for conserving biodiversity and an increase in their coverage has long been the aim of international conventions and initiatives. With progress to achieve target 11 of the Convention on Biological Diversity of protecting 17 % of terrestrial areas, the focus has now shifted towards assessing the protected area effectiveness in maintaining species or avoiding land conversions. In my doctoral thesis I develop a novel way of assessing PA effectiveness, based on the counterfactual thinking, and use this to link it to different management and ecological factors. I link different aspects of PA effectiveness conceptually to the quality of governance and show how spatial prioritizations can change with the inclusion of these socio-political factors. Using Madagascar as a case study, and in line with other studies elsewhere, I find that the protected area network is effective to some extent in mitigating the pressure of deforestation. I show the importance of considering the temporal dimension of protected area effectiveness measures and how protected area effectiveness changes over time due to increasing or decreasing pressures. These results link directly to considerations of vulnerability and irreplaceability in Systematic conservation planning and I show that accounting for governance factors in a global spatial prioritization analysis change the identification of areas. My thesis shows the relative nature of protected area effectiveness measures and how important it is to get the assessments right, especially because of the massive focus on protected area effectiveness as a panacea to stopping biodiversity declines. Improving protected area effectiveness needs to be linked to governance factors affecting not only the management but also the drivers of threat, something that previous studies have overlooked. With my thesis I make an attempt to bridge the themes of protected area effectiveness, considerations of quality of governance, and how it all links to conservation prioritizations. Our methodology has been developed with the aim to be computationally efficient and conceptually more robust than existing matching methods, with the potential to be scaled up for larger studies. However, how the two methods perform needs to be tested in the future. My dissertation has clear practical implications for the conservation of Madagascar s biodiversity and the results are of potential interest for both NGOs and the Madagascar National Park administration. The conceptual contribution of this thesis should be incorporated into mainstream thinking and the discourse of setting global priorities for biodiversity conservation, such as by the International Union for Conservation of Nature and Natural Resources (IUCN), the World Parks Congress (WPC) and ultimately the Convention on Biological Diversity (CBD).
  • Natri, Heini (Helsingin yliopisto, 2015)
    Sex chromosomes are involved in several fundamental biological processes such as sex determination, sexual selection and dimorphism, as well as speciation. Structurally distinct sex chromosomes have evolved multiple times independently in various taxa, and different sex determination and sex chromosome systems are often found in closely related species of non-mammalian vertebrates. While the evolution of heteromorphic sex chromosomes from an ordinary pair of autosomes that obtain a sex-determining role has been hypothesized, the exact process and mechanisms of sex chromosome differentiation are not well understood. The restriction of recombination is known to be a crucial step in the process of sex chromosome evolution, and two main models have been proposed to explain the process of recombination suppression: (1) the gradual reduction of cross-overs driven by genetic modifiers of recombination rates, and (2) a stepwise model based on chromosomal rearrangements, such as inversions. It has been hypothesized that chromosomal transitions are connected with the formation of new species. However, it is unknown whether such transitions lead to, or result from, the restriction of genetic exchange between groups that ultimately results in speciation. Sex chromosomes may have a substantial role in speciation by contributing to reproductive isolation between different taxa, particularly through hybrid sterility. Sex chromosomes are a plausible source of the effects of Haldane s rule one the most consistent rules of evolutionary biology which states that the heterogametic sex (XY or ZW) is more likely to exhibit hybrid incompatibility than the homogametic sex. Furthermore, genetic factors associated with reproductive isolation are often located on sex chromosomes. In this thesis I have investigated the molecular evolution of sex chromosomes specifically the molecular process of recombination suppression and sex chromosome differentiation and the role of sex chromosomes in speciation by using stickleback fishes as a model system. By utilising various genetic methods, I have investigated the inter- and intraspecific variation in sex chromosome differentiation in three-spined and nine-spined sticklebacks. I have examined the neo-sex chromosomes of the Japan Sea lineage of the three-spined stickleback in order to gain insight into the process of recombination suppression and genetic differentiation of sex chromosomes at the initial stages of their evolution. Furthermore, through comprehensive breeding experiments and genetic analyses, I studied the evolution of sex determination and sex chromosome systems, as well as the genetic mechanisms of hybrid incompatibility in nine-spined sticklebacks. The results presented in this thesis illustrate a striking variety in sex chromosome and sex determination systems between and within these stickleback species. My findings suggest that recombination suppression and genetic differentiation of sex chromosomes may develop in various ways: my results show that the differentiation process has proceeded in a gradual manner in the earliest stages of neo-sex chromosome evolution in three-spined sticklebacks, yet they demonstrate a rapid process of sex chromosome evolution within the nine-spined stickleback species driven by a chromosomal inversion. Moreover, this thesis provides evidence for the role of sex-chromosomal inversions in the formation of postzygotic reproductive isolation and thus speciation.
  • Karell, Patrik (Helsingin yliopisto, 2007)
    Life-history theory states that although natural selection would favour a maximisation of both reproductive output and life-span, such a combination can not be achieved in any living organism. According to life-history theory the reason for the fact that not all traits can be maximised simultaneously is that different traits compete with each other for resources. These relationships between traits that constrain the simultaneous evolution of two or more traits are called trade-offs. Therefore, during different life-stages an individual needs to optimise its allocation of resources to life-history components such as growth, reproduction and survival. Resource limitation acts on these traits and therefore investment in one trait, e.g. reproduction, reduces the resources available for investment in another trait, e.g. residual reproduction or survival. In this thesis I study how food resources during different stages of the breeding event affect reproductive decisions in the Ural owl (Strix uralensis) and the consequences of these decisions on parents and offspring. The Ural owl is a suitable study species for such studies in natural populations since they are long-lived, site-tenacious, and feed on voles. The vole populations in Fennoscandia fluctuate in three- to four-year cycles, which create a variable food environment for the Ural owls to cope with. The thesis gives new insight in reproductive costs and their consequences in natural animal populations with emphasis on underlying physiological mechanisms. I found that supplementary fed Ural owl parents invest supplemented food resources during breeding in own self-maintenance instead of allocating those resources to offspring growth. This investment in own maintenance instead of improving current reproduction had carry-over effects to the following year in terms of increased reproductive output. Therefore, I found evidence that reduced reproductive costs improves future reproductive performance. Furthermore, I found evidence for the underlying mechanism behind this carry-over effect of supplementary food on fecundity. The supplementary-fed parents reduced their feeding investment in the offspring compared to controls, which enabled the fed female parents to invest the surplus resources in parasite resistance. Fed female parents had lower blood parasite loads than control females and this effect lasted until the following year when also reproductive output was increased. Hence, increased investment in parasite resistance when resources are plentiful has the potential to mediate positive carry-over effects on future reproduction. I further found that this carry-over effect was only present when potentials for future reproduction were good. The thesis also provides new knowledge on resource limitation on maternal effects. I found that increased resources prior to egg laying improve the condition and health of Ural owl females and enable them to allocate more resources to reproduction than control females. These additional resources are not allocated to increase the number of offspring, but instead to improve the quality of each offspring. Fed Ural owl females increased the size of their eggs and allocated more health improving immunological components into the eggs. Furthermore, the increased egg size had long-lasting effects on offspring growth, as offspring from larger eggs were heavier at fledging. Limiting resources can have different short- and long-term consequences on reproductive decisions that affect both offspring number and quality. In long-lived organisms, such as the Ural owl, it appears to be beneficial in terms of fitness to invest in long breeding life-span instead of additional investment in current reproduction. In Ural owls, females can influence the phenotypic quality of the offspring by transferring additional resources to the eggs that can have long-lasting effects on growth.
  • Matveinen-Huju, Katja (Helsingin yliopisto, 2007)
    Forestry has influenced forest dwelling organisms for centuries in Fennoscandia. For example, in Finland ca. 30% of the threatened species are threatened because of forestry. Nowadays forest management recommendations include practices aimed at maintaining biodiversity in harvesting, such as green-tree retention. However, the effects of these practices have been little studied. In variable retention, different numbers of trees are retained, varying from green-tree retention (at least a few live standing trees in clear-cuts) to thinning (only individual trees removed). I examined the responses of ground-dwelling spiders and carabid beetles to green-tree retention (with small and large tree groups), gap felling and thinning aimed at an uneven age structure of trees. The impacts of these harvesting methods were compared to those of clear-cutting and uncut controls. I aimed to test the hypothesis that retaining more trees positively affects populations of those species of spiders and carabids that were present before harvesting. The data come from two studies. First, spiders were collected with pitfall traps in south-central Finland in 1995 (pre-treatment) and 1998 (after-treatment) in order to examine the effects of clear-cutting, green-tree retention (with 0.01-0.02-ha sized tree groups), gap felling (with three 0.16-ha sized openings in a 1-ha stand), thinning aiming at an uneven age structure of trees and uncut control. Second, spiders and carabids were caught with pitfall traps in eastern Finland in 1998-2001 (pre-treatment and three post-treatment years) in eleven 0.09-0.55-ha sized retention-tree groups and clear-cuts adjacent to them. Original spider and carabid assemblages were better maintained after harvests that retained more trees. Thinning maintained forest spiders well. However, gap felling and large retention-tree groups maintained some forest spider and carabid species in the short-term, but negatively affected some species over time. However, use of small retention-tree groups was associated with negative effects on forest spider populations. Studies are needed on the long-term effects of variable retention on terrestrial invertebrates; especially those directed at defining appropriate retention patch size and on the importance of structural diversity provided by variable retention for invertebrate populations. However, the aims of variable retention should be specified first. For example, are retention-tree groups planned to constitute life-boats , stepping-stones or to create structural diversity? Does it suffice that some species are maintained, or do we want to preserve the most sensitive ones, and how are these best defined? Moreover, the ecological benefits and economic costs of modified logging methods should be compared to other approaches aimed at maintaining biodiversity.
  • Saj, Stéphane (Helsingin yliopisto, 2008)
    Plant species differ in their effects on ecosystem productivity and it is recognised that these effects are partly due to plant species-specific influences on soil processes. Until recently, however, not much attention was given to the potential role played by soil biota in these species-specific effects. While soil decomposers are responsible for governing the availability of nutrients for plant production, they simultaneously depend on the amount of carbon provided by plants. Litter and rhizodeposition constitute the two basal resources that plants provide to soil decomposer food webs. While it has been shown that both of these can have effects on soil decomposer communities that differ among plant species, the putative significance of these effects for plant nitrogen (N) acquisition is currently understudied. My PhD work aimed at clarifying whether the species-specific influences of three temperate grassland plants on the soil microfood-web, through rhizodeposition and litter, can feed back to plant N uptake. The methods and approach used (15N labelling of plant litter in microcosm experiments) revealed to be an effective combination of tools in studying these feedbacks. Plant effects on soil organisms were shown to differ significantly between plant species and the effects could be followed across several trophic levels. The labelling of litter further permitted the evaluation of plant acquisition of N derived from soil organic matter. The results show that the structure of the soil microfood-web can have a significant role in plant N acquisition when the structure is experimentally manipulated, such as when comparing systems consisting of microbes to those consisting of microbes and their grazers. However, despite this, the results indicate that differences in N uptake from soil organic matter between different plant species are not related to the effects these species exert on the structure of the soil microfood-web. Rather, these differences in N uptake seem to be determined by other species-specific traits of live plants and their litter. My results thus indicate that different resources provided by different plant species may not induce species-specific decomposer feedbacks on plant N uptake from soil organic matter. This further suggests that the species-specific plant effects on soil decomposer communities may not, at least in the short term, have significant consequences on plant production.
  • Pohjamo, Maria (Helsingin yliopisto, 2008)
    The area of intensively managed forests, in which required conditions for several liverwort species are seldom found, has expanded over the forest landscape during the last century. Liverworts are very sensitive to habitat changes, because they demand continuously moist microclimate. Consequently, about third of the forest liverworts have been classified as threatened or near threatened in Finland. The general objective of this thesis is to increase knowledge of the reproductive and dispersal strategies of the substrate-specific forest bryophytes. A further aim was to develop recommendations for conservation measures for species inhabiting unstable and stable habitats in forest landscape. Both population ecological and genetic methods have been applied in the research. Anastrophyllum hellerianum inhabits spatially and temporally limited substrate patches, decaying logs, which can be considered as unstable habitats. The results show that asexual reproduction by gemmae is the dominant mode of reproduction, whereas sexual reproduction is considerably infrequent. Unlike previously assumed, not only spores but also the asexual propagules may contribute to long-distance dispersal. The combination of occasional spore production and practically continuous, massive gemma production facilitates dispersal both on a local scale and over long distances, and it compensates for the great propagule losses that take place preceding successful establishment at suitable sites. However, establishment probability of spores may be restricted because of environmental and biological limitations linked to the low success of sexual reproduction. Long-lasting dry seasons are likely to result in a low success of sexual reproduction and decreased release rate of gemmae from the shoots, and consequent fluctuations in population sizes. In the long term, the substratum limitation is likely to restrict population sizes and cause local extinctions, especially in small-sized remnant populations. Contrastingly, larger forest fragments with more natural disturbance dynamics, to which the species is adapted, are pivotal to species survival. Trichocolea tomentella occupies stable spring and mesic habitats in woodland. The relatively small populations are increasingly fragmented with a high risk for extinction for extrinsic reasons. The results show that T. tomentella mainly invests in population persistence by effective clonal growth via forming independent ramets and in competitive ability, and considerably less in sexuality and dispersal potential. The populations possess relatively high levels of genetic diversity regardless of population size and of degree of isolation. Thus, the small-sized populations inhabiting stable habitats should not be neglected when establishing conservation strategies for the species and when considering the habitat protection of small spring sites. Restricted dispersal capacity, also on a relatively small spatial scale, is likely to prevent successful (re-)colonization in the potential habitat patches of recovering forest landscapes. By contrast, random short-range dispersal of detached vegetative fragments within populations at suitable habitat seems to be frequent. Thus, the restoration actions of spring and streamside habitats close to the populations of T. tomentella may contribute to population expansion. That, in turn, decreases the harmful effects of environmental stochasticity.
  • Tallberg, Petra (Helsingin yliopisto, 2000)