Tree-ring records from long-lived trees are instrumental for understanding climate variability during the Common Era. Some of the oldest and most valuable conifers used to reconstruct past climate exhibit strip-bark morphology, in which vertical segments of the tree have died in response to environmental stress. This form of localized stem mortality, also referred to as partial cambial dieback, is particularly common on conifers growing in xeric, cold, or exposed environments. Some studies note that strip-bark trees have increasing ring-width trends relative to trees with a fully living stem circumference, but there is substantial uncertainty as to what extent partial cambial dieback can influence tree-ring records and subsequent climate reconstructions. This dissertation explores the environmental drivers of partial cambial dieback on Siberian pine (Pinus sibirica Du Tour) from Mongolia, the effect of cambial dieback on the radial growth and physiology of affected trees, and methods for reducing strip-bark biases in tree-ring records. Chapter 1 assesses the causes and radial growth impacts of partial cambial dieback on Siberian pine trees growing on an ancient lava flow in central Mongolia. Using a combination of field observations and dendrochronological methods, this chapter demonstrates that strip-bark trees from this site exhibit dieback primarily on the southern side of stems, and that dieback was most common during a cold and dry period in the mid-19th century. Given the directionality and timing of dieback on these strip-bark trees, it is hypothesized that localized mortality events are linked to physiological injuries spurred from solar heating combined with unfavorable climatic conditions. This chapter also reveals that strip-bark trees from this site have increasing radial growth trends relative to trees with a full circular morphology (“whole-bark” trees). Strip-bark trees showed an especially rapid increase in ring widths following the cambial dieback period in the mid-19th century, providing initial evidence that dieback events can lead to increasing ring widths in strip-bark Siberian pine. Chapter 2 seeks to discern the physiological mechanisms of increasing radial growth trends in the Siberian pine strip-bark trees using stable carbon and oxygen isotopes from tree rings. One simple hypothesis is that strip-bark trees show increasing ring-width trends because radial growth is restricted to a smaller stem area after cambial dieback events. Conversely, some studies have hypothesized that increasing ring widths in strip-bark trees reflect a CO2 fertilization effect on growth that is not readily apparent in whole-bark trees. This chapter finds that strip-bark and whole-bark trees responded similarly to increasing atmospheric CO2 and climate variability in their radial growth and leaf-level gas exchange inferred from tree-ring stable isotopes. However, strip-bark and whole-bark trees showed notably different behavior following documented cambial dieback events. After dieback events, strip-bark trees exhibited an increase in ring widths and an enrichment in stable carbon and oxygen isotopes that was not apparent in whole-bark trees. These results further support the notion that partial cambial dieback leads directly to increasing ring widths in strip-bark trees, and that this response could reflect an increase in the ratio of leaf to live stem area after dieback occurs. Chapters 1 and 2 demonstrate that partial cambial dieback events and morphological changes impact the radial growth and physiology of strip-bark trees. Therefore, prior to developing climate reconstructions, it is necessary to remove variance associated with these non-climatic, morphological changes in tree-ring series. Chapter 3 outlines two chronology development methods for reducing strip-bark biases in tree-ring records. These methods, applied to Siberian pine and Great Basin bristlecone pine (Pinus longaeva Bailey), successfully reduce a strip-bark bias without removing low-to-medium frequency climate variance inferred from whole-bark trees, which were not impacted by dieback activity. While one approach directly corrects the bias in strip-bark series using a whole-bark chronology as a target, another method is based on the development of a low-percentile chronology, which can be applied to a site collection where the stem morphology of individual trees is unknown. Some limitations and caveats of these methods are discussed in context of the analyzed tree species. The findings from this dissertation have significantly contributed to our understanding of the radial growth and physiological responses of Siberian pine to partial cambial dieback and environmental changes. This dissertation also provides new methods for removing strip-bark biases in tree-ring chronologies. The conclusions presented here have important implications regarding the potential effects of partial cambial dieback on tree-ring records from other tree species and climate reconstructions derived from them. Continued and detailed study of the causes and impacts of partial cambial dieback on other tree species will be critical for understanding the interactions between ancient trees and their environment, and for improving the reliability of climate reconstructions based fully or partly on strip-bark trees.

Le genre Rickettsia est composé de bactéries Gram-négatives, intracellulaires obligatoires qui causent un éventail de maladies humaines à travers le monde. Des nouvelles techniques ont permis de progresser dans l'identification et la classification des Rickettsia, y compris l'introduction de méthodes moléculaires comme la comparaison de séquences de gènes (ARNr 16S, ompA, ompB, gltA, sca4 …) et la création du statut de sous-espèce. La génomique et les techniques de séquençage de nouvelle génération ont permis d’accéder à une nouvelle façon d’en apprendre davantage sur la pathogenèse et l'évolution de Rickettsia. La première partie de cette thèse est une revue sur les avantages et les limites de la génomique en taxonomie des procaryotes, tandis que la seconde partie est constituée des analyses génomiques de cinq sous-espèces de Rickettsia et une nouvelle espèce de Rickettsia. En utilisant des méthodes de séquençage à haut débit, nous avons obtenu les génomes de R. sibirica sibirica, R. sibirica mongolitimonae, R. conorii indica, R. conorii caspia, R. conorii israelensis et R. gravesii. Ce travail constitue la base d’autres études qui permettront de mieux comprendre les mécanismes physiopathologiques, l’évolution, et la taxonomie des rickettsies. / The Rickettsia genus is composed of Gram-negative, obligate intracellular bacteria that cause a range of human diseases around the world. New techniques have led to progress in the identification and classification of Rickettsia, including the introduction of molecular methods like sequence comparison (16S rRNA, ompA, ompB, gltA, sca4 …) and the creation of the subspecies status. Genomics and next-generation sequencing have opened a new way to learn more about the pathogenesis and evolution of Rickettsia. The first part of this thesis is a review on the advantages and limitations of genomics in prokaryotic taxonomy, while the second part consists of the genomic analyses of five Rickettsia subspecies and a new Rickettsia species. Using high-throughput sequencing methods, we obtained the draft genomes of R. sibirica sibirica, R. sibirica mongolitimonae, R. conorii indica, R. conorii caspia, R. conorii israelensis, and R. gravesii. This work can be a basis of further studies to increase the understanding on the disease-causing mechanisms, evolutionary relationships, and taxonomy of rickettsiae.

Siberian weasel, Mustela sibirica is a widespread carnivora mammal in Eurasia. In Taiwan, it inhabits a variety of environments restricted to altitude above 800 m. Based on mitochondrial control region sequences, I constructed phylogeography and analyzed population interflow about the species in Taiwan. The mean length of D-loop in Siberian weasel is 1038.9 bp. The D-loop structure can be divided into ETAS, CD and CSB domain. Among these, CD is the most conserved region while the two flank domains are variable. There are tandem repeat sequences in CSB domain, common in other carnivores. In phylogenetic analyses, three major lineages were found in phylogenetic trees and MSN topology. In general, haplotypes in clades are correlated to geographic distribution. The haplotypes of clade I were sampled from southern Taiwan, while the majority of those clade II and clade III were from northern Taiwan. The gene flow among clades were low. However no significant geographic boundaries existed between clades. It is speculated that the genetic isolation among clades may have been resulted from bottleneck effect, like other high altitude mammals in Taiwan, and not from geographic barriers mainly.

Treelines in high-mountain regions are constrained by heat deficiency, although the working mechanisms are still not entirely understood. Observational and paleoecological studies on treeline performance may contribute to increased understanding of the treeline phenomenon in general. The present thesis addresses elevational shifts of alpine treelines in the Swedish Scandes. By various analytical tools, the studies embrace widely different temporal scales. The concept treeline refers to the elevation (m a.s.l.) at a specific site of the upper individual tree of a certain tree species, at least 2 m tall. All the principal tree species in the Scandes are concerned, i.e. mountain birch (Betula pubescens ssp. czerepanovii), Norway spruce (Picea abies) and Scots pine (Pinus sylvestris). Paper I deals with regional treeline dynamics at more than 100 sites over the past 100 years. Concurrent with temperature rise by c. 1.4 °C over the same period, maximum treeline advances of all species amount to about 200 m. Thus, under ideal conditions, treelines respond in close equilibrium with air temperature evolution. However, over most parts of the landscape, treeline upshifts have been much smaller than 200 m, which relates to the combined action of geomorphology, wind, snow distribution and soil depth. After 1975, the birch has lost its role as the most rapidly advancing tree species, being superseded by pine and spruce. Paper II is a short-term (2005/2007-2010/2011) study of mountain birch treeline performance along a regional maritimity-continentality gradient. Upshift by 3.0 yr-1 in the maritime part of the gradient contrasts to retreat by 0.4 m yr-1 in the continental part. In the latter area, earlier and more complete melting of late-lying snow patches has seemingly progressed to a state when soil drought sets back the vigour of existing birches and precludes sexual regeneration and upslope advance of the treeline. In the maritime area, extensive and deep snow packs still exist above the treeline and constrain its position, although some release is taking place in the current warm climate. Paper III explores treeline change by phenotypic transformation of old-established stunted and prostrate spruce individuals (krummholz) growing high above the treeline and is based on analyses of radiocarbon-dated megafossils, preserved in the soil underneath clonal groups of spruce. Living spruce clones, which in some cases may date back to the early Holocene (9500 cal. yr BP), suggests that spruce immigrated from “cryptic” ice age refugia much closer to Scandinavia than conventionally thought. As the krummholz form presupposes open and windy habitats, it is inferred that permanently open spots prevailed in the high-mountain landscape even during periods when treelines in general were much higher than today. Paper IV reports radiocarbon dates of wood samples, retrieved from newly exposed glacier forefields at three main sites, located high above the modern treelines and embracing the entire Swedish Scandes. It appears that pine colonized early emerging nunataks already during the Late Glacial. Around 9600-9500 cal. yr BP a first massive wave of tree establishment, birch and pine, took place in “empty” glacier cirques. Both species grew 400-600 m above their present day treeline position and accordingly, the summer temperatures may have been 3.5 °C warmer than present (uncorrected for land uplift). During the entire interval 9600 to 4400 cal. yr BP, birch prospered 100-150 m above the uppermost pines. In response to Neoglacial cooling, treelines of both birch and pine descended until their final disappearance from the record 4400 and 5900 cal. yr BP, respectively. Thereafter, these habitats experienced increased snow accumulation and glacier inception. / Avhandlingen belyser förskjutningar i olika tidsskalor av den alpina trädgränsens läge i de svenska Skanderna. Trädgränsen definieras som den högsta nivån (m ö.h.) för minst 2 m höga individer av en viss art i en definierad del av en fjällsluttning. Avhandlingen består av fyra separata uppsatser, publicerade i olika välrenommerade vetenskapliga tidskrifter.  I Paper I analyseras förändringar av trädgränserna för fjällens vanligaste trädarter, fjällbjörk, gran och tall (Betula pubescens ssp. czerepanovii, Picea abies och Pinus sylvestris) mellan 1915 och 2007. Undersökningen omfattar ett 8000 km2 stort, naturgeografiskt heterogent område, med mer än 100 lokaler. De maximala trädgränsförskjutningarna för samtliga trädarter uppgår till omkring 200 m. Resultaten motsvarar de trädgränsförskjutningar som teoretiskt kan förutsägas utifrån den temperaturhöjning med cirka 1,4 °C som skett under samma tidsperiod, förutsatt ideala förhållanden. För större delen av området råder emellertid andra, icke-ideala förhållanden, varför trädgränsernas uppflyttning i allmänhet blivit avsevärt mindre än 200 m. Den främsta anledningen till detta är lokala topoklimatiska begränsningar, d.v.s. kombinerade effekter av geomorfologi, vind, snöfördelning, jorddjup, etc., som i stora delar av det starkt brutna fjällandskapet mer eller mindre effektivt hindrar träden från att nå sina potentiellt högst belägna växtplatser betingade av temperaturen. Efter 1975 har björken förlorat sin roll som arten med den snabbast expanderande trädgränsen. I stället har tall och gran avancerat med större hastighet. Det innebär att även om klimatets uppvärmning fortsätter, så kommer det subalpina björkbältet att expandera i avsevärt mindre omfattning än vad som ofta förebådats. Möjligtvis kommer det att ersättas av tall. Paper II behandlar björkens trädgränsdynamik under perioden 2005/2007-2010/2011 längs en regional klimatgradient med avseende på maritimitet/kontientalitet. Trädgränsen har under den aktuella perioden avancerat 3,0 m/år i den maritimt präglade delen av gradienten, vilket kontrasterar signifikant mot en sänkning med 0,4 m/år i området med mer kontinentalt klimat. Skillnaderna diskuteras i termer av klimatförändringens varierande effekter på snötäckets utbredning och varaktighet och dess inverkan på markfuktigheten. En allt tidigare total utsmältning av snölegorna i de kontinentala områdena har av allt att döma resulterat i vattenbrist under sommaren. Torka medför reducerad vitalitet för existerande björkar och förhindrar både sexuell förökning och uppflyttning av trädgränsen. I de maritima delarna kvarligger alltjämt mycket snö under en stor del av sommaren. Trädgränsens position har därför kunnat bibehållas eller flyttas upp. Vissa omständigheter tyder på att trädgränsens stigning i högre grad har varit baserad på fröföryngring efter 1975, jämfört med perioden 1915-1975. Utgångspunkten för Paper III är erfarenheter från Paper I, som visar att trädgränsens uppflyttning för gran och björk huvudsakligen är resultatet av ökad höjdtillväxt av äldre, i vissa fall flertusenåriga, mer eller mindre buskformiga individer (krummholz), som vuxit på nivåer långt ovanför trädgränsen. Som ett svar på de senaste hundra årens varmare klimat har dessa antagit trädform, varigenom trädgränsen höjts. För en fördjupad förståelse av den här mekanismen har megafossil, d.v.s. grova vedrester bevarade i marken under gamla grankloner i trädgränsekotonen, 14C-daterats. Resultaten tyder på att granar i exponerad fjällmiljö kan uppnå i det närmaste ”evigt” liv genom sin förmåga till vegetativ förökning och möjligheten att växla mellan busk- och trädform i takt med klimatets växlingar. Vissa nu levande kloner existerade av allt att döma redan för 9500 år sedan. Den nu dokumenterat tidiga förekomsten av gran, bekräftar den på senare tid allt tydligare bilden av granen som en tidig invandrare till fjällkedjan. Möjligtvis har granen ”övervintrat” den senaste istiden närmare Skandinavien än vad som till helt nyligen varit den gängse uppfattningen. Paper IV behandlar en för Skandinavien ny metod för historisk trädgränsrekonstruktion. I uppsatsen analyseras 14C-dateringar av totalt 78 större veddelar (megafossil) som nyligen exponerats i anslutning till smältande glaciäris och ”perenna” snölegor i tre huvudområden, Helags-Sylarna, Tärna och Abisko, högt ovanför dagens trädgräns. Det framkommer att tall (Pinus sylvestris) koloniserade tidigt framsmälta nunatakker redan under senglacial tid. För omkring 9600-9500 år sedan inträffade en första massiv våg av björk- och talletablering i isfria glaciärnischer. Båda arterna växte 400-600 m ovanför sina nuvarande trädgränspositioner, i ett klimat som kan ha varit 3,5 °C varmare än idag. Under intervallet 9600 till 4400 BP uppträdde björken i ett 100-150 m brett bälte ovanför de översta tallarna. Som ett svar på klimatets successiva avkylning under senare delen av Holocen sänktes både björkens och tallens trädgränser i de aktuella miljöerna, till dess de för 4400 respektive 5900 år sedan helt försvann från lokaler där glaciärer och perenna snöfält började bildas. De analyserade trädresterna, som länge bevarats av glaciäris och perenn snö representerar en period med ett klimat långt varmare än under det senaste århundradet. Med denna analogi från det förflutna kan det därför antas att i en framtid där sommartemperaturerna rent hypotetiskt är 3,5 °C högre än i nutiden, skulle trädgränserna lokalt kunna flyttas upp med ungefär 600 m.

ABSTRACT The epidemiological study of intestinal helminths and ticks of Siberian weasel (Mustela sibirica) was conducted from June 2001 to May 2002 in Shan-Ping, southern Taiwan. Nine helminths were found, including seven nematodes, Filaroides sp. (prevalence 94.4%), Ancylostoma sp. (77.4%), Uncinaria sp. (35.5%), Trichuris sp. 1 (35.5%), Trichuris sp. 2 (19.3%), Capillaria sp. (6.5%) and Physaloptera sp. (3.2%); one trematode, Platynosomum sp. (74.1%) and one acanthocephalans, Macracanthorhynchus sp. (10%). There was a significant seasonal difference of intensity of the Platynosomum sp. Two species of ticks were observed, Ixodes ovatus (prevalence 55.56%) and Haemaphysalis sp. Seasonal differences were significant in the prevalence and intensity of the Ixodes ovatus infection. The intensities of ticks and helminths in different sampling area were similar. The diet composition was possibly the factor affecting the seasonal change of intensity of the Platynosomum sp. and host availability affecting the seasonal change of ticks, Ixodes ovatus.

Abstract The amount and distribution of genetic diversity are likely to affect the evolutionary potential of a species. When feasible and cost-effective policies for management and monitoring of endangered populations or species are planned, knowledge of the spatial genetic structure and the type of population dynamics is of great concern. In this thesis the genetic diversity and population structures of two endangered arctic plant species was examined on different geographical scales in Northern Europe. The species were Siberian primrose (Primula nutans) and pendant grass (Arctophila fulva), which both grow in a seashore habitat and have similar distribution patterns on the shores of the Arctic Ocean and the Bothnian Bay. The goal of the present study was to provide basic population genetic information for the study species using microsatellite and AFLP markers. Both markers were used for the first time in these species, and species-specific microsatellite markers were developed during the study. A further aim was to interlink the population genetic processes of the species into distribution patterns at the regional and population levels and to compile a synthesis of the impact of hierarchical spatiotemporal processes and autocorrelation in genetic variation at different levels. The studies of this thesis provided new information on the diversity and population structure of the endangered study species and new markers that are useful in future genetic studies of primrose species. The diversity of Siberian primrose was low, and there was no dispersal between the study regions. In pendant grass, a relatively high amount of variation was found considering the evident clonal reproduction and gene flow that was detected between populations connected by waterways. The results suggested that both clonal and sexual reproduction are important in this species. On a local scale, pendant grass populations had characteristics of “stepping stone” and classical metapopulation models. The results indicated that on a long time scale, both species will continue to decline without efficient management efforts. Most critical for the persistence of the species is the conservation of suitable habitats. Translocations could be considered in order to enhance the diversity of existing populations and establish new populations. By examining the present day structure of Siberian primrose, it was possible to make inferences regarding the colonisation history of the species in the North European area. The current distribution of Siberian primrose seemed to result from a vicariant process that took place after the last ice-age, when the species colonised the area. It spread first to the White Sea area, probably from the east, and subsequently colonised the Bothnian Bay and the Barents Sea in the west. The isostatic land uplift after the retreat of the Eurasian ice sheet uncovered large areas of land from the Baltic Sea basin that previously were under water. These geological changes resulted in the current disjunct distribution of Siberian primrose.

Plants and insects have been interacting with each other for millions of years which have resulted in a coevolution, forcing both to maximize their fitness and not to be left behind in the race of survival. Insects select which individuals to graze on based on plant qualities that enhance their fitness, yet the factors influencing their choice remain understudied. This study aimed to elucidate why certain plant individuals suffer higher rates of herbivory within populations. Three plant species from different habitats in Scandinavia were surveyed: Sorbus aucuparia (rowan), Salix herbacea (dwarf willow), and Lactuca sibirica (Siberian lettuce). Using standardized protocols from the Herbivory Variability Network, 30 plant individuals were randomly selected in each site and surveyed for herbivore damage. Additionally, data were collected on the nearest neighbor of each plant (representing the same species), resulting in a total of 60 surveyed plants. Results revealed varied herbivory patterns among the species, indicating differential influences of plant size, growth stage, and neighboring plants on herbivory rates. An association between leaf and berry herbivory was found, suggesting that berries are less likely to sustain damage when leaves are already damaged. It suggests that trees retaining undamaged leaves are more proficient in photosynthetic processes and, thus capable of synthesizing berries enriched with higher concentrations of sugars and essential nutrients making them more attractive to insects. There is reason to believe that chemical defenses within the plants play an important role in the result seen in this study. This result provides insight into the behavior of insects, highlighting the complexity of plant-insect interactions and the need for further research to understand the factors driving herbivory patterns.

Affectant près d'un milliard de personnes dans le monde, l'hypertension artérielle représente un facteur de risque majeur de pathologies cardiovasculaires et d'insuffisance rénale et constitue l'une des principales causes de mortalité. L'identification de traitements anti-hypertenseurs efficaces et tenant compte des particularités des différentes populations du globe présente ainsi un intérêt capital en termes de santé publique. Notre travail a été consacré à l'étude de plantes anti-hypertensives de la Pharmacopée ouïghoure, principale ethnie de la Région autonome du Xinjiang, vaste territoire montagneux et désertique situé au Nord-Ouest de la Chine. L'objectif de la thèse a été d'apporter des arguments scientifiques, phytochimiques et pharmacologiques, permettant de valider et valoriser l'utilisation traditionnelle de ces plantes. La première partie du travail a démontré sur le modèle d'aortes isolées de rat l'effet vasodilatateur de Ziziphora clinopodioides Lam. (Lamiaceae). L'étude des mécanismes impliqués a permis d'identifier une action indépendante de l'endothélium vasculaire et secondaire à une modification des conductances calciques et potassiques. La réalisation d'un fractionnement bioguidé a permis l'identification de 7 métabolites vasoactifs d'origine phénolique. Dans une deuxième partie, les propriétés vasodilatatrices et hypotensives des fruits Nitraria sibirica Pall. (Nitrariaceae) ont été démontrées. L'endothélium vasculaire et la voie du monoxyde d'azote ont été identifiés comme les éléments fondamentaux de cette action vasodilatatrice. Dans une troisième partie, nos travaux ont étudié pour la première fois les effets vasorelaxants et la composition chimique d'Echinops integrifolius Kar. & Kir. (Asteraceae) et ont permis de caractériser 11 métabolites incluant des triterpènes, des flavonoïdes ainsi qu'une coumarine. En conclusion, notre travail de thèse a permis d'apporter, pour la première fois, des arguments expérimentaux soutenant l'usage anti-hypertensif des espèces Ziziphora clinopodioides et Nitraria sibirica. L'étude phytochimique d'Echinops integrifo/ius a également offert des informations chimiotaxonomiques utiles concernant cette espèce et le genre Echinops / Affecting nearly one billion people worldwide, hypertension is the most important risk factor for cardiovascular disease and kidney failure and it is also one of the leading causes of death. The identification of efficient antihypertensive treatments taking into account the specificities of different populations of the world is an important public-health challenge. Our work has been dedicated to the study of anti-hypertensive plants from the Uighur Pharmacopoeia, one of the major ethnie groups in the Xinjiang Autonomous Region, a large desert and mountainous area from the northwestern China. The aim of this work was to provide phytochemical and pharmacological evidences to validate and to enhance the traditional use of these plants. First, the vasodilating properties of Ziziphora clinopodioides Lam. (Lamiaceae) have been shown by using the in vitro model of isolated rat aortic rings. Our data reported an endothelium-independent effect related to changes in calcium and potassium conductances. ln addition, a bioguided fractionation has been carried out and led to the identification of seven vasorelaxant phenolic compounds. Second, the vasodilating and the hypotensive effects of the fruits of Nitraria sibirica Pail. (Nitrariaceae) have been demonstrated and the contribution of vascular endothelium and nitric oxide pathway has been pointed out. Finally, the vasorelaxant properties and the chemical composition of Echinops integrifolius Kar. & Kir. have been investigated for the first time. Eleven secondary metabolites have been isolated including triterpenes, flavonoids and coumarins. ln conclusion, our results provide scientific evidences supporting the traditional use of Ziziphora clinopodioides and Nitraria sibirica as antihypertensive therapy. Additionaly, the phytochemical study of Echinops integrifolius gives chemotaxonomical data about that species and Echinops genus

No description available.

The purpose of this thesis was to study interactions between systemic fungal diseases and perennial plants. Using the systemic rust Puccinia minussensis on the host plant Lactuca sibirica, and the rust Puccinia pulsatillae on the host plant Pulsatilla pratensis, this thesis focused on: (i) the effects of systemic diseases on their hosts (ii) host and pathogen responses to abiotic factors, (iii) the importance of life history strategies for understanding host-pathogen interactions, and (iv) the evolutionary consequences of living in close associations. Results of greenhouse experiments showed that Lactuca sibirica had a high plasticity in growth, since it produced significantly more shoots in favourable than in unfavourable growth conditions. Both the disease levels and the number of healthy shoots (i.e. escape) were significantly higher under favourable conditions. Disease spread within the rhizome was found to be incomplete, and the risk of aecidial- infection decreased with distance from the parent. Furthermore, one isolate of the fungus had highest success and reduced the host plant biomass and shoot production more on the clone it was collected on compared to four other clones . In the field, disease levels were found to fluctuate more at localities subjected to disturbance, the host and pathogen abundances were found to be in phase and the pathogen showed no delayed response to increasing host densities. The rust Puccinia pulsatillae on Pulsatilla pratensis showed no fluctuations between years, low infection rates, and disease levels were higher in ungrazed compared to grazed sites. There was no escape from the disease in this system. A comparison of characteristics of different systemic fungi and hosts with different growth patterns indicated that the life history strategies of both host plants and pathogens need to be studied if the long-term consequences of host-pathogen interactions are to be predicted. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1993, härtill 5 uppsatser.</p> / digitalisering@umu