Roots and leaves are integrated structural elements that together sustain plant growth and development. Insect herbivores pose a constant threat to both above- and belowground plant tissues. To ward off herbivorous insects, plants have developed different strategies such as direct and indirect chemical defense mechanisms. Research has primarily focused on visible aboveground interactions between plants and herbivores. Root-feeding insects, although often overlooked, play a major role in inducing physical and physiological changes in plants. However, little is known about how plants deploy chemical defense against root herbivores. We have developed an Arabidopsis aeroponic culture system based on clay granulate, which provides access to root tissue and accommodates subterranean insect herbivores. Using this system, feeding performance and plant tissue damage by the root herbivore Bradysia (fungus gnat) were evaluated. Larval feeding was found to reduce Arabidopsis root biomass and water uptake. Furthermore, we have characterized a root-specific terpene synthase AtTPS08, which is responsible for the constitutive formation of the novel volatile diterpene compound, rhizathalene, in Arabidopsis roots. Rhizathalene synthase is a class I diterpene synthase that has high affinity for the substrate geranylgeranyl diphosphate (GGPP) and is targeted to the root leucoplast. Expression of the β-glucuronidase (GUS) reporter gene fused to the upstream genomic region of AtTPS08 demonstrated constitutive promoter activity in the root vascular tissue and root tips. Using the established bioassay with Arabidopsis and Bradysia larvae, in aeroponic culture we could show that roots deficient in rhizathalene synthesis were more susceptible to herbivory. Our work provides in vivo-evidence that diterpene compounds are involved in belowground direct defense against root-feeding insects. Future work is still required to improve our understanding of plant root defense. This study has provided a basis for future investigations on the biochemistry, molecular regulation and defensive function of Arabidopsis root chemicals in interaction with both above- and belowground herbivores (and pathogens). / Ph. D.

To test factors limiting regeneration of large-seeded hardwoods in the Upper Coastal Plain of South Carolina, we planted one-year old bare root Quercus alba L. and Cornus florida L. seedlings in pine plantation understories and adjacent clearcuts. We hypothesized that soil moisture, light, and leaf and stem herbivory would have relatively strong effects on growth and survival during the first two years after planting. Next to each seedling, we measured five abiotic factors (soil carbon and moisture, gap light index (GLI), and available nitrogen and phosphorus). We also estimated percent stem and leaf herbivory and harvested seedlings after the second year to measure seedling growth. Survival was not significantly different between clearcut (62.9%) and understory (64.6%) treatments. Biomass growth was significantly greater (P<0.05) in the clearcuts for both species. All abiotic variables measured except soil carbon were greater in the clearcuts (P<0.05). Each seedling growth response was regressed against all variables using forward selection (P=0.15). Soil moisture significantly affected survival in 12.5% and biomass growth in 16.7% of the regressions. Light availability significantly impacted biomass growth in 8.3% of the regressions. Neither leaf nor stem herbivory frequently affected survival, but one or the other or both significantly influenced the biomass growth of seedlings in 41.5% of the regressions. Herbivory had the strongest impact on seedling responses. Neither water nor light was very influential for growth or survival responses. We conclude that hardwood restoration in the uplands of the Upper Coastal Plain is best accomplished by planting in recent clearcuts. / Master of Science

Palatability of 20 meadow plant species was assessed in the slug grazing experiment conducted. Monocots exhibited significantly lower palatability than dicots. Litter decomposition rate was assessed in the field litter-bag test. Linear regression analysis was performed to answer the main question whether species palatability is related to litter decomposition rate and whether it is determined by the carbon or nitrogen content. Phylogenetically independent contrasts were used to eliminate correlated phylogeny effect. Regression trees were used to detect the effect of species traits on species palatability and litter decomposition rate.

<p>Diss. (sammanfattning) Umeå : Univ., härtill 6 uppsatser.</p> / digitalisering@umu

Insect herbivory on forest canopies strongly affects ecosystem nutrient cycling and availability in a variety of ways, e.g. by changing the quantity, quality and timing of nutrient input to forest soils. A qualitative method for measurements of ingestion, egestion and exuviation rates of the insect Chrysomela tremulae on leaves of the hybrid Populus tremula x tremuloides were tested in this study with the aim to detect differences in relative nutrient cycling efficiencies. The assimilation efficiency (AD), efficiency of conversion of digested food (ECD) and efficiency of conversion of ingested food (ECI) increased from 1st, through 2nd and 3rd instar larvae with generally higher efficiencies for nitrogen than carbon. Effects on nutrient limitations for the insect were also tested by increasing the C:N ratio of insect diet. A carbohydrate solution was painted onto leaves which resulted in a significant increase in C:N (p&lt;0.0001). This lead to a trend of lengthened developmental time for each ontogenetic stage, as well as higher ingestion rate and lower egestion- and exuviation rates. However, a different method of increasing the C:N ratio is recommended in future experiments since the leaves never truly absorbed the solution.

Mycorrhizal fungi are soil-borne organisms that form symbiotic associations with the majority of land plants. These fungi gather and exchange mineral nutrients with plants for photosynthetically derived carbohydrates. Mycorrhizal fungi can also confer other benefits onto plants, e.g. defense against pathogens, improved water relations, tolerance to heavy metal toxicity and herbivory. The influence of mycorrhizal fungi on plant mineral nutrition and response to stress suggests that these organisms may have a role to play sustainable agriculture as well as in bioremediation and ecosystem restoration. In contributing to this important research, I investigated host-specific interactions between mycorrhizal fungi and the sex morphs of the gynodioecious perennial herb Polemonium foliosissimum (Polemoniaceae) and their mycorrhizal associates in the field. I hypothesized that the genders of this species differed in their associations with mycorrhizal fungi in benefits received. I performed a full factorial simulated herbivory experiment and evaluated the extent of mycorrhizal colonization in the roots as well as the concentrations of nutrients in leaf tissue. Mycorrhizal colonization and leaf nutrient concentrations did not differ between the genders nor were influenced by the experimental treatments. This suggests that the genders of Polemonium foliosissimum do not interact differently with mycorrhizal fungi, and thus do not represent different "hosts". Also, I investigated local adaptation of mycorrhizal associations by exploring the effect of large herbivore grazing on plant-mycorrhizal associations. I hypothesized that grazing by large herbivores results in locally adapted symbioses that enhance plant response to herbivory. I grew the perennial bunchgrass Themeda triandra (Poaceae) in inoculum prepared from soils collected from three field exclosures with differing histories of large herbivore exclusion in the Kenya Long Term Exclosure Experiment. I conducted a full factorial simulated herbivory experiment in which plants were subject to two clipping events over the course of 5-months, and evaluated plant regrowth as well as mycorrhizal colonization for plants in the experiment. Plants grown in inoculum from exclosures in which large herbivores have had access produced more root mass when mycorrhizal fungi were present. Further, I found equivalent biomass production of clipped and non-clipped plants in inoculum prepared from the exclosure with only native large herbivore access while equivalent biomass production was not found in the substrate prepared from areas with a history of large herbivore exclusion. This suggests that mycorrhizal fungi mediate plant growth and response to herbivory in this system.

Estimating herbivore density is an important part of understanding their impact on vegetation.  Many studies have been carried out on the impact of reindeer and other herbivores on arctic and sub-arctic vegetation, but they are difficult to compare as they typically use different methods to estimate herbivore activities.  The aim of this study was to compare three methods that were based on the recent International Tundra Experiment herbivory protocol to measure the activities of three herbivore groups: reindeer, rodents and invertebrates. The robustness of the methods themselves was then evaluated.  Fieldwork was carried out at 12 sites in the Fennoscandian mountain area, with controls inside reindeer exclosures.  The results showed that the methods were the most robust when measuring reindeer activities.  The reindeer measurements were also well correlated with a reindeer-density estimate calculated from official reindeer population data.  This study recommends considering the use of photographs to increase the time-efficiency of pellet-counts.  The rodent activity estimates were good, but the patterns inside exclosures differed to the patterns outside exclosures.  The results for invertebrates were deemed to be less reliable as the measurements for one method were not recorded at an appropriate scale.  In conclusion, the findings of this study will help improve the comparability of future studies on the impact of reindeer herbivory and other herbivores, and gives suggestions for more accurate ways of measuring herbivore pressure in arctic and sub-arctic vegetation.

This Ph.D. Thesis is focused on the effect of submerged vegetation on the structure of lake ecosystem and trophic relationships among fishes. Succession of submerged vegetation is a dynamic process and the vegetation community may change dramatically even during a year. Many environmental factors have impact on the succession of submerged vegetation and consequently the presence of the vegetation has substantial impact on the aquatic ecosystem. Nutrient level (mainly nitrogen and phosphorus) plays a key role in the succession of freshwater ecosystems. Further, herbivory significantly influences species composition and biomass of macrophytes and macroalgae. Herbivory of fish is a foraging strategy that is dependent on temperature. Foraging preferences of fish may suppress the palatable species. The rate of herbivory affects plant growth patterns and thus inpalatable species may be advantaged in the competition among plants. In aquatic ecosystems, herbivory is often performed by omnivorous species. The diet preferences of omnivorous fish differ among aquatic ecosystems and submerged vegetation can shape their trophic niches substantially.

Entender como as interações ecológicas moldaram a dinâmica evolutiva dos caracteres das espécies continua sendo um desafio em ecologia evolutiva. Combinando modelos de evolução de caracteres e filogenias, nós analisamos a evolução de caracteres associadas à dispersão de sementes (tamanho e cor do fruto) e herbivoria (espinhos) em palmeiras neotropicais para inferir o papel das interações positivas e negativas entre plantas e animais na condução dos padrões evolutivos. Nós encontramos que o tamanho e a coloração dos frutos é evolutivamente correlacionada ao longo da história evolutiva das palmeiras neotropicais, suportando a interpretação adaptativa das síndromes de dispersão e destacando o papel de frugívoros em moldar caracteres de plantas. Além disso, nós encontramos uma associação positiva nas linhagens de palmeiras entre o tamanho de fruto e a presença de espinhos nas folhas e caule. Nós hipotetizamos que interações entre palmeiras e grandes mamíferos extintos podem explicar a relação entre tamanho de frutos e espinhos nas linhagens de palmeiras. Frugívoros de grande porte, como a megafauna extinta, além de consumir os frutos e dispersar sementes grandes, também podem consumir e/ou danificar outras partes da planta, favorecendo simultaneamente a evolução de grandes frutos e estruturas de defesa. Nossos resultados mostram como os padrões de caracteres atuais de um determinado clado podem ser entendidos como o resultado da interação entre interações antagonistas e mutualistas que aconteceram ao longo da história evolutiva do clado / Understanding how ecological interactions have shaped the evolutionary dynamics of species traits remains a challenge in evolutionary ecology. Combining trait evolution models and phylogenies, we analyzed the evolution of traits associated with seed dispersal (fruit size and color) and herbivory (spines) in Neotropical palms to infer the role of opposing animal-plant interactions in driving evolutionary patterns. We found that the evolution of fruit color and fruit size were associated in Neotropical palms, supporting the adaptive interpretation of seed-dispersal syndromes and highlighting the role of frugivores in shaping plant evolution. Furthermore, we reveal a positive association between fruit size and the presence of spines on palm leaves and stems. We hypothesize that interactions between palms and extinct large-bodied frugivores may explain the relationship between fruit size and spines. Large-bodied frugivores, such as extinct megafauna, besides consuming the fruits and dispersing large seeds, may also have consumed the leaves or damaged the plants, thus simultaneously favoring the evolution of large fruits and defensive structures. Our findings show how current trait patterns can be understood as the result of the interplay between antagonistic and mutualistic interactions that have happened throughout the evolutionary history of a clade

Os tricomas são estruturas de origem epidérmicas que podem ser classificados em dois tipos: glandulares e não glandulares (tectores) e estão relacionados, principalmente, com estratégias de defesas de plantas. Pouco se conhece sobre a via de desenvolvimento dos tricomas glandulares, já que a maior parte dos estudos é em Arabidopsis thaliana, modelo no qual os tricomas glandulares são ausentes. O gênero Solanum possui uma grande diversidade de tricomas, em especial glandulares (tipos I, IV, VI e VII). O estudo de tais estruturas vem ganhando cada vez mais destaque, já que são fontes de diversos metabólitos secundários de importância econômica e ecológica. Espécies selvagens são consideradas recursos genéticos para o tomateiro (S. lycopersicum), tais como S. galapagense, a qual possui variações genéticas naturais que lhe confere maior resistência ao ataque de herbívoros. Entre essas variações está a presença de tricomas glandulares do tipo IV, uma fonte do aleloquimico acilaçúcar. A ausência de tricomas glandulares do tipo IV é considerada uma das causas da suscetibilidade do tomateiro cultivado a insetos. No presente trabalho, foi demonstrado que o tomateiro cultivado na verdade forma tricomas do tipo IV, mas estas estruturas estão presentes somente até o primeiro par de folhas, além dos cotilédones. Desse modo, a presença de tricomas tipo IV em espécies selvagens seria considerada uma neotenia, ou seja, a manutenção de estruturas juvenis na fase adulta. Além de se determinar que mutantes de tomateiro afetando a juvenilidade (e.g. Mouse ears e fasciated) apresentam tricomas tipo IV na fase adulta, a formação dessas estruturas correlacionou se com a expressão de miR156, sendo também presentes em grandes quantidades em uma linhagem transgênica superexpressando esse micro RNA relacionado à juvenilidade. Quanto à base genética da presença de tricomas tipo IV nas espécies selvagens, no presente trabalho foi criada uma linhagem quase isogênica ao modelo genética Micro-Tom (MT) contendo a variação genética natural por nós denominada Galapagos enhanced trichomes (Get). Tal variação é derivada de S. galapagense e condiciona a presença de tricomas tipo IV em folhas adultas, quando introgredida em tomateiro cultivado (cv. Micro-Tom). O mapeamento preliminar de Get no cromossomo 2 de tomateiro também foi realizado através do mapa de \"single nucleotide polymorphism\" (SNPs) entre MT e a linhagem MT-Get. A eventual clonagem de GET irá contribuir não somente para se desvendar a base genética da formação de tricomas glandulares, como também contribuir para se criar variedades resistentes a insetos, reduzindo o uso de agrotóxicos. / Trichomes are epidermal structures that can be classified into two types: glandular or non-glandular, and they are mainly related to plant defense strategies. Little is known about the glandular trichome development pathway, since most of the studies are in Arabidopsis thaliana, a model in which this kind of trichome is absent. The Solanum genus has a wide variety of trichomes, especially glandular ones (Types I, IV, VI and VII). The study of these structures are gaining more prominence, since they are sources of several secondary metabolites of economic and ecological importance. Wild species are considered genetic resources for tomato (S. lycopersicum), such as S. galapagense which has natural genetic variations that gives resistance to herbivores attack. Among these variations is the presence of type IV glandular trichomes, a source of the acyl sugar allelochemical. The absence of type IV glandular trichomes is considered to be one of the causes of tomato susceptibility to insects. In this study, it was determined that tomato actually has type IV trichomes, but these structures are present only in the cotyledons and the first pair of leaves. Thus, the presence of type IV trichomes in wild species would be considered a neotenic feature, i.e. the maintenance of juvenile structures in adulthood. In addition, it was determined that tomato mutants affecting youthfulness (e.g. Mouse ears and fasciated) have type IV trichomes in adulthood. Moreover, the presence of these structures was correlated with the expression of miR156, besides the increased formation of type IV trichomes in a transgenic line overexpressing this micro RNA related to youthfulness. On the genetic basis of type IV trichomes presence in wild species, in this work it was created a near isogenic line (NIL) containing the natural genetic variation here named Galapagos enhanced trichomes (Get). This variation is derived from S. galapagense and harbors type IV trichomes in adult leaves, when introgressed in cultivated tomato (cv. Micro-Tom). The preliminary genetic map of Get in the tomato chromosome 2 was conducted through the analysis of \"single nucleotide polymorphism\" (SNPs) between MT and MT-Get. The eventual cloning of GET will contribute not only to unravel the genetic basis of glandular trichomes formation, but will also contribute to create varieties resistant to insects, reducing the pesticides use.