The role of herbivorous water birds in aquatic systems through interactions with aquatic macrophytes, with special reference to the Bewick’s Swan – Fennel Pondweed system

The role of aquatic macrophytes in stimulating biodiversity and maintaining clear waters is currently undisputed. The management of (eutrophic) shallow waters is therefore often directed at (re-)establishing macrophyte domination. In contrast, the role of water birds has long been considered of minor importance for the functioning of fresh water ecosystems. Indeed, in terms of biomass and production, water birds constitute only a minor part of these systems. However, water birds may graze heavily on water plants under certain circumstances, and the question arises whether herbivorous water birds have an important indirect effect on shallow fresh water systems. Mainly illustrated with the interaction between Bewick’s Swans and Fennel Pondweed, we present data on the role that water plants may play in the life of water birds and how water birds may impact water plants’ fitness in terms of survival, production, dispersal and competitive ability. It appears that water plants may be crucial for water birds during periods of high-energy requirements, such as migration. Despite the plants’ costs associated with water bird grazing, the interaction between water birds and water plants varies in nature from an apparent predator–prey relationship to a mutually beneficial interaction depending on the context and the perspective. For the case of the Bewick’s Swan–Fennel Pondweed interaction, regular bird grazing is sustainable and may actually favour the plant’s dispersal. Thus, Bewick’s Swans themselves may in fact play a crucial role in establishing and maintaining the Fennel Pondweed rich staging sites between the swans’ wintering and breeding grounds, which are vital for the swans’ successful migration.

Efeitos da nutrição mineral na competição inter e intraespecífica de Eucalyptus grandis e brachiaria decumbens: 1- crescimento

The present work was conducted with the objective to study the effects of mineral nutrition on Eucalyptus grandis and Brachiaria decumbens (#BRADC) growth, when submitted to inter- and intra-specific competition. The treatments consisted of two plants of Eucalypts/pot, two plants of BRADC/pot, and one plant of each species/pot. The plants were nourished with the Hoagland e Arnon (1950) complete solution; with no K, P or N; or only with either N, P or K. Sixty days after growing side by side, no effect of the inter- and intra-specific competition on eucalypts plant high, branch number and leaf dry mass was observed. When mineral nutrition did not limit plant growth (complete solution or solution with no K), intra-specific competition reduced on average, 23% of eucalypts root length, leaf area, and stem and root dry mass, and inter-specific competition reduced, on average, 75% of BRADC dry mass. When mineral nutrition became a limiting factor, no plant competition effect on the parameters studied was detected.

Desempenho agronômico de híbridos de milho em diferentes arranjos populacionais em Jaboticabal-SP

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Interferência intra e interespecífica de Urochloa decumbens e Synedrellopsis grisebachii

Pós-graduação em Agronomia (Produção Vegetal) - FCAV

Interferência do caruru-roxo no crescimento e na produtividade da pimenta dedo-de-moça

Pós-graduação em Agronomia (Produção Vegetal) - FCAV

Interferência das plantas daninhas na produtividade e na qualidade tecnológica da cana-de-açúcar no manejo cana-crua e queimada

Pós-graduação em Agronomia (Produção Vegetal) - FCAV

Genotype and maternal environment affect belowground interactions between Arabidopsis thaliana and its competitors

Ecological interactions between different species are not fixed, but they may depend, at least to some extent, on the particular genotypes involved as well as on the environmental conditions experienced by previous generations. We used a set of natural genotypes of Arabidopsis thaliana, that previously experienced contrasting nutrient and herbivory conditions, to test for the influences of genetic variation and maternal effects on competitive interactions between Arabidopsis and the weedy annuals Anagallis arvensis and Senecio vulgaris. We used activated carbon to discriminate between resource competition and allelopathy components of plant-plant interactions. There was a clear competitive hierarchy: Senecio > Arabidopsis > Anagallis. Although we found no evidence for allelopathic potential of Arabidopsis, our results indicate that both Anagallis and Senecio exerted negative (direct or indirect) allelopathic effects on Arabidopsis. There were significant differences among Arabidopsis genotypes in their competitive effects on both neighbor species, as well as in their response to competition. Maternal environments significantly influenced not only the growth and fitness of Arabidopsis itself, but also its competitive effect on Anagallis. We found, however, no evidence that maternal environments affected the competitive effect on Senecio or overall competitive response of Arabidopsis. Generally, resource competition played a greater role than allelopathy, and genotype effects were more important than maternal effects. Our study demonstrates that ecological interactions, such as plant competition, are complex and multi-layered, and that, in particular, the influence of genetic variation on interactions with other species should not be overlooked.

Activated carbon may have undesired side effects for testing allelopathy in invasive plants

Activated carbon has become a widely used tool to investigate root-mediated allelopathy of plants, especially in plant invasion biology, because it adsorbs and thereby neutralizes root exudates. Allelopathy has been a controversially debated phenomenon for years, which revived in plant invasion biology as one possible reason for the success of invasive plants. Noxious plant exudates may harm other plants and provide an advantage to the allelopathic plant. However, root exudates are not always toxic, but may stimulate the microbial community and change nutrient availability in the rhizosphere. In a greenhouse experiment, we investigated the interacting effects of activated carbon, arbuscular mycorrhiza and plant competition between the invasive Senecio inaequidens and the native Artemisia vulgaris. Furthermore, we tested whether activated carbon showed any undesired effects by directly affecting mycorrhiza or soil chemistry. Contrary to the expectation, S. inaequidens was a weak competitor and we could not support the idea that allelopathy was involved in the competition. Activated carbon led to a considerable increase in the aboveground biomass production and reduced the infection with arbuscular mycorrhiza of both plant species. We expected that arbuscular mycorrhiza promotes plant growth by increasing nutrient availability, but we found the contrary when activated carbon was added. Chemical analyses of the substrate showed, that adding activated carbon resulted in a strong increase in plant available phosphate and in a decrease of the C(organic)/N(total) ration both of which suggest stimulated microbial activity. Thus, activated carbon not only reduced potential allelopathic effects, but substantially changed the chemistry of the substrate. These results show that activated carbon should be handled with great care in ecological experiments on allelopathy because of possible confounding effects on the soil community.

Plot size matters: interference from intergenotypic competition in plant phenotyping studies

Genetic and physiological studies often comprise genotypes diverse in vigour, size and flowering time. This can make the phenotyping of complex traits challenging, particularly those associated with canopy development, biomass and yield, as the environment of one genotype can be influenced by a neighbouring genotype. Limited seed and space may encourage field assessment in single, spaced rows or in small, unbordered plots, whereas the convenience of a controlled environment or greenhouse makes pot studies tempting. However, the relevance of such growing conditions to commercial field-grown crops is unclear and often doubtful. Competition for water, light and nutrients necessary for canopy growth will be variable where immediate neighbours are genetically different, particularly under stress conditions, where competition for resources and influence on productivity is greatest. Small hills and rod-rows maximise the potential for intergenotypic competition that is not relevant to a crop’s performance in monocultures. Response to resource availability will typically vary among diverse genotypes to alter genotype ranking and reduce heritability for all growth-related traits, with the possible exception of harvest index. Validation of pot experiments to performance in canopies in the field is essential, whereas the planting of multirow plots and the simple exclusion of plot borders at harvest will increase experimental precision and confidence in genotype performance in target environments.

Meadow plant growth and competition under elevated ozone and carbon dioxide

The main aim of my thesis project was to assess the impact of elevated ozone (O3) and carbon dioxide (CO2) on the growth, competition and community of meadow plants in northern Europe. The thesis project consisted of three separate O3 and CO2 exposure experiments that were conducted as open-top-chamber (OTC) studies at Jokioinen, SW Finland, and a smaller-scale experiment with different availabilities of resources in greenhouses in Helsinki. The OTC experiments included a competition experiment with two- and three-wise interactions, a mesocosm-scale meadow community with a large number of species, and a pot experiment that assessed intraspecific differences of Centaurea jacea ecotypes. The studied lowland hay meadow proved to be an O3-sensitive biotope, as the O3 concentrations used (40-50 ppb) were moderate, and yet, six out of nine species (Campanula rotundifolia, Centaurea jacea, Fragaria vesca, Ranunculus acris, Trifolium medium, Vicia cracca) showed either significant reductions in biomass or reproductive development, visible O3 injury or any two as a response to elevated O3. The plant species and ecotypes exhibited large intra- and interspecific variation in their response to O3, but O3 and CO2 concentrations did not cause changes in their interspecific competition or in community composition. However, the largest O3-induced growth reductions were seen in the least abundant species (C. rotundifolia and F. vesca), which may indicate O3-induced suppression of weak competitors. The overall effects of CO2 were relatively small and mainly restricted to individual species and several measured variables. Based on the present studies, most of the deleterious effects of tropospheric O3 are not diminished by a moderate increase in CO2 under low N availability, and variation exists between different species and variables. The present study indicates that the growth of several herb species decreases with increasing atmospheric O3 concentrations, and that these changes may pose a threat to the biodiversity of meadows. Ozone-induced reductions in the total community biomass production and N pool are likely to have important consequences for the nutrient cycling of the ecosystem.

Defoliation, nitrogen, and competition: effects on plant growth and resource allocation of Cleistogenes squarrosa and Artemisia frigida

Two species, Artemisia frigida Willd. (C-3, semishrub, and dominant on overgrazed sites) and Cleistogenes squarrosa (Trin.) Keng (C-4, perennial bunchgrass, and dominant or codominant on moderately grazed sites) were studied to determine the effects of defoliation, nitrogen (N) availability, competition, and their interactions on growth, biomass, and N allocation in a greenhouse experiment. The main treatments were: two nitrogen levels (NO = 0 mg N pot(-1), N1 = 60 mg N pot(-1)), two defoliation intensities (removing 60% of total aboveground biomass and no defoliation), and three competitive replacement series (monocultures of each species and mixtures at 0.5:0.5). Our results were inconsistent with our hypothesis on the adaptive mechanisms of A. frigida regarding the interactive effects of herbivory, N, and competition in determining its dominant position on overgrazed sites. Cleistogenes squarrosa will be replaced by A. frigida on over-grazed sites, although C. squarrosa had higher tolerance to defoliation than did A. frigida. Total biomass and N yield and N-15 recovery of C. squarrosa in mixed culture were consistently lower than in monocultures, whereas those of A. frigida grown in mixtures were consistently higher than in monocultures, suggesting higher competitive ability of A. frigida. Our results suggest that interspecific competitive ability may be of equal or greater importance than herbivory tolerance in determining herbivore-induced species replacement in semi-arid Inner Mongolian steppe. In addition, the dominance of A. frigida on overgrazed sites has been attributed to its ability to shift plant-plant interactions through (lap colonization, root niche differentiation, and higher resistance to water stress.

A trait specific model of competition in a spatially structured plant community

John Warren and Chris Topping (2004). A trait specific model of competition in a spatially structured plant community. Ecological Modelling, 180 pp.477-485 RAE2008