Showing papers by "Kalevi Kull published in 2003"

Leaf structure vs. nutrient relationships vary with soil conditions in temperate shrubs and trees

Abstract: Often there are significant positive interspecific relationships between leaf area per unit dry mass (SLA) and foliar phosphorus and nitrogen concentrations ([P] and [N]). Most of these studies have been conducted on moderately acidic soils, and little is known of the generality of these relations as potentially affected by soil characteristics. We investigated foliage mineral composition in relation to leaf structure in a wooded meadow on calcareous alkaline soil, in a bog on strongly acidic soil, and in a flood plain on moderately acidic soil. Foliar nutrient contents and fertilization experiments indicated that foliage physiological activity was co-limited by both P and N availabilities in the wooded meadow, by P in the bog, and by N in the flood plain. In the wooded meadow and in the bog, there were positive relationships between SLA and P concentration ([P]), and no relationship between SLA and nitrogen concentration [N]. Given that the fraction of support tissues generally increases with decreasing SLA, the requirement for mineral nutrients is lower at low SLA. Thus, these contrasting relations between mineral nutrients and SLA suggest that P was distributed in a more “optimal” manner among the leaves with varying structure than N in P-limited communities. In the flood plain, SLA was positively related to both [P] and [N], possibly manifesting a strategy to cope with N limitations by enhancing N turnover, and accordingly, greater P requirement for nucleic acid formation in N-limited soils. Total variation in foliar structural and chemical characteristics was similar in all sites, and was mainly determined by variation among the species. Part of this variability was explained by life form and plant size. [P] was higher in trees than in shrubs, and [P] and P/N ratio increased with increasing total plant height, indicating that P nutrition was improved relative to N nutrition with increasing plant size. Since the capture of less mobile soil elements such as P is dependent on extensive root systems, but not that of readily mobile and temporarily variable elements such as N, this correlation was attributed to more extensive root systems in larger plants. Our study indicates that foliar structure vs. [N] and [P] relations may be separately regulated, but also that the generality of leaf structure vs. nutrient content relations may vary depending on soil conditions.

Clonal growth in a species-rich grassland: Results of a 20-year fertilization experiment

Abstract: We investigated the influence of fertilization on the abundance of species with different clonal growth characteristics using the data from a 20-year fertilization experiment from the Laelatu wooded meadow, in Estonia. The experiment comprised four different fertilization treatments and created a gradient of nitrogen availability. The vegetation composition was recorded every year by measuring the proportions of aboveground biomass for all species. For each species, four parameters of vegetative propagation were measured: speed of ramet vegetative mobility (annual increment of rhizome length), frequency of rhizome branching, placement of branches, and ramet life span. The weighted average of each parameter was calculated for each plot both at the beginning and at the end of the experiment using the relative abundances of the species in the plot as weights. The community changes resulting from the fertilization are reflected in the significant changes of the average values of all studied clonal growth parameters. Increased levels of phosphorus and potassium led to a community with an increased average vegetative mobility and rhizome branching. Both of these traits, however, declined with the increasing availability of nitrogen. The proportion of species with long-living ramets in the community decreased with the increase in the productivity irrespective of the fertilizer used. There was a strong positive correlation between the average ramet life span of the community and the number of species on the plot. We concluded that fertilization increased the ramet turnover rate in this meadow community and reduced species richness. Thus, our results contradict the prediction of a higher ramet turnover rate in species-rich compared to the species-poor grasslands.

Imagining Nature: Practices of Cosmology and Identity

Abstract: During the last decade, many social scientists have sought to show that nature is not an eternal constant but an intrinsically unstable concept - a historical, cultural and social construct with powerful emotional, moral and political connotations. Imagining Nature sets out to explore some of the implications of and lacunae in this recent push to "denaturalise nature". But rather than asking, What is nature? as many academic writers have been doing, the contributors here ask, How is nature established as an entity? Through what processes and practices does nature achieve reality? The first section of the book, "Cosmologies", focuses on ways the practices of nature are embedded in overarching conceptual worldviews. Chapters in the second section illustrate some of the means by which identity unfolds and becomes established in interacting with and imagining nature. The chapters examine nature and identity in the national mythologies of Scandinavia and Germany; two Fulani status groups in Burkina Faso; the confrontational Sami community of Manndalen, Norway; the spatial world of the Tsaatang nomads in Mongolia; and two neoclassic houses by Le Corbusier and Wright. While the individual contributions here will certainly interest specialists in the particular fields they represent, Imagining Nature is broadly interdisciplinary in appeal, and it is especially recommended to anyone intrigued by recent constructivist debate and the multiplying conceptions of nature in the social sciences.

Ladder, tree, web: The ages of biological understanding

Abstract: Fundamental turns in biological understanding can be interpreted as replacements of deep models that organise the biological knowledge. Three deep models distinguished here are a holistic ladder model that sees all levels of nature being complete (from Aristotle to the 18th century), a modernist tree model that emphasises progress and evolution (from Enlightenment to the recent times), and a web model that evaluates diversity (since the 20th century). The turn from the tree model to the web model in biology includes (1) a transfer from modern to postmodern approaches, (2) a shift of semiotic threshold to the border of life, and (3) building the semiotic models of living systems, i.e., the rise of biosemiotics. The main issue of the 20th century has been the end of modernity. However, it has not yet been understood very well that this will also mean the end of the modern model of natural science. The modern age, as starting in the 17th century and being characterized particularly via the formation of experimental science together with the philosophy of Descartes and Bacon, would be replaced by anything that also replaces the experimental science, a strive for technological progress or innovation, and cartesianism. As John Deely (2001; 2004) has stated, this can be semiotics. Several analyses have shown that much of what has been called post-modern is more like late modern, or ultra-modern (Deely 2003: 22), which means that we still see the extension of modern era. This particularly seems to be true for the modernist science, the current situation of which demonstrates large fluctuations and extremist approaches. It is not an entire end of

Thomas A. Sebeok and biology: Building biosemiotics.

Abstract: The paper attempts to review the impact of Thomas A. Sebeok (1920–2001) on biosemiotics, or semiotic biology, including both his work as a theoretician in the field and his activity in organising, publishing, and communicating. The major points of his work in the field of biosemiotics concern the establishing of zoosemiotics, interpretation and development of Jakob v. Uexkull’s and Heini Hediger’s ideas, typological and comparative study of semiotic phenomena in living organisms, evolution of semiosis, the coincidence of semiosphere and biosphere, research on the history of biosemiotics.

Semiotics is a theory of life

Abstract: “It is important to realize that only living things and their inanimate extensions undergo semiosis, which thereby becomes uplifted as a necessary, if not sufficient, criterial attribute of life” (Sebeok 1994: 6). A statement as firm as this — the difference Sebeok makes — asks for attention. Moreover, both in biology and in semiotics, relating life to semiosis makes a big difference. Its role can be seen in the context of major paradigms in scientific approaches to living nature over the ages. This lecture is about the semiotic approach in biology. In other words — about the role of semiotics for biology, or about a semiotic theory of life, a semiotic biology — biosemiotics. Despite the fact that under any circumstances semiotics and biology would have found each other some day, sooner or later — because this is just a “necessity” of the development of human knowledge — despite this the whole story and the entire situation today would not be as it is without the work and role of Thomas A. Sebeok.