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Water sources of plant uptake along a salt marsh flooding gradient
No full textSalt marsh plants are affected by regular tidal inundation exposing them to saline water as a potential water source. This study aimed at quantifying the water uptake of plants depending on their distance from the sea and exploring plant responses to changing inundation regimes. We used stable isotope ratios (δ18O) to determine the proportions of seawater and precipitation water used by three salt marsh species (Spartina anglica, Atriplex portulacoides and Elytrigia atherica) from a German North Sea coast salt marsh. Additionally, A. portulacoides was transplanted to experimental islands at three elevation levels to investigate its plasticity in water use in the course of future sea level rise. We found a marked gradient in plant seawater use from the lowermost pioneer zone (79-98% seawater uptake by S. anglica) to the lower marsh (61-95% by A. portulacoides) and the upper marsh (25-39% by E. atherica). Seasonal differences in water use were not pronounced, likely due to the absence of longer dry periods during summer in these temperate salt marshes. Contradicting our expectation, roots in deeper soil showed higher water uptake rates per fine root mass than topsoil roots suggesting effective root adaptation to the anoxic subsoil. Transplanted A. portulacoides plants significantly increased the uptake of seawater with increasing inundation indicating flexibility in the use of water sources by this species which may facilitate acclimation to rising sea levels. We conclude that the zonation of salt marsh vegetation reflects the availability of water sources along the inundation gradient
Effects of Inundation, Nutrient Availability and Plant Species Diversity on Fine Root Mass and Morphology Across a Saltmarsh Flooding Gradient
No full textSaltmarsh plants are exposed to multiple stresses including tidal inundation, salinity, wave action and sediment anoxia, which require specific root system adaptations to secure sufficient resource capture and firm anchorage in a temporary toxic environment. It is well known that many saltmarsh species develop large below-ground biomass (roots and rhizomes) but relations between fine roots, in particular, and the abiotic conditions in salt marshes are widely unknown. We studied fine root mass (<2 mm in diameter), fine root depth distribution and fine root morphology in three typical communities (Spartina anglica-dominated pioneer zone, Atriplex portulacoides-dominated lower marsh, Elytrigia atherica-dominated upper marsh) across elevational gradients in two tidal salt marshes of the German North Sea coast [a mostly sandy marsh on a barrier island (Spiekeroog), and a silty-clayey marsh on the mainland coast (Westerhever)]. Fine root mass in the 0–40 cm profile ranged between 750 and 2,500 g m−2 in all plots with maxima at both sites in the lower marsh with intermediate inundation frequency and highest plant species richness indicating an effect of biodiversity on fine root mass. Fine root mass and, even more, total fine root surface area (maximum 340 m2 m−2) were high compared to terrestrial grasslands, and were greater in the nutrient-poorer Spiekeroog marsh. Fine root density showed only a slight or no decrease toward 40 cm depth. We conclude that the standing fine root mass and morphology of these salt marshes is mainly under control of species identity and nutrient availability, but species richness is especially influential. The plants of the pioneer zone and lower marsh possess well adapted fine roots and large standing root masses despite the often water-saturated sediment
Root system structure and functions across coastal saltmarsh flooding gradients
Full text linkSalt marshes are ecosystems with extreme environmental conditions such as regular tidal inundation, mechanical disturbances, salinity, waterlogged and anoxic soils, and potentially toxic compounds in the soil. This adverse abiotic environment requires a high degree of adaptation of inhabiting plants and animals and results in a highly specialized community in this ecosystem. The gradual elevation from sea level from the lowermost pioneer zone, where the establishment of salt marshes begins, to the upper salt marsh is characterized by a gradient of these abiotic factors leading to a distinct zonation of salt marsh communities.
The presented PhD thesis is part of the joint research project BEFmate (Biodiversity and Ecosystem Functioning across marine and terrestrial ecosystems) with the aim to study BEF relations during the succession from marine (tidal flat) to semi-terrestrial (salt marsh) ecosystems. As part of this project, the thesis investigated different root system functions and their relation to the abiotic conditions across the salt marsh flooding gradient. It thereby contributes to the understanding of ecological processes involved in the development of salt marsh zonation as well as their sensitivity to environmental change. To fulfill these objectives, the study included in situ investigations at two natural salt marsh sites on the German North Sea coast, investigations of communities transplanted to experimental islands, as well as an additional greenhouse experiment.
Under the controlled conditions of a greenhouse experiment, we investigated effects of waterlogged sediments on seedlings of three saltmarsh species characteristic for the three zones in NW European salt marshes (Salicornia europaea from the pioneer zone, Atriplex portulacoides from the lower salt marsh, Elytrigia atherica from the upper salt marsh). Seedlings of these species were grown under different sediment waterlogging treatments within mesocosms simulating tidal inundation and subsequently subjected to an erosion treatment. The upper marsh species E. atherica showed fastest root and shoot growth under drained conditions but suffered strongest in the waterlogged sediment compared to A. portulacoides and S. europaea from the lower salt marsh and pioneer zone, respectively. Resistance against erosion decreased in all three species from drained to completely waterlogged soil conditions with the strongest negative impact of waterlogging on the otherwise strongly competitive species E. atherica. We found that resistance towards erosion was strongly influenced by root growth of the seedlings. This indicates that species-specific responses of root growth of seedlings under waterlogged soil conditions may be a first determinant of the distribution of species across the saltmarsh elevational and flooding gradient.
In our second study we conducted an inventory of fine root mass across the saltmarsh gradient and across two geomorphologically different sites. Fine root biomass was dependent on soil texture and plant-available nutrient concentrations in soil: we found higher fine root biomass at the sandy (and nutrient poorer) site on the back-barrier island of Spiekeroog compared to the clayey mainland salt marsh near Westerhever. According to the optimal resource partitioning theory, fewer nutrients in the soil require increased investments in fine root growth for nutrient uptake. Furthermore, the more erosion-prone sandy sediment may require increased root biomass for plant stability under mechanical disturbances. However, the most important predictor variable for fine root biomass was species diversity. At both sites, fine root mass was greatest in communities with highest plant species richness (in the intermediate lower salt marsh), potentially caused by root space partitioning in this community. With this study we could demonstrate that salt marsh plants have adapted their below-ground organs to the harsh environmental conditions which allows them to successfully develop extensive root systems and ensures survival. Furthermore, their high below-ground biomass is an important contribution to the carbon and nitrogen pools in salt marshes.
In our third study we used stable isotope measurements (δ18O) to investigate plant water use patterns (i.e. the use of saline vs. freshwater) across the saltmarsh flooding gradient. We found a marked gradient in plant water use from the pioneer zone (79-98 % seawater uptake by Spartina anglica) to the lower marsh (61-95 % in A. portulacoides) and the upper marsh (25-39 % in E. atherica) reflecting the predominant inundation regime at the three elevational levels. Only minor seasonal differences in water use patterns were detected, likely due to the absence of longer dry periods during summer in these temperate salt marshes. A. portulacoides significantly increased its uptake of seawater following transplantation to lower elevations with higher inundation frequencies on experimental islands which were set up within the BEFmate project. This indicates that certain species are able to show a flexible water use strategy under changing inundation frequencies which may enable long-term adaptation to rising sea levels. Integrating the data on vertical fine root distribution and the soil depth of water uptake, we found that fine root mass distribution correlated positively with water uptake across the soil profile. However, contradicting our expectations, the physiological activity of fine roots (determined by the water uptake/root mass ratio) did not decrease with soil depth demonstrating a good functionality of roots in deep and anoxic sediment layers in this habitat.
In conclusion, this thesis demonstrates that saltmarsh plants have developed various species-specific adaptations of their below-ground organs enabling their survival under the harsh environmental conditions prevailing in salt marshes. Interspecific differences particularly corresponded to the gradient of inundation frequency and associated salinity, waterlogging and mechanical disturbance in all three studies. Supporting previous studies, it was underlined that the initial establishment as well as further ecological processes in salt marshes are driven by the gradient of abiotic conditions
A hierarchical testing strategy for micropollutants in drinking water regarding their potential endocrine-disrupting effects : towards health-related indicator values
No full textData collection on phytoplankton from the Elbe River near Hamburg
No full textData on phytoplankton in the Elbe River near Hamburg from 2006 to 2023. This dataset comprises the results of a monthly survey of phytoplankton at two sites along the Elbe River in Hamburg (Zollenspieker and Seemannshöft). Data was collected as part of the Water Framework Directive. The phytoplankton contained in the routinely collected water samples was concentrated in sedimentation chambers (Uthermöhl). Finally, reverse microscopy was used to examine the phytoplankton taxa, cell number and biovolume
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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