1,720,957 research outputs found
Controls of temporal and spatial variability of methane uptake in soils of a temperate deciduous forest with different abundance of European beech (Fagus sylvatica L.)
No full textAerated forest soils are a significant sink for atmospheric methane (CH(4)). Soil properties, local climate and tree species can affect the soil CH(4) sink. A two-year field study was conducted in a deciduous mixed forest in the Hainich National Park in Germany to quantify the sink strength of this forest for atmospheric CH(4) and to determine the key factors that control the seasonal, annual and spatial variability of CH(4) uptake by soils in this forest. Net exchange of CH(4) was measured using closed chambers on 18 plots in three stands exhibiting different beech (Fagus sylvatica L) abundance and which differed in soil acidity, soil texture, and organic layer thickness. The annual CH(4) uptake ranged from 2.0 to 3.4 kg CH(4)-C ha(-1). The variation of CH(4) uptake over time could be explained to a large extent (R(2) = 0.71, P < 0.001) by changes in soil moisture in the upper 5 cm of the mineral soil. Differences of the annual CH(4) uptake between sites were primarily caused by the spatial variability of the soil clay content at a depth of 0-5 cm (R(2) = 0.5, P < 0.01). The CH(4) uptake during the main growing period (May-September) increased considerably with decreasing precipitation rate. Low CH(4) uptake activity during winter was further reduced by periods with soil frost and snow cover. There was no evidence of a significant effect of soil acidity, soil nutrient availability, thickness of the humus layer or abundance of beech on net-CH(4) uptake in soils in this deciduous forest. The results show that detailed information on the spatial distribution of the clay content in the upper mineral soil is necessary for a reliable larger scale estimate of the CH(4) sink strength in this mixed deciduous forest. The results suggest that climate change will result in increasing CH(4) uptake rates in this region because of the trend to drier summers and warmer winters. (C) 2009 Elsevier Ltd. All rights reserved.Deutsche Forschungsgemeinschaft (DFG) [1086
Variability of soil N cycling and N2O emission in a mixed deciduous forest with different abundance of beech
Full text linkThe mixture of other broadleaf species into beech forests in Central Europe leads to an increase of tree species diversity, which may alter soil biochemical processes. This study was aimed at 1) assessing differences in gross rates of soil N cycling among deciduous stands of different beech (Fagus sylvatica L.) abundance in a limestone area, 2) analyzing the relationships between gross rates of soil N cycling and forest stand N cycling, and 3) quantifying N2O emission and determining its relationship with gross rates of soil N cycling. We used N-15 pool dilution techniques for soil N transformation measurement and chamber method for N2O flux measurement. Gross rates of mineral N production in the 0-5 cm mineral soil increased across stands of decreasing beech abundance and increasing soil clay content. These rates were correlated with microbial biomass which, in turn, was influenced by substrate quantity, quality and soil fertility. Leaf litter-N, C:N ratio and base saturation in the mineral soil increased with decreasing beech abundance. Soil mineral N production and assimilation by microbes were tightly coupled, resulting in low N2O emissions. Annual N2O emissions were largely contributed by the freeze-thaw event emissions, which were correlated with the amount of soil microbial biomass. Our results suggest that soil N availability may increase through the mixture of broadleaf species into beech forests.Deutsche Forschungsgemeinschaft (DFG) [Graduiertenkolleg 1086
L.)
No full textThe production and composition of leaf litter, soil acidity, exchangeable nutrients, and the amount and distribution of soil organic matter were analyzed in a broad-leaved mixed forest on loess over limestone in Central Germany. The study aimed at determining the current variability of surface-soil acidification and nutrient status, and at identifying and evaluating the main factors that contributed to the variability of these soil properties along a gradient of decreasing predominance of European beech (Fagus sylvatica L.) and increasing tree-species diversity. Analyses were carried out in (1) mature monospecific stands with a predominance of beech (DL 1), (2) mature stands dominated by three deciduous-tree species (DL 2: beech, ash [Fraxinus excelsior L.], lime [Tilia cordata Mill. and/or T platyphyllos Scop.]), and (3) mature stands dominated by five deciduous-tree species (DL 3: beech, ash, lime, hombeam [Carpinus betulus L.], maple [Acer pseudoplatanus L. and/or A. platanoides L.]). The production of leaf litter was similar in all stands (3.2 to 3.9 Mg dry matter ha(-1) y(-1)) but the total quantity of Ca and Mg deposited on the soil surface by leaf litter increased with increasing tree-species diversity and decreasing abundance of beech (47 to 88 kg Ca ha(-1) y(-1); 3.8 to 7.9 kg Mg ha(-1) y(-1)). The soil pH((H2O)) and base saturation (BS) measured at three soil depths down to 30 cm (0-10 cm, 10-20 cm, 20-30 cm) were lower in stands dominated by beech (pH = 4.2 to 4.4, BS = 15% to 20%) than in mixed stands (pH = 5.1 to 6.5, BS = 80% to 100%). The quantities of exchangeable Al and Mn increased with decreasing pH and were highest beneath beech. Total stocks of exchangeable Ca (0-30 cm) were 12 to 15 times larger in mixed stands (6660 to 9650 kg ha(-1)) than in beech stands (620 kg ha(-1)). Similar results were found for stocks of exchangeable Mg that were 4 to 13 times larger in mixed stands (270 to 864 kg ha(-1)) than in beech stands (66 kg ha(-1)). Subsoil clay content and differences in litter composition were identified as important factors that contributed to the observed variability of soil acidification and stocks of exchangeable Ca and Mg. Organic-C accumulation in the humus layer was highest in beech stands (0.81 kg m(-2)) and lowest in stands with the highest level of tree-species diversity and the lowest abundance of beech (0.27 kg m(-2)). The results suggest that redistribution of nutrients via leaf litter has a high potential to increase BS in these loess-derived surface soils that are underlain by limestone. Species-related differences of the intensity of soil-tree cation cycling can thus influence the rate of soil acidification and the stocks and distribution of nutrients.Deutsche Forschungsgemeinschaft (DFG) [1086
Nährstoffvorräte, Acidität, Prozesse der N-Transformation und Nettomethanaufnahme in Böden eines temperaten Laubwaldes mit unterschiedlicher Buchenhäufigkeit (Fagus sylvatica L.)
No full textBaumarten können Bodeneigenschaften, Prozesse und zugehörige Bodenfunktionen beeinflussen. Während Unterschiede zwischen Nadelbäumen und Laubbäumen hinsichtlich ihrer Auswirkungen auf Bodeneigenschaften und Funktionen häufig untersucht wurden, ist der Einfluss verschiedener Laubbaumarten in Mischbeständen auf Bodenprozesse und die Biogeochemie von Ökosystemen weitgehend unbekannt. Deshalb wurde im Rahmen dieser Arbeit ein temperater Laubwald mit unterschiedlicher Buchenhäufigkeit und Baumartendiversität auf Acidität, Nährstoffvorräte und Gehalte der organischen Bodensubstanz sowie die Umsätze von Stickstoff (N) im Boden und die Senkenstärke des Waldbodens für atmosphärisches Methan (CH4) untersucht. Ziel war es, die Hauptfaktoren der räumlichen Variabilität dieser Bodeneigenschaften und Prozesse in einem Laubmischwald zu bestimmen und den Einfluss der Buchenhäufigkeit zu klären. Aus diesem Grund wurden im Nationalpark Hainich/Thüringen Flächen mit i) Buche (Fagus sylvatica L.) (diversity level 1, DL1), mit ii) Buche, Esche (Fraxinus excelsior L.) und Linde (Tilia cordata Mill. and/or T. platyphyllos Scop.) (DL2) und mit iii) Buche, Esche, Linde, Ahorn (Acer pseudoplatanus L. and/or A. platanoides L.) und Hainbuche (Carpinus betulus L.) (DL3) ausgewählt. Alle Bestände haben eine langjährige Waldgeschichte und einen hohen Anteil von alten Bäumen. Sie unterliegen den gleichen klimatischen Bedingungen und stocken auf dem selben geologischen Ausgangssubstrat (Löss (60-120 cm) über Kalkstein). Der Bodentyp ist eine Parabraunerde, die im Winter Staunässe aufweist. Auf diesen Flächen wurden Produktion und Zusammensetzung der Laubstreu sowie Bodenacidität, austauschbare Nährstoffe und die Menge und Verteilung der organischen Bodensubstanz in der organischen Auflage und im Mineralboden (0−30 cm) bestimmt. Drei Flächen (je 6 Plots) mit unterschiedlicher Buchenhäufigkeit wurden ausgewählt, um die N Vorräte und N-Umsätze des Bestandes, Netto- und Bruttoraten der N-Transformationen im Mineralboden und jährliche N-Verluste durch N2O-Emissionen sowie die Beziehungen zwischen N-Pools und N-Flüssen zu analysieren. Auf diesen Flächen wurde ebenfalls die Senkenstärke des Waldbodens für CH4 über zwei Jahre mit geschlossenen Hauben untersucht und es wurden die Hauptsteuergrößen für die räumliche und zeitliche Variabilität des Netto-CH4-Umsatzes bestimmt.Die Streuproduktion war in allen Beständen vergleichbar (3,2 bis 3,9 Mg Trockenmasse ha 1 yr-1), die Menge an mit der Streu eingetragenem Ca und Mg stieg jedoch mit zunehmender Baumartendiversität und abnehmender Buchenhäufigkeit an (von 47 auf 88 kg Ca ha-1 yr-1; von 3,8 auf 7,9 kg Mg ha-1 yr-1). Die pH-Werte und die Basensättigung in den obersten 30 cm des Mineralbodens waren geringer unter Buche als in Mischbeständen (pH: 4,2−4,4 vs. 5,1−6,5; BS: 15−20% vs. 80−100%). Die Mengen an austauschbaren Al und Mn waren unter Buche am höchsten. Die Vorräte von Ca und Mg in den obersten 30 cm des Mineralbodens waren 12−15 bzw. 4−13-mal höher unter Mischbeständen als unter Buche. Die Akkumulation von organischem Kohlenstoff in der organischen Auflage war am höchsten unter Buche. Mit abnehmender Buchenhäufigkeit stieg der jährliche N-Eintrag mit der Streu (21 bis 51 kg N ha 1 yr-1) und der N-Vorrat im Mineralboden (800−1500 kg N ha-1). Die Umsatzrate des Streu-N ist höher in den Mischbeständen als in den Buchenbeständen, während die mittlere geschätzte Verweildauer von N in der organischen Auflage 2−4 bzw. 13 Jahre betrug. Die Nettoraten der N-Mineralisation und Nitrifikation unterschieden sich nicht zwischen den Beständen. Die Brutto-N-Mineralisation stieg von 2,4 auf 7,0 mg N kg-1 d-1 mit abnehmender Buchenhäufigkeit. Fünf bis vierzehn Prozent des produzierten NH4+-N wurden nitrifiziert. Beide Prozesse waren eng korreliert mit der mikrobiellen Biomasse, welche wiederum mit dem N-Eintrag durch die Streu und deren C:N-Verhältniss, sowie mit dem N-Vorrat im oberen Mineralboden und der Basensättigung korrelierte. Die N2O-Emissionen waren in der Regel in allen Beständen gering. Eine Ausnahme bildete eine Frostperiode im Winter 2006 mit stark erhöhten Emissionen, die zu 46% bis 94% der jährlichen N2O-Verluste beitrugen. Die mittleren kumulativen N2O-Emissionen nahmen mit abnehmender der Buchenhäufigkeit zu. Sie waren auf der DL3-Fläche am höchsten (0,39±0,21 kg N2O-N ha-1 a-1) und auf der DL1-Fläche am niedrigsten (0,10±0,11 kg N2O-N ha-1 a-1). Die jährliche CH4-Aufnahme lag bei 2,0 bis 3,4 kg CH4-C ha-1. Die zeitliche Variation der CH4 Aufnahme konnte zu einem großen Teil (R2 = 0,71) mit der Änderung des Wassergehaltes in den obersten 5 cm des Mineralbodens erklärt werden. Unterschiede in der Jahresaufnahme zwischen den Flächen resultierten vorwiegend aus der räumlichen Variabilität des Tongehaltes in 0-5 cm (R2 = 0,50). Während der Vegetationsperiode (Mai bis September) sank die CH4 Aufnahme mit zunehmenden Niederschlägen. Geringe CH4-Aufnahmeraten im Winter wurden zusätzlich durch Bodenfrost und Schneeauflage reduziert. Es gab keinen Hinweis auf einen signifikanten Einfluss der Bodenacidität, der Nährstoffverfügbarkeit, der Mächtigkeit der Humusauflage oder der Buchenhäufigkeit auf die Nettoaufnahme von CH4 in diesem Laubwald. Die wichtigsten Faktoren, die die Variabilität der Bodenversauerung und der Nährstoffvorräte im Boden und in der organischen Auflage verursachten, waren der Tongehalt im Unterboden und die unterschiedliche Qualität der Laubstreu. Die Zusammensetzung und Qualität der Streu in den untersuchten Beständen wurde von der Buchenhäufigkeit beeinflusst, da die Nährstoffgehalte (z.B. N, Ca, Mg) der Laubstreu und deren biologische Verfügbarkeit unter Buche geringer waren als in Mischbeständen. Die Umverteilung von Nährstoffen mit der Laubstreu hat ein hohes Potential der Bodenversauerung entgegenzusteuern und die Basensättigung in diesen Lössböden über Kalkstein zu erhöhen. Baumartenspezifische Unterschiede in der Intensität des Kationenkreislaufes zwischen Boden und Baum waren ein Schlüsselfaktor, der zu den beobachteten Unterschieden in Bodenacidität und Nährstoffvorräten im Boden beitrug. Neben einer zunehmenden Basensättigung stiegen auch die N-Einträge mit der Streu und die Qualität der Streu mit abnehmender Buchenhäufigkeit. Diese Faktoren beeinflussten die Menge der mikrobiellen Biomasse und damit die Bruttoraten der N-Transformation und die N-Verluste durch N2O-Emissionen. Die Nettoaufnahme von CH4 wurde nicht von der Buchenhäufigkeit beeinflusst. Für eine zuverlässige großräumige Abschätzung der CH4-Senkenstärke dieses Laubwaldes sind detaillierte Informationen über die räumliche Verteilung der Tongehalte im obersten Mineralboden von großer Bedeutung. Aus den Ergebnissen lässt sich schlussfolgern, dass die Klimaveränderung mit dem Trend zu trockeneren Sommern und wärmeren Wintern in steigende CH4-Aufnahmeraten in dieser Region resultieren wird.Die Ergebnisse dieser Studie zeigen, dass zwei Faktoren die räumliche Variabilität der analysierten Bodeneigenschaften und Prozesse in dem untersuchten Laubmischwald bestimmen: 1. Die Buchenhäufigkeit und die damit verbundene geringere Umverteilung von Nährstoffen mit der Laubstreu und 2. die kleinräumige Variabilität des Tongehaltes im Ausgangsmaterial (d.h. in der Lössauflage). Die Trennung dieser beiden Faktoren war schwierig, da sich die räumlichen Muster von Buchenhäufigkeit und Tongehalt in dieser cross-site Studie in natürlichen Beständen überlagerten. Dennoch tragen die hier gewonnenen Ergebnisse zu einer verbesserten Kenntnis über den Einfluss der Buchenhäufigkeit in temperaten Laubmischwäldern auf Bodeneigenschaften und Bodenprozesse bei.Tree species can influence soil properties, processes and related soil functions. Whilst differences between conifers and deciduous tree species in affecting soils properties and functions have frequently been reported, the influence of different deciduous tree species in mixed stands on soil processes and ecosystem biogeochemistry is rarely understood. Therefore, a temperate deciduous forest with differing beech abundance and tree species diversity was investigated regarding acidity, nutrient stocks and organic matter content as well as nitrogen (N) transformations in the soil and the soil sink strength for atmospheric methane (CH4). The aim was to analyze the key factors that determine the spatial variability of these soil properties and processes in a deciduous mixed forest and to elucidate the influence of beech abundance on soil properties and functions. For that purpose, stands were selected in the Hainich National Park in Central Germany with i) European Beech (Fagus sylvatica L.) as dominant tree species (diversity level 1, DL1), with ii) beech, ash (Fraxinus excelsior L.) and lime (Tilia cordata Mill. and/or T. platyphyllos Scop.) (DL2) and with iii) beech, ash, lime, hornbeam (Carpinus betulus L.) and maple (Acer pseudoplatanus L. and/or A. platanoides L.) (DL3). All stands had a long-term forest history and a high proportion of mature trees. They experienced similar climatic conditions, as they are found growing on the same geological substrates (loess (60-120 cm) which is underlain by limestone), and the soil type was a Luvisol which showed stagnic properties during winter. In these stands the production and composition of the litterfall, soil acidity, exchangeable nutrients, and the amount and the distribution of soil organic matter in the humus layer and in the mineral soil (0-30 cm) were investigated. Three stands (each with 6 subplots) with different beech abundance were selected to analyze stand N stocks and N turnover, net and gross rates of N transformation in the mineral soil and N losses via N2O emissions as well as the relationships amongst N pools and fluxes. The sink strength of the soil for atmospheric CH4 was measured over two years in these stands with closed chambers and the main controls of the spatial and temporal variability of the net CH4 exchange were determined.Litter production was similar in all stands (3.2 to 3.9 Mg dry mass ha-1 yr-1). The amount of Ca and Mg input via litterfall increased with decreasing beech abundance and increasing tree species diversity (47 to 88 kg Ca ha-1 yr-1; 3.8 to 7.9 kg Mg ha-1 yr-1). The pH and base saturation in the upper 30 cm of the mineral soil were smaller under beech than in mixed stands (pH: 4.2-4.4 vs. 5.1-6.5, BS: 15-20% vs. 80-100%). The quantities of exchangeable Al and Mn were highest under beech. The stocks of Ca and Mg in the upper 30 cm of the mineral soil were 12-15 and 4 13 times higher in mixed stands than in beech stands, respectively. The accumulation of organic carbon in the humus layer was highest in beech stands. The annual N input via tree leaf litter (21 to 51 kg N ha-1 yr-1) and the N storage in the upper mineral soil (800-1500 kg N ha-1) increased with decreasing beech abundance. Litter N turnover was faster in the mixed stands than beech stands, with the mean apparent residence time of N in the organic surface layer being 2-4 years and 13 years, respectively. Net rates were not different between stands. Gross N mineralization increased from 2.4 to 7.0 mg N kg 1 d-1 with decreasing beech abundance. Five to fourteen percent of the produced NH4+-N was nitrified. Both processes were closely correlated with microbial biomass which in turn correlated with N input via leaf litter and litter C:N ratio as well as with the N stocks in the upper mineral soil and base saturation. N2O emission rates were generally low in all stands except for a frost period in 2006 with strongly increased emissions which accounted for 46% to 94% of the annual N2O loss. The mean cumulative N2O emission decreased with the abundance of beech. It was highest at the DL3 stand (0.39±0.21 kg N2O-N ha-1 a-1) and lowest at the DL1 stand (0.10±0.11 kg N2O N ha-1 a-1). The annual uptake of atmospheric CH4 was between 2.0 and 3.4 kg CH4-C ha-1. The temporal variation of the CH4 uptake could be explained to a large extent (R2 = 0.71) by changes of the water content in the upper 5 cm of the mineral soil. Differences in the annual uptake between stands predominantly result from the spatial variability of the clay content in the 0-5 cm layer (R2 = 0.50). During the growing period (May till November) CH4 uptake increased with decreasing precipitation. There was no evidence for a significant impact of soil acidity, nutrient availability, the thickness of the humus layer or beech abundance on the net uptake of CH4 in this deciduous forest.The subsoil clay content and the litter quality were the most important factors, which determined the spatial variability of soil acidification and nutrients stocks in the upper mineral soil and the organic surface layer. Litter composition and quality in the analyzed stands were influenced by the abundance of beech since nutrient concentrations (e.g. N, Ca, Mg) in leaf litter and litter bioavailability were lower under beech than in mixed stands. The results show that the redistribution of nutrients with tree leaf litter has a high potential to counteract soil acidification and to increase the base saturation in these loess derived soils over limestone. Tree species related differences in the intensity of soil-tree cation cycling were a key factor, which contributed to the observed differences in soil acidity and soil nutrient stocks. The increase in base saturation, leaf litter N input and litter quality with decreasing beech abundance influenced the amount of microbial biomass and, therefore, the gross rates of N transformation and N losses via N2O emissions. The net uptake of atmospheric CH4 was not influenced by the abundance of tree species. For a reliable larger scale estimate of the CH4 sink strength in this mixed deciduous forest detailed information on the spatial distribution of the clay content in the upper mineral soil is necessary. The results suggest that climate change will result in increasing CH4 uptake rates in this region because of the trend towards drier summers and warmer winters.The results of this study show that there are two key factors which determined the spatial variability of the analyzed soil properties and processes in the investigated mixed deciduous forest: 1. The abundance of beech and the associated lower nutrient redistribution in its leaf litter, and 2. the small scale variability of the clay content in the parent material (i.e. in the loess cover). It was difficult to separate these two factors due to the interfering spatial pattern of beech abundance and clay content in this cross-site study within natural stands. Nevertheless, the results contribute to an improved knowledge on the influence of European beech abundance in deciduous mixed forests on soil properties and soil related processes
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
- …
