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Spatial distribution and chemical composition of soil organic matter fractions in rhizosphere and non-rhizosphere soil under European beech (Fagus sylvatica L.)
No full textLittle is known about how trees and their roots may influence the spatial distribution and chemical composition of soil organic matter (SOM) in subsoils with subsequent effects on soil organic carbon (SOC) storage and turnover. The aim of this study was to assess the impact of individual trees and their root system on the spatial distribution and chemical composition of SOM fractions and the storage of SOC in subsoils. A Dystric Cambisol was sampled along three vertical replicate transects (3.15 m in length, 2.00 m in depth) in a regular grid (45 cm horizontal spaces, 25 cm vertical spaces) at increasing distance from three individual mature European beech trees (Fagas sylvatica L.). Soil OM fractions were obtained from rhizosphere soil and bulk soil samples taken at 10 and 85 cm depth increments by a combined density and particle size fractionation. Carbon and nitrogen measurements were performed, and the chemical composition of the SOM fractions was further characterized by solid state cross polarization magic angle spinning C-13 nuclear magnetic resonance spectroscopy. The distance from the individual trees had no influence on the SOC contents and stocks or the chemical composition of the SOM fractions. This was ascribed to the dense and even rooting at 0-40 cm depth across all sampled distances. Instead, the SOC contents and stocks highly differed between 10 cm depth (11.4 g SOC kg(-1)), where particulate organic matter (POM) dominated, and 85 cm depth (0.5 g SOC kg(-1)), where clay associated SOC dominated. These differences seemed to be strongly influenced by the roots of the trees which were almost completely absent from depths >= 60 cm. Elevated SOC contents in the rhizosphere soil (40.1 g SOC kg(-1)) were ascribed to root exudates in the root's vicinity and a very high amount (109.3 g kg(-1)) of fresh POM (allcy1/0/N alkyl C ratio of 0.8). The data revealed that, besides root exudates, also root derived POM contributed significant amounts of SOC to the soil. Although only low amounts of the clay fraction were found at 85 cm depth (22.8 g clay kg(-1)), it accounted for high amounts of SOC and played a crucial role for the storage of SOM. The relatively high SOC stocks at 40-200 cm depth (1.4 kg C m(-2)) compared to the SOC stocks at 0-40 cm depth (3.8 kg C m(-2)) indicate that also sandy forest subsoils with low SOC contents have to be considered in terrestrial carbon inventories. (C) 2015 Elsevier B.V. All rights reserved
Dependence on soil depth, root morphology, and environment
No full textForest subsoils may represent an important C sink in a warming world, but rhizodeposition as the key biogeochemical process determining the C sink strength of mature forests has not yet been quantified in subsoils. According to studies conducted in topsoil or laboratory experiments, soil C inputs by root exudation are increasing with increasing temperature and decreasing nutrient availability. We examined whether these relationships apply to forest subsoil by analyzing the response of root exudation to increasing soil depth up to 130 cm in a mature European beech (Fagus sylvatica L.) forest. In two subsequent growing seasons differing in temperature and precipitation, we investigated in situ root exudation with a cuvette-based method and analyzed root morphology, microbial biomass, and soil nutrient availability. We proved that root exudation greatly decreases with soil depth as a consequence of a significant decrease in root-mass specific exudation activity to nearly a fifth of topsoil activity. The decrease in specific metabolic activity from 312 mg C g−1 yr−1 in the topsoil to 80 mg C g−1 yr−1 at 130 cm depth was amplified by an exponential decrease in root biomass per soil volume, leading to a relative decrease in root exudation per volume in the deep subsoil to 2% of topsoil root exudation (1 g C 10 cm−1 m−2 yr−1 at 130 cm depth). Specific root area decreased and mean fine root diameter and root tissue density increased with soil depth, indicating a shift in primary root functionality from fibrous roots in the topsoil to pioneer roots in the subsoil. The decrease in root exudation was accompanied by decreases in soil microbial biomass, extractable organic C (EOC), and N and P availability and increases in the aromatic C portion in SOM, but it did not relate to seasonal differences in climatic conditions. More specifically, it responded positively to an increase in EOC and ETN in the topsoil, but remained at its minimum rate in the SOC-poor subsoil, probably due to a lower organic N and higher mineral N content. The vertical pattern of beech root exudation is in accordance with a strategy to maximize whole-tree carbon-use efficiency, as it reduces C loss by exudation in soil spots where positive priming effects are unlikely, but enhances C exudation where microbes can mine less bioavailable SOM. The exudation patterns further suggest that increased C allocation to root systems as a likely tree response to elevated atmospheric [CO2] may not lead to enhanced soil C input by root exudation to subsoils poor in SOM
Which are important soil parameters influencing the spatial heterogeneity of 14C in soil organic matter?
No full textRadiocarbon (14C) analysis is an important tool that can provide information on the dynamics of organic matter in soils. Radiocarbon concentrations of soil organic matter (SOM) however, reflect the heterogeneous mixture of various organic compounds and are affected by different chemical, biological, and physical soil parameters. These parameters can vary strongly in soil profiles and thus affect the spatial distribution of the apparent 14C age of SOM considerably. The heterogeneity of SOM and its 14C signature may be even larger in subsoil horizons, which are thought to receive organic carbon inputs following preferential pathways. This will bias conclusions drawn from 14C analyses of individual soil profiles considerably. We thus investigated important soil parameters, which may influence the 14C distribution of SOM as well as the spatial heterogeneity of 14C distributions in soil profiles. The suspected strong heterogeneity and spatial variability, respectively of bulk SOM is confirmed by the variable 14C distribution in three 185 cm deep profiles in a Dystric Cambisol. The 14C contents are most variable in the C horizons because of large differences in the abundance of roots there. The distribution of root biomass and necromass and its organic carbon input is the most important factor affecting the 14C distribution of bulk SOM. The distance of the soil profiles to a beech did not influence the horizontal and vertical distribution of roots and 14C concentrations. Other parameters were found to be of minor importance including microbial biomass-derived carbon and soil texture. The microbial biomass however, may promote a faster turnover of SOM at hot spots resulting in lower 14C concentration there. Soil texture had no statistically significant influence on the spatial 14C distribution of bulk SOM. However, SOM in fine silt and clay sized particles (< 6.3 µm) yields slightly higher 14C concentrations than bulk SOM particularly at greater soil depth, which is in contrast to previous studies where silt and clay fractions contained older SOM stabilized by organo-mineral interaction. 14C contents of fine silt and clay correlate with the microbial biomass-derived carbon suggesting a considerable contribution of microbial-derived organic carbon. In conclusion, 14C analyses of bulk SOM mainly reflect the spatial distribution of roots, which is strongly variable even on a small spatial scale of few meters. This finding should be considered when using 14C analysis to determine SOM
Climate-dependent plant responses to earthworms in two land-use types
No full textAbstract Plant nutrient uptake and productivity are driven by a multitude of factors that have been modified by human activities, like climate change and the activity of decomposers. However, interactive effects of climate change and key decomposer groups like earthworms have rarely been studied. In a field microcosm experiment, we investigated the effects of a mean future climate scenario with warming (+ 0.50 °C to + 0.62 °C) and altered precipitation (+ 10% in spring and autumn, − 20% in summer) and earthworms (anecic—two Lumbricus terrestris , endogeic—four Allolobophora chlorotica and both together within 10 cm diameter tubes) on plant biomass and stoichiometry in two land-use types (intensively used meadow and conventional farming). We found little evidence for earthworm effects on aboveground biomass. However, future climate increased above- (+40.9%) and belowground biomass (+44.7%) of grass communities, which was mainly driven by production of the dominant Festulolium species during non-summer drought periods, but decreased the aboveground biomass (− 36.9%) of winter wheat. Projected climate change and earthworms interactively affected the N content and C:N ratio of grasses. Earthworms enhanced the N content (+1.2%) thereby decreasing the C:N ratio (− 4.1%) in grasses, but only under ambient climate conditions. The future climate treatment generally decreased the N content of grasses (aboveground: − 1.1%, belowground: − 0.15%) and winter wheat (− 0.14%), resulting in an increase in C:N ratio of grasses (aboveground: + 4.2%, belowground: +6.3%) and wheat (+5.9%). Our results suggest that climate change diminishes the positive effects of earthworms on plant nutrient uptakes due to soil water deficit, especially during summer drought.China Scholarship Council http://dx.doi.org/10.13039/501100004543Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Helmholtz-Zentrum für Umweltforschung GmbH - UF
Vliv úbytku sněhu na dekompozici a respiraci půdy
Full text linkThe global decline in snow cover affects biochemical processes in soil, potentially leading to changes in the carbon cycle. This thesis describes global and regional snow cover trends and summarizes current knowledge and methods used in decomposition and soil respiration research. Soil biochemical processes during winter depend on the frequency of freeze-thaw cycles, litter input, and the activity of soil biota. However, the results of individual studies are inconsistent due to varying experimental conditions across ecosystems and the lack of standardized methodical approaches. Decomposition and soil respiration contribute to the annual carbon exchange even under reduced snow conditions and may alter the annual carbon balance between soil and the atmosphere. The objective of the practical part of this thesis was to study the effect of snow reduction on winter soil temperature, decomposition, and respiration at Králický Sněžník. An observation of plots with different snow depth combined with snow manipulation experiment was conducted in two winters, 2023 and 2024. Significantly lower decomposition was found with lower snow depth in plots measured in spring 2024. Significantly lower soil respiration was found with lower snow depth in plots measured in winter 2024. Decomposition was influenced by...Globální úbytek sněhové pokrývky ovlivňuje biochemické procesy v půdě, které vedou k potenciálním změnám uhlíkového cyklu. V této práci jsou zhodnoceny globální i regionální trendy sněhové pokrývky a shrnuty poznatky a metody ve výzkumu dekompozice a respirace půdy. Půdní biochemické procesy během zimy závisí na četnosti freeze-thaw cycles, přísunu opadu a aktivitě půdní bioty. Výsledky jednotlivých studií však nejsou konzistentní vlivem odlišných experimentálních podmínek napříč ekosystémy a nejednotným metodickým přístupem. Dekompozice a respirace půdy přispívají k jejich celoroční míře i za redukovaných sněhových podmínek a potenciálně mění celoroční bilanci uhlíku mezi půdou a atmosférou. Cílem praktické části práce je odpovědět na hypotézy týkající se vlivu úbytku sněhu na teplotu půdy, dekompozici a respiraci půdy na Králickém Sněžníku. Zkoumání ploch s různými výškami sněhové pokrývky v kombinaci s experimentem manipulace sněhu bylo prováděno během dvou zim, roku 2023 a 2024. Signifikantně nižší respirace půdy byla za nižší sněhové pokrývky na plochách měřených na jaře 2024. Signifikantně nižší dekompozice byla za nižší sněhové pokrývky na plochách měřených v zimě 2024. Dekompozice byla ovlivněna dlouhodobými teplotami, zatímco respirace půdy reagovala na aktuální stav teploty půdy. Zaměřit...Institute for Environmental StudiesÚstav pro životní prostředíFaculty of SciencePřírodovědecká fakult
Impact of snow reduction on decomposition and soil respiration
No full textThe global decline in snow cover affects biochemical processes in soil, potentially leading to changes in the carbon cycle. This thesis describes global and regional snow cover trends and summarizes current knowledge and methods used in decomposition and soil respiration research. Soil biochemical processes during winter depend on the frequency of freeze-thaw cycles, litter input, and the activity of soil biota. However, the results of individual studies are inconsistent due to varying experimental conditions across ecosystems and the lack of standardized methodical approaches. Decomposition and soil respiration contribute to the annual carbon exchange even under reduced snow conditions and may alter the annual carbon balance between soil and the atmosphere. The objective of the practical part of this thesis was to study the effect of snow reduction on winter soil temperature, decomposition, and respiration at Králický Sněžník. An observation of plots with different snow depth combined with snow manipulation experiment was conducted in two winters, 2023 and 2024. Significantly lower decomposition was found with lower snow depth in plots measured in spring 2024. Significantly lower soil respiration was found with lower snow depth in plots measured in winter 2024. Decomposition was influenced by..
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
Earthworms as catalysts in the formation and stabilization of soil microbial necromass
No full textMicrobial necromass is a central component of soil organic matter (SOM), whose management may be essential in mitigating atmospheric CO(2) concentrations and climate change. Current consensus regards the magnitude of microbial necromass production to be heavily dependent on the carbon use efficiency of microorganisms, which is strongly influenced by the quality of the organic matter inputs these organisms feed on. However, recent concepts neglect agents relevant in many soils: earthworms. We argue that the activity of earthworms accelerates the formation of microbial necromass stabilized in aggregates and organo‐mineral associations and reduces the relevance of the quality of pre‐existing organic matter in this process. Earthworms achieve this through the creation of transient hotspots (casts) characterized by elevated contents of bioavailable substrate and the efficient build‐up and quick turnover of microbial biomass, thus converting SOM not mineralized in this process into a state more resistant against external disturbances, such as climate change. Promoting the abundance of earthworms may, therefore, be considered a central component of management strategies that aim to accelerate the formation of stabilized microbial necromass in wide locations of the soil commonly not considered hotspots of microbial SOM formation
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
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