1,721,008 research outputs found
Mineralization and temperature sensitivity of soil organic matter pools of contrasting lability
No full textAbstract
Understanding the temperature sensitivity (Q
10
) of soil organic matter (SOM) decomposition is crucial to predict CO
2
emissions and carbon (C) stocks under global warming. This study describes the decomposition and Q
10
of four soil C pools: (1) very labile (glucose addition (GLU), representing root exudates), (2) labile (microbial turnover, MT), (3) potentially labile (primed C pool, PE), and (4) resistant (inherent soil C, RES). The soil (loamy Luvisol) was incubated for 4 and 144 days at five temperatures (0, 10, 20, 30, and 40°C) with or without
14
C‐labeled glucose. The dynamics of CO
2
fluxes were measured during short (0–4 days) and long (5–144 days) term incubations. Glucose was mineralized following a two‐pool exponential function. The half‐life of the decomposition of the GLU pool decreased by 3 times as temperature increased from 10 to 40 °C. The flux of unlabeled CO
2
over 4 days reflects a strong contribution to the apparent priming especially at high temperature, which was due to the accelerated microbial biomass turnover. Accordingly, the CO
2
flux increased during short‐term incubation and was dominated by the decomposition of labile SOM and microbial biomass turnover, whereas during the long‐term incubation, the CO
2
was mainly released from the temperature‐stimulated decomposition of RES pool. The short‐term Q
10
of the soil C pools decreased in the order: GLU (2.1) > MT (1.8) > PE (1.3) ≈ RES (1.6) over a few days (0–4 days), but the Q
10
measured over the long‐term period (144 days) was in the range of 1.2 (PE) to 1.8 (RES) and decreased in the order RES > MT > PE > GLU. In conclusion, CO
2
emissions linearly increased with temperature in all pools over short‐ and long‐term incubation, except for the GLU pool during long‐term incubation. The Q
10
strongly depends on the availability of C pools for microorganisms and decreases over time with the exhaustion of available substances in soil. This needs to be considered when estimating temperature effects on CO
2
emissions and C turnover in soil.Alexander von Humboldt-Stiftung https://doi.org/10.13039/10000515
Black Soldier Fly Diet Impacts Soil Greenhouse Gas Emissions From Frass Applied as Fertilizer
Full text linkIncreased global production of animal-based protein results in high greenhouse gas (GHG) emissions and other adverse consequences for human and planetary health. Recently, commercial insect rearing has been claimed a more sustainable source of animal protein. However, this system also leaves residues called frass, which—depending on the insect diet—is rich in carbon (C) and nitrogen (N), and could thus be used as fertilizer in agriculture. The impact of this kind of fertilizer on soil GHG emissions is yet unknown. Therefore, we investigated the effect of black soldier fly (Hermetia illucens L.) frass derived from a carbohydrate (Carb-) or a protein (Prot-) based diet applied at two different application rates to an arable soil on C and N fluxes and microbial properties in a 40-day incubation experiment. CO2, N2O, NO, N2, CH4, water extractable organic C (WEOC), and inorganic N were continuously measured quantitatively. At the end of the incubation, microbial biomass (MB), stoichiometry, community composition, and abundance of functional genes were assessed. Along with a strong increase in WEOC and CO<jats:sub>2, Carb-frass caused strong initial N<jats:sub>2O emissions associated with high N and C availability. In contrast, Prot-frass showed lower CO<jats:sub>2 emissions and N<jats:sub>2O release, although soil nitrate levels were higher. At the end of incubation, MB was significantly increased, which was more pronounced following Carb-frass as compared to Prot-frass application, and at higher amendment rates. Fungal abundance increased most from both frass types with an even stronger response at higher application rates, whereas bacterial abundance rose following Carb-frass as compared to Prot-application. Abundance of functional genes related to ammonia-oxidizing bacteria and archaea were enhanced by high frass application but did not clearly differ between frass types. C use efficiency of microorganisms, as revealed by the metabolic quotient, was most strongly reduced in the high Prot-frass application rate. Overall, insect diet influenced available C and N in frass and thus affected mineralization dynamics, GHG emissions, and microbial growth. Overall, emissions were very high undermining the potential environmental benefit of insect based protein production and calling for more detailed analyses before frass is widely applied in agriculture
Interactions of mustard plants and soil microorganisms after application of sugarcane filter cake and pea residues to an Andosol
No full textIn a pot experiment using a strongly P-fixing Andosol from Nicaragua, the effects of sugarcanefilter cake application on the growth of white mustard (Sinapis alba L.) were compared with those of 13C-labeled pea residues. The application of pea residues led to a 50% increase and the application of filter cake to a 30% decrease in soil organic matterderived microbial biomass C compared with the control. In contrast, the application of filter cake resulted in a four times higher content of substrate-derived microbial biomass C than that of pea residues. The application of organic substrates generally increased microbial biomass N. Mustard growth led to significant increases in microbial biomass P in the control, but also in the organic-amendment treatments, which always resulted in decreased microbial biomass C : P ratios. Mustard growth also led to increased contents of Bray-1-extractable P, but this increase was only significant in the filter cake treatment. The application of pea residues had no effect on the yield of shoot C, but a positive effect on the yield of root C in comparison with the nonamended control. In contrast, the application of filter cake significantly depressed yields of shoot C and root C, due to N immobilization, presumably due to the high concentration of lignin.Alexander von Humboldt Foundation; DAA
Priming effects of Aporrectodea caliginosa on young rhizodeposits and old soil organic matter following wheat straw addition
No full textPrevious work has shown that endogeic earthworms cause different, i.e. apparent as well as true positive priming effects, presumably due to unknown interactions of substrate-colonising fungi and labile SOM, e.g. rhizodeposits. To explore these interactions, a soil that had previously been enriched with C-13- and N-15-labelled rhizodeposits of pea (Pisum sativum L) plants was used in an incubation experiment. The objective was to determine whether Aporrectodea caliginosa causes a priming effect on the decomposition of young rhizodeposits and old soil organic matter (SOM) following wheat straw addition. After 56 days of incubation at 12 degrees C, earthworm effects on autochthonous SOM-derived CO2 (+88%) were higher than on rhizodeposit-derived CO2 (+16%), indicating a stronger true positive priming effect on old SOM than on young rhizodeposits. Feeding of A. caliginosa significantly reduced microbial biomass C (-12%) and N (-30%) derived from rhizodeposits. In contrast, SOM-derived microbial biomass C and N remained unaffected, indicating a higher palatability of rhizodeposits. However, they were not catabolized to CO2, but preferentially anabolized, i.e. transferred to the biomass of microorganisms and earthworms. Not only straw but also A. caliginosa generally caused a shift in the microbial community towards saprotrophic fungi, as indicated by increased ergosterol contents and ergosterol to microbial biomass C ratios. A. caliginosa decreased delta N-15, total N, and N derived from rhizodeposits in the non-decomposed straw recovered as particulate organic matter, indicating the importance of rhizodeposits as an N source. (C) 2015 Elsevier Masson SAS. All rights reserved.Research Training Group of the German Research Foundation (DFG) [1397
Get on your boots: estimating root biomass and rhizodeposition of peas under field conditions reveals the necessity of field experiments
No full textI have the touch – evidence for considerable N transfer from peas to oats by rhizodeposition
No full textAbstract Aims The current study quantified the carbon (C) and nitrogen (N) transfer from peas to oats under field conditions to assess the effects of intercropping. The data obtained were compared with previously published pot and field experiments. Methods Pea ( Pisum sativum L. cv. Santana) and oat ( Avena sativa L. cv Dominik) plants were grown as intercrops for 105 days. Pea plants were labelled with a solution of 2% 13 C glucose (99 atom%) and 0.5% 15 N urea (95 atom%), using the cotton wick technique. Results Pea rhizodeposits reached 540 kg C ha −1 and 17 kg N ha −1 . CdfR (C derived from rhizodeposition) and NdfR corresponded to a proportion of 18.2 and 12.7%, respectively, of total pea biomass C and N. In the intercropped oat plants, only 0.6% of the total pea CdfR amount was found, but nearly 30% of the total pea NdfR amount. Conclusions CdfR and NdfR as proportion of total pea biomass C and N, respectively, were 2.5 times higher in peas intercropped with oat plants than in sole-cropped pea plants, comparing the current results with those from previously published pot and field experiments. Future studies on intercropping should consider root formation and rhizodeposition more often
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
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