1,721,118 research outputs found
State of the scientific knowledge on properties and genesis of Anthropogenic Dark Earths in Central Amazonia (terra preta de Índio)
No full textTropical rainforests are highly important for the global climate regulation and for global biodiversity. However, these ecosystems are characterized by nutrient-poor and highly weathered soils and by high turnover rates of organic matter. Thus, they are fragile ecosystems prone to loss of ecosystem services when anthropogenically disturbed. Currently, the major threat to these ecosystems is deforestation leading to irreversible destruction of rainforests. Surprising and not expected is that within these ecosystems small patches of highly fertile soils occur which are known as Anthropogenic Dark Earths or terra preta de Índio (terra preta). These soils exhibit high nutrient and soil organic matter stocks and allow sustainable agriculture. Frequent occurrence of pot-sherds of pre-Columbian origin and further evidence for settlement activities clearly demonstrate that terra preta is of anthropogenic origin. In recent years, the terra preta phenomenon has gained increasing interest because it is assumed that terra preta could act as a model for promoting sustainable agricultural practices in the humid tropics and because terra preta is an example for long-term CO2 sequestration into terrestrial ecosystems with additional positive benefits for ecosystem services. These potentials of terra preta initiated a great number of studies but also stimulated fantasy about their genesis. Therefore, the aim of this review is to summarize the scientific knowledge about terra preta properties and to discuss their genesis. From our own and literature data it is evident that terra preta is the product of inorganic [e.g. ash, bones (esp. fish)] and organic (e.g. biomass wastes, manure, excrements, urine, and biochar) amendments to infertile Ferralsols. These ingredients were microbially metabolized and stabilized by humification in soil, fungi playing a bigger role in this process compared to bacteria in surrounding ecosystems. Biochar is a key component for this process due to its stability and its enrichment in terra preta. It is still unclear if terra preta was produced intentionally or un-intentionally. In addition, it is unclear how much time was needed after the disposal of the materials mentioned above to develop a terra preta. Further research is highly desired to investigate these latter two issues
Biochar stability in soil: Decomposition during eight years and transformation as assessed by compound-specific C-14 analysis
No full textStability and transformation products of incomplete combustion of vegetation or fossil fuel, frequently called pyrogenic or black carbon and of biochar in soil, remains unknown mainly because of their high recalcitrance compared to other natural substances. Therefore, direct estimations of biochar decomposition and transformations are difficult because 1) changes are too small for any relevant experimental period and 2) due to methodological constraints (ambiguity of the origin of investigated compounds). We used C-14-labeled biochar to trace its decomposition to CO2 during 8.5 years and transformation of its chemical compounds: neutral lipids, glycolipids, phospholipids, polysaccharides and benzenepolycarboxylic acids (BPCA). C-14-labeled biochar was produced by charring C-14-labeled Lolium residues. We incubated the C-14-labeled biochar in a Haplic Luvisol and in loess for 8.5 years under controlled conditions. In total only about 6% of initially added biochar were mineralized to CO2 during the 8.5 years. This is probably the slowest decomposition obtained experimentally for any natural organic compound. The biochar decomposition rates estimated by (CO2)-C-14 efflux between the 5th and 8th years were of 7 x 10(-4) % per day. This corresponds to less than 0.3% per year under optimal conditions and is about 2.5 times slower as reported from the previous shorter study (3.5 years). After 3.5 years of incubation, we analyzed C-14 in dissolved organic matter, microbial biomass, and sequentially extracted neutral lipids, glycolipids, phospholipids, polysaccharides and BPCA. Biochar-derived C (C-14) in microbial biomass ranged between 0.3 and 0.95% of the C-14 input. Biochar-derived C in all lipid fractions was less than 1%. Over 3.5 years, glycolipids and phospholipids were decomposed 1.6 times faster (23% of their initial content per year) compared to neutral lipids (15% year(-1)). Polysaccharides contributed ca. 17% of the C-14 activity in biochar. The highest portion of C-14 in the initial biochar (87%) was in BPCA decreasing only 7% over 3.5 years. Condensed aromatic moieties were the most stable fraction compared to all other biochar compounds and the high portion of SPCA in biochar explains its very high stability and its contribution to long-term C sequestration in soil. Our new approach for analysis of biochar stability combines C-14-labeled biochar with C-14 determination in chemical fractions allowed tracing of transformation products not only in released CO2 and in microbial biomass, but also evaluation of decomposition of various biochar compounds with different chemical properties. (C) 2014 Elsevier Ltd. All rights reserved.German Academic Exchange Service (DAAD
Anthropogenic Dark Earth in Northern Germany - The Nordic Analogue to terra preta de Indio in Amazonia
No full textDuring an archaeological excavation of a Slavic settlement (10th/11th C. A.D.) in Briinkendorf (Wendland region in Northern Germany), a thick black soil (Nordic Dark Earth) was discovered that resembled the famous terra preta phenomenon. For the humid tropics, terra preta could act as model for sustainable agricultural practices and for long-term CO2-sequestration into terrestrial ecosystems. The question was whether this Nordic Dark Earth had similar properties and genesis as the famous Amazonian Dark Earth in order to find a model for sustainable agricultural practices and long term CO2-sequestration in temperate zones. For this purpose, a multi-analytical approach was used to characterise the sandy-textured Nordic Dark Earth in comparison to less anthropogenically influenced soils in the adjacent area in respect of ecological conditions (pH, electric conductivity, cation exchange capacity, amino sugar) and input materials. Total element contents (C, N, P, Ca, Mg, K, Na, Fe, Cu, K, Zn, Mn and Ba) were highly enriched in the Nordic Dark Earth compared to the reference soil. Faecal biomarkers such as stanols and bile acids indicated animal manure from omnivores and herbivores but also human excrements. Amino sugar analyses showed that Nordic Dark Earth contained higher amounts of microbial residues being dominated by soil fungi. Black carbon content of about 30 Mg ha(-1) in the Nordic Dark Earth was about four times higher compared to the adjacent soil and in the same order of magnitude compared to terra preta. The input materials and resulting soil chemical characteristics of the Nordic Dark Earth were comparable to those of Amazonian Dark Earth suggesting that their genesis was also comparable. Amazonian Dark Earth and Nordic Dark Earth were created by surface deposition and/or shallow soil incorporation of waste materials including human and animal excrements together with charred organic matter. Over time, soil organisms degraded and metabolized these materials leaving behind deep black stable soil organic matter. The existence of the Nordic Dark Earth in the temperature zone of Europe demonstrates the capability of sandy-textured soils to maintain high soil organic matter contents and nutrient retention over hundreds of years. Deeper insights are needed urgently to understand soil organic matter stabilization mechanisms in this sandy soil to promote conceptual models for sustainable land use and long-term C sequestration. It is argued that the knowledge of Nordic Dark Earth probably was an important part of the Viking-Slavic subsistence agriculture system, which could have had a great impact on the development of the Viking age emporia in the 9th/10th C AD. (C) 2014 Elsevier B.V. All rights reserved.Federal Ministry of Education and Research (BMBF) [FKZ: 01LY1110B
Biochemical pathways of amino acids in soil: Assessment by position-specific labeling and 13C-PLFA analysis
No full textAbstractMicrobial utilization is a key transformation process of soil organic matter (SOM). For the first time, position-specific 13C labeling was combined with compound-specific 13C-PLFA analysis to trace metabolites of two amino acids in microbial groups and to reconstruct detailed biochemical pathways. Short-term transformation was assessed by applying position-specifically 13C labeled alanine and glutamic acid to soil in a field experiment. Microbial utilization of the amino acids' functional groups was quantified by 13C incorporation in total microbial biomass and in distinct microbial groups classified by 13C-PLFA.Loss from PLFAs was fastest for the highly oxidized carboxyl group of both amino acids, whereas the reduced C positions, e.g. C3–5, were preferentially incorporated into microorganisms and their PLFAs. The incorporation of C from alanines' C2 position into the cell membrane of gram negative bacteria was higher by more than one order of magnitude than into all other microbial groups. Whereas C2 of alanine was still bound to C3 at day 3, the C2 and C3 positions were partially split at day 10. In contrast, the C2 of glutamic acid was lost faster from PLFAs of all microbial groups. The divergence index, which reflects relative incorporation of one position to the incorporation of C from all positions in a molecule, revealed that discrimination between positions is highest in the initial reactions and decreases with time.Reconstruction of microbial transformation pathways showed that the C2 position of alanine is lost faster than its C3 position regardless of whether the molecule is used ana- or catabolically. Glutamic acid C2 is incorporated into PLFAs only by two out of eight microbial groups (fungi and part of gram positive prokaryotes). Its incorporation in PLFA can only be explained by either the utilization of the glyoxolate bypass or the transformation of glutamic acid into aspartate prior to being fed into the citric acid cycle. During these pathways, no C is lost as CO2 but neither is energy produced, making them typical C deficiency pathways. Glutamic acid is therefore a promising metabolic tracer in regard to ecophysiology of cells and therefore changing environmental conditions.Analyzing the fate of individual C atoms by position-specific labeling allows insight into the mechanisms and kinetics of microbial utilization by various microbial groups. This approach will strongly improve our understanding of soil C fluxes
Fate of low molecular weight organic substances in an arable soil: From microbial uptake to utilisation and stabilisation
No full textMicrobial uptake and utilisation are the main transformation pathways of low molecular weight organic substances (LMWOS) in soil, but details on transformations are strongly limited. As various LMWOS classes enter biochemical cycles at different steps, we hypothesize that the percentage of their carbon (C) incorporation into microbial biomass and consequently stabilisation in soil are different. Representatives of the three main groups of LMWOS: amino acids (alanine, glutamate), sugars (glucose, ribose) and carboxylic acids (acetate, palmitate) - were applied at naturally-occurring concentrations into a loamy arable Luvisol in a field experiment. Incorporation of C-13 from these LMWOS into extractable microbial biomass (EMB) and into phospholipid fatty acids (PLFAs) was investigated 3 d and 10 d after application. The microbial utilisation of LMWOS for cell membrane construction was estimated by replacement of PLFA-C with C-13. 35-80% of initially applied LMWOS-C-13 was still present in the composition of soil organic matter after 10 days of experiment, with 10-24% of C-13 incorporation into EMB at day three and 1-15% at day 10. Maximal incorporation of C-13 into EMB was observed from sugars and the least from amino acids. Strong differences in microbial utilisation between LMWOS were observed mainly at day 10. Thus, despite similar initial rapid uptake by microorganisms, further metabolism within microbial cells accounts for the specific fate of C from various LMWOS in soils. C-13 from each LMWOS was incorporated into each PLFA. This reflects the ubiquitous utilisation of all LMWOS by all functional microbial groups. The preferential incorporation of palmitate into PLFAs reflects its role as a direct precursor for fatty acids. Higher C-13 incorporation from alanine and glucose into specific PLFAs compared to glutamate, ribose and acetate reflects the preferential use of glycolysis-derived substances in the fatty acids synthesis. Gram-negative bacteria (16:1 omega 7c and 18:1 omega 7c) were the most abundant and active in LMWOS utilisation. Their high activity corresponds to a high demand for anabolic products, e.g. to dominance of pentose-phosphate pathway, i.e. incorporation of ribose-C into PLFAs. The C-13 incorporation from sugars and amino acids into filamentous microorganisms was lower than into all prokaryotic groups. However, for carboxylic acids, the incorporation was in the same range (0.1-0.2% of the applied carboxylic acid C-13) as that of gram-positive bacteria. This may reflect the dominance of fungi and other filamentous microorganisms for utilisation of acidic and complex organics. Thus, we showed that despite similar initial uptake, C from individual LMWOS follows deviating metabolic pathways which accounts for the individual fate of LMWOS-C over 10 days. Consequently, stabilisation of C in soil is mainly connected with its incorporation into microbial compounds of various stability and not with its initial microbial uptake. (C) 2014 Elsevier Ltd. All rights reserved.Deutsche Forschungsgemeinschaft (DFG) [KU 1184 19/1]; MolTer; DAA
Organic nitrogen uptake by plants: reevaluation by position-specific labeling of amino acids
No full textCurrent studies suggest that many plants are able to take up not only inorganic nitrogen (N) but also organic N. We used the novel tool of position-specific isotope labeling to improve the quantification of intact amino acid uptake and to deepen our understanding of the processes occurring at the root-soil-microorganism interface. Position-specific C-14 and N-15 labeled alanine enabled us to trace the uptake of C from individual molecule positions by Zea mays, Lupinus albus and Cichorium intybus. Uniformly C-14 labeled alanine and acetate and inorganic (NH4)-N-15 (+) and (NO3)-N-15 (-) were applied as controls. Equal uptake of uniformly C-14 labeled alanine and acetate showed that plant uptake of low molecular weight organic substances (LMWOS) is independent of N in the molecule. C-14 uptake from individual molecule positions of alanine strongly differed: this confirmed that soil microorganisms cleaved alanine within 6 h into transformation products, which were then taken up by the plants. Microbial utilization strongly outcompeted the plant uptake of LMWOS in agricultural soils. This study revealed that position-specific labeling is an innovative tool that enables separation of the intact uptake from the uptake of molecule fragments and improves the understanding of competing processes for LMWOS utilization in the rhizosphere.Deutsche Forschungsgemeinschaft DFG [DFG KU 1184/19-1
Soil microbial C and N turnover under Cupressus lusitanica and natural forests in southern Ethiopia assessed by decomposition of C-13- and (15) N-labelled litter under field conditions
No full textNatural forests in Ethiopia are frequently replaced by Cupressus lusitanica plantations, but little is known about consequences of this land use change for soil C and N dynamics. The objectives of the study were: (i) quantification of microbial incorporation of litter-derived C and N under field conditions, (ii) identification of forest management effects on microbial incorporation of litter-derived C and N and (iii) elucidation of soil moisture effects on microbial utilization of litter-derived C and N. Natural litter in the Munessa forest was replaced by C-13 and (15) N labelled litter and its degradation was studied over 2 years. Microbial incorporation of litter-derived C and N was measured by chloroform fumigation extraction and stable isotope analysis. Most of the C-13 and (15) N tracer remained in the litter or was incorporated into bulk soil, whereas soil microbial biomass showed minor incorporation. Silvicultural management practices influenced microbial litter-derived C utilization with increased microbial incorporation under wet soil conditions under plantations. Thinning of Cupressus trees led to increased litter decomposition during dry soil conditions. Soil humidity is the main influencing factor for microbial turnover of litter-derived C in this ecosystem. Fast-growing tree plantations had no negative effects on microbial C and N turnover when compared to natural forests
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
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