Role of termites for the distribution patterns of carbon and phosphorus fractions and the genesis of tropical soils, Brazil

Tropical soil fertility is limited by low phosphorus (P) availability, limited accumulation of organic matter and by advanced stages of pedogenesis. Termites are well-known soil-engineers, which accumulate clay, organic matter and many nutrients inside their nests. However, the differences between the effects of various termite feeding guilds on soil properties, the influence of termite activities on the properties and genesis of surrounding soil, and the persistence of the termite-induced changes in soils are largely unknown. The aim of the present work was, therefore, (i) to study the effect of different termite feeding guilds on P forms in termite nests across seven tropical ecosystems of Brazil, (ii) to elucidate the spatial and temporal effects of the termites dominant in Cerrado pastures on P distribution patterns and soil genesis, (iii) to use lignin, which is not digested by termites, as a tracer of their influence on soil organic matter accumulation, and finally, (iv) to decipher the impact of the Cerrado termites on nutrients in water drained from termite mounds. To achieve these objectives I characterized termite nests and transects of surrounding soils by sequential P analyses, 31P NMR spectroscopy, and detection of the contents of organic carbon (OC), nitrogen and lignin-derived phenols. Due to the large sample size, mid-infrared spectroscopy followed by partial least squares regression helped in screening these soil properties for the first time also in the matrix of tropical soils. The P contents were higher in nests and exceeded those of the surrounding soil by up to 3650%. Especially the wood-feeding termites changed the P availability to more labile forms; whereas the soil/wood interface-feeder termites enriched also mineral-bound P in their nests. For the Cornitermes silvestrii of the Cerrado, higher contents of labile soil P were documented vertically down to 30 cm below the lower nest border, and to a lateral distance of 60 cm away from it. Similar patterns were found for OC and lignin, whereas the enrichment and the spatial extension of those constituents were smaller below older, secondarily inhabited mounds. Hence, the lignin was initially accumulated in younger mounds, but it was oxidized and decomposed in older nests. The volume of draining water was reduced below both the younger and the older termite mounds in comparison to the soil, but five times lower dissolved organic carbon fluxes, and three times higher nitrate concentrations were only recorded under older mounds. Also the effect of termites on the physical composition of the soil was only significant below older mounds. There, the argic horizon disappeared, thus changing the soil type from Alisols and Acrisols to Umbrisols or Regosols. In summary, my data show that wood-feeding termites of Brazil enhance the availability of P, and that the termites of the Cerrado transport clay upwards and accumulate labile P as well as lignin inside their mounds and the adjacent soil in comparison to reference soils. Such elevated contents are, to a lesser degree, also persistent below older mounds, as are the changed soil types. Those changes in soil types comprise the most long-lasting impact of the termites on the soil in the introduced pasture agro-ecosystem, as the upward transport of clay inverts soil genesis.Die Bedeutung von Termiten für die Verteilungsmuster von Kohlenstoff- und Phosphor-Fraktionen sowie die Genese Tropischer Böden, Brasilien Die Bodenfruchtbarkeit in den Tropen ist durch eine geringe Verfügbarkeit von Phosphor (P), die fehlende Anreicherung von organischer Substanz und die fortgeschrittene Pedogenese eingeschränkt. Termiten sind als Boden-Ingenieure bekannt, die Ton, organische Substanz und viele Nährstoffe in ihren Nestern anreichern. Die Unterschiede zwischen den Effekten von Termiten unterschiedlicher Nahrungsgilden auf Bodeneigenschaften sind jedoch ebenso wenig bekannt wie die Beeinflussung von Eigenschaften und Genese des nestumgebenden Bodens durch Termitenaktivitäten sowie die Persistenz der von Termiten verursachten Veränderungen im Boden. Das Ziel der vorliegenden Arbeit war es deshalb (i) die Effekte von Termiten unterschiedlicher Nahrungsgilden auf P-Fraktionen in ihren Nestern in sieben tropischen Ökosystemen Brasiliens zu beschreiben, (ii) die räumlichen und zeitlichen Effekte von Termiten, welche in Weiden des Cerrado dominieren, auf die Verteilungsmuster von P und die Pedogenese zu verdeutlichen, (iii) Lignin, welches von Termiten nicht verdaut wird, als Marker für die Anreicherung von organischer Substanz durch Termiten zu nutzen und schließlich (iv) den Einfluss der Termiten des Cerrados auf Nährstoffe in der Bodenlösung zu untersuchen. Um diese Ziele zu erreichen, habe ich Termitennester und Transekte der angrenzenden Böden mit sequenzieller P-Extraktion, 31P-NMR-Spektroskopie, sowie den Gehalten von organischem Kohlenstoff (OC), Stickstoff und ligninbürtigen Phenolen charakterisiert. Infrarot-Spektroskopie in Kombination mit dem PLS-Verfahren half bei der Analyse dieser Bodeneigenschaften in dem großen Probensatz und wurde zum ersten Mal für tropische Böden angewendet. Die P-Gehalte waren in Termitennestern teilweise bis zu 3650% höher als im nestumgebenden Boden. Insbesondere die holzfressenden Termiten erhöhten den Anteil leicht verfügbarer P-Formen, während geophage Termiten auch mineralgebundenen P in ihren Nestern anreicherten. Höhere Gehalte von leicht verfügbarem P wurden für Cornitermes silvestrii im Cerrado bis 30 cm unterhalb der unteren Nestgrenze und bis zu einer horizontalen Entfernung vom Nest von 60 cm nachgewiesen. Ähnliche Verteilungsmuster wurden für OC und Lignin dokumentiert, wobei die Gehalte und die räumliche Ausdehnung aller genannten Komponenten unter alten, sekundär bewohnten Termitennestern etwas geringer waren. Das bedeutet, dass Lignin zwar in jungen Nestern angereichert wird, aber dass es während der Nestalterung oxidiert und abgebaut wird. Das Volumen des Sickerwassers war sowohl unter jungen als auch unter alten Nestern im Vergleich zum Boden reduziert, aber nur unter den alten Nestern wurden fünfmal so niedrige Flüsse des gelösten organischen Kohlenstoffs und dreifach erhöhte Nitrat-Konzentration verzeichnet. Auch der Einfluss der Termiten auf die Bodenstruktur war nur unter alten Nestern signifikant. Dort war kein argic-Bodenhorizont vorhanden, was den Bodentyp von Alisols und Acrisols zu Umbrisols und Regosols veränderte. Insgesamt zeigen meine Daten, dass holzfressende Termiten aus allen Teilen Brasiliens die Verfügbarkeit von P erhöhen, und dass die Termiten des Cerrado Ton aufwärts transportieren, sowie verfügbaren P und Lignin in ihren Nestern und im angrenzenden Boden im Vergleich zum Referenzboden anreichern. Auf einem niedrigeren Level sind solche erhöhten Gehalte, genauso wie die geänderten Bodentypen, auch unter älteren Nestern feststellbar. Diese geänderten Bodentypen beinhalten den langfristigsten Einfluss der Termitenaktivität auf den Boden im neuentstandenen Weideland, da die aufwärts gerichtete Tonverlagerung der Pedogenese entgegenläuft.A fertilidade dos solos tropicais é limitada pela baixa disponibilidade de fósforo, a falta de acumulação de matéria orgânica, e por estados avançados de pedogênese. Os térmitas ou cupins são bem-conhecidos 'engenheiros de ecossistemas', acumulando argila, matéria orgánica e muitos nutrientes nos seus ninhos, os cupinzeiros. Porém, as diferenças entre os efeitos de várias guildas alimentares de cupins sobre as propriedades de solo, a influência das atividades dos cupins na qualidade e gênese do solo adjacente, e o grau de persistência dos câmbios observados, são fatores não muito bem conhecidos. Por isso, o objetivo do presente trabalho foi de (i) estudar o efeito de diferentes guildas alimentares de cupins sobre as formas de fósforo nos cupinzeiros em sete ecossistemas tropicais do Brasil; (ii) elucidar os efeitos espaciais e temporais das espécies dominantes em pastagens do cerrado sobre padrões de distribuição de fósforo e sobre a gênese dos solos; (iii) usar a lignina, a qual não é digerida pelos cupins, como um indicador da influência dos cupins sobre a acumulação da matéria orgânica do solo, e (iv) decifrar o impacto das espécies de cerrado sobre os nutrientes na água drenada dos cupinzeiros. Para alcançar estes objetivos, eu caracterizei ninhos de cupins e transectos de solos ad- jacentes através de análises sequenciais de fósforo, espectroscopia NMR usando o isótopo 31P, e detecção dos conteúdos de carbono, nitrogênio e de fenóis derivados de lignina. Por causa do grande número de amostras, espectroscopía das bandas médias de infravermelho, seguida de regressão de least squares, ajudou em avaliar estas propriedades de solo pela primeira vez também na matriz dos solos tropicais. Os conteúdos de fósforos nos ninhos foram elevados e excederam os dos solos adja- centes em até 3650%. Particularmente os cupins xilófagos mudaram a disponibilidade de fósforo para formas mais instáveis; enquanto que os cupins que se alimentam na interface do solo com a madeira enriqueceram nos seus ninhos também fósforo ligado a minerais. Para Cornitermes silvestrii do cerrado, conteúdos mais altos de fósforo lábil foram docu- mentados até uma profundidade de 30 cm abaixo da margem inferior dos cupinzeiros, e numa distância horizontal de até 60 cm do ninho. Padrões similares foram encontrados para carbono orgânico e lignina, mas o enriquecimento e a extensão espacial destes cons- tituentes foram menores abaixo de ninhos mais velhos, habitados secundáriamente. Por isso, a lignina inicialmente se acumulou em ninhos mais jovens, e se encontrou oxidada e decomposta em ninhos envelhecidos. O volume de água drenada em baixo de ninhos no- vos e velhos foi menor que no solo, mas fluxos de carbono orgânico dissolvido cinco vezes menores e concentrações de nitrato tres vezes menores foram somente observados abaixo de ninhos velhos. Também, o efeito dos cupins sobre a composição química do solo foi mais significativo abaixo de ninhos velhos. Nestes, o horizonte argico desapareceu, assim mudando o tipo de solo de Alisols e Acrisols para Umbrisols e Regosols. Somando, meus dados mostram que os cupins xilófagos aumentam a disponibilidade de fósforo e que os cupins do cerrado transportam argila para cima e acumulam fósforo lábil e lignina dentro dos seus ninhos e no solo adjacente. Tanto estes conteúdos elevados quanto a modificação do tipo de solo foram também persistentes em cupinzeiros envelhecidos, po- rém num nível inferior. Estas mudanças no tipo de solo apresentam o impacto das térmitas mais duradouro nos solos da pastagem, que é um agro-ecossistema introduzido, porque o transporte da argila para cima inverte a gênese dos solos

Comparative investigation and inter-calibration of different soil P tests

Ziel dieser Arbeit war es, zu ermitteln inwieweit die Ergebnisse verschiedener P-Extraktionsmethoden miteinander vergleichbar sind. Dazu wurden 8 Methoden untersucht und interkalibriert. Alle untersuchten P Tests waren signifikant miteinander korreliert. Die Extraktionsstärke nahm in der Reihenfolge PAR > PAL, PM3 ≥ PAAAc-EDTA, PDL ≥ PCAL ≥ POlsen, PAAAc ≥ PW ab. Grundsätzlich war es möglich, die Werte einer Methode in die einer anderen zu übertragen, allerdings hing die Qualität der Ergebnisse stark von den jeweils verglichenen Methoden ab. Basierend auf dem in dieser Arbeit verwendeten Datenmaterial zeigten die Ex­traktionen mit CAL, AL, M3, AAAc-EDTA und Wasser die stärksten Korrelationen und waren entsprechend am besten für die Berechnung hoch signifikanter Regressionsgleichungen mit hohem Bestimmtheitsmaß geeignet. Während für einige dieser Methoden einfache Regressionsgleichungen bereits zu einem Bestimmtheitsmaß von > 80% führten, mussten in einigen Fällen weitere Bodenparameter (z.B. Bodenreaktion, ZnWH, FeWH, AlWH, CaWH und Ctotal) mitberücksichtigt werden, um diese Genauigkeit zu erlangen. Die Ergebnisse der Extraktion mit NaHCO3 (Olsen), DL, und AAAc zeigten dagegen schwächere Korrelationen. Entsprechend konnten für diese drei Methoden keine Regressionsgleichungen mit einem ausreichend hohen Bestimmtheitsmaß (z.B. R2 > 80%) abgeleitet werden. Als wichtigste Hindernisse wurden die Unterschiede in der chemischen Zusammensetzung, dem Säuregrad und der Extraktionsstärke der Extrakte identifiziert. DOI: 10.5073/JfK.2015.02.02, https://doi.org/10.5073/JfK.2015.02.02To allow the comparison and interpretation of data obtained by different soil P tests, different established extraction methods were investigated and statistically inter-calibrated. All soil P tests applied in this study were significantly correlated with each other. Their extracting force varied considerably, decreasing in the order PAR > PAL, PM3 ≥ PPAAAc-EDTA, PDL ≥ PCAL ≥ POlsen, PAAAc ≥ PW. Generally, it was possible to transform data from one soil P test into another one. However, the quality of the resulting values depended on the pair of soil tests at question. Based on the present set of data, values from CAL, AL, M3, AAAc-EDTA and water extracts showed strong correlations and consequently allowed for the calculation of highly significant regression equations with a strong coefficient of determination. While in some cases, simple regressions already yielded a coefficient of determination > 80%, in other cases additional soil parameters (such as soil-pH, ZnWH, FeWH, AlWH, CaWH and Ctotal) had to be included in order to achieve this high level of accuracy. In contrast, values obtained from extractions with NaHCO3 (Olsen), DL, and AAAc displayed weaker correlations. Accordingly, no satisfactory regression equations (i.e. with R2 > 80%) could be produced for these three methods. As major obstacles, differences in chemical composition, acidity and extraction force of the various extractants were identified. DOI: 10.5073/JfK.2015.02.02, https://doi.org/10.5073/JfK.2015.02.0

Europium Underneath Graphene on Ir(111): Intercalation Mechanism, Magnetism, and Band Structure

The intercalation of Eu underneath Gr on Ir(111) is comprehensively investigated by microscopic, magnetic, and spectroscopic measurements, as well as by density functional theory. Depending on the coverage, the intercalated Eu atoms form either a $(2 \times 2)$ or a $(\sqrt{3} \times \sqrt{3})$R$30^{\circ}$ superstructure with respect to Gr. We investigate the mechanisms of Eu penetration through a nominally closed Gr sheet and measure the electronic structures and magnetic properties of the two intercalation systems. Their electronic structures are rather similar. Compared to Gr on Ir(111), the Gr bands in both systems are essentially rigidly shifted to larger binding energies resulting in n-doping. The hybridization of the Ir surface state $S_1$ with Gr states is lifted, and the moire superperiodic potential is strongly reduced. In contrast, the magnetic behavior of the two intercalation systems differs substantially as found by X-ray magnetic circular dichroism. The $(2 \times 2)$ Eu structure displays plain paramagnetic behavior, whereas for the $(\sqrt{3} \times \sqrt{3})$R$30^{\circ}$ structure the large zero-field susceptibility indicates ferromagnetic coupling, despite the absence of hysteresis at 10 K. For the latter structure, a considerable easy-plane magnetic anisotropy is observed and interpreted as shape anisotropy.Comment: 18 pages with 14 figures, including Supplemental Materia

Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+)

We present the result of the third Marine Ice Sheet Model Intercomparison Project, MISMIP+. MISMIP+ is intended to be a benchmark for ice-flow models which include fast sliding marine ice streams and floating ice shelves and in particular a treatment of viscous stress that is sufficient to model buttressing, where upstream ice flow is restrained by a downstream ice shelf. A set of idealized experiments first tests that models are able to maintain a steady state with the grounding line located on a retrograde slope due to buttressing and then explore scenarios where a reduction in that buttressing causes ice stream acceleration, thinning, and grounding line retreat. The majority of participating models passed the first test and then produced similar responses to the loss of buttressing. We find that the most important distinction between models in this particular type of simulation is in the treatment of sliding at the bed, with other distinctions - notably the difference between the simpler and more complete treatments of englacial stress but also the differences between numerical methods - taking a secondary role. © 2020 Wolters Kluwer Medknow Publications. All rights reserved

Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+)

We present the result of the third Marine Ice Sheet Model Intercomparison Project, MISMIP+. MISMIP+ is intended to be a benchmark for ice-flow models which include fast sliding marine ice streams and floating ice shelves and in particular a treatment of viscous stress that is sufficient to model buttressing, where upstream ice flow is restrained by a downstream ice shelf. A set of idealized experiments first tests that models are able to maintain a steady state with the grounding line located on a retrograde slope due to buttressing and then explore scenarios where a reduction in that buttressing causes ice stream acceleration, thinning, and grounding line retreat. The majority of participating models passed the first test and then produced similar responses to the loss of buttressing. We find that the most important distinction between models in this particular type of simulation is in the treatment of sliding at the bed, with other distinctions – notably the difference between the simpler and more complete treatments of englacial stress but also the differences between numerical methods – taking a secondary role

The future sea-level contribution of the Greenland ice sheet: A multi-model ensemble study of ISMIP6

The Greenland ice sheet is one of the largest contributors to global mean sea-level rise today and is expected to continue to lose mass as the Arctic continues to warm. The two predominant mass loss mechanisms are increased surface meltwater run-off and mass loss associated with the retreat of marine-terminating outlet glaciers. In this paper we use a large ensemble of Greenland ice sheet models forced by output from a representative subset of the Coupled Model Intercomparison Project (CMIP5) global climate models to project ice sheet changes and sea-level rise contributions over the 21st century. The simulations are part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6).We estimate the sea-level contribution together with uncertainties due to future climate forcing, ice sheet model formulations and ocean forcing for the two greenhouse gas concentration scenarios RCP8.5 and RCP2.6. The results indicate that the Greenland ice sheet will continue to lose mass in both scenarios until 2100, with contributions of 90-50 and 32-17mm to sea-level rise for RCP8.5 and RCP2.6, respectively. The largest mass loss is expected from the south-west of Greenland, which is governed by surface mass balance changes, continuing what is already observed today. Because the contributions are calculated against an unforced control experiment, these numbers do not include any committed mass loss, i.e. mass loss that would occur over the coming century if the climate forcing remained constant. Under RCP8.5 forcing, ice sheet model uncertainty explains an ensemble spread of 40 mm, while climate model uncertainty and ocean forcing uncertainty account for a spread of 36 and 19 mm, respectively. Apart from those formally derived uncertainty ranges, the largest gap in our knowledge is about the physical understanding and implementation of the calving process, i.e. the interaction of the ice sheet with the ocean. © Author(s) 2020

The future sea-level contribution of the Greenland ice sheet: a multi-model ensemble study of ISMIP6

The Greenland ice sheet is one of the largest contributors to global mean sea-level rise today and is expected to continue to lose mass as the Arctic continues to warm. The two predominant mass loss mechanisms are increased surface meltwater run-off and mass loss associated with the retreat of marine-terminating outlet glaciers. In this paper we use a large ensemble of Greenland ice sheet models forced by output from a representative subset of the Coupled Model Intercomparison Project (CMIP5) global climate models to project ice sheet changes and sea-level rise contributions over the 21st century. The simulations are part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We estimate the sea-level contribution together with uncertainties due to future climate forcing, ice sheet model formulations and ocean forcing for the two greenhouse gas concentration scenarios RCP8.5 and RCP2.6. The results indicate that the Greenland ice sheet will continue to lose mass in both scenarios until 2100, with contributions of 90±50 and 32±17 mm to sea-level rise for RCP8.5 and RCP2.6, respectively. The largest mass loss is expected from the south-west of Greenland, which is governed by surface mass balance changes, continuing what is already observed today. Because the contributions are calculated against an unforced control experiment, these numbers do not include any committed mass loss, i.e. mass loss that would occur over the coming century if the climate forcing remained constant. Under RCP8.5 forcing, ice sheet model uncertainty explains an ensemble spread of 40 mm, while climate model uncertainty and ocean forcing uncertainty account for a spread of 36 and 19 mm, respectively. Apart from those formally derived uncertainty ranges, the largest gap in our knowledge is about the physical understanding and implementation of the calving process, i.e. the interaction of the ice sheet with the ocean

Future Sea Level Change Under Coupled Model Intercomparison Project Phase 5 and Phase 6 Scenarios From the Greenland and Antarctic Ice Sheets

Projections of the sea level contribution from the Greenland and Antarctic ice sheets (GrIS and AIS) rely on atmospheric and oceanic drivers obtained from climate models. The Earth System Models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) generally project greater future warming compared with the previous Coupled Model Intercomparison Project phase 5 (CMIP5) effort. Here we use four CMIP6 models and a selection of CMIP5 models to force multiple ice sheet models as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We find that the projected sea level contribution at 2100 from the ice sheet model ensemble under the CMIP6 scenarios falls within the CMIP5 range for the Antarctic ice sheet but is significantly increased for Greenland. Warmer atmosphere in CMIP6 models results in higher Greenland mass loss due to surface melt. For Antarctica, CMIP6 forcing is similar to CMIP5 and mass gain from increased snowfall counteracts increased loss due to ocean warming

Lagrangian basal melt rates at 79°N Glacier between 2017 and 2018

Estimated Lagrangian basal melt rates from phase-sensitive radar (pRES) measurements at 41 locations at 79°N Glacier (Nioghalvfjerdsfjorden Glacier) in northeast Greenland between 2017 and 2018 (see link in "Further details"). Basal melt rates are based on pRES derived ice thicknesses in 2017 and 2018, ablation/accumulation measurements (https://doi.pangaea.de/10.1594/PANGAEA.922131) and simulated vertical strain rates with the Ice-Sheet and Sea-level System Model (ISSM). Off-nadir melt rate estimates are minimum values. Data were measured in the field by Daniel Steinhage, Niklas Neckel and Ole Zeising. Data processing was done by Ole Zeising, data analysis by Ole Zeising and Angelika Humbert. The ISSM simulation was done by Martin Rückamp. This dataset has been planned by Angelika Humbert as part of the iGRIFF expeditions and as contribution to GROCE. If you have questions, please contact Ole Zeising ([email protected]) or co-authors