Rupert Bäumler

Heterotrophic microbial communities use ancient carbon following glacial retreat.

When glaciers retreat they expose barren substrates that become colonized by organisms, beginning the process of primary succession. Recent studies reveal that heterotrophic microbial communities occur in newly exposed glacial substrates before autotrophic succession begins. This raises questions about how heterotrophic microbial communities function in the absence of carbon inputs from autotrophs. We measured patterns of soil organic matter development and changes in microbial community composition and carbon use along a 150-year chronosequence of a retreating glacier in the Austrian Alps. We found that soil microbial communities of recently deglaciated terrain differed markedly from those of later successional stages, being of lower biomass and higher abundance of bacteria relative to fungi. Moreover, we found that these initial microbial communities used ancient and recalcitrant carbon as an energy source, along with modern carbon. Only after more than 50 years of organic matter accumulation did the soil microbial community change to one supported primarily by modern carbon, most likely from recent plant production. Our findings suggest the existence of an initial stage of heterotrophic microbial community development that precedes autotrophic community assembly and is sustained, in part, by ancient carbon.

Microbial reduction of Fe(III) and turnover of acetate in Hawaiian soils

Soils contain anoxic microzones, and acetate is an intermediate during the turnover of soil organic carbon. Due to negligible methanogenic activities in well-drained soils, acetate accumulates under experimentally imposed short-term anoxic conditions. In contrast to forest, agricultural, and prairie soils, grassland soils from Hawaii rapidly consumed rather than formed acetate when incubated under anoxic conditions. Thus, alternative electron acceptors that might be linked to the anaerobic oxidation of soil organic carbon in Hawaiian soils were assessed. Under anoxic conditions, high amounts of Fe(II) were formed by Hawaiian soils as soon as soils were depleted of nitrate. Rates of Fe(II) formation for different soils ranged from 0.01 to 0.31 micromol (g dry weight soil)(-1) h(-1), but were not positively correlated to increasing amounts of poorly crystallized iron oxides. In general, sulfate-reducing and methanogenic activities were negligible. Supplemental acetate was rapidly oxidized to CO2 via the sequential reduction of nitrate and Fe(III) in grassland soil (obtained near Kaena State Park). Supplemental H2 stimulated the formation of Fe(II), but H2-utilizing acetogens appeared to also be involved in the consumption of H2. Approximately 270 micromol Fe(III) (g dry weight soil)(-1) was available for Fe(III)-reducing bacteria, and acetate became a stable end product when Fe(III) was depleted in long-term incubations. Most-probable-number estimates of H2- and acetate-utilizing Fe(III) reducers and of H2-utilizing acetogens were similar. These results indicate that (i) the microbial reduction of Fe(III) is an important electron-accepting process for the anaerobic oxidation of organic matter in Fe(III)-rich Hawaiian soils of volcanic origin, and (ii) acetate, formed by the combined activity of fermentative and acetogenic bacteria, is an important trophic link in anoxic microsites of these soils.

Atmospheric deposition and impact of forest thinning on the throughfall of mountain forest ecosystems in the Bavarian Alps

Abstract The input into two forested watersheds in the Bavarian Alps is characterised by 2000 mm mean annual precipitation. Evaporation from the tree crown surfaces varies between 25 and 30%. The input is influenced by multiple natural and man-made processes. In addition to the general climate, these are local weather conditions, the growing season, processes of combustion (traffic and domestic fuel), tourism, farming, and not least by processes in the canopy. The input of SO4-S is comparatively low, while high amounts of acidity and nitrogen are deposited. The input occurs mainly as dissolved salts. A considerable amount of the acidity deposited is buffered in the canopy by cation exchange and by calcareous dusts, which are blown out from the limestone and dolomite mountains nearby, and redeposited on leaf surfaces. Forest thinning (removal of 40% of the stem volume) caused marked changes in the deposition pattern. Interception and deposition rates of individual ions were reduced by up to 45%. The amount and chemical composition of the throughfall occupied an intermediate position between bulk precipitation and the throughfall of the control watershed. Ions which are preferentially exchanged and leached from the leaves, e.g. potassium and organic compounds, were affected the most.

Soil organic matter transformations induced by Hieracium pilosella L. in tussock grassland of New Zealand

Abstract To study the effect of Hieracium pilosella L. invasion on the transformations of soil organic matter of New Zealand tussock grassland soils (Ustochrepts), plant material and soils underneath Hieracium, the surrounding halo, and the adjacent herbfield (depleted tussock grassland) were examined for their chemical composition. An attempt was made to reveal possible changes in chemical composition of the soil organic matter induced by H. pilosella invasion. Small differences were detected by solid-state 13C nuclear magnetic resonance (NMR) spectroscopy in the composition of the plant and soil materials from these zones. Most of the differences in soil organic matter occurred due to differences in the amount and quality of plant-residue inputs. Comparable amounts of phenolic C were detected in the solid-state 13C NMR spectra of H. pilosella and herbfield vegetation, while alkaline CuO oxidation yielded considerable lower lignin oxidation products for H. pilosella. A slightly higher proportion of these compounds in H. pilosella soil revealed an accumulation and a low degradation rate of lignin compounds under H. pilosella. The HCl hydrolysis and solid-state 15N NMR spectroscopy showed similar chemical compositions of the N fractions of the three different soils. The absence of 15N NMR signal intensity assignable to aniline derivatives or aromatic heterocyclic N indicates that the condensation of phenolic compounds with N groups plays a minor role in N sequestration in these soils.

Chemical composition of the organic matter in neolithic soil material as revealed by CPMAS 13C NMR spectroscopy, polysaccharide analysis, and CuO oxidation

The archaeological site in Murr, Upper Bavaria, was settled throughout the entire Neolithic period, between 5500 and 2700 BC. Various pits and a ditch found in the area are distinct from the surrounding loamy soil because of the dark brown color of their filling materials. Although several artifacts have been discovered, at the present stage of research neither the nature of the filling material nor the function of pits and the ditch are well understood. Thus, the organic matter composition of 30 filling layers from 11 Neolithic pits found in this settlement was investigated and compared with that of a nearby Luvisol profile and two A horizons from contemporary Phaeozems. All samples were subjected to C and N analysis, soil lightness measurements, solid-state 13C CPMAS nuclear magnetic resonance (NMR) spectroscopy, and polysaccharide and lignin analysis. The organic carbon contents are higher in the Neolithic samples than in the Luvisol horizons, but they are generally lower than in the A horizons of contemporary phaeozemic soils developed from loess. The Neolithic samples have a much higher intensity in darkness than do the surrounding Luvisol horizons. The organic carbon content of the Neolithic samples correlates with the lightness value. Solid-state 13C NMR measurements revealed that this correlation is primarily because of their aromatic C content, which is considerably higher in the Neolithic samples than in the contemporary soils. Small polysaccharide amounts and no lignin-derived phenols were found in the Neolithic samples. Thus, the organic material filling the Neolithic pits is significantly different in overall chemical composition from the surrounding soil. It represents a highly altered, highly aromatic material showing no evidence of lignin degradation products and probably deriving from nonsoil origins.

CHARACTERIZATION OF ANDISOLS DEVELOPED FROM NONVOLCANIC MATERIAL IN EASTERN NEPAL

Soils developed from mica schist in Eastern Nepal (The Himalayas) were investigated. All soil horizons were characterized by high organic carbon and extractable aluminum contents. Chemical and physical analyses indicated andic soil properties. No short-range order minerals could be detected. It is assumed that aluminum is linked to the organic matter, which leads to insolubilization and stabilization of the organic material against microbial degradation. The formation of Al-humus complexes instead of short-range order minerals is preferred if enough Al and water-soluble organic compounds are present. Al-humus complexes are considered responsible for the formation of Andisols from nonvolcanic parent material. The soil is classified as Dystric Haplustand, medial, mesic (US Soil Taxonomy)

Small scale distribution of Al, heavy metals, and PAHs in an aggregated Alpine Podzol

Abstract Aggregates of the EA horizon, the Bhs and the Bs horizons of an Alpine Podzol were separated into core and surface fractions. In the air-dried aggregate fractions CEC, C org , 7 fractions of Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn using a sequential extraction procedure, and PAHs were determined. Cation exchange capacity, C org and PAHs were determined in homogenized bulk soil samples, too. Both cation exchange capacity and C org were higher in the aggregate surface than in the core fractions. Total concentrations of Al, Mn, Fe, Cr, Ni, and Zn were lower in the aggregate surface fraction of the EA horizon and generally higher in the B horizons. Total Cu, Cd, and Pb, however, were enriched in the aggregate surface compared to the core fractions, at least in the upper two horizons. All metals were more available in the aggregate surface than in the core fractions. The total concentration of PAHs was higher in the aggregate surface than in the core fractions. The enrichment in the aggregate surface fraction was highest for the more soluble compounds with low molecular weight and decreased with depth. These results suggest that the small scale heterogeneity of metals and PAHs is the result of both atmospheric input with preferential sorption at aggregate surfaces, and soil internal redistribution due to eluvial and illuvial processes. Implications may arise for interpreting plant availability of heavy metals and PAHs as well as for modeling transport in aggregated soils.

Investigations on the intensity of weathering of soils developed from glacial and fluvioglacial deposits and their relationship with the history of the landscape in the mt. everest region

Abstract Soils developed from glacial and fluvioglacial deposits in the Mt. Everest region (Eastern Nepal) were differentiated analytically with regard to weathering intensity and age. Iron fractionation, clay mineral analysis and the calculation of weathering indices resulted in a separation of the soils into two groups. One group, of “young soils’ with their main weathering zone in the top horizons, has developed from deposits of the last ice age or postglacial events; this was supported by radiocarbon dating. The other group, of considerably older, highly weathered soils, was presumably derived from interglacial deposits. Based on these results and according to the soil geographical evidence, indications on the Pleistocene history of the landscape and the extent of the last major glaciation could be deduced.

Quaternary paleosols, tephra deposits and landscape history in South Kamchatka, Russia.

Abstract Paleosols developed in various glacial and glaciofluvial deposits of potentially different ages in the southern Kamchatka peninsula of Russia are covered by multiple layers of volcanic ash and have been affected by permafrost. Weathering indices and iron fractionation data indicate slight differences in soil development between the paleosols on terminal moraines and associated terraces of two different ages in the central part of the region, suggesting that the two depositional phases were separated by an interstadial rather than an interglacial. According to the extent of weathering and the age of the oldest tephra overlying the paleosols (ca. 8000 BP), both sets of deposits are of Late Pleistocene age. Glacial deposits on the west coast of the peninsula differ from those on the east in containing ice-wedge casts. Also, the paleosol here is less developed and is covered by lake sediments as well as tephra units. The oldest tephra, dated to ca. 40,000 BP, is present only in the west, suggesting that the western glacial deposits date from an older (Middle Pleistocene?) glaciation.

Weathering of soils developed in eolian material overlying glacial deposits in Eastern Nepal

We used the ratio between well crystallized Fe-oxides and total Fe (Fe d-o /Fe t ) and weathering indices to study eight soils developed in eolian material overlying glacial deposits in Eastern Nepal with regard to intensity of soil development. Together with selected radiocarbon analyses and information on soil morphology, we tried to interpret the data in terms of relative and absolute age distinctions of the deposits. The results suggest no clear relationship between weathering intensity and morphostratigraphical development and the age of the geomorphic surface. We assume that this is attributable to different orographic conditions for sedimentation of the eolian dust at the study sites and to different degrees of pre-weathering of the eolian covers. However, we can show that formation of organic matter and soil development, in general, started around 2500-2800 years B.P. in the eolian cover of most soils studied. This indicates deposition of the bulk eolian sediments around 2800 years B.P. and earlier. Two soils have greater relative ages in the subsoil with respect to the weathering indices. In these soils, parts of the eolian sediments are of late glacial origin or even older. Distinct variation of soil development and weathering indices within a vertical distance of 200 m provided evidence of marginal ice.