Ancient manuring of Amazonian Dark Earths as assessed by molecular markers.

Analytical procedures and the applicability of this methods to detect ancient human manuring in those soils, which were as far as we know, not used before in the humid tropics, will be discussed

Hot moments in the Antarctic due to climate warming?

Climate warming is severely affecting maritime Antarctica, causing accelerated glacier retreat and thus leading to an ongoing exposure of once ice- covered land. This initiates a succession of plant and soil development. Nevertheless, the temporal dynamics and controlling factors of these processes, like C and N status of soils and the effect of root exudation are widely unknown under these harsh climatic conditions. Topsoil samples from three different sites of a chronological soil sequence in the forefront of a retreating glacier of the Fildes Peninsula, King George Island, were collected and incubated at 2 °C for three weeks. To mimic the influence of C and N containing root exudates (primers) on the mineralization of soil C, we added 13C labeled glucose or alanine and compared CO2 evolution in comparison to samples without C and N addition. Soil microbes covered up to 90% of their C demand for anabolic functions with the added C-sources in the case of late soil successions while it was only 50% for the young soils. These findings were independent of the form of primer. Both primers increased the mineralization of soil carbon in the young soils as compared to the control. For the later stages of soil development, we found negative priming which was strongest for the latest stage. These results give evidence for a clear shift in the microbial community of the three investigated sites. While sites with initial soil formation seem to be dominated by k-strategists with low turnover rates that rather use complex C-sources, a significant number of r-strategists in the soils of the older sites uses simple C-substrates very efficiently. As this leads to a relative decrease in SOM mineralization for the late stages of soil development, it is questionable if higher plants can improve their nutrition by stimulating free living soil microbes with root exudates or if they rather have to rely on mycorrhiza

Rapid remediation of sandy sulfuric subsoils using straw-derived dissolved organic matter

When acid sulfate soils dry, oxidation of pyrite can cause acidification and formation of iron (Fe) oxyhydroxy sulfate phases such as jarosite. Remediation via re-establishment of reducing conditions requires submergence and addition of biodegradable organic carbon (OC) to stimulate activity of reducing bacteria. Addition of fresh plant litter has been shown to activate reducing bacteria, likely due to the release of readily available soluble organic matter. However, the effectiveness of soluble organic matter from plant residues has not been tested yet. Here, we tested the potential of wheat straw-derived dissolved OC (DOC) for remediation of a sandy sulfuric (pH < 4) soil. In a second set of experiments, we used combinations of wheat straw-derived DOC with lactate, which is a preferred substrate of sulfate reducing bacteria. All incubation experiments were conducted in the dark at 20 ◦C. The results showed that addition of DOC from wheat straw induces reduction reactions and rapidly increases the pH by 2–3 units after 3 weeks of incubation under submerged conditions. Mossbauer ¨ spectroscopy and X-ray diffraction revealed that jarosite was lost after 200 days of anoxic incubation. Short range-ordered FeIII oxyhydroxides were formed, most likely by FeII-catalysed transformation of jarosite. A second addition of DOC, as well as the addition of lactate, resulted in the almost complete loss of jarosite with increased proportions of FeIII oxyhydroxides in the remaining solids, but not in the formation of FeII sulfides. The formation of FeIII oxyhydroxides reduces the risk of both Fe leaching and renewed acidification in the event of future oxidation. The results suggest that deep injection of wheat straw-derived DOC is a promising approach for rapid and sustainable remediation of sandy sulfuric subsoilsAngelika Kolbl, Klaus Kaiser, Aaron Thompson, Luke Mosley, Rob Fitzpatrick, Petra Marschner, Leopold Sauheitl, Robert Mikutt

Biogenic weathering bridges the nutrient gap in pristine ecosystems - a global comparison

In many pristine ecosystems there seems to be negative nutrient budget existent, meaning that export exceeds the input received by aeolian deposition and physico-chemical weathering. Such ecosystems should degrade rather quickly, but are often found surprisingly stable on the long run. Our hypothesis was that this nutrient gap is an artefact caused by not considering the contribution of photoassimilatory-mediated biogenic weathering to the overall nutrient input, which might constitute an additional, energetically directed and demand driven pathway. Here, we firstly evaluated the evolution of mutualistic biogenic weathering along an Antarctic chronosequence and secondly compared the biogenic weathering rates under mycorrhized ecosystems over a global gradient of contrasting states of soil development. We found the ability to perform biogenic weathering increasing along its evolutionary development in photoautotroph-symbiont interaction and furthermore a close relation between fungal biogenic weathering and available potassium across all 16 forested sites in the study, regardless of the dominant mycorrhiza type (AM or EM), climate, and plant-species composition. Our results point towards a general alleviation of nutrient limitation at ecosystem scale via directional, energy driven and on-demand biogenic weathering

Gradient studies reveal the true drivers of extreme life in the atacama desert.

Studies of hyper-arid sites contribute to our understanding on how life adapted to extreme conditions. They are often used to further deduce implications for extraterrestrial biology by the so-called analogue site-approach. The Atacama Desert, Chile, is one of the most prominent analogue sites despite its neighboring productive ecosystems due to its hyper-aridity and geochemical features resembling Martian environments. We hypothesize that many drivers of extremophile life in analogue sites are only mistakenly attributed to aridity alone, thus obscuring a clear view of the far more complex process interactions originating in nearby earthly ecosystems. To test this, we investigated 54 soil profiles up to 60&nbsp;cm of soil depth along of four transects in the Atacama Desert, either running parallel (S-N) or perpendicular (W-E) to the Andes. Our objective was to reveal the processes controlling the formation of soil organic carbon (SOC) as the most reliable proxy for microbial life in order to understand the boundary conditions of life in extreme habitats. Further, we aimed at identifying analogue sites as uncompromised as possible by external influences of for example, vegetated or marine ecosystems. We found a mixture of influences driving habitable conditions on gradients perpendicular to the Andes, for example, fog and precipitation scavenging caused by altitudinal variations and differing proximity to the Pacific Ocean, while transects parallel to the Andes were much less biased by external factors. Our results show that studies on life under extreme conditions should clarify the explanatory strength of the investigated factors by a gradient study approach