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

Einfluss von N-Düngermenge und Nitrifikationshemmung auf die direkten N2O-Emissionen eines gemüsebaulich genutzten Ackerbodens

Lachgas (N2O) ist ein klimarelevantes Spurengas, es trägt zum Ozonabbau in der Stratosphäre sowie zu 8% am anthropogenen Treibhauseffekt bei und stammt zum Großteil aus landwirtschaftlich genutzten Böden. Ziel dieser Studie war die Ermittlung belastbarer annueller Daten zur N2O-Freisetzung aus gemüsebaulich genutzten Ackerböden Mitteleuropas, d.h. aus einer Gegend mit ausgeprägten Frost-Tau-Zyklen. Ferner sollte das Potential zur Minderung der direkten N2O-Emissionen untersucht werden. Hierzu wurde sowohl eine reduzierte Düngung als auch der Zusatz eines Nitrifikationshemmstoffs getestet. Die Beiträge von N-Dünger und Ernterückständen an den untersuchten Emissionen wurden mittels 15N-markiertem Dünger ermittelt. Die Emissionsfaktoren der verschiedenen Düngerstufen lagen zwischen 0,9 und 1,7. Durch Düngerreduktion bzw. Zusatz von Nitrifikationshemmstoff wurde bei konstantem Ertrag die N2O-Freisetzung um 24 bzw 43% reduziert. Die Blumenkohlernterückstände verursachten 21% der Jahresemissionen und sorgten für hohe Winteremissionen, während Tau-Peaks kaum ausgeprägt waren

Global patterns in endemicity and vulnerability of soil fungi

Fungi are highly diverse organisms, which provide multiple ecosystem services. However, compared with charismatic animals and plants, the distribution patterns and conservation needs of fungi have been little explored. Here, we examined endemicity patterns, global change vulnerability and conservation priority areas for functional groups of soil fungi based on six global surveys using a high-resolution, long-read metabarcoding approach. We found that the endemicity of all fungi and most functional groups peaks in tropical habitats, including Amazonia, Yucatan, West-Central Africa, Sri Lanka, and New Caledonia, with a negligible island effect compared with plants and animals. We also found that fungi are predominantly vulnerable to drought, heat and land-cover change, particularly in dry tropical regions with high human population density. Fungal conservation areas of highest priority include herbaceous wetlands, tropical forests, and woodlands. We stress that more attention should be focused on the conservation of fungi, especially root symbiotic arbuscular mycorrhizal and ectomycorrhizal fungi in tropical regions as well as unicellular early-diverging groups and macrofungi in general. Given the low overlap between the endemicity of fungi and macroorganisms, but high conservation needs in both groups, detailed analyses on distribution and conservation requirements are warranted for other microorganisms and soil organisms

Rhizospheric NO affects N uptake and metabolism in Scots pine (<em>Pinus sylvestris</em> L.) seedlings depending on soil N availability and N source.

We investigated the interaction of rhizospheric nitric oxide (NO) concentration (i.e. low, ambient or high) and soil nitrogen (N) availability (i.e. low or high) with organic and inorganic N uptake by fine roots of Pinus sylvestris L. seedlings by (15) N feeding experiments under controlled conditions. N metabolites in fine roots were analysed to link N uptake to N nutrition. NO affected N uptake depending on N source and soil N availability. The suppression of nitrate uptake in the presence of ammonium and glutamine was overruled by high NO. The effects of NO on N uptake with increasing N availability showed different patterns: (1) increasing N uptake regardless of NO concentration (i.e. ammonium); (2) increasing N uptake only with high NO concentration (i.e. nitrate and arginine); and (3) decreasing N uptake (i.e. glutamine). At low N availability and high NO nitrate accumulated in the roots indicating insufficient substrates for nitrate reduction or its storage in root vacuoles. Individual amino acid concentrations were negatively affected with increasing NO (i.e. asparagine and glutamine with low N availability, serine and proline with high N availability). In conclusion, this study provides first evidence that NO affects N uptake and metabolism in a conifer

Composition and authentication of commercial and home-made white truffle-flavored oils.

Truffle-flavored olive oils sell at a high premium compared to unflavored oils, yet, their rarely contain either real truffles or natural truffle aroma. Our aim here was to characterize truffle oils and explore techniques for authentication. Specifically, we characterized and compared by metabolic profiling and stable isotope ratio analysis the flavors emitted by commercial and home-made truffle-flavored oils (prepared with natural and synthetic flavors), non-flavored oils, and actual fruiting bodies of the white truffle Tuber magnatum. Stable isotope ratio analysis (delta C-13) of 2,4-dithiapentane, a characteristic truffle odorant detected in most flavored oil samples, could not differentiate between natural and synthetic flavors. By contrast, metabolic profiling revealed that truffle flavor was imprinted to oils by four to six sulfur containing volatiles, two of which (dimethyl sulfoxide and dimethyl sulfone) were exclusively detected in commercial oils, regardless of their synthetic or natural labeling. Overall our results also highlight inconsistencies in product labelling and question the authenticity of oils claiming to contain only natural truffle flavors. (C) 2017 Elsevier Ltd. All rights reserved

Microbial use of organic amendments in saline soils monitored by changes in the 13C/12C ratio.

An incubation experiment was carried out to investigate whether salinity at high pH has negative effects on microbial substrate use, i.e. the mineralization of the amendment to CO2 and inorganic N and the incorporation of amendment C into microbial biomass C. In order to exploit natural differences in the 13C/12C ratio, substrate from two C4 plants, i.e. highly decomposed and N-rich sugarcane filter cake and less decomposed N-poor maize leaf straw, were added to two alkaline Pakistani soils differing in salinity, which had previously been cultivated with C3 plants. In soil 1, the additional CO2 evolution was equivalent to 65% of the added amount in the maize straw treatment and to 35% in the filter cake treatment. In the more saline soil 2, the respective figures were 56% and 32%. The maize straw amendment led to an identical immobilization of approximately 48 ?g N g-1 soil over the 56-day incubation in both soils compared with the control soils. In the filter cake treatment, the amount of inorganic N immobilized was 8.5 ?g N g-1 higher in soil 1 than in soil 2 compared with the control soils. In the control treatment, the content of microbial biomass C3-C in soil 1 was twice that in soil 2 throughout the incubation. This fraction declined by about 30% during the incubation in both soils. The two amendments replaced initially similar absolute amounts of the autochthonous microbial biomass C, i.e. 50% of the original microbial biomass C in soil 1 and almost 90% in soil 2. The highest contents of microbial biomass C4-C were equivalent to 7% (filter cake) and 11% (maize straw) of the added C. In soil 2, the corresponding values were 14% lower. Increasing salinity had no direct negative effects on microbial substrate use in the present two soils. Consequently, the differences in soil microbial biomass contents are most likely caused indirectly by salinity-induced reduction in plant growth rather than directly by negative effects of salinity on soil microorganisms

Impact of fertilization on the abundance of nitrifiers and denitrifiers at the root-soil interface of plants with different uptake strategies for nitrogen.

Exploitative fast-growing plants have higher demands for nutrients compared to conservative slow-growing plants. We presume that these differences in nutrient uptake highly influence the microbial performance mainly in the rhizosphere of nutrient-poor soils. In order to investigate the influence of plants with contrasting exploitation types on microbial communities at the root-soil interface, we performed a greenhouse experiment in a N-poor, sandy soil using the fast-growing plant Dactylis glomerata and the conservative, slow-growing plant Festuca rubra. We applied four different amounts of the inorganic fertilizer ammonium nitrate (0, 50, 100, and 200 kg NH4NO3 ha-1). After 6 weeks, the abundance of nitrifiers and denitrifiers was investigated in the root-rhizosphere complex (RRC) based on the quantification of the marker genes amoA, nirK, nirS, and nosZ. Furthermore, soil chemical properties and the plant biomass were determined. Independent from the investigated plant species, fertilizer applications up to 100 kg ha-1 resulted in a clear depletion of ammonium and nitrate in the RRC, with ammonium and nitrate concentrations &lt;1 mg kg-1 dry weight (dw). Only the highest fertilizer rate increased both ammonium and nitrate concentrations in the RRC of both plants reaching concentrations of 9.5 mg kg-1 dw for ammonium and 92.5 mg kg-1 dw for nitrate. The abundance of bacterial ammonia oxidizers (AOB) followed this trend (increase in abundance in response to the highest fertilizer rate), and copy numbers up to 3.2 &times; 107 copies g-1 dw were measured in the RRC of treatments with F. rubra where 200 kg N ha-1 was applied. As the archaeal ammonia oxidizers (AOA) did respond neither to plant species nor to the fertilizer application, the AOA/AOB ratio decreased from 10 in the non-fertilized treatments to 2 in treatments with 200 kg N ha-1. Also the abundance of microbes involved in denitrification strongly increased in response to higher fertilization rates in the RRC of both plant species, although higher gene copy numbers were detected in the rhizosphere of D. glomerata mainly for nitrous oxide reducers (up to 2.7 &times; 108 copies g-1 dw). Surprisingly, the highest fertilization rates resulted in a 50 % decrease in abundance of microbes involved in nitrite as well as nitrous oxide reduction

Nitrous oxide emissions after incorporation of winter oilseed rape (Brassica napus L.) residues under two different tillage treatments.

The aim of this study was to investigate the effect of crop residues from winter oilseed rape on N2O emissions from a loamy soil and to determine the effect of different tillage practices on N2O fluxes. We therefore conducted a field experiment in which crop residues of winter oilseed rape (Brassica napus L., OSR) were replaced with N-15 labelled OSR residues. Nitrous oxide (N2O) emissions and N-15 abundance in the N2O were determined for a period of 11 months after harvest of OSR and in the succeeding crop winter wheat (Triticum aestivum L.) cultivated on a Haplic Luvisol in South Germany. Measurements were carried out with the closed chamber method in a treatment with conventional tillage (CT) and in a treatment with reduced soil tillage (RT). In both tillage treatments we also determined N2O fluxes in control plots where we completely removed the crop residues. High N2O fluxes occurred in a short period just after OSR residue replacement in fall and after N-fertilization to winter wheat in the following spring. Although N2O emissions differed for distinct treatments and sub-periods, cumulative N2O emissions over the whole investigation period (299 days) ranged between 1.7 kg and 2.4 kg N2O-N ha(-1) with no significant treatment effects. More than half of the cumulative emissions occurred during the first eight weeks after OSR replacement, highlighting the importance of this post-harvest period for annual N2O budgets of OSR. The contribution of residue N to the N2O emission was low and explained by the high C/N-ratio fostering immobilization of mineral N. In total only 0.03% of the N2O-N emitted in the conventional tillage treatment and 0.06% in the reduced tillage treatment stemmed directly from the crop residues. The N-15 recovery in the treatments with crop residues was 62.8% (CT) and 75.1% (RT) with more than 97% of the recovered N-15 in the top soil. Despite our measurements did not cover an entire year, the low contribution of the OSR residues to the direct N2O emissions shows, that the current IPCC tier 1 approach, which assumes an EF of 1%, strongly overestimated direct emissions from OSR crop residues. Furthermore, we could not observe any relationship between tillage and crop residues on N2O emission, only during the winter period were N2O emissions from reduced tillage significantly higher compared to conventional tillage. Annual N2O emission from RT and CT did not differ