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An optimized spectroscopic method combining quantitative evolved gas analysis via Fourier transform infrared spectroscopy (FTIR-EGA) in combination with a qualitative in situ thermal reaction monitoring via diffuse reflectance Fourier transform infrared spectroscopy (in situ_T DRIFTS) is being proposed to rapidly characterize soil organic matter (SOM) to study its dynamics and stability. A thermal reaction chamber coupled with an infrared gas cell was used to study the pattern of thermal evolution of carbon dioxide (CO₂) in order to relate evolved gas (i.e., CO₂) to different qualities of SOM. Soil samples were taken from three different arable sites in Germany: (i) the Static Fertilization Experiment, Bad Lauchstädt (Chernozem), from treatments of farmyard manure (FYM), mineral fertilizer (NPK), their combination (FYM + NPK) and control without fertilizer inputs; (ii) Kraichgau; and (iii) Swabian Alb (Cambisols) areas, Southwest Germany. The two latter soils were further fractionated into particulate organic matter (POM), sand and stable aggregates (Sa + A), silt and clay (Si + C), and NaOCl oxidized Si + C (rSOC) to gain OM of different inferred stabilities; respiration was measured from fresh soil samples incubated at 20 °C and 50% water holding capacity for 490 days. A variable long path length gas cell was used to record the mid-infrared absorbance intensity of CO₂ (2400 to 2200 cm⁻¹) being evolved during soil heating from 25 to 700 °C with a heating rate of 68 °C min⁻¹ and holding time of 10 min at 700 °C. Separately, the heating chamber was placed in a diffuse reflectance chamber (DRIFTS) for measuring the mid-infrared absorbance of the soil sample during heating. Thermal stability of the bulk soils and fractions was measured via the temperature of maximum CO₂ evolution (CO_2max).

Results indicated that the FYM + NPK and FYM treatments of the Chernozem soils had a lower CO_2max as compared to both NPK and CON treatments. On average, CO_2max of the Chernozem was much higher (447 °C) as compared to the Cambisol sites (Kraichgau 392 °C; Swabian Alb 384 °C). The POM fraction had the highest CO_2max (477 °C), while rSOC had a first peak at 265 °C at both sites and a second peak at 392 °C for the Swabian Alb and 482 °C for the Kraichgau. The CO_2max increased after 490 day incubation, while the C lost during incubation was derived from the whole temperature range but a relatively higher proportion from 200 to 350 °C. In situ_T DRIFTS measurements indicated decreases in vibrational intensities in the order of C-OH = unknown C vibration < C-H < −COO/C =C < C = C with increasing temperature, but interpretation of vibrational changes was complicated by changes in the spectra (i.e., overall vibrational intensity increased with temperature increase) of the sample during heating. The relative quality c...

Beauveria and Metarhizium fungi are facultative plant endophytes that provide plant growth-stimulating, immunomodulatory, and other beneficial effects. However, little is known about the level of plant colonization by these fungi under natural conditions. We assessed the endophytic colonization of potatoes (Solanum tuberosum) with entomopathogenic fungi at their natural load in soils (102–104 colony-forming units per g). Microbiological analyses of soils and plant organs, as well as a metagenomic analysis of potato roots and leaves, were conducted in three locations in Western Siberia, consisting of conventional agrosystems and kitchen gardens. The fungi were isolated at a relatively high frequency from unsterilized roots (up to 53% of Metarhizium-positive plants). However, the fungi were sparsely isolated from the internal tissues of roots, stems, and leaves (3%). Among the genus Metarhizium, two species, M. robertsii and M. brunneum, were detected in plants as well as in soils, and the first species was predominant. A metagenomic analysis of internal potato tissues showed a low relative abundance of Beauveria and Metarhizium (<0.3%), and the communities were represented primarily by phytopathogens. We suggest that colonization of the internal tissues of potatoes occurs sporadically under a natural load of entomopathogenic fungi in soils. The lack of stable colonization of potato plants with Beauveria and Metarhizium may be due to competition with phytopathogens.

Measurements of carbon dioxide (CO2)-evolution from soils are important in evaluating biomass and activity of soil microorganisms, as well as decomposition of soil organic matter. The Respicond VI is a fully computerized system allowing continuous measurement of CO2 evolution in short-and long-term soil incubation experiments in up to 96 incubation vessels. The measurement of CO2 evolution is based on the absorption of CO2 by an electrolyte (KOH solution) producing a change in the cell conductance measured using two electrodes. In this study, the Respicond VI was recalibrated yielding 174.5 mg CO2 as constant A expressing the theoretical maximum amount of CO2 absorbed in 10 ml 0.5 M KOH. This value of A corresponds to 34.9 mg CO2 ml −1 1 M KOH. The constant A does neither depend on the investigated incubation temperatures (5˚C-25˚C) nor on the concentrations of the KOH solutions (0.5, 0.1, 0.05 M KOH). To eliminate any influence of changing incubation temperatures, either induced by uncertainties in temperature control or as a part of the experimental setup, on the conductance of KOH solution, a correction procedure was developed using a factor calculated from changing conductance of KOH solutions in incubation vessels without soil.

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