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No abstract is provided for this article.

Die Zersetzungsgeschwindigkeiten im Podzoluvisol von den zwei Aminosäuren Glycin und Alanin, die jeweils an zwei verschiedenen Positionen mit I4C markiert worden waren, wurden durch die 14CO2‐Emission im 48 tägigen Laborversuch untersucht. Die Kurven des kumulativen l4CO2‐Effluxes wurden in drei Komponenten entsprechend einem früher erarbeitenden Modell zerlegt: Abbau der freien Aminosäuren selbst (Abbauraten (k) = 0,085 ‐ 0,052 h−1), Metabolisierung des Kohlenstoffs durch die Biomasse (k = 0, 15 ‐ 0,32 d‐1) und des an Humus und Tonminerale sorbierten Kohlenstoffs (k = 0,0089–0,012 d−1) Der Kohlenstoffanteil, der für den mikrobiellen Anabolismus verwendet wird, ist für die AlkylAminogruppe beider Aminosäuren ca. 2 fach größer (29–49 %) als für die Carboxylgruppe (17–20 %). Die mikrobielle Gesamtnutzung des Kohlenstoffs aus der Carboxylgruppe von Alanin ist ca. 5 fach geringer als die des Kohlenstoffs aus der Alkyl‐Aminogruppe. Die Gesamtverweilzeit des Kohlenstoffs aus der Carboxylgruppe im Boden war ebenfalls wesentlich kürzer. Das entspricht einer vollständigeren und schnelleren Oxidation des Kohlenstoffs aus der Carboxylgruppe im Vergleich zum Kohlenstoff aus der Alkyl‐Aminogruppe beider Aminosäuren. Da im Laufe seiner Oxidation jedes Kohlenstoffatom den Zustand der sauren Carboxylgruppe passiert, trägt es so zur Bodenversauerung bei. Die Decarboxylierung der organischen Säuren im Boden wird als einer der natürlichen Neutralisationsmechanismen betrachtet, der sich wegen unzureichender Menge an Kationen als eine Alternative der basischen Neutralisation evolutionär entwickelt hat. In soil, decomposition rates of the amino acids glycine and alanine, specifically labeled with 14C on two different molecular positions, were investigated in 48 day laboratory experiment with 14CO2 fixation. The cumulative 14CO2 emission was characterized by 3 components corresponding to the model previously developed: decomposition of the amino acids themselves (rate (k) = 0.085 ‐ 0.052 h−1), carbon metabolized by microorganisms (k = 0.15 ‐ 0.32 d−1) and carbon sorbed on humus and clay minerals (k = 0.0089–0.012d−1). Use of the alkyl‐amino group for microbia] anabolism was 2‐fold greater (29–49%) than that of the carboxyl group (17–20%) for both amino acids. The total use of carbon from the carboxyl group of ala‐nine was about 5 times less than that of the alkyl‐amino group. The total residence time of carbon from the carboxyl group in the soil also was significantly less. This suggests that the oxidation of carbon from the carboxyl group was more rapid and complete in comparison to carbon from the alkyl‐amino group of both amino acids. During the oxidation process in soil, carboxyl groups develop, thereby contributing to soil acidification. The decarboxylation of organic acids in soil is an important evolutionarly neutralisation mechanism which developed as an alternative to the base neutralisation because of an insufficient amount of cations. Stichworte: AminosäurenAbbaurateDecarboxylierungBodenversauerungpH 14CKey words: Amino acidsdecomposition ratesdecarboxylationsoil aciditypH 14C

The double-stranded DNA (dsDNA) content in soil can serve as a measure of microbial biomass under near steady-state conditions and quantitatively reflect the exponential microbial growth initiated by substrate addition. The yield of respired CO2 per microbial biomass unit (expressed as DNA content) could be a valuable physiological indicator reflecting state of soil microbial community. Therefore, investigations combining both analyses of DNA content and respiration of soil microorganisms under steady-state and during periods of rapid growth are needed. We studied the relationship between CO2 evolution and microbial dsDNA content in native and glucose-amended samples of root-free and rhizosphere soil under Beta vulgaris (Cambisol, loamy sand from the field experiment of the Institute of Agroecology FAL, Braunschweig, Germany). Quantity of dsDNA was determined by direct DNA isolation from soil with mechanic and enzymatic disruption of microbial cell walls with following spectrofluorimetric detection with PicoGreen (Blagodatskaya et al., 2003). Microbial biomass and the kinetic parameters of microbial growth were estimated by dynamics of the CO2 emission from soil amended with glucose and nutrients (Blagodatsky et al., 2000). The CO2 production rate was measured hourly at 22 using an automated infrared-gas analyzer system. The overall increase in microbial biomass, DNA content, maximal specific growth rate and therefore, in the fraction of microorganisms with r-strategy were observed in rhizosphere as compared to bulk soil. The rhizosphere effect for microbial respiration, biomass and specific growth rate was more pronounced for plots with half-rate of N fertilizer compared to full N addition. The DNA content was significantly lower in bulk compared to rhizosphere soil both before and during microbial growth initiated by glucose amendment. Addition of glucose to the soil strongly increased the amount of CO2 respired per DNA unit. Without substrate addition the VCO2-to-total DNA ratios were lower than 0.1 μg CO2-C μg-1 total DNA h-1 whereas during exponential microbial growth these values increased consistently and exceeded 1 μg CO2-C μg-1 DNA h-1. Thus, the VCO2-to-total DNA ratio strongly changes along with the physiological state of soil microorganisms and can be used as valuable physiological parameter. In growing microorganisms the quantity of CO2 evolved per unit of newly formed DNA was identical in rhizosphere and root free soil and averaged for 13.5 ± 1.1 μg CO2-C μg-1 newly formed DNA. The CO2 yield per unit of newly formed DNA allows the estimation of microbial growth efficiency and validation of specific growth rates obtained during kinetic analysis of respiration curves.

. Abstract. Peatlands’ microtopography units – hummocks and hollows – are mainly differing by hydrological characteristics (water table level, i.e. oxic-anoxic conditions) and vegetation communities. These factors affect the fluxes of key greenhouse gases (GHG) – methane (CH4) and carbon dioxide (CO2). However, the effects of microrelief forms on belowground CO2 and CH4 production and pathways of methanogenesis need deeper understanding. We hypothesized increasing CH4 and CO2 production potentials from naturally drier hummocks to more wet hollows during anaerobic incubation. GHG production in peat was expected to decrease with depth (decreasing inputs of recent plant-derived deposits) but the contribution of hydrogenotrophic vs. acetoclastic pathway to the total methanogenesis should be higher in deeper peat layers as compared to upper layers. To test the hypotheses, we measured CH4 and CO2 productions together with the respective δ13C values under controlled anaerobic conditions with- and without addition of specific inhibitor of methanogenesis (2-bromo-ethane sulfonate, BES) in a peat soil of hummocks and hollows of five depths (15, 50, 100, 150 and 200 cm). The concentration of BES (1 mM) aimed to block acetoclastic but not the hydrogenotrophic pathway of methanogenesis. As expected, CH4 production was ca. 2 times higher in hollows than in hummocks, though no differences in CO2 were measured between the microforms. With depth, CO2 production rates decreased by 77 % (15 cm vs. 200 cm) in both microforms, whereby the highest CH4 production was measured at 15 cm in hollows (91 % of total produced CH4) and at 50 cm in hummocks (82 %). Noteworthy, at 15 cm of hummocks less than 1 % of total CH4 production was observed. Decreasing GHG production rates with depth positively correlated to an increase in the extractable total N and NH4+ concentrations. The hydrogenotrophic pathway of methanogenesis in deep vs. surface layers was depicted by lower (more negative) δ13C-CH4 and higher δ13C-CO2 values, respectively. Between the microforms, overall higher contribution of hydrogenotrophic vs. acetoclastic methanogenesis corresponded to hollows as compared to hummocks. Contrary to the expectation, the addition of 1mM BES was not selective and inhibited both pathways of methanogenesis. Concluding, peatlands’ microrelief is an important factor regulating the GHG fluxes. However, the effects of microforms on the production of CH4 and pathways of methanogenesis were pronounced for the upper 50 cm layer. Finally, inhibition with BES appeared to be less effective tool for the partitioning between pathways of methanogenesis as compared with the isotope method.

Partitioning the root‐derived CO 2 efflux from soil (frequently termed rhizosphere respiration) into actual root respiration (RR, respiration by autotrophs) and rhizomicrobial respiration (RMR, respiration by heterotrophs) is crucial in determining the carbon (C) and energy balance of plants and soils. It is also essential in quantifying C sources for rhizosphere microorganisms and in estimation of the C contributing to turnover of soil organic matter (SOM), as well as in linking net ecosystem production (NEP) and net ecosystem exchange (NEE). Artificial‐environment studies such as hydroponics or sterile soils yield unrealistic C‐partitioning values and are unsuitable for predicting C flows under natural conditions. To date, several methods have been suggested to separate RR and RMR in nonsterile soils: 1) component integration, 2) substrate‐induced respiration, 3) respiration by excised roots, 4) comparison of root‐derived 14 CO 2 with rhizomicrobial 14 CO 2 after continuous labeling, 5) isotope dilution, 6) model‐rhizodeposition technique, 7) modeling of 14 CO 2 efflux dynamics, 8) exudate elution, and 9) δ 13 C of CO 2 and microbial biomass. This review describes the basic principles and assumptions of these methods and compares the results obtained in the original papers and in studies designed to compare the methods. The component‐integration method leads to strong disturbance and non‐proportional increase of CO 2 efflux from different sources. Four of the methods (5 to 8) are based on the pulse labeling of shoots in a 14 CO 2 atmosphere and subsequent monitoring of 14 CO 2 efflux from the soil. The model‐rhizodeposition technique and exudate‐elution procedure strongly overestimate RR and underestimate RMR. Despite alternative assumptions, isotope dilution and modeling of 14 CO 2 ‐efflux dynamics yield similar results. In crops and grasses (wheat, ryegrass, barley, buckwheat, maize, meadow fescue, prairie grasses), RR amounts on average to 48±5% and RMR to 52±5% of root‐derived CO 2 . The method based on the 13 C isotopic signature of CO 2 and microbial biomass is the most promising approach, especially when the plants are continuously labeled in 13 CO 2 or 14 CO 2 atmosphere. The “difference” methods, i.e. , trenching, tree girdling, root‐exclusion techniques, etc., are not suitable for separating the respiration by autotrophic and heterotrophic organisms because the difference methods neglect the importance of microbial respiration of rhizodeposits.

Priming effects are strong short-term changes in the turnover of soil organic matter caused by comparatively moderate treatments of the soil. In the course of priming effects large amounts of C, N and other nutrients can be released or immobilized in soil in a very short time. These effects have been measured in many field and laboratory experiments; however, only a few of the studies were aimed at an extended investigation of the mechanisms of such phenomena. The aim of this overview is to reveal possible causes and processes leading to priming actions using the references on agricultural ecosystems and model experiments. Multiple mechanisms and sources of released C and N are presented and summarized in Tables for positive and negative real and apparent priming effects induced after the addition of different organic and mineral substances to the soil. Soil microbial biomass plays the key role in the processes leading to the real priming effects. The most important mechanisms for the real priming effects are the acceleration or retardation of soil organic matter turnover due to increased activity or amount of microbial biomass. Isotopic exchange, pool substitution, and different uncontrolled losses of mineralized N from the soil are responsible for the apparent N priming effects. Other multiple mechanisms (predation, competition for nutrients between roots and microorganisms, preferred uptake, inhibition, etc.) in response to addition of different substances are also discussed. These mechanisms can be distinguished from each other by the simultaneous monitoring of C and N release dynamics; its comparison with the course of microbial activity; and by the labelling of different pools with 14C or 13C and 15N. Quantitative methods for describing priming effects and their dynamics using 14C and 15N isotopes, as well as for non-isotopic studies are proposed.