University of Hohenheim

About: University of Hohenheim is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Population & Soil water. The organization has 8585 authors who have published 16406 publications receiving 567377 citations.

Dynamics of litter carbon turnover and microbial abundance in a rye detritusphere

Abstract: Factors determining C turnover and microbial succession at the small scale are crucial for understanding C cycling in soils. We performed a microcosm experiment to study how soil moisture affects temporal patterns of C turnover in the detritusphere. Four treatments were applied to small soil cores with two different water contents (matric potential of −0.0063 and −0.0316 MPa) and with or without addition of 13C labelled rye residues (δ13C=299‰), which were placed on top. Microcosms were sampled after 3, 7, 14, 28, 56 and 84 days and soil cores were separated into layers with increasing distance to the litter. Gradients in soil organic carbon, dissolved organic carbon, extracellular enzyme activity and microbial biomass were detected over a distance of 3 mm from the litter layer. At the end of the incubation, 35.6% of litter C remained on the surface of soils at −0.0063 MPa, whereas 41.7% remained on soils at −0.0316 MPa. Most of the lost litter C was mineralised to CO2, with 47.9% and 43.4% at −0.0063 and −0.0316 MPa, respectively. In both treatments about 6% were detected as newly formed soil organic carbon. During the initial phase of litter decomposition, bacteria dominated the mineralisation of easily available litter substrates. After 14 days fungi depolymerised more complex litter compounds, thereby producing new soluble substrates, which diffused into the soil. This pattern of differential substrate usage was paralleled by a lag phase of 3 days and a subsequent increase in enzyme activities. Increased soil water content accelerated the transport of soluble substrates, which influenced the temporal patterns of microbial growth and activity. Our results underline the importance of considering the interaction of soil microorganisms and physical processes at the small scale for the understanding of C cycling in soils.

Effects of genotype and genotype—environment interaction on deoxynivalenol accumulation and resistance to Fusarium head blight in rye, triticale, and wheat

Abstract: Fusarium culmorum is one of the most important Fusarium species causing head blight infections in wheat, rye, and triticale. It is known as a potent mycotoxin producer with deoxynivalenol (DON), 3-acetyl deoxynivalenol (3-ADON), and nivalenol (NIV) being the most prevalent toxins. In this study, the effect of winter cereal species, host genotype, and environment on DON accumulation and Fusarium head blight (FHB) was analysed by inoculating 12 rye, eight wheat, and six triticale genotypes of different resistance levels with a DON-producing isolate at three locations in 2 years (six environments). Seven resistance traits were assessed, including head blight rating and relative plot yield. In addition, ergosterol, DON and 3-ADON contents in the grain were determined. A growth-chamber experiment with an artificially synchronized flowering date was also conducted with a subset of two rye, wheat and triticale genotypes. Although rye genotypes were, on average, affected by Fusarium infections much the same as wheat genotypes, wheat accumulated twice as much DON as rye. Triticale was least affected and the grain contained slightly more DON than rye. In the growth-chamber experiment, wheat and rye again showed similar head blight ratings, but rye had a somewhat lower relative head weight and a DON content nine times lower than wheat (3.9 vs. 35.3 mg/kg). Triticale was least susceptible with a five times lower DON content than wheat. Significant (P = 0.01) genotypic variation for DON accumulation existed in wheat and rye. The differences between and within cereal species in the field experiments were highly influenced by environment for resistance traits and mycotoxin contents. Nevertheless, mean mycotoxin content of the grain could not be associated with general weather conditions in the individual environments. Strong genotype-environment interactions were found for all cereal species. This was mainly due to three wheat varieties and one rye genotype being environmentally extremely unstable. The more resistant entries, however, showed a higher environmental stability of FHB resistance and tolerance to DON accumulation. Correlations between resistance traits and DON content were high in wheat (P = 0.01), with the most resistant varieties also accumulating less DON, but with variability in rye. In conclusion, the medium to large genotypic variation in wheat and rye offers good possibilities for reducing DON content in the grains by resistance selection. Large confounding effects caused by the environment will require multiple locations and/or years to evaluate FHB resistance and mycotoxin accumulation.

The proteasome and its role in the degradation of oxidized proteins.

Abstract: The generation of free radicals and the resulting oxidative modification of cell structures are omnipresent in mammalian cells. This includes the permanent oxidation of proteins leading to the disruption of the protein structure and an impaired functionality. In consequence, these oxidized proteins have to be removed in order to prevent serious metabolic disturbances. The most important cellular proteolytic system responsible for the removal of oxidized proteins is the proteasomal system. For normal functioning, the proteasomal system needs the coordinated interaction of numerous components. This review describes the fundamental functions of the 20S "core" proteasome, its regulators, and the roles of the proteasomal system beyond the removal of oxidized proteins in mammalian cells.

Separating microbial respiration of exudates from root respiration in non-sterile soils: A comparison of four methods

Abstract: Partitioning the root-derived CO2 efflux from the soil into actual root respiration (RR) and microbial respiration of exudates and root residues is very important for determining the carbon (C) and energy balance of soils. Studies based on artificial root environments like hydroponics or sterile soils give unrealistic figures for C partitioning and are unsuitable for predicting C flows under natural conditions. To date, only four methods have been suggested to separate RR and rhizomicrobial respiration in non-sterile soils: (1) the isotope dilution method, (2) the model rhizodeposition technique, (3) modeling of 14CO2 efflux dynamics, and (4) the exudate elution procedure. All four methods are based on the pulse labeling of shoots in a 14CO2 atmosphere and subsequent monitoring of 14CO2 efflux from the soil. However, the basic assumptions and principles of these methods, as well as the results observed in the original papers, all differ from one another. This study describes the separation of RR of Lolium perenne grown on a loamy Haplic Luvisol from microbial respiration of rhizodeposits by means of all four methods under the same experimental conditions. In spite of alternative principles, the isotope dilution and the 14CO2 dynamics methods show a similar level of RR: accordingly, 39 and 45% of total root-derived CO2 efflux were accounted for by RR. The remainder is rhizomicrobial respiration. The exudate elution method, which underestimates the total rhizodeposition, shows that at least 19% of root-derived CO2 is produced by exudate decomposition. The microbial respiration of rhizodeposits calculated using the model rhizodeposition technique is also underestimated. The exudate elution method is the only procedure allowing physical separation of both C flows. The assumptions and principles of all four methods are reviewed and the effects of possible shortcomings on the separation results are discussed. In conclusion, RR contributes about 40–50% to the root-derived CO2 efflux. The remaining 50–60% comprise the microbial decomposition of root exudates and other rhizodeposits. The longer the period of monitoring the CO2 efflux after the pulse labeling is, the higher the contribution of rhizomicrobial respiration to the total root-derived CO2 efflux from soil.

Isotopic tree thermometers

Abstract: Evidence is summarised here that trees store a record of atmospheric temperature in their rings. In each ring, the ratios of the stable isotopes of hydrogen and oxygen vary with the air temperature prevailing when the ring was formed. We have shown that the temperature records in three modern trees seem to follow the local mercury thermometer records, and have found that a Japanese cedar indicates a temperature fall of ∼1.5°C in the past 1,800 yr.