Methods for evaluating human impact on soil microorganisms based on their activity,biomass, and diversity in agricultural soils

The present review is focused on microbiological methods used in agricultural soils accustomed to human disturbance. Recent developments in soil biology are analyzed with the aim of highlighting gaps in knowledge, unsolved research questions, and controversial results. Activity rates (basal respiration, N mineralization) and biomass are used as overall indices for assessing microbial functions in soil and can be supplemented by biomass ratios (C : N, C : P, and C : S) and eco‐physiological ratios (soil organic C : microbial‐biomass C, qCO₂, qN_min). The community structure can be characterized by functional groups of the soil microbial biomass such as fungi and bacteria, Gram‐negative and Gram‐positive bacteria, or by biotic diversity. Methodological aspects of soil microbial indices are assessed, such as sampling, pretreatment of samples, and conversion factors of data into biomass values. Microbial‐biomass C (µg (g soil)^–1) can be estimated by multiplying total PLFA (nmol (g soil)^–1) by the F_PLFA‐factor of 5.8 and DNA (µg (g soil)^–1) by the F_DNA‐factor of 6.0. In addition, the turnover of the soil microbial biomass is appreciated as a key process for maintaining nutrient cycles in soil. Examples are briefly presented that show the direction of human impact on soil microorganisms by the methods evaluated. These examples are taken from research on organic farming, reduced tillage, de‐intensification of land‐use management, degradation of peatland, slurry application, salinization, heavy‐metal contamination, lignite deposition, pesticide application, antibiotics, TNT, and genetically modified plants.     

Mycorrhizal colonization and lead distribution in root tissues of Norway spruce seedlings

Non-inoculated spruce seedlings (Picea abies Karst.) and spruce seedlings colonized with Lactarius rufus Fr., Pisolithus tinctorius Coker & Couch or Paxillus involutus Fr. were grown for 35 or 37 weeks in a microcosm system on two types of natural forest humus differing in Pb content. Using X-ray microanalysis, the distribution and content of Pb in the tissues of mycorrhizal and non-mycorrhizal root tips were compared. No significant difference in the Pb contents of root cortex cell walls of non-mycorrhizal and seedlings colonized by Lactarius rufus, Pisolithus tinctorius, or indigenous mycorrhizal fungi (mainly Tylospora sp.) was found. However, in root tips of seedlings colonized by Paxillus involutus, due to a higher binding capacity for cations, the Pb content in cell walls of the root cortex were higher than in non-mycorrhizal roots. Pb contents in cell walls of the cortex of mycorrhizal and non-mycorrhizal roots were 3 times higher in plants growing in humus with a high Pb content than in plants growing in humus with a low Pb content. It is concluded that increasing contents of Pb in the organic matter may lead to an increased loading of the apoplast with Pb. The mycobionts tested in this investigation did not exclude Pb from root tissues.     

The problem of pretreatment and unintentional variations in the fumigation-extraction method for time-course measurements in the field

A control soil stored at 4°C was analyzed 38 times by fumigation-extraction during a period of 11 months to correct for variations caused by the analytical procedure. The difference in extractable C between fumigated and unfumigated samples oscillated around the average without a positive or negative trend. When data from contemporaneously extracted field samples were corrected with control soil data the variations were lowered. The deviations between corrected and uncorrected biomass C values had maxima of ±12%. Data obtained for seven dates using pre-extraction, wet-sieving, and centrifuging were compared with data obtained by the conventional procedure without any pretreatment. A negative difference from data obtained without pretreatment was found when the soil water content was decreased to 6%. The largest positive difference (+38%) was found in May during the period of highest root growth.     

Beurteilung des Kalkbedarfes von Waldb?den im mittelfr?nkischen Keupergebiete

Ohne Zusammenfassung     

Epidemiological investigations of bovine Chorioptes mange in Germany

Chorioptic mange in cattle has long been recognised as a common external parasitosis in livestock. In order to evaluate the economic importance of Chorioptes bovis-mange, the seasonal prevalence in several types of husbandry in the states of Germany, location of clinical skin symptoms, procedure of diagnosis, influence on milk or meat production, and treatment especially in dairy farming, 1190 German large animal practicioners have been asked by questionnaires from which 367 responded. This paper gives an update on important epidemiological investigations on bovine chorioptic mange due to this inquiry. Since more than one third of the questioned veterinarians see tail mange often, it is of high importance for farm cattle. Chorioptes mange mainly occurs in dairy cattle stocks, and has especially negative effects on milk production and meat productivity. For treatment of this external parasitosis mainly macrocyclic lactons and pyrethroids are used.     

Genotype effects of milk protein polymorphisms on milk production in East Friesian dairy sheep

The frequencies of milk protein variants alphas1-casein, alphas2-casein, beta-casein and beta-lactoglobulin were determined in 182 milk sheep from 7 flocks in Lower Saxony and Saxony. The genotype effects of these polymorphic milk protein variants on milk performance traits were estimated for 173 ewes using a test day model with fixed regression.The model included the fixed effects of colour variant of the breed, region, lambing season, lambing year, lactation number and number of lambs born. The herd and animal effect were treated as random and the days in milk as linear and non-linear covariates. The milk protein variants of alphas1-casein and beta-casein showed a significant relationship to protein content and the variants of beta-casein to milk fat content. Milk fat yield was significantly associated with the milk protein variants of alphas2-casein, whereas the other milk performance traits were not significantly correlated.     

Cassini dust measurements at Enceladus and implications for the origin of the E ring

During Cassini's close flyby of Enceladus on 14 July 2005, the High Rate Detector of the Cosmic Dust Analyzer registered micron-sized dust particles enveloping this satellite. The dust impact rate peaked about 1 minute before the closest approach of the spacecraft to the moon. This asymmetric signature is consistent with a locally enhanced dust production in the south polar region of Enceladus. Other Cassini experiments revealed evidence for geophysical activities near Enceladus' south pole: a high surface temperature and a release of water gas. Production or release of dust particles related to these processes may provide the dominant source of Saturn's E ring.     

Metabolite profiling of wheat grains (Triticum aestivum L.) from organic and conventional agriculture

In some European community countries up to 8% of the agricultural area is managed organically. The aim was to obtain a metabolite profile for wheat (Triticum aestivum L.) grains grown under comparable organic and conventional conditions. These conditions cannot be found in plant material originating from different farms or from products purchased in supermarkets. Wheat grains from a long-term biodynamic, bioorganic, and conventional farming system from the harvest 2003 from Switzerland were analyzed. The presented data show that using a high throughput GC-MS technique, it was possible to determine relative levels of a set of 52 different metabolites including amino acids, organic acids, sugars, sugar alcohols, sugar phosphates, and nucleotides from wheat grains. Within the metabolites from all field trials, there was at the most a 50% reduction comparing highest and lowest mean values. The statistical analysis of the data shows that the metabolite status of the wheat grain from organic and mineralic farming did not differ in concentrations of 44 metabolites. This result indicates no impact or a small impact of the different farming systems. In consequence, we did not detect extreme differences in metabolite composition and quality of wheat grains.