Pflanzliche Insektizide IV*. Die insektizide Wirkung des ätherischen Öls aus dem Balsamkraut,Chrysanthemum balsamita L

The essential oil ofChrysanthemum balsamita L. revealed insecticidal properties when tested againstM. dirhodum aphids. The insecticidal activity was attributed to the presence of pyrethrine I in the oil. By an appropriate testing procedure, the dependence of the activity upon the time of harvesting of the plants was determined. Furthermore, the insecticidal effect of the oil was compared with that of a commercially available pyrethrum preparation.     

Effects of selection felling and gap felling on forest arthropod communities: a case study in a spruce-beech stand of southern Bavaria

The effects of selection felling and gap felling on arthropod communities were studied over 3 years in a spruce-beech stand in southern Bavaria, Germany. The arthropods were sampled in three strata, using pitfall traps on the forest floor as well as flight-interception traps near the forest floor and in the tree crowns. Coleoptera, Araneae, Opiliones, Heteroptera, Isopoda, Diplopoda and Neuropterida were determined to species level and assigned to ecological guilds. In general, the effects of both treatments on arthropod communities were small. An increase of eurytopic species and species of open woodland as well as of indwellers of deadwood was observed, mainly in the first year after felling. However, forest species dominated the communities in all plots, strata and years. In contrast to selection fellings, gap fellings might favour potential pest species. Nevertheless, in the studied managed spruce-dominated forest site out of the natural growth range of spruce, negative ecological effects such as the repression of forest arthropod species are not expected by small scale fellings.     

A model ensemble approach to determine the humus building efficiency of organic amendments in incubation experiments

Organic amendments are important to sustain soil organic matter (SOM) and soil functions in agricultural soils. Information about the contribution of organic amendments to SOM can be derived from incubation experiments. In this study, data from 72 incubated organic amendments including plant residues, digestates and manure were analysed. The incubation data was compiled from three experimental setups with varying incubation times, soils and incubation temperatures, in which CO₂ release was measured continuously. The analysis of the incubation data was performed with an approach relying on conceptual parts of C-TOOL, CCB, Century, ICBM, RothC and Yasso which are all well-approved first-order carbon models that differ in structure and abstraction level. All models are an approximation of reality, whereby each model differs in understanding of the processes involved in soil carbon dynamics. To accumulate the advantages from each model a model ensemble was performed for each substrate. With the ability of each carbon model to compute the distribution of carbon into specific SOM pools a new approach for evaluating organic amendments in terms of humus building efficiency is presented that, depends on the weighted model fit of each ensemble member. Depending on the organic substrate added to the soil, the time course of CO₂ release in the incubation studies was predicted with different accuracy by the individual model concepts. Averaging the output of the individual models leads to more robust prediction of SOM dynamics. The E_HUM value is easy to interpret and the results are in accordance with the literature.     

Effects of decreasing soil water content on seminal lateral roots of young maize plants

Soil micropores that contain water at or below field capacity cannot be invaded by seminal or first‐order lateral roots of maize plants because their root diameters are larger than 10 μm. Hence, at soil‐water levels below field capacity plant roots must establish a new pore system by displacement of soil particles in order to access soil water. We investigated how decreasing soil water content (SWC) influences growth and morphology of the root system of young maize plants. Plants were grown in rhizotrons 40 cm wide, 50 cm high, and approximately 0.7 cm thick. Five SWC treatments were established by addition of increasing amounts of water to soil and thorough mixing before filling the rhizotrons. No water was added to treatments 1–4 throughout the experiment. Treatment 5 was watered frequently throughout the experiment to serve as a control. Seminal‐root length and SWC in soil layers 0–10, 10–20, 20–30, 30–40, and 40–50 cm were measured at intervals of 2–3 d on scanner images by image analysis. At 15 d after planting, for treatments 1–4 shoot dry weight and total root length were directly related to the amount of water added to the soil, and for treatments 4 and 5, total root length and shoot dry weights were similar. Length of seminal roots visible at the transparent surface of the rhizotron for all treatments was highest in the uppermost soil layer and decreased with distance from the soil surface. For all layers, seminal‐root elongation rate was at maximum above a SWC of 0.17 cm³ cm^–3, corresponding to a matric potential of –30 kPa. With decreasing SWC, elongation rate decreased, and 20% of maximum seminal root elongation rate was observed below SWC of 0.05 cm³ cm^–3. After destructive harvest for treatment 1–4, number of (root‐) tips per unit length of seminal root was found uninfluenced over the range of initial SWC from 0.10 to 0.26 cm³ cm^–3. However, initial SWC close to the permanent wilting point strongly increased number of tips. Average root length of first‐order lateral (FOL) roots increased as initial SWC increased, and the highest length was found for the frequently watered treatment 5. The results of the study suggest that the ability to produce new FOL roots across a wide range of SWC may give maize an adaptive advantage, because FOL root growth can rapidly adapt to changing soil moisture conditions.     

A comparison of transpiration rates of young rape plants grown on salinized soils of different texture

During periods of water depletion the water supply of plants from saline soils is reduced due to the simultaneous decrease of the soil osmotic and the soil matric water potential. Common models on the water uptake from saline soils assume a similar depressing effect of osmotic and matric water potentials on the water uptake by plants. As plants differ in their ability to overcome salt stress and soils differ in their water retention curves there is some doubt for the general validity of this assumption. The paper presents results of an experiment with rape grown in a sandy and a silty soil at three salinity levels. The transpiration rate of the plants was determined during a period of 34 hours and related to the total water potential of the two soils. In case of the silty soil, the transpiration was related to the total soil water potential at all salinity levels. In the sandy soil, however, the transpiration was much more affected by decreasing soil matric potential than by equivalent decreases of the soil osmotic potential. The results show that the effect of both potentials on the water supply of plants is not the same and has to be treated separately.     

Der Einfluß von Bodenart,Durchlüftung des Bodens,N-Ernährung und Rhizosphärenflora auf die Morphologie des seminalen Wurzelsystems von Mais

Influence of soil type, soil aeration, nitrogen supply and rhizosphere flora on the morphology of the seminal root system of maize The influence of the soil type (quartz sand – humous loamy sandy soil), soil aeration, nitrogen supply and rhizosphere flora on the morphology of the seminal root system of maize plants grown in pot culture was investigated. The morphological parameters of number, length, diameter and root hair formation (both length and density) of the main and the lateral roots were determined in addition to the total root length and number and the lateral root density. 1. The biomass production of the shoot and root system was nearly identical in both soils. The total root length growth, however, was enhanced in the sandy soil due to the stimulated formation of first order lateral roots. This increase was correlated with a decrease in the mean diameter and root hair length of the main and lateral roots. 2. A decreased O₂-supply to the soil resulted in a drastic reduction of root biomass, which was correlated, however, with a (relative) increase in total root length (due to the stimulation of the length growth of the first order lateral roots). The root hair length, on the other hand, was reduced under O₂-deficiency. 3. Reduced N-supply resulted in a decrease of the shoot/root-ratio with both substrates which could be ascribed to the enhanced formation and length of the first order lateral roots. 4. The presence of soil microorganisms in quartz sand culture resulted in a reduction of shoot biomass. In comparison with the sterile control culture the total length of the main roots was retarded, the main and lateral roots were more slender and root hair formation was reduced. 5. The experimental results show that the lateral root system demonstrates a significantly greater plasticity than does the main root system.     

Impacts of population growth, economic development, and technical change on global food production and consumption

Over the next decades mankind will demand more food from fewer land and water resources. This study quantifies the food production impacts of four alternative development scenarios from the Millennium Ecosystem Assessment and the Special Report on Emission Scenarios. Partially and jointly considered are land and water supply impacts from population growth, and technical change, as well as forest and agricultural commodity demand shifts from population growth and economic development. The income impacts on food demand are computed with dynamic elasticities. Simulations with a global, partial equilibrium model of the agricultural and forest sectors show that per capita food levels increase in all examined development scenarios with minor impacts on food prices. Global agricultural land increases by up to 14% between 2010 and 2030. Deforestation restrictions strongly impact the price of land and water resources but have little consequences for the global level of food production and food prices. While projected income changes have the highest partial impact on per capita food consumption levels, population growth leads to the highest increase in total food production. The impact of technical change is amplified or mitigated by adaptations of land management intensities.     

First-principles theory for the H + CH4 --> H2 + CH3 reaction

A full-dimensional quantum dynamics simulation of a hydrogen atom reacting with methane on an accurate ab initio potential energy surface is reported. Based on first-principles theory, thermal rate constants are predicted with an accuracy comparable to (or even exceeding) experimental precision. The theoretical prediction is within the range of the significantly varied experimental rate constants reported by different groups. This level of accuracy has previously been achieved only for smaller, three-or four-atom reactive systems. Comparison with classical transition state theory confirms the importance of quantum mechanical tunneling for the rate constant below 400 kelvin.