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41.
Gerald Jandl Christel Baum Peter Leinweber 《Archives of Agronomy and Soil Science》2013,59(1):119-125
Although lipids are involved in diverse soil processes and affect various soil properties, the contribution of rhizodeposits and the root zone to lipid concentrations and distributions in soils is unknown. For the first time, we determined the concentrations of alkanoic acids, n-alkanes and n-alkenes in root zone leachates and roots of maize and potato using gas chromatography/mass spectrometry (GC/MS). In total, the lipid concentrations of leachates were 100 μg g?1 (maize) and 17 μg g?1 (potato). The saturated n-alkanoic acids, ranging from n-C14 to n-C28 and having the maximum at n-C22 (maize) and at n-C16 (potato), were more abundant than the other compounds. Maize leachates had more alkanes (20 μg g?1) than potato leachates (3.1 μg g?1), but the members of the homologues were nearly the same. Comparison of these distributions with data for roots, microorganisms and soil indicated that the lipids in the leachates from the root zone mainly originated from abrasion of fine roots, rhizodeposits and rhizosphere microorganisms. 相似文献
42.
Jens Kruse Marion Abraham Wulf Amelung Christel Baum Roland Bol Oliver Kühn Hans Lewandowski Jörg Niederberger Yvonne Oelmann Christopher Rüger Jakob Santner Meike Siebers Nina Siebers Marie Spohn Johan Vestergren Angela Vogts Peter Leinweber 《植物养料与土壤学杂志》2015,178(1):43-88
Phosphorus (P) is an indispensable element for all life on Earth and, during the past decade, concerns about the future of its global supply have stimulated much research on soil P and method development. This review provides an overview of advanced state‐of‐the‐art methods currently used in soil P research. These involve bulk and spatially resolved spectroscopic and spectrometric P speciation methods (1 and 2D NMR, IR, Raman, Q‐TOF MS/MS, high resolution‐MS, NanoSIMS, XRF, XPS, (µ)XAS) as well as methods for assessing soil P reactions (sorption isotherms, quantum‐chemical modeling, microbial biomass P, enzymes activity, DGT, 33P isotopic exchange, 18O isotope ratios). Required experimental set‐ups and the potentials and limitations of individual methods present a guide for the selection of most suitable methods or combinations. 相似文献
43.
44.
A closely spaced (1 x 1 m) cottonwood (Populus deltoides Bartr.) plantation was established to evaluate the effects of nutrient availability on fine root dynamics. Slow-release fertilizer (17:6:12 N,P,K plus micronutrients) was applied to 225-m(2) plots at 0, 50, 100 and 200 kg N ha(-1), and plots were monitored for two growing seasons. Fine root production, mortality, live root standing crop and life span were analyzed based on monthly minirhizotron observations. Fine root biomass was measured in soil cores. Fine root dynamics were controlled more by temporal, depth and root diameter factors than by fertilization. Cumulative fine root production and mortality showed strong seasonal patterns; production was greatest in the middle of the growing season and mortality was greatest after the growing season. Small diameter roots at shallow soil depths cycled more rapidly than larger or deeper roots. The strongest treatment effects were found in the most rapidly cycling roots. The standing crop of live roots increased with fertilizer treatment according to both minirhizotron and soil coring methods. However, production and mortality had unique treatment response patterns. Although cumulative mortality decreased in response to increased fertilization, cumulative production was intermediate at 0 kg N ha(-1), lowest with 50 kg N ha (-1), and highest with 200 kg N ha(-1). Aboveground growth responded positively to fertilization up to an application rate of 50 kg N ha(-1), but no further increases in growth were observed despite a threefold increase in application rate. Median fine root life span varied from 307 to over 700 days and increased with depth, diameter and nutrient availability. 相似文献
45.
46.
Christel?FaesEmail author Helena?Geys Marc?Aerts Geert?Molenberghs Paul?J.?Catalano 《Journal of Agricultural, Biological & Environmental Statistics》2004,9(4):515-530
Measurements of both continuous and categorical outcomes appear in many statistical problems. One such example is the study
of teratology and developmental toxicity, where both the probability that a live fetus is malformed (ordinal) or of low birth
weight (continuous) are important measures in the context of teratogenicity. Although multivariate methods of the analysis
of continuous outcomes are well understood, methods for jointly continuous and discrete outcomes are less familiar. We propose
a likelihood-based method that is an extension of the Plackett-Dale approach. Specification of the full likelihood will be
avoided using pseudo-likelihood methodology. The estimation of safe dose levels as part of quantitative risk assessment will
be illustrated based on a developmental toxicity experiment of diethylene glycol dimethyl ether in mice. 相似文献
47.
Variability of soil parameters in a uniformity trial on a Luvisol evaluated by means of spatial statistics The relationships between soil parameters and indicators of soil genesis were investigated in a uniformity trial on Luvisol by means of classical and spatial statistics. The following properties were investigated in the topsoil (0–30 cm) and subsoil (31–40 cm): content of total carbon (Ct), content of clay plus fine silt (FAT), concentrations of available potassium (K) and phosphorus (P), and pH values. The depth loamy Bt horizon and microrelief were considered as indicators of soil genesis. Smoothing of the raw data by means of block kriging eliminated the small scale variability of all parameters. In this way, the rank correlation coefficients between soil parameters increased by factor 2 and were to 0.52 for Ct–FAT; 0.69 for Ct–K, and 0.55 for Ct–P in the top soil. The maps for smoothed data allowed a much better visual analysis of spatial distribution of investigated properties compared to the raw data. The significant correlations as well as the similarity of maps and variograms suggested that the spatial variability of FAT, Ct, K, and P in the top soil was determined by the same factors. The depth of the loamy Bt horizon and the relief were the most important factors defining the distribution of the investigated soil parameters. The rank correlation coefficients of the smoothed and detrended relief with the soil parameters amount to –0.63, –0.77, –0.71, and –0.57 for FAT, Ct, K, and P, respectively. 相似文献
48.
The species‐specific microbial root and rhizosphere colonization contributes essentially to the plant nutrient supply. The species number and colonization densities of cultivable saprotrophic microfungi and the activities of nutrient‐releasing soil enzymes (protease, acid and alkaline phosphatase, arylsulfatase) were investigated in the rhizosphere of one low mycorrhizal (Salix viminalis) and one higher mycorrhizal (S. × dasyclados) willow clone at a Eutric Cambisol in N Germany. After soil washing, in total 32 and 28 saprotrophic microfungal species were isolated and identified microscopically from the rhizosphere of S. viminalis and S. × dasyclados, respectively. The fungal species composition changed within the growing season but the species number was always lower under S. × dasyclados than under S. viminalis. Under both willow clones, the fungal colonization density was largest in spring, and the species number was largest in autumn. Acid‐phosphatase activity (p < 0.001) and protease activity (p < 0.003) were significantly affected by the Salix clone, whereas arylsulfatase and alkaline‐phosphatase activities did not show clone‐specific differences. All enzyme activities reached their maxima in the summer sampling. Rhizosphere colonization with Acremonium butyri, Cladosporium herbarum, and Penicillium janthinellum contributed significantly to explain the activities of acid phosphatase. Rhizosphere colonization with Cylindrocarpon destructans, Penicillium spinulosum, Plectosphaerella cucumerina, and Trichoderma polysporum contributed significantly to explain the arylsulfatase activities. Effects of the saprotrophic fungal colonization densities on the protease activities in the rhizosphere were low. Acid‐ and alkaline‐phosphatase and arylsulfatase activities in the rhizosphere soil were stronger affected by the composition of the saprotrophic fungal communities than by the Salix clone itself. In conclusion, the colonization density of some saprotrophic microfungi in the rhizosphere contributed to explain shifts in soil‐enzyme activities of the P and S cycles under different willow clones. 相似文献
49.
Effect of wheeling on stress distribution and changes in the macro- and microstructure of a cambic phaeozem derived from loess The determination of stress induced changes in the poresystem due to repeated wheeling of a cambic phaeozem derived from loess as well as in the aggregate size distribution, arrangement, and stage are reported. It could be shown, that repeated wheeling always results in a further stress distribution to deeper depths and that the vertical stresses dominate with repeated wheeling. Furthermore the octahedral shear stresses and mean normal stresses exceed the maximum strength defined by the Mohr Coulomb failure line and define a further soil deformation. The process of aggregate deterioration can be verified by radiographs from which not only the changes in bulk density on a mesoscale can be derived but from which also the crack patterns can be defined for the different stages of structure deterioration. Under the well known assumption that pore water pressure is increased due to wheeling, soil compaction and consecutive soil homogenisation by kneading can be differentiated. The consequences for ecological parameters will be discussed. 相似文献
50.
Characterization of soil structure by X-ray analysis Frequently the use of morphological observation of soil structure to assess effects of tillage operations has been restricted by the extreme slowness of sample preparation. A method for rapid analysis of structure with the help of X-ray radiographs is described. The method is based on differences in attenuation of transmitted X-rays by soil pores and the adjoining soil mass. After digitizing X-ray pictures of unimpregnated soil cores using a video scanner and digitizer we found a close relationship between the average bulk density of soil within a core and the mean greylevel value of the digital image when sample thickness, origin and organic matter content of soil material, energy of radiation and sensitivness of X-ray film are the same. Application of a universal image processing system (DIAS) for the quantification of image parameters by procedures of binarization, skeletonization and direction coding demonstrated that radiographs are useful for analyzing spatial distribution, shape and orientation of soil structure elements. Results are illustrated by examples of soil tillage experiments. 相似文献