How relevant is recalcitrance for the stabilization of organic matter in soils?

Traditionally, the selective preservation of certain recalcitrant organic compounds and the formation of recalcitrant humic substances have been regarded as an important mechanism for soil organic matter (SOM) stabilization. Based on a critical overview of available methods and on results from a cooperative research program, this paper evaluates how relevant recalcitrance is for the long‐term stabilization of SOM or its fractions. Methodologically, recalcitrance is difficult to assess, since the persistence of certain SOM fractions or specific compounds may also be caused by other stabilization mechanisms, such as physical protection or chemical interactions with mineral surfaces. If only free particulate SOM obtained from density fractionation is considered, it rarely reaches ages exceeding 50 y. Older light particles have often been identified as charred plant residues or as fossil C. The degradability of the readily bioavailable dissolved or water‐extractable OM fraction is often negatively correlated with its content in aromatic compounds, which therefore has been associated with recalcitrance. But in subsoils, dissolved organic matter aromaticity and biodegradability both are very low, indicating that other factors or compounds limit its degradation. Among the investigated specific compounds, lignin, lipids, and their derivatives have mean turnover times faster or similar as that of bulk SOM. Only a small fraction of the lignin inputs seems to persist in soils and is mainly found in the fine textural size fraction (<20 µm), indicating physico‐chemical stabilization. Compound‐specific analysis of ¹³C : ¹²C ratios of SOM pyrolysis products in soils with C3‐C4 crop changes revealed no compounds with mean residence times of > 40–50 y, unless fossil C was present in substantial amounts, as at a site exposed to lignite inputs in the past. Here, turnover of pyrolysis products seemed to be much longer, even for those attributed to carbohydrates or proteins. Apparently, fossil C from lignite coal is also utilized by soil organisms, which is further evidenced by low ¹⁴C concentrations in microbial phospholipid fatty acids from this site. Also, black C from charred plant materials was susceptible to microbial degradation in a short‐term (60 d) and a long‐term (2 y) incubation experiment. This degradation was enhanced, when glucose was supplied as an easily available microbial substrate. Similarly, SOM mineralization in many soils generally increased after addition of carbohydrates, amino acids, or simple organic acids, thus indicating that stability may also be caused by substrate limitations. It is concluded that the presented results do not provide much evidence that the selective preservation of recalcitrant primary biogenic compounds is a major SOM‐stabilization mechanism. Old SOM fractions with slow turnover rates were generally only found in association with soil minerals. The only not mineral‐associated SOM components that may be persistent in soils appear to be black and fossil C.     

Spatial econometric analysis of a field-scale site-specific nitrogen fertilizer experiment on wheat (Triticum aestuvum L.) yield and quality

Knowledge of site-specific response may help farmers to tailor their management decisions with the help of precision farming technologies. However, farmers often have only a vague idea of the economic potential for site-specific management of their fields, which is important for investment decisions on precision farming technologies. This study presents an on-farm experimental approach to identify the economic potential of site-specific fertilization strategies at low costs. A strip trial with winter wheat (Triticum aestivum, L.) was established with precision farming technologies. Twelve different nitrogen fertilizer rates split in two applications were applied to 30 plots over a total strip length of 1.5 km. Geo-referenced yield was recorded with the harvester. Furthermore, electrical conductivity of the soil was measured and grain quality was surveyed with hand selected samples. With the help of advanced spatial statistical methods, within-field site-specific response was modeled with sufficient accuracy at comparably low costs. Electrical conductivity of the soil, elevation above sea level, and derivates of a digital elevation model were used as covariates to identify a possible economic potential for site-specific fertilization. Yield and protein response was best predicted with spatially adjusted regression models with site-characteristics or their interaction with management variables. Protein content was essential for achieving best economic results. The economic potential for site-specific fertilization strategies for the analyzed field was below 2 €/ha. However, the approach to identify the potential may be transferred to other locations with greater potential for site-specific farming.     

Studies on contamination of beef with tissues of the central nervous system (CNS) as pertaining to slaughtering technology and human BSE-exposure risk

Contamination of beef by tissues of the central nervous system (CNS) due to slaughter technology causes some concern considering the potential health hazard by food borne exposure to the infectious agent of BSE. The present study was designed to quantify the extent of CNS contamination as pertaining to stunning and splitting technology. Of the 726 animals 48 contained a total of 58 emboli-like particles in lungs and/or right ventricles. The incidence of emboli-like particles was found to be slightly higher in animals slaughtered without pithing (5.9%) than in the animals slaughtered with pithing (4.1%). Of the 58 emboli-like particles only two were positive in the anti-NSE western immunoblotting (0.3% of the 726 animals). The immuno reaction of these NSE-positive particles was several orders of magnitude lower as obtained by pure brain material. The microscopical analysis of the two NSE-positive emboli-like particles for presence of CNS-like tissues was negative. Following splitting of carcasses by sawing with and without prior removing the spinal cord we found NSE-positive reactions in 32% and 17% of the samples, respectively. The immuno reaction, however, was predominantly comparable to standard material containing less than 0.5% CNS. Overall the results show that CNS contamination of bovine carcasses cannot be excluded by current slaughter technology. However, the additional human BSE-exposure risk can be judged to be at least minor when considering extent of contamination, dilution effects and BSE-testing.     

Outcrossing frequencies from multiple high erucic acid oilseed rape fields to a central receptor field

Genetically modified oilseed rape is currently grown on about 23 % of the global oilseed rape acreage. In order to separate transgenic and non-transgenic oilseed rape production and to ensure co-existence of different agricultural cultivation schemes, as is specified by the European legislation, confinement measures have to be defined. Pollen-mediated gene flow is the most important means by which transgenes are dispersed between fields. In contrast to the majority of the previous investigations the objective of this study was to assess the extent of gene flow in the case of multiple pollen-donor fields. A high erucic acid rape genotype was used as biochemical marker for the quantification of outcrossing into a low erucic acid oilseed rape variety. Outcrossing data were obtained from two experimental locations. As expected, multiple pollen sources in a fragmented landscape can result in high gene transfer frequencies, thus requiring larger isolation distances than a field design with a single pollen donor source. The results of the study are transferable to homozygous transgenic oilseed rape varieties.     

COMPARISON BETWEEN COMPUTED TOMOGRAPHY AND 99m TC‐ PERTECHNETATE SCINTIGRAPHY CHARACTERISTICS OF THE THYROID GLAND IN CATS WITH HYPERTHYROIDISM

Scintigraphy is currently the reference standard for diagnosing feline hyperthyroidism; however, computed tomography (CT) is more widely available in veterinary practice. The purposes of this prospective study were to describe the CT appearance of thyroid glands in cats with hyperthyroidism and compare CT findings with findings from ^99mTc–pertechnetate scintigraphy. Twenty‐five adult hyperthyroid cats were included. Plain CT images were acquired for each cat and the following characteristics recorded for each thyroid lobe: visibility, delineation, position, attenuation, shape, and subjective size. Scintigraphic images were also acquired and the following characteristics recorded: radiopharmaceutical uptake, delineation, ectopic foci, shape, and subjective size. In CT images, thyroid lobes were most commonly found between the second and fourth cervical vertebrae, dorsolateral to the trachea. Affected thyroid lobes (based on scintigraphy reference standard) were most commonly oval and moderately enlarged in CT images. A heterogeneous attenuation pattern (isoattenuating to adjacent soft tissues with hypo‐ and hyperattenuating foci) was most commonly found in affected thyroid lobes. A positive correlation (P < 0.01) was identified between CT and scintigraphy for left‐to‐right thyroid lobe size relationship and subjective size of the larger thyroid lobe. The CT estimated mass was significantly higher (median = 148.8; range = [0;357.6]) for the more active thyroid lobe compared to the less active thyroid lobe (median = 84.6; range = [0;312.3]); (W = 154; P < 0.01). Findings indicated that CT may not reliably differentiate unilateral vs. bilateral hyperthyroidism in cats; however, CT may be a reliable alternative test for correctly identifying the more active thyroid lobe.     

Extending the rapeseed genepool with resynthesized Brassica napus L. I: Genetic diversity

Resynthesized Brassica napus L. could be employed to increase the genetic variation in the narrow oilseed rape genepool and to establish a genetically distant genepool for hybrid breeding. One important criterion for selecting appropriate resynthesized lines is their genetic distance to adapted breeding material. In this study we estimated the genetic distances in a wide collection of 142 resynthesized lines and 57 winter and spring rapeseed cultivars from Europe, North America and Asia using RFLP marker data. The highest in-group genetic distance (0.36) was observed in 142 resynthesized lines compared to 0.21 in winter, 0.23 in summer, and 0.28 in Asian genotypes. The group of adapted breeding material clustered into three groups of winter-, spring-type, and Asian genotypes. Resynthesized lines did not form distinct subgroups in the cluster analysis, but large differences were revealed in the genetic distance of resynthesized lines to the adapted winter oilseed rape genepool. The highest distance to winter oilseed rape was found in resynthesized lines with parental lines from the Asian genepool as B. oleracea convar. botrytis var. alboglabra (Bail.) Sun or B. rapa ssp. chinensis (L.) Hanelt.     

Beziehungen zwischen Stengel- und Knollenzahl bei der Kartoffel in Abhängigkeit von wichtigen Einflußfaktoren. I. Der Einfluß der Pflanzgutvorbehandlung und der Sorte

Zusammenfassung Die Pflanzgutvorbehandlung beeinflu?te die Stengelzahl signifikant. Abgekeimtes Pflanzgut der Sorten ‘Adretta’ und ‘Mariella’ entwickelte weniger Stengel und Knollen pro Pflanze jedoch mehr Knollen pro Stengel als vorgekeimtes und keimgestimmtes Pflanzgut. Die st?rker negativen Korrelationen zwischen Stengelzahl pro Pflanze und Knollenzahl pro Stengel sowie die h?here Reduktionsrate der angelegten Knollen bei der Sorte ‘Adretta’ weisen auf Sortenunterschiede in der Sch?rfe der Konkurrenz zwischen den Stengeln und innerhalb der Knollenanlagen eines Stengels hin. Die Ernteknollenzahl wurde bei ‘Mariella’ wesentlich durch die Zahl der Knollenanlagen, bei ‘Adretta’ hingegen st?rker durch die Reduktionsrate bestimmt.

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Summary Three different seed treatments and two cultivars were studied over seven years of field experiments (Table 1). Differences were detected between the cultivars in all characteristics studied: numbers of stems, maximum number of tubers (tuber initials), the number of harvestable tubers (>3 cm) at maturity per plant and per stem, and tuber reduction (percentage of initiated tubers that did not develop). Apart from the number of harvestable tubers, there were also differences between seed treatments (Tables 2, 3 and 4). Chitted seed of ‘Mariella’ and sprouted seed of ‘Adretta’ gave the greatest number of tubers per plant (Tables 3 and 4). In both cases desprouting reduced the numbers of stems and tubers per plant but increased the number of harvestable tubers per stem. Chitted seed set the most tubers per plant and per stem but had the highest levels of tuber reduction (Table 4). Due to intra- and inter-stem competition in both cultivars the percentage tuber reduction is significantly correlated with the number of tuber initials (maximum tuber number, Table 5). Smaller numbers of tubers per stem (Table 3) and significantly negative correlations between the number of stems and the maximum and harvestable number of tubers per stem (Table 5) highlight the effect of strong inter-stem competition in ‘Adretta’. Moreover, in this cultivar intra-stem competition seems to play an important role too. The rate of tuber reduction was significantly higher than in ‘Mariella’ (Table 3), and the final number of tubers significantly depended on the percentage of tuber reduction during the period of tuber growth (r=0,57^*, Table 5). In contrast, the number of harvestable tubers per plant in ‘Mariella’ was significantly correlated with the maximum tuber number during the period of tuber set (r=0,61^*, Table 5).

     

Die Photosyntheserate während der Entwicklung der Kartoffelpflanze

Zusammenfassung W?hrend der Ontogenese wurde mit Hilfe von¹⁴CO₂ die Photosyntheserate von Blattscheiben der im mittleren bis oberen Stengel inserierten Bl?tter von Gew?chshaus-und Feldpflanzen bestimmt. Folgender Verlauf erwies sich als typisch: eine hohe Photosynthesarate w?hrend der Jugendentwicklung, ein Abfall w?hrend des Knollenansatzes, ein Maximum in der Speicherphase, dem ein starker Abfall infolge zunehmender Senescenz bei 60–70% des maximalen Knollenertrages folgt. Vergleichende Untersuchungen der Photosyntheserate an Genotypen unterschieldlicher Vegetationsl?nge sollten im Maximum zu Beginn der Blüte (Ende Juni bis Anfang Juli) erfolgen. Unter Schwachlicht gezogene Pflanzen wiesen einen atypischen Verlauf auf, die Photosyntheserate fiel mit zunehmender Alterung kontinuierlich ab.

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Summary The rate of photosynthesis in discs removed from leaves taken from the central to the upper stem zone was determined with the help of¹⁴CO₂. The following were the most important experimental conditions to establish a potential rate: plants were subjected to light saturation and high (0.06–0.4%) CO₂ concentration. Experimental plants were grown in pots of varying size in the glasshouse during the summer or with supplementary lighting during the winter. In addition, during one year, experiments were carried out on plants in the field. Samples were taken at close intervals during the development of the plants. With the exception of plants grown during the winter, the following typical trend in the rate of photosynthesis was observed: high values during the early stages of development, with a minimum at the time of tuber initiation and a maximum during the period of linear bulking of the tubers and, finally, a fall at the time when the crop reached 60–70% of the maximal yield (Figs. 3 and 4). In the case of single-stemmed plants, the minimum and maximum were sharply defined (Fig. 1A), whereas, in the case of multistemmed plants, the curves showed a greater degree of similarity (Figs. 2,3 and 4). The rate of photosynthesis shown by plants grown under low light intensities showed a steady fall with increasing age (Fig. 1B). Comparable experiments on the rate of photosynthesis of genotypes having a variation in the length of their period of vegetative growth, grown under field conditions, should be carried out during the period of maximal photosynthetic activity following the beginning of flowering towards the end of June until the beginning of July (Fig. 4).

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Résumé L'activité photosynthétique a été étudiée à l'aide du marquage au¹⁴CO₂ de rondelles de feuilles de la partie médiane à la partie supérieure de la tige. Les principales conditions expérimentales furent les suivantes: saturation de lumière et concentration élevée de CO₂ (0.06–0.4%) pour que les valeurs correspondent à un taux potentiel de photosynthèse. Les plantes d'essais ont été cultivées en pots de différents volumes, en serre en été et en saison hivernale avec une lumière d'appoint. D'autre part, un contr?le annuel a également été réalisé sur des plantes de plein champ. L'échantillonnage a été effectué à mesure pendant la période de croissance. A l'exception des plantes cultivées en hiver, une activité photosynthétique typique suivante a été observée: activité très élevée sur les plantes jeunes, un minimum lors de la formation des tubercules, le maximum est atteint pendant l'accroissement linéaire des tubercules, et une diminution lorsque 60–70% du rendement maximum est atteint (fig. 3 et 4). Pour les plantes à tige unique cultivées en pots, le minimum et le maximum se distinguaient nettement (fig. 1A); en revanche, chez les plantes à multiples tiges, l'évolution de la courbe était plus régulière (fig. 2, 3, 4). Pour les plantes obtenues par une faible luminosité, le taux de photosynthèse diminuait régulièrement avec leur vieillissement (fig. 1B). Les mesures comparatives de la photosynthèse des génotypes de différentes maturités au champ devraient être effectuées durant l'activité maximale, soit après début de floraison, fin juin jusqu'à début juillet (fig. 4).