Forest fires: An example of self-organized critical behavior   总被引：1，自引：0，他引：1  

BD Malamud  G Morein  DL Turcotte 《Science (New York, N.Y.)》1998,281(5384):1840-1842

Despite the many complexities concerning their initiation and propagation, forest fires exhibit power-law frequency-area statistics over many orders of magnitude. A simple forest fire model, which is an example of self-organized criticality, exhibits similar behavior. One practical implication of this result is that the frequency-area distribution of small and medium fires can be used to quantify the risk of large fires, as is routinely done for earthquakes.  相似文献   

Compensation of horizontal temperature and salinity gradients in the ocean mixed layer   总被引：1，自引：0，他引：1  

DL Rudnick  R Ferrari 《Science (New York, N.Y.)》1999,283(5401):526-529

Establishment of the temperature-salinity relationship in the ocean has concerned oceanographers for decades because of its importance for understanding ocean circulation. High-resolution measurements in the ocean mixed layer are used to show that temperature and salinity gradients on horizontal scales of 20 meters to 10 kilometers tend to compensate in their effect on density. These observations support the notion of a horizontal mixing in the mixed layer that depends on density gradient.  相似文献   

Induced resistance: a tool for fungicide resistance management     

Felipe Ortega  Ulrike Steiner  Heinz W. Dehne 《Pest management science》1998,53(2):193-196

Induced resistance to the apple scab fungus Venturia inaequalis was demonstrated in greenhouse tests with 12-day-old seedlings of the apple cultivar Golden Delicious treated with methyl 2,6-dichloro-isonicotinate or 3,5-dichlorosalicylic acid prior to inoculation with the causal fungus. Studies of the dose-response of flusilazole on induced resistant plants revealed synergistic effects between both crop protection principles. Therefore, the use of such resistance-inducing compounds in the field might allow a reduction in the number of fungicide applications, and possibly a reduction in dose, thus resulting in improved efficacy of fungicides. There was also evidence that induced resistance could prove to be a valid strategy for the treatment of pathogen populations with reduced sensitivity to a given fungicide. © 1998 SCI  相似文献   

Kommentar zum Diskussionsbeitrag zur Ermittlung der effektiven Durchwurzelungstiefe für geschichtete Profile von T. Tenholtern und S. Seiffert     

Heinz Peter Schrey 《植物养料与土壤学杂志》1999,162(4):458-461

Tenholtern and Seiffert (this issue) improved the calculation of the effective rooting depth of laminated soils after Mueller (1197). The new procedure remains however a heigh weighting of subsoil, opposing extensive results of plant cultivation. The calculation after Schrey (1996) follows better the results from plant cultivation and should therefore be used if – with the exception of the textural composition – all factors of influence of rooting depth are sufficiently uniform. Instead of calculated root depths the following generalized values proved to be acceptable in water supply and distribution as well as in plant cultivation: 4 dm for grassland (meadow and pasture) 10 dm for arable land (without special cultures) 15 dm for forests and woodland. Viewing individual cultures the usable capacity should be calculated as sum curve in steps of one dm over the depth of profile and combined as static value to time‐dependent root growth and weather‐dependent water requirement of the culture.  相似文献   

Dissolved and colloidal phosphorus fluxes in forest ecosystems—an almost blind spot in ecosystem research          下载免费PDF全文

Roland Bol  Dorit Julich  Dominik Brödlin  Jan Siemens  Klaus Kaiser  Michaela Anna Dippold  Sandra Spielvogel  Thomas Zilla  Daniela Mewes  Friedhelm von Blanckenburg  Heike Puhlmann  Stefan Holzmann  Markus Weiler  Wulf Amelung  Friederike Lang  Yakov Kuzyakov  Karl‐Heinz Feger  Nina Gottselig  Erwin Klumpp  Anna Missong  Carola Winkelmann  David Uhlig  Jakob Sohrt  Klaus von Wilpert  Bei Wu  Frank Hagedorn 《植物养料与土壤学杂志》2016,179(4):425-438

Understanding and quantification of phosphorus (P) fluxes are key requirements for predictions of future forest ecosystems changes as well as for transferring lessons learned from natural ecosystems to croplands and plantations. This review summarizes and evaluates the recent knowledge on mechanisms, magnitude, and relevance by which dissolved and colloidal inorganic and organic P forms can be translocated within or exported from forest ecosystems. Attention is paid to hydrological pathways of P losses at the soil profile and landscape scales, and the subsequent influence of P on aquatic ecosystems. New (unpublished) data from the German Priority Program 1685 “Ecosystem Nutrition: Forest Strategies for limited Phosphorus Resources” were added to provide up‐to‐date flux‐based information. Nitrogen (N) additions increase the release of water‐transportable P forms. Most P found in percolates and pore waters belongs to the so‐called dissolved organic P (DOP) fractions, rich in orthophosphate‐monoesters and also containing some orthophosphate‐diesters. Total solution P concentrations range from ca. 1 to 400 µg P L^?1, with large variations among forest stands. Recent sophisticated analyses revealed that large portions of the DOP in forest stream water can comprise natural nanoparticles and fine colloids which under extreme conditions may account for 40–100% of the P losses. Their translocation within preferential flow passes may be rapid, mediated by storm events. The potential total P loss through leaching into subsoils and with streams was found to be less than 50 mg P m^?2 a^?1, suggesting effects on ecosystems at centennial to millennium scale. All current data are based on selected snapshots only. Quantitative measurements of P fluxes in temperate forest systems are nearly absent in the literature, probably due to main research focus on the C and N cycles. Therefore, we lack complete ecosystem‐based assessments of dissolved and colloidal P fluxes within and from temperate forest systems.  相似文献   

RNA/DNA ratio is an early responding,accurate performance parameter in growth experiments of noble crayfish Astacus astacus (L.)          下载免费PDF全文

Claudia Grimm  Kai Lehmann  Catriona Clemmesen  Heinz Brendelberger 《Aquaculture Research》2015,46(8):1937-1945

Recent intensification efforts of astacid culture considerably depend on the appropriate assessment of the animal's physiological condition both for research and application. We conducted a 4 weeks feeding experiment to assess temporal resolution and accuracy of different response parameters (RNA/DNA ratio, RNA per wet weight, carapace length, wet weight, specific growth rate). Juvenile noble crayfish were exposed to five feeding regimes that differed in feeding frequency and food availability. Continuous growth was detected in all feeding regimes with individual increase up to 90% (wet weight) and 17% (carapace length), respectively. Morphometric parameters allowed separation of three weight‐groups or two length‐groups. During the experimental period RNA/DNA ratios showed both decrease (?17%) and increase (+35%), with superior accuracy than morphometric parameters, separating four groups. Based on RNA/DNA ratios, different feeding regimes were detected earlier, with two groups separated already after 3 weeks. RNA/DNA ratio was clearly superior to RNA per unit wet weight, as the latter failed to detect any differences between groups. In conclusion, RNA/DNA ratio is a valuable tool in nutritional studies with freshwater crayfish if overall growth is the key variable of interest.  相似文献   

Tree girdling provides insight on the role of labile carbon in nitrogen partitioning between soil microorganisms and adult European beech     

Michael Dannenmann  Judy Simon  Rainer Gasche  Jutta Holst  Ingrid Kögel-Knabner  Helmut Mayer  Rodica Pena  Heinz Rennenberg 《Soil biology & biochemistry》2009,41(8):1622-1631

Nitrogen (N) cycling in terrestrial ecosystems is complex since it involves the closely interwoven processes of both N uptake by plants and microbial turnover of a variety of N metabolites. Major interactions between plants and microorganisms involve competition for the same N species, provision of plant nutrients by microorganisms and labile carbon (C) supply to microorganisms by plants via root exudation. Despite these close links between microbial N metabolism and plant N uptake, only a few studies have tried to overcome isolated views of plant N acquisition or microbial N fluxes. In this study we studied competitive patterns of N fluxes in a mountainous beech forest ecosystem between both plants and microorganisms by reducing rhizodeposition by tree girdling. Besides labile C and N pools in soil, we investigated total microbial biomass in soil, microbial N turnover (N mineralization, nitrification, denitrification, microbial immobilization) as well as microbial community structure using denitrifiers and mycorrhizal fungi as model organisms for important functional groups. Furthermore, plant uptake of organic and inorganic N and N metabolite profiles in roots were determined.Surprisingly plants preferred organic N over inorganic N and nitrate (NO₃⁻) over ammonium (NH₄⁺) in all treatments. Microbial N turnover and microbial biomass were in general negatively correlated to plant N acquisition and plant N pools, thus indicating strong competition for N between plants and free living microorganisms. The abundance of the dominant mycorrhizal fungi Cenococcum geophilum was negatively correlated to total soil microbial biomass but positively correlated to glutamine uptake by beech and amino acid concentration in fine roots indicating a significant role of this mycorrhizal fungus in the acquisition of organic N by beech. Tree girdling in general resulted in a decrease of dissolved organic carbon and total microbial biomass in soil while the abundance of C. geophilum remained unaffected, and N uptake by plants was increased. Overall, the girdling-induced decline of rhizodeposition altered the competitive balance of N partitioning in favour of beech and its most abundant mycorrhizal symbiont and at the expense of heterotrophic N turnover by free living microorganisms in soil. Similar to tree girdling, drought periods followed by intensive drying/rewetting events seemed to have favoured N acquisition by plants at the expense of free living microorganisms.  相似文献   

High HEV presence in four different wild boar populations in East and West Germany     

Cornelia Adlhoch  Alexander Wolf  Helga Meisel  Marco Kaiser  Heinz Ellerbrok  Georg Pauli 《Veterinary microbiology》2009,139(3-4):270-278

Swine Hepatitis E virus (HEV) can be transmitted from pigs to humans causing hepatitis. A high prevalence of HEV in wild boar populations is reported for several European countries, but actual data for Germany are missing. During the hunting season from October to December 2007 liver, bile and blood samples were collected from wild boars in four different German regions. The samples were tested for HEV RNA by quantitative PCR (qPCR) and anti-HEV IgG antibodies by two different ELISAs and a Line immunoassay. A seroprevalence of 29.9% using ELISA and 26.2% in the Line immunoassay was determined. The seroprevalence rate varied greatly within the analyzed regions. However, qPCR analysis revealed a higher prevalence of 68.2% positive animals with regional differences. Surprisingly, also adult wild sows and wild boars were highly HEV positive by qPCR. Compared to liver and serum samples, bile samples showed a higher rate of positive qPCR results. Sequencing and phylogenetic analysis of a 969 nt fragment within ORF 2 revealed that all isolates clustered within genotype 3 but differed in the subtype depending on the hunting spot. Isolates clustered within genotypes 3i, 3h, 3f and 3e. Within one population HEV isolates were closely related, but social groups of animals in close proximity might be infected with different subtypes. Two full-length genomes of subtypes 3i and 3e from two different geographic regions were generated. The wild boar is discussed as one of the main sources of human autochthonous infections in Germany.  相似文献   

Collaboration and distances between German immunological institutes – a trend analysis     

Frank Havemann  Michael Heinz  Hildrun Kretschmer 《Journal of Biomedical Discovery and Collaboration》2006,1(1):6

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Neospora caninum: Serological follow-up in dairy cows during pregnancy     

Häsler B  Hernandez JA  Reist M  Sager H  Steiner-Moret C  Staubli D  Stärk KD  Gottstein B 《Veterinary parasitology》2006,137(3-4):222-230

We conducted a longitudinal study to follow-up the anti-Neospora caninum serologic status in 30 initially seropositive and 83 initially seronegative cows during their pregnancy. Study cows were blood-sampled every other month during pregnancy until parturition. Blood serum samples were screened for anti-N. caninum antibodies by ELISA. Cows that seroconverted were re-tested by immunoblot as a confirmation test. Among 30 seropositive cows, 28 cows remained seropositive during the whole pregnancy, whereas 2 cows transiently tested negative at least once during pregnancy. Among 83 seronegative cows, 82 cows remained seronegative and 1 cow tested positive three times during the sixth, eighth and last month of pregnancy. As only 2 out of 30 seropositive animals and 1 out of 83 animals changed their serologic status during pregnancy, the study results indicate that there is only a minor temporal instability of anti-N. caninum antibody reactivity in adult cattle.  相似文献