Persisting soil drought reduces leaf specific conductivity in Scots pine (Pinus sylvestris) and pubescent oak (Quercus pubescens)     

Sterck FJ  Zweifel R  Sass-Klaassen U  Chowdhury Q 《Tree physiology》2008,28(4):529-536

Leaf specific conductivity (LSC; the ratio of stem conductivity (K(P)) to leaf area (A(L))), a measure of the hydraulic capacity of the stem to supply leaves with water, varies with soil water content. Empirical evidence for LSC responses to drought is ambiguous, because previously published results were subject to many confounding factors. We tested how LSC of similar-sized trees of the same population, under similar climatic conditions, responds to persistently wet or dry soil. Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) trees were compared between a dry site and a wet site in the Valais, an inner alpine valley in Switzerland. Soil water strongly influenced A(L) and K(P) and the plant components affecting K(P), such as conduit radius, conduit density and functional sapwood area. Trees at the dry site had lower LSC than trees with the same stem diameter at the wet site. Low LSC in trees at the dry site was associated with a smaller functional sapwood area and narrower conduits, resulting in a stronger reduction in K(P) than in A(L). These observations support the hypothesis that trees maintain a homeostatic water pressure gradient. An alternative hypothesis is that relatively high investments in leaves compared with sapwood contribute to carbon gain over an entire season by enabling rapid whole-plant photosynthesis during periods of high water availability (e.g., in spring, after rain events and during morning hours when leaf-to-air vapor pressure deficit is small). Dynamic data and a hydraulic plant growth model are needed to test how investments in leaves versus sapwood and roots contribute to transpiration and to maximizing carbon gain throughout entire growth seasons.  相似文献   

Can goats be used as sentinels for tick-borne encephalitis (TBE) in nonendemic areas? Experimental studies and epizootiological observations     

Klaus C  Hoffmann B  Moog U  Schau U  Beer M  Süss J 《Berliner und Münchener tier?rztliche Wochenschrift》2010,123(11-12):441-445

A goat flock grazing year-round on a meadow in a "TBE non-risk area" in Thuringia, Germany, with a history of only isolated human TBE cases was examined repeatedly for TBE virus-(TBEV)-specific antibodies and TBEV RNA between October 2008 and December 2009. Surprisingly, TBEV specific antibodies were detected in one goat, which had never left this area. To compare the results of a natural contact to TBEV with a defined contact to TBEV, two goats were immunized experimentally. Both animals developed TBEV-specific antibodies, one goat however in a delayed and reduced manner. In addition, 177 ticks were collected from the meadow in May and June 2009, and were examined by real-time RT-PCR. However, noTBEV RNA could be detected. The results suggest that goats can be used as TBEV sentinels in defined areas. To verify this observation further investigations with a large number of animals are recommended.  相似文献   

Microbial activity and community structure in degraded soils on the Loess Plateau of China     

Ute Hamer  Franz Makeschin  Shaoshan An  Fenli Zheng 《植物养料与土壤学杂志》2009,172(1):118-126

Soil erosion is the main process leading to soil degradation on the Loess Plateau of China. The effects of soil‐erosion intensity (sheet, rill, and gully erosion) and different land use (140 y–old secondary forest site, 16 y–old bare site, 6 y–old succession site, and 43 y–old arable site) on gross and net N mineralization, soil organic‐carbon (SOC) turnover, the size and structure of the soil microbial community (phospholipid fatty acid analysis) were assessed. Erosion intensity in the bare plot increased from top slope (sheet erosion) to down slope (gully erosion). The more severe the soil erosion the stronger was the decline of SOC, total N, and microbial biomass (MB). The MBC/SOC ratio decreased whereas the metabolic quotient (qCO₂) increased. Differences in nutrient turnover in the different erosion zones of the bare plot were not significant. The microbial community changed towards less Gram negative bacteria and relative more fungi in the gully‐erosion zone. In forest soils, qCO₂ and the MBC/SOC ratio demonstrate a higher substrate‐use efficiency of the microbial biomass than in bare soils. Gross N mineralization and gross NH consumption clearly indicated a higher microbial activity in forest than in bare soils. Arable land use shifted the soil microbial community towards a higher relative abundance of fungi and a lower one of actinomycetes. During 6 y of natural succession on former bare plots, soil nutrient content and turnover as well as microbial biomass and structure developed towards forest conditions.  相似文献   

The effect of soil texture and soil drainage on emissions of nitric oxide and nitrous oxide   总被引：7，自引：0，他引：7  

U. Skiba  B Ball 《Soil Use and Management》2002,18(1):56-60

Abstract. Agricultural soils are important sources of the tropospheric ozone precursor NO and the greenhouse gas N₂O. Emissions are controlled primarily by parameters that vary the soil mineral N supply, temperature and soil aeration. In this field experiment, the importance of soil physical properties on emissions of NO and N₂O are identified. Fluxes were measured from 13 soils which belonged to 11 different soil series, ranging from poorly drained silty clay loams to freely drained sandy loams. All soils were under the same soil management regime and crop type (winter barley) and in the same maritime climate zone. Despite this, emissions of NO and N₂O ranged over two orders of magnitude on all three measurement occasions, in spring before and after fertilizer application, and in autumn after harvest. NO emissions ranged from 0.3 to 215 μg NO-N m^–2 h^–1, with maximum emissions always from the most sandy, freely drained soil. Nitrous oxide emissions ranged from 0 to 193 μg N₂O-N m^–2 h^–1. Seasonal shifts in soil aeration caused maximum N₂O emissions to switch from freely drained sandy soils in spring to imperfectly drained soils with high clay contents in autumn. Although effects of soil type on emissions were not consistent, N₂O emission was best related to a combination of bulk density and clay content and the NO/N₂O ratio decreased logarithmically with increasing water filled pore space.  相似文献   

Priming effects in soil size fractions of a podzol Bs horizon after addition of fructose and alanine     

Heike Ohm  Ute Hamer  Bernd Marschner 《植物养料与土壤学杂志》2007,170(4):551-559

It is well known that the addition of easily available substrates to soils can affect microbial activity and thus the mineralization of soil organic carbon (SOC). Up to now, little is known about the processes leading to these priming effects and which fractions of organic matter (OM) are affected. The objectives of this study were to determine if SOC associated with isolated soil size fractions showed different susceptibility to priming effects, whether these pools are easily depleted, or whether the amount of substrate addition affects the extent of priming effects. In an incubation experiment, the effect of the uniformly ¹⁴C‐labeled substrates fructose and alanine on the mineralization of the SOC of a Bs horizon of a Haplic Podzol was investigated. The soil sample was fractionated into the three soil size fractions sand, silt, and clay by a mild sonication followed by sieving and sedimentation. Additionally, nonfractionated soil of the horizon was included in the experiment. Every soil sample received four substrate additions repeated at weekly intervals with 3.325 μg substrate‐C (mg SOC)^–1 and a final addition of 13.3 μg substrate‐C (mg SOC)^–1 after 4 weeks. The respiration was determined hourly and ¹⁴CO₂ was analyzed every 2, 4, and 7 d after the respective substrate addition. After 56 d, between 42% and 58% of the added substrates had been mineralized. Both substrates strongly increased the mineralization of the OM in all fractions (positive priming effects). The priming effects were always higher after the addition of the high substrate dose than during the first 4 weeks when four small doses were added. In general, the priming effects increased with decreasing particle size. Alanine generally caused higher priming effects than fructose in the soil size fractions (up to 280% vs. 231%, respectively). This indicates that alanine serves not only as an energy substrate but also as a N source and, thus, also promotes microbial growth. The strong priming effects in the silt and clay fraction (133% and 125% with fructose, 172% and 168% with alanine) showed, that not only the labile pool of OM is affected, but also a more stable pool characterized by higher ¹⁴C ages. We assume that the stability of the OM in these fractions is not only due to recalcitrance or to interactions with the minerals, but that it may also be caused by a substrate limitation of the degrading microorganisms.  相似文献   

Quantification of Wheat spindle streak mosaic virus and Soil borne cereal mosaic virus in resistance testing of field samples of triticale using real-time RT-PCR     

Ziegler  Angelika  Klingebeil  Karin  Papke  Viola  Kastirr  Ute 《植物病害和植物保护杂志》2014,121(4):149-155

Journal of Plant Diseases and Protection - Triticale, a cross between rye and wheat, is a crop important for animal feed and the production of biogas and ethanol. Soil-borne viruses found in wheat...  相似文献   

An improved method for measuring soil N2O fluxes using a quantum cascade laser with a dynamic chamber     

N. J. Cowan  D. Famulari  P. E. Levy  M. Anderson  M. J. Bell  R. M. Rees  D. S. Reay  U. M. Skiba 《European Journal of Soil Science》2014,65(5):643-652

A dynamic chamber method was developed to measure fluxes of N₂O from soils with greater accuracy than previously possible, through the use of a quantum cascade laser (QCL). The dynamic method was compared with the conventional static chamber method, where samples are analysed subsequently on a gas chromatograph. Results suggest that the dynamic method is capable of measuring soil N₂O fluxes with an uncertainty of typically less than 1–2 µg N₂O‐N m^?2 hour^?1 (0.24–0.48 g N₂O‐N ha^?1 day^?1), much less than the conventional static chamber method, because of the greater precision and temporal resolution of the QCL. The continuous record of N₂O and CO₂ concentration at 1 Hz during chamber closure provides an insight into the effects that enclosure time and the use of different regression methods may introduce when employed with static chamber systems similar in design. Results suggest that long enclosure times can contribute significantly to uncertainty in chamber flux measurements. Non‐linear models are less influenced by effects of long enclosure time, but even these do not always adequately describe the observed concentrations when enclosure time exceeds 10 minutes, especially with large fluxes.  相似文献   

DanTox—a novel joint research project using zebrafish (Danio rerio) to identify specific toxicity and molecular modes of action of sediment-bound pollutants     

Steffen Keiter  Sabrina Peddinghaus  Ute Feiler  Britta von der Goltz  Christoph Hafner  Nga Yu Ho  Sepand Rastegar  Jens C. Otte  Richard Ottermanns  Georg Reifferscheid  Uwe Strähle  Thomas Braunbeck  Monika Hammers-Wirtz  Henner Hollert 《Journal of Soils and Sediments》2010,10(4):714-717

Introduction

The European Water Framework Directive aims to achieve a good ecological and chemical status in surface water of European rivers by the year 2015. Since sediments and particulate matter act as secondary sources for pollutants, applied sediment toxicology is perceived to play a major role for obtaining new knowledge that can contribute to successful attainment of the goal. However, the existing bioassays for sediment toxicity analyses do not provide sufficient data concerning bioavailability of environmental pollutants. In this regard, there is an urgent need to combine sediment contact assays with gene expression analysis to investigate mechanism-specific sediment toxicity.

Purpose

The aim of the novel joint research project is to develop a eukaryotic test system, which can be used to investigate the ecotoxicological effects of contaminated sediments on gene expression level (DNA-array and RT-PCR). Current ecotoxicological research customarily involves a battery of bioassays to cover different toxicological endpoints (e.g., teratogenicity, genotoxicity, mutagenicity, Ah-receptor-mediated toxicity, neurotoxicity). In contrast, methods that detect alterations in gene expression offer deeper insight by elucidating how chemical exposure and/or environmental challenge affect multiple metabolic pathways leading to these particular kinds of toxic response. Gene expression profiles reflect the way cells and organisms adapt or respond to a changing environment.

Conclusion

The present project aspires to increase the fundamental molecular and physiological knowledge concerning the mode of action of environmental toxicants in zebrafish (Danio rerio). By working with partners from the academic and research institutions as well as from industry and waterway regulations, the success of this basic research-driven joint project in terms of development and implementation of novel sediment toxicity methods will be realized.  相似文献   

Comparative effect of low temperature on virulence and twitching motility of Ralstonia solanacearum strains present in Florida     

Bocsanczy AM  Achenbach UC  Mangravita-Novo A  Yuen JM  Norman DJ 《Phytopathology》2012,102(2):185-194

Ralstonia solanacearum causes bacterial wilt on a wide range of plant hosts. Most strains of R. solanacearum are nonpathogenic below 20°C; however, Race 3 Biovar 2 (R3B2) strains are classified as quarantine pathogens because of their ability to infect crops, cause disease, and survive in temperate climates. We have identified race 1 biovar 1 Phylotype IIB Sequevar 4 strains present in Florida which were able to infect and produce wilt symptoms on potato and tomato at 18°C. Moreover they infected tomato plants at rates similar to strains belonging to R3B2. We determined that strains naturally nonpathogenic at 18°C were able to multiply, move in planta, and cause partial wilt when inoculated directly into the stem, suggesting that low temperature affects virulence of strains differently at early stages of infection. Bacterial growth in vitro was delayed at low temperatures, however it was not attenuated. Twitching motility observed on growing colonies was attenuated in nonpathogenic strains at 18°C, while not affected in the cool virulent ones. Using pilQ as a marker to evaluate the relative expression of the twitching activity of R. solanacearum strains, we confirmed that cool virulent strains maintained a similar level of pilQ expression at both temperatures, while in nonpathogenic strains pilQ was downregulated at 18°C.  相似文献   

Quantitative assessment of hydrolase production and persistence in soil     

Giancarlo Renella  Ute Szukics  Loretta Landi  Paolo Nannipieri 《Biology and Fertility of Soils》2007,44(2):321-329

The aim of this work was to calculate indices of hydrolase production (Pr) and persistence (Pe) through simple arithmetical calculations. Changes in acid and alkaline phosphomonoesterase, phosphodiesterase, urease, protease, and β-glucosidase activities were monitored under controlled conditions in seven soils with a wide range of properties, in which microbial growth was stimulated by adding glucose and nitrogen. Glucose mineralization was monitored by CO₂–C evolution, and microbial growth was quantified by determining the soil adenosine triphosphate (ATP) content. Hydrolase Pr and Pe indices were numerically quantified by the following relationships: Pr = H / t _H and Pe = (r / H)Δt, respectively, where H indicates the peak value of each measured hydrolase activity, t _H is the time of the peak value, r indicates the residual activity value, and Δt is the time interval t _r − t _H, where t _r is the time of the residual activity value. Addition of glucose and N-stimulated soil respiration increased ATP content and stimulated the production of the measured hydrolase activities in all soils; the measured variable reached a maximum value and then decreased, returning to the value of the control soil. Apart from β-glucosidase activity, whose activity was not stimulated by glucose and N addition, the other measured hydrolase activities showed a trend that allowed us to calculate the Pr and Pe indices using the above-mentioned equations. Acid phosphomonoesterase and protease Pr values were significantly higher in soils under forest or set aside management; the alkaline phosphomonoesterase and phosphodiesterase Pr values were generally higher in the neutral and alkaline soils, and the urease Pr values showed no obvious relationships with soil pH or management. Concerning the persistence of enzyme activities, Pe values of the acid phosphomonoesterase activity were significantly higher in the acidic soils, and those of urease activity were higher in acidic soils and the Bordeaux neutral soil. No relationships were observed between Pe values of alkaline phosphomonoesterase, phosphodiesterase, or protease activities and soil pH or management. The different responses of hydrolases were discussed in relation to soil properties, microbial growth, and regulation at the enzyme molecular level.  相似文献