Nodulation and N2 fixation of faba bean (Vicia faba L.) after soil amendment with crop residues

The effect of prior soil amendment with different N sources at 50 mg N (kg soil)^—1 on nodulation and N₂ fixation of faba bean (Vicia faba L. cv. Troy) using wheat (Triticum aestivum L. cv. Star) as reference crop was assessed in a pot experiment. Four treatments viz legume manure (LEGM) as clover shoots, cereal manure (CEREM) as barley straw, N fertilizer (FERT‐N) as Ca(NO₃)₂, and no‐manure control (NOMAN) were investigated consecutively at 45, 70, and 90 days after sowing (DAS). Faba bean nodulated profusely, with an increase on average from 629 nodules per pot at 45 DAS to nearly 2.3‐ and 3.3‐fold at 70 and 90 DAS, respectively. Low nodule numbers and nodule dry matter occurred under FERT‐N and CEREM, whereas high values were found for NOMAN and LEGM. Soil amendment affected percent N₂ fixation in relation to N source and plant age. Highest percent N₂ fixation (≥ 90 %) was found under the lowest N‐supplying amendments, no‐manure, and cereal manure, respectively. FERT‐N depressed N₂ fixation particularly at 45 DAS when N₂ fixation was reduced to as low as 23 %. The rise in N₂ fixation thereafter suggests that faba bean adjusted after depletion of mineral N in the soil. N₂ fixation was also decreased after cereal straw application, even though N concentration in faba bean plants was high. The results indicate that plant residues, both with high and low N concentration, applied to soil to raise its fertility may interfere with N₂ fixation of faba bean.     

Design and evaluation of nematode 18S rDNA primers for PCR and denaturing gradient gel electrophoresis (DGGE) of soil community DNA

Consensus nematode 18S ribosomal DNA primers were designed by aligning available 18S sequences and identifying a variable region flanked by highly conserved regions. These primers were then used to amplify nematode 18S rDNA from whole soil community DNA extracted from a range of European grassland types. Cloning of the PCR amplicons (778 bp) followed by restriction digest analysis (RFLP) resulted in the recovery of 34 unique nematode sequences from the four grasslands studied. Comparison of these data with the limited number of 18S rDNA nematode sequences currently held in on-line databases revealed that all of the sequences could be assigned to known nematode taxa albeit tentatively in some cases. Two of the sequences recovered from the site in the Netherlands (wet, hay-grassland) were recovered in a clade that included a sequence of the genus Trichodorus whilst other sequences from this site showed similarity with 18S rDNA sequences of the genus Prismatolaimus (five sequences), Xiphinema (one sequence) and Enoplus (one sequence). Of the remaining sequences, two showed some affinity with Mylonchulus (UK, upland peat), four with Steinernema (UK) and one sequence with Mesorhabditis (Hungary, east European Steppe). Three sequences from the Netherlands and one from Hungary were recovered in a clade that included a sequence of the genus Pratylenchoides whilst three further sequences from the Netherlands and two from Hungary were recovered in a clade encompassing the genus Globodera. Of the remaining nine sequences, two (NL6, NL62) formed a distinct lineage within the Adenophorea with 90% bootstrap recovery in a paraphyletic clade that included sequences of Prismatolaimus and Trichodorus. Seven sequences (three from the Netherlands, three from the UK and one from Greece) were left unassigned though the tree topology suggested some relationship (58% bootstrap recovery) with the genus Cephalobus. To assess whether primers used to amplify 18S rDNA might be used to fingerprint genetic diversity in nematode communities in soil, the environmental sequence data were used to design a second set of primers carrying a GC-clamp. These primers amplified a 469 bp fragment internal to the region flanked by the primer set used to derive the nematode trees and were used to amplify 18S rDNA for subsequent analysis using denaturing gradient gel electrophoresis (DGGE). DGGE analysis of six major European grassland types revealed considerable genetic diversity between sites. However, the relationships seen with the DGGE data were inconsistent with previous studies where the same soils had been characterized with respect to functional and morphological diversity. To confirm that this second set of primers was amplifying nematode sequences, selected bands on the DGGE gels were extracted, PCR amplified and sequenced. The final alignment was 337 bases. These analyses revealed the presence of sequence signatures from the genera Paratrichodorus, Plectus, Steinernema, Globodera, Cephalobus and Pratylenchoides.     

Structural and functional changes of neuronal and glial components of the feline enteric nervous system in cats with chronic inflammatory and non-inflammatory diseases of the gastrointestinal tract

Immunohistochemical examinations of the enteric nervous system (ENS) were performed on biopsies of healthy cats and compared to findings in cats suffering from inflammatory bowel disease or intestinal lymphoma. In lymphocytic–plasmacytic enterocolitis all affected samples had significant reductions in glial fibrillary acidic protein and vasoactive intestinal peptide (VIP) and mostly of neuron-specific enolase (NSE) possibly reflecting alterations in enteric glial cells and neurons. In cases with eosinophilic gastroenterocolitis significantly reduced phosphorylated neurofilament (PN) expression was present suggesting a disturbance in neuronal cytoskeleton, whereas cats with fibrosing enteropathy had reduced expression of NSE, non-phosphorylated neurofilaments (NPN), PN and VIP, possibly reflecting neuronal disturbances. In cases with intestinal lymphoma only the reduction in PN and the increase in NPN were obvious suggesting direct damage or interference of neoplastic cells with enteric neurons. In conclusion, structural and functional alterations of the ENS may contribute to clinically evident signs of vomiting and/or diarrhea.     

Physiologic evaluation of capture and anesthesia with medetomidine-zolazepam-tiletamine in brown bears (Ursus arctos)

Physiologic variables during anesthesia with medetomidine-zolazepam-tiletamine were evaluated in 52 free-ranging brown bears (Ursus arctos) darted from a helicopter and in six captive brown bears darted at a zoo. During anesthesia, rectal temperature, respiratory rate, heart rate, and pulse oximetry derived hemoglobin oxygen saturation were recorded. Arterial blood samples were collected and immediately analyzed for evaluation of pulmonary gas exchange, acid-base status, and selected hematologic and plasma variables. At the end of anesthesia, atipamezole was administered intramuscularly at five times the medetomidine dose. Capture-induced hyperthermia and lactic acidemia were documented in free-ranging bears. Hypoxemia during anesthesia was documented in both free-ranging and captive bears. In free-ranging bears, rectal temperature, heart rate, lactate, hematocrit, and hemoglobin decreased significantly during anesthesia, whereas partial pressure of arterial carbon dioxide, pH, potassium, and glucose increased. Yearlings had a significantly higher heart rate, pH, base excess, bicarbonate, and glucose, and had a significantly lower rectal temperature, sodium, hematocrit, and hemoglobin when compared with subadult and adult brown bears. In conclusion, alterations in pulmonary gas exchange and acid-base status in brown bears during anesthesia with medetomidine-zolazepam-tiletamine with the doses and capture methods used in this study were identified. Oxygen supplementation is recommended to counteract hypoxemia during anesthesia.     

Invertase activity limits grain yield of maize under salt stress

Salt stress reduces grain yield of maize (Zea mays L.) due to poor kernel setting but not due to decreased grain filling. In the present study, it was tested whether acid invertase activity is decreased in developing kernels of maize under salt stress, and if assimilate supply is limited. The relatively salt‐sensitive maize hybrid Pioneer 3906 was compared with the more salt‐resistant hybrid SR 12. Salt stress caused a significant decrease in grain yield which was due to a 50% decrease in kernel number. No source limitation was observed, as the sucrose concentrations in kernels were significantly increased under salt stress for both genotypes. In contrast, glucose and fructose concentrations in kernels were significantly decreased. Salt stress caused a significant inhibition of soluble acid invertase activity to 19% in hydroponics 5 d after pollination (5 DAP) and to 50% in the soil culture experiment (2 DAP). The decrease in enzyme activity was the same for both genotypes. In the soil experiment, the highest soluble acid invertase activity was found 2 DAP with a steep decline until 8 DAP in Pioneer 3906. It is concluded that a decrease in acid invertase activity is a key factor associated with limited kernel setting under salt stress but additional factors may be responsible for genotypic differences.     

Mineralization and carbon turnover in subarctic heath soil as affected by warming and additional litter

Arctic soil carbon (C) stocks are threatened by the rapidly advancing global warming. In addition to temperature, increasing amounts of leaf litter fall following from the expansion of deciduous shrubs and trees in northern ecosystems may alter biogeochemical cycling of C and nutrients. Our aim was to assess how factorial warming and litter addition in a long-term field experiment on a subarctic heath affect resource limitation of soil microbial communities (measured by thymidine and leucine incorporation techniques), net growing-season mineralization of nitrogen (N) and phosphorus (P), and carbon turnover (measured as changes in the pools during a growing-season-long field incubation of soil cores in situ). The mainly N limited bacterial communities had shifted slightly towards limitation by C and P in response to seven growing seasons of warming. This and the significantly increased bacterial growth rate under warming may partly explain the observed higher C loss from the warmed soil. This is furthermore consistent with the less dramatic increase in the contents of dissolved organic carbon (DOC) and dissolved organic N (DON) in the warmed soil than in the soil from ambient temperature during the field incubation. The added litter did not affect the carbon content, but it was a source of nutrients to the soil, and it also tended to increase bacterial growth rate and net mineralization of P. The inorganic N pool decreased during the field incubation of soil cores, especially in the separate warming and litter addition treatments, while gross mineralized N was immobilized in the biomass of microbes and plants transplanted into the incubates soil cores, but without any significant effect of the treatments. The effects of warming plus litter addition on bacterial growth rates and of warming on C and N transformations during field incubation suggest that microbial activity is an important control on the carbon balance of arctic soils under climate change.     

Occurrence of acidic groundwater in precambrian crystalline bedrock aquifers,Southwestern Sweden

The pH and alkalinity of groundwater from 7651 wells drilled in the Precambrian crystalline bedrock of southwestern Sweden has been evaluated. The wells are generally less than 100 m deep. Analytical results were collected from different laboratories and authorities in the region. In areas with thin soil cover or coarse-grained deposits overlying the bedrock, alkalinity is normally less than 100 mg HCO₃ L^?1. Below the marine limit, where clayey sediments predominate, alkalinity sometimes even exceeds 200 mg HCO₃ L^?1. When comparing pH and alkalinity of groundwaters from Quaternary deposits with bedrock groundwaters, the latter always have higher pH and alkalinity values. The most acidic bedrock groundwaters are found in small areas close to the city of Göteborg due to additional factors of high acid loadings, high groundwater discharge and thin soil layers. A study of data from 1949 to 1985 in the province of Värmland suggests that no regional acidification of importance is in progress. However, results from public water supplies support the hypothesis that the groundwaters which are most sensitive to acidification are those where discharge from wells in small bedrock aquifers induces rapid groundwater recharge of acidic surficial water.     

A simple and accurate method for determining wheat grain fructan content and average degree of polymerization

An improved method for the measurement of fructans in wheat grains is presented. A mild acid treatment is used for fructan hydrolysis, followed by analysis of the released glucose and fructose with high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Not only the amount of fructose set free from fructans but also the released glucose can be quantified accurately, allowing determination of the average degree of polymerization of fructans (DP(av)). Application of the mild acid treatment to different grain samples demonstrated that a correction should be made for the presence of sucrose and raffinose, but not for stachyose or higher raffinose oligosaccharides. The fructan content and DP(av) of spelt flour, wheat flour, and whole wheat flour were 0.6%, 1.2%, and 1.8% of the total weight and 4, 5, and 6, respectively. Validation experiments demonstrate that the proposed quantification method is accurate and repeatable and that also the DP(av) determination is precise.