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

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.     

Direct aqueous injection liquid chromatography/electrospray ionization-mass spectrometry/mass spectrometry analysis of water for atrazine, simazine, and their chlorotriazine metabolites

A method is reported for the determination of atrazine, simazine, and their respective dealkylated chlorotriazine metabolites in ground, surface, and finished drinking water. Water samples are diluted 1:4 in an injection vial prior to analysis using liquid chromatography/electrospray ionization-mass spectrometry/mass spectrometry (LC/ESI-MS/MS). The lower limit of method validation is 0.10 microg/L (ppb) for 2-chloro-4-(ethylamino)-6-isopropylamino)-s-triazine (atrazine, G-30027), 2-chloro-4, 6-(diethylamino)-s-triazine (simazine, G-27692), 2-amino-4-chloro-6-(isopropylamino)-s-triazine (deethylatrazine, DEA, or G-30033), 2-amino-4-chloro-6-(ethylamino)-s-triazine (deisopropylatrazine, DIA, or G-28279), and 2,4-diamino-6-chloro-s-triazine (didealkylatrazine, DDA, or G-28273). The overall mean procedural recoveries (and % relative standard deviations) for atrazine, simazine, DEA, DIA, and DDA are 98 (4.4), 102 (3.6), 99 (4.8), 103 (4.0), and 109% (4.8%), respectively, in finished drinking water; 108 (2.7), 104 (5.4), 113 (4.5), 111 (5.2), and 105% (5.3%), respectively, in groundwater; and 96 (6.9), 103 (4.2), 102 (4.4), 102 (5.2), and 102% (8.2%), respectively, in surface water. The method validation was conducted under U.S. EPA FIFRA Good Laboratory Practice Guidelines 40 CFR 160.     

Intensity of browsing on trees and shrubs under experimental variation of cattle stocking densities in southern Bolivia

Mountain forests are traditionally used for cattle grazing during the dry season in southern Bolivia. To evaluate browsing intensity and damage to young trees and shrubs, a forest grazing area was monitored for about 3 months in both 2006 and 2007. Three similar paddocks of about 3 ha each, consisting of grassland and forest in a ratio of about 1:3 were stocked with 0.9, 1.6 and 2.6 tropical livestock units per ha (equivalents of 250 kg of body weight), reflecting low, medium and high stocking densities. Six 5 m × 5 m plots were mapped out within each paddock in 2006. Three additional plots per paddock were added in 2007. Within plots, the individuals of 18 woody species were coded and evaluated weekly for intensity of browsing. Intensity was quantified using five-scale categories reflecting the proportions of plant tissue removed (0 = no browsing, 1 = 1–25%, 2 = 26–50%, 3 = 51–75% and 4 = 76–100%). Across all plant species, the average category of browsing intensity, as determined in the post-grazing evaluation, was affected (P < 0.001) by stocking density. Browsing intensity increased in an approximately linear manner from 1.58 to 2.18 and 2.77 with low, medium and high stocking density, respectively. There was no significant difference between years. Most woody species followed the same general response pattern to stocking density, although some species were only noticeably browsed at high stocking density while a few others were intensively browsed at all stocking densities. The onset of browsing on woody species was observed only after some weeks had passed, indicating that herbaceous plants were preferred as a forage resource. The proportion of fatally damaged individuals, as assessed about 8 months after grazing in 2006, were 10.6%, 8.6% and 11.4% for low, medium and high stocking density, respectively. The percentage of completely browsed individuals increased with stocking density, but 80% of those plant individuals recovered following a resting period of 8 months. However, although most woody species recovered from browsing and fatal damage was infrequent, long-term changes in woody plant species composition and structure caused by grazing cannot be excluded. High stocking density in particular may reduce the vigour of heavily browsed species.     

Glycerophospholipid and triacylglycerol distribution in corn kernels (Zea mays L.)

The distribution of various molecular species of triacylglycerols (TAGs) and phospholipids among three corn kernel parts was determined by LC/ESI-MS. A comparison between three corn kernel parts demonstrated that there was a significant (p < 0.05) difference in their contents of various glycerophospholipid classes. Phosphatidylcholine was the most abundant class in germ and pericarp fractions (51.4–70.6% of the total glycerophospholipids), followed by phosphatidylinositol (11.3–25.1%) and phosphatidylethanolamine (8.4–12.6%). In contrast, phosphatidylethanolamine was found to be the most abundant class in the endosperm fraction (41.4–48.5%), followed by phosphatidylcholine (30.2–33.4%) and phosphatidylinositol (13.2–14.4%). Various molecular species were detected in each class of glycerophospholipid and their levels were significantly (p < 0.05) different among three corn kernel fractions. The major molecular species of triacylglycerol detected in three corn parts were OLL, OOL, LLL, POL, PLL, OOO and POO; where L represents linoleic acid; O, oleic acid; and P, palmitic acid. The TAG composition was significantly different among three corn kernel fractions. In Astro germ fraction, LLL (27.2%) was detected as the dominant TAG molecular species, followed by OLL (21.9%) and PLL (13.4%); however in Astro endosperm fraction, OLL (21.5%) was the major form followed by PLL (18.6%) and LLL (13.5%).     

Clonality and phenotyping of canine lymphomas before chemotherapy and during remission using polymerase chain reaction (PCR) on lymph node cytologic smears and peripheral blood

Polymerase chain reaction (PCR) assays for the immunoglobulin and T-cell receptor genes were utilized to determine phenotype and clonality from lymph node cytologic smears and peripheral blood lymphocytes from 10 dogs with lymphoma, before chemotherapy and during remission. Results were compared with those from 13 dogs with a cytologic diagnosis of lymph node hyperplasia. Clonality was identified in 7 of the lymphomas on the basis of either lymph node cytology or peripheral blood lymphocytes before treatment. No lymph node hyperplasia samples were clonal. In 6 of the dogs with lymphoma, clonality was demonstrated during clinical remission. Detection of PCR clonality during clinical remission is an effective means of identifying minimal residual disease in canine lymphoma and thus additional work is warranted to determine if molecular remission is prognostic or predictive for outcome in well-controlled and well-defined lymphoma subtypes.     

Apparent electrical conductivity integrated from layered soil profiles

Time domain reflectometry (TDR) trace analysis aims at extracting the water content profile along TDR probes. This can be done by applying a TDR forward solver inversely. Thus, TDR‐trace inversion is basically an optimization problem. As in any optimization procedure, it is worthwhile to include as much a priori information as possible about the problem to be solved. In this study, we discuss the feasibility to use the apparent electrical conductivity as constraint for the TDR inversion. The resistors‐in‐parallel circuit can be used to integrate a multislice soil model to obtain the apparent electrical conductivity. We apply additionally Archie's law to link the water content of a particular slice with its electrical conductivity. We compare the results from this approach with measured TDR traces and show that the problem is solved exactly. Finally, we address the thin‐layer issue because thin layers with a high permittivity contrast result in a delay of the run time of an electromagnetic pulse. We test numerically whether a similar behavior can be observed for a thin layered electrical conductivity profile. Our results show that the thickness of the soil layer with respect to electrical conductivity has no effect on the apparent electrical conductivity. We conclude that the apparent electrical conductivity is appropriate as boundary condition in TDR inversion as long as a procedure is known to convert the water content of a slice to its electrical conductivity     

Use of polymorphisms in the γ-gliadin gene of spelt and wheat as a tool for authenticity control

Partial sequencing of the γ-gliadin gene of 62 spelt and 14 soft wheat cultivars was performed. Fifty-six of the 62 spelt cultivars and 13 of the 14 soft wheat cultivars were shown to exhibit the typical spelt or soft wheat γ-gliadin sequence, respectively. Exceptions were ascribed to crossbreeding of soft wheat and spelt. Using the typical soft wheat γ-gliadin sequence, two alternative DNA-based analytical methods were developed for the detection and quantification of spelt flour "adulteration" with soft wheat. A simple and fast detection of soft wheat in spelt flours could be achieved by restriction fragment length (RFLP) analysis. In combination with lab-on-a-chip capillary gel electrophoresis (LOC-CE) the soft wheat proportion could be estimated. Heteroduplex formation served as additional confirmation for the presence of spelt besides soft wheat. Hence, RFLP-LOC-CE constitutes a perfect analysis tool for the quality control of cereal seeds and pure cultivars. A precise quantification of soft wheat "adulterations" in spelt flour down to 1% could be achieved by the developed real-time PCR method. The calibration parameters of the real-time PCR assay fulfilled the minimum performance requirements of the European Network of GMO (genetically modified organisms) Laboratories (ENGL).