Soil microbial diversity and community composition during conversion from conventional to organic agriculture.

It is generally assumed that the dependence of conventional agriculture on artificial fertilizers and pesticides strongly impacts the environment, while organic agriculture relying more on microbial functioning may mitigate these impacts. However, it is not well known how microbial diversity and community composition change in conventionally managed farmers' fields that are converted to organic management. Here, we sequenced bacterial and fungal communities of 34 organic fields on sand and marine clay soils in a time series (chronosequence) covering 25 years of conversion. Nearby conventional fields were used as references. We found that community composition of bacteria and fungi differed between organic and conventionally managed fields. In the organic fields, fungal diversity increased with time since conversion. However, this effect disappeared when the conventional paired fields were included. There was a relationship between pH and soil organic matter content and the diversity and community composition of bacteria and fungi. In marine clay soils, when time since organic management increased, fungal communities in organic fields became more dissimilar to those in conventional fields. We conclude that conversion to organic management in these Dutch farmers' fields did not increase microbial community diversity. Instead, we observed that in organic fields in marine clay when time since conversion increased soil fungal community composition became progressively dissimilar from that in conventional fields. Our results also showed that the paired sampling approach of organic and conventional fields was essential in order to control for environmental variation that was otherwise unaccounted for.

Optimal current frequency for the detection of changes in extracellular water in patients on hemodialysis by measurement of total body electrical resistance.

BACKGROUND & AIMS: Measurement of total body electrical resistance (TBER) to an alternating current is useful to monitor extracellular water (ECW) in patients on hemodialysis (HD). Which current frequency is preferable is subject of ongoing debate. The aim of this study was to quantify the implications of TBER measurements at current frequencies ranging from 0 to 1000 kHz for ECW monitoring in patients on HD. METHODS: Bioimpedance spectroscopy measurements were performed in 39 patients on HD using the Body Composition Monitor (BCM, Fresenius Medical Care). TBER data at 5, 50, 200, 500, and 1000 kHz were compared with the extrapolated TBER at 0 kHz (TBER0) assessed by Cole-Cole analysis. Sensitivity of each TBER configuration was evaluated at individual level, by assessment of the smallest ultrafiltration (UF) volume that induced a significant change in TBER, i.e. a change in TBER ≥ 2.7%. RESULTS: TBER precision was very high for all frequencies, with coefficients of variation of 0.25%-0.28%. Baseline TBER decreased with increasing current frequency. TBER was 2.9% lower at 5 kHz (P < 0.001), 11.6% lower at 50 kHz, and up to 22.0% lower at 1000 kHz. This pattern is attributed to a progressive increase in intracellular current conduction at higher frequencies. Sensitivity to volume changes induced by UF also decreased with increasing current frequency. At 0 and 5 kHz, an UF volume ≤ 0.5 L was sufficient to induce a significant increase in TBER in 87% of patients. This decreased to 69% at higher frequencies. CONCLUSION: ECW monitoring by TBER requires measurement at 5 kHz or less to ensure optimal performance.

Prediction of total body electrical resistance normal values based on limb muscle thickness assessed by ultrasound.

BACKGROUND: Recently, a new model has been proposed to assess hydration in patients by measurement of total body electrical resistance (TBER), with results expressed in ohm rather than in liter body water. According to this approach, hydration is considered to be normal if TBER is within the normal range. As TBER is inversely related to the size of the limb muscle compartment, this relationship can be used to calculate the patient-specific TBER normal value (TBERnorm). The present study investigates whether the prediction of TBERnorm can be improved by the use of ultrasound (US) instead of anthropometrically derived parameters of limb muscularity. METHODS: In total, 129 healthy subjects (60 men and 69 women) ranging in age from 18 to 75 yr, and in BMI from 17.4 to 52.0 kg/m2 were included in the study. Arm muscle cross-sectional area assessed by anthropometry (AMAcaliper) was compared with mean muscle thickness (MMT) of arm and leg assessed by B-mode US. RESULTS: MMT correlated stronger with TBER than AMA, and reduced the standard error of the estimate (SEE) by 15% in men and by 26% in women. Muscularity was overestimated by AMAcaliper due to a systematic error directly proportional to subcutaneous fat layer thickness. The gender independent relation between MMT and TBERnorm is described by the equation: TBERnorm = 705-75.4⋅MMT (R2 = 0.85, SEE = 22.3 Ω/m, P < 0.001). CONCLUSIONS: US-based measurement of limb muscularity provides a more precise prediction of TBERnorm, in particular in obese subjects, and is recommended as the method of choice.

Sensitivity of total body electrical resistance measurements in detecting extracellular volume expansion induced by infusion of NaCl 0.9.

BACKGROUND: Fluid balance management in hospitalized patients is hampered by the limited sensitivity of currently available tools. The aim of this study was to assess the sensitivity of total body electrical resistance (TBER) measurements for the detection of extracellular volume (ECV) expansion. METHODS: TBER and plasma resistivity (ρplasma) were measured during a 4-h infusion of NaCl 0.9% at a rate of 500 mL/h in 23 patients undergoing a diagnostic saline infusion test for primary hyperaldosteronism. Extracellular fluid gain (EFG) was defined as infusion volume minus urinary volume. RESULTS: Infusion of 2.0 L NaCl 0.9% was associated with a mean diuresis of 1.1 ± 0.5 L, an EFG of 0.9 ± 0.5 L, a decrease in ρplasma of 1.1 ± 0.7 Ω·cm or 1.7 ± 1.0% (P < 0.001), and a decline in TBER of 23.2 ± 10.9 Ω or 4.6 ± 2.2% (P < 0.001). At group level, infusion of 80 mL saline was sufficient to induce a statistically significant decline in mean TBER. At personal level, the decline in TBER was significant on 76% of occasions after an EFG of 0.5-0.75 L, and on all occasions after an EFG of 1.0 L or greater. CONCLUSION: Raw TBER data are very informative for the detection of ECV expansion induced by the infusion of NaCl 0.9%, with a sensitivity at a personal level that is relevant for clinical practice.

Towards personalized hydration assessment in patients, based on measurement of total body electrical resistance: Back to basics.

BACKGROUND & AIMS: Assessment of tissue hydration by conventional bioelectrical impedance analysis (BIA) has produced conflicting results because of flaws in the algorithms that are used to translate measurements of total body electrical resistance (TBER) into liters of body water. This type of error can be eliminated by a return to the TBER measurement itself, without attempting to convert Ohms into liters of body water. Aims of this study were to quantify tissue hydration based on TBER, to establish TBER normal values (TBERnorm), to improve the prediction of TBERnorm values in individual patients, and to evaluate this approach in patients on hemodialysis (HD). METHODS: TBERnorm values were obtained in 213 healthy controls and corrected for body height (H-TBERnorm). Inter-individual H-TBERnorm variability was reduced by correction for arm muscle cross-sectional area (AMA). Performance of this approach was evaluated in 94 patients on HD. RESULTS: H-TBERnorm was inversely related to AMA. Correction for AMA reduced the H-TBERnorm standard deviation by 31% in men and 23% in women. When applied to patients on HD, H-TBER changes within subjects were inversely related to ultrafiltration volumes, with a mean R2 of 0.95 ± 0.04 in men and 0.93 ± 0.07 in women. Clinically significant H-TBER increments occurred after volume reductions of 0.39 ± 0.25 L in men and 0.37 ± 0.18 L in women. CONCLUSIONS: TBER measurements, corrected for height and AMA, have the potential to become an objective and sensitive method to assess hydration in patients. Its clinical value remains to be shown in intervention studies.

Assessment of Plasma Resistivity as a Surrogate for Extracellular Fluid Resistivity: Analytical Performance and Impact of Fluid Composition.

Bio-electrical impedance analysis (BIA) is frequently used to assess body composition in man. Its accuracy in patients is limited, possibly because the employed algorithms are based on the assumption that total body electrical resistance (TBER) is exclusively related to body water volume, and that variation in fluid composition and its effect on fluid resistivity can be ignored. This may introduce substantial calculation errors. The aim of this study was to develop an objective method to assess plasma resistivity (ρplasma) based on measurements by a conductivity probe, as a surrogate for extracellular fluid resistivity (ρe). Sample measurements were standardized at body temperature. Analytical variation was 0.6% within runs and 0.9% between runs. The critical difference, i.e. the smallest difference needed to consider changes within individuals significant, was 1.8% for measurements within runs and 4.3% for measurements between runs. The normal range was defined by a mean ± SD of 66.9 ± 1.8 Ω cm. Multiple regression demonstrated that ρplasma was inversely related to plasma sodium and chloride concentrations, and positively related to total protein (overall R2 = 0.92, p < 0.001). In conclusion, ρplasma measurements were sufficiently robust to be useful as a tool to examine and improve the validity of BIA in clinical settings.

Formation of unreduced megaspores (diplospory) in apomictic dandelions (Taraxacum officinale, s.l.) is controlled by a sex-specific dominant locus.

In apomictic dandelions, Taraxacum officinale, unreduced megaspores are formed via a modified meiotic division (diplospory). The genetic basis of diplospory was investigated in a triploid (3x = 24) mapping population of 61 individuals that segregated approximately 1:1 for diplospory and meiotic reduction. This population was created by crossing a sexual diploid (2x = 16) with a tetraploid diplosporous pollen donor (4x = 32) that was derived from a triploid apomict. Six different inheritance models for diplospory were tested. The segregation ratio and the tight association with specific alleles at the microsatellite loci MSTA53 and MSTA78 strongly suggest that diplospory is controlled by a dominant allele D on a locus, which we have named DIPLOSPOROUS (DIP). Diplosporous plants have a simplex genotype, Ddd or Dddd. MSTA53 and MSTA78 were weakly linked to the 18S-25S rDNA locus. The D-linked allele of MSTA78 was absent in a hypotriploid (2n = 3x - 1) that also lacked one of the satellite chromosomes. Together these results suggest that DIP is located on the satellite chromosome. DIP is female specific, as unreduced gametes are not formed during male meiosis. Furthermore, DIP does not affect parthenogenesis, implying that several independently segregating genes control apomixis in dandelions.

Population Dynamics of Rhizobium leguminosarum Tn5 Mutants with Altered Cell Surface Properties Introduced into Sterile and Nonsterile Soils.

The influence of cell surface properties on attachment to soil particles and on population dynamics of introduced bacteria was studied in sterilized and nonsterilized loamy sand and silt loam. Rhizobium leguminosarum RBL5523 and three Tn5 mutants (RBL5762, RBL5810, and RBL5811) with altered cell surface properties were used. Cellulose fibrils were not produced by RBL5762. Both RBL5810 and RBL5811 produced 80 to 90% less soluble exopolysaccharides and RBL5811 had, in addition, an altered lipopolysaccharide composition. In sterilized soil the total number of cells as well as the number of particle-associated cells of RBL5523 and RBL5810 were, in general, higher as compared with cell numbers of RBL5762 and RBL5811. Differences between strains in percentage of particle-associated cells in sterilized soil were only found at high inoculum densities, when populations increased little. In the nonsterilized silt loam, final population sizes, as well as numbers of particle-associated cells, of the parental strain (RBL5523) were higher than those of strains with altered cell surface properties after 56 and 112 days of incubation. But in general, differences in survival among the strains were not very marked. The importance of association with soil particles or aggregates for the survival of introduced cells was affirmed by the pronounced increase of the percentage of particle-associated cells during incubation in nonsterilized as well as sterilized soil. However, no clear relation among altered cell surface properties, particle association, and survival was found.