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Evidence for non-additive influence of single nucleotide polymorphisms within the apolipoprotein E gene.

We analyzed 13 single nucleotide polymorphisms (SNPs) within the apolipoprotein E (APOE) gene, to identify pairs of SNPs that interact in a non-additive manner to influence genotypic mean levels of the ApoE protein in blood. An overparameterized general linear model of two-SNP genotype means was applied to data from 456 female and 398 male unrelated European Americans from Rochester, MN, USA. We found statistically significant evidence for non-additivity between SNPs within the male sample, but not within the female sample. We observed nine pairs of SNPs with evidence of non-additivity at the alpha=0.05 level of statistical significance within the male sample, when approximately three were expected by chance. Five of the nine pairs involved three SNPs (560, 624 and 1163) that did not have a statistically significant influence when considered separately in a single-site analysis. Three of the nine pairs involving four SNPs (832, 1998, 3937 and 4951) showed significant evidence for non-additivity in at least one of two other male samples from Jackson, MS, USA and North Karelia, Finland. Although all four of these SNPs had a statistically significant influence in Rochester when considered separately, only SNP 3937 gave a significant result in the other male samples. The four SNPs are located in the promoter, intronic and exonic regions, and 3' to the polyadenylation signal in the APOE gene. Our study suggests that analyses that only consider SNPs located in exons and ignore contexts such as those indexed by gender and population, and disregard non-additivity of SNP effects, may inappropriately model the contribution of a gene to the genetic architecture of a trait that has a complex multifactorial etiology.

Apolipoproteins E↗

Application of a computer program to exclude additional unexpected antibodies.

BACKGROUND: When a patient has produced red cell (RBC) antibodies in the past, he or she is at risk of producing additional antibodies after antigen challenge. The presence of these antibodies should be excluded before each transfusion. The following criteria are applied when using commercial test RBCs: RBCs should not express the antigen against which the previously documented antibody is directed. For other clinically significant antigens, at least one RBC sample should be from a donor who is homozygous for the encoding gene. The manual selection of such RBCs is tedious and requires experience. STUDY DESIGN AND METHODS: A computer program has been developed that generates exclusion panels (EPs) by selecting a minimum number of RBCs from commercial test panel complying with current criteria. When RBCs from a donor who is homozygous for the encoding gene are absent, the program selects, as a second-best option, RBCs from a donor who is heterozygous for that gene. The computer program developed for this study investigated the usefulness of commercially available panels from separate manufactures in excluding the presence of additional antibodies. A list of 488 antibodies detected by a regional blood bank in 1994 was used as cases of antibodies documented in the past. RESULTS: In 61 percent of the cases, successful EPs (i.e., those complying with the criteria), consisting of three to four different phenotypes, were selected. In the remaining 39 percent of cases, it was impossible to generate successful EPs: 1 to 2 additional antibodies could not be excluded or could be excluded only by using RBCs from heterozygotes. Commercial panels differed only slightly in their efficiency in providing suitable RBCs. None of the commercial panels could provide suitable RBCs to exclude all additional antibodies in the presence of anti-c, anti-e, or anti-M. Increasing the number of RBCs from which to select EPs only slightly increased the percentage of success. CONCLUSION: Computer-aided construction of EPs quickly shows whether strict criteria can be met or whether alternative techniques should be used. It leads to a significant reduction in the number of RBC suspensions necessary to exclude additional antibodies. Results with various commercial panels differed only slightly.

Antibodies↗

Addition of clonidine increases duration and magnitude of vasodilative effect induced by sympathetic block with mepivacaine in dogs.

BACKGROUND AND OBJECTIVES: The aim of this study is to examine the duration and magnitude of vasodilative effect induced by sympathetic block with the addition of clonidine to mepivacaine. METHODS: We measured mean arterial pressure (MAP), heart rate (HR), and right and left brachial artery blood flow (BABF) before and after stellate ganglion block (SGB) in dogs. The experimental protocol was designed as follows: (1) left SGB using 1.0 mL 0.5% mepivacaine (n = 6) and (2) left SGB using the addition of clonidine 0.5 microg to 1.0 mL 0.5% mepivacaine (n = 6). RESULTS: MAP and HR did not change significantly throughout the study in either group. Left SGB with mepivacaine increased left BABF significantly from 10 minutes through 50 minutes after SGB (baseline, 100%; peak at 10 minutes after SGB, 176% +/- 28%; P <.01). Left SGB with the addition of clonidine to mepivacaine induced a significant increase of left BABF from 10 minutes through 70 minutes after SGB (baseline, 100%; peak at 10 minutes after SGB, 223% +/- 42%; P <.01). The values of left BABF after SGB with the addition of clonidine to mepivacaine were significantly higher than those of SGB with mepivacaine alone from 10 minutes through 80 minutes after SGB (P <.05). Right BABF decreased significantly after SGB throughout the study in both groups. CONCLUSIONS: The addition of clonidine increases both duration and magnitude of the vasodilative effect induced by sympathetic block over that caused by mepivacaine alone.

Adrenergic alpha-Agonists↗

Assessment of the value of anorganic bone additives in sinus floor augmentation: a review of clinical reports.

In order to objectively assess the value of anorganic bone additives in sinus floor augmentation, a review of the English literature till May 2002 was carried out. The studies or parts of studies had to include at the least two patients, with a follow-up of at least 3 months, whilst histomorphometric data ought to be available of biopsies taken from the core of the graft. Only 12 studies fulfilled these criteria. Firm conclusions could not be drawn because there were substantial differences in histomorphometric techniques, healing periods and ratio autogenous bone anorganic additives, but it seemed that autogenous bone without anorganic additives resulted in the highest amount of bone after a 4-6 months healing period, while hydroxyapatite and bovine bone mineral, used as a bone substitute, gave the lowest amount of bone. No correlation between bone volume and time of graft healing could be found. The consequences, however, for implant placement and survival are at present, not fully understood. A plea is made for systematic prospective clinical and experimental studies to assess the various bone additives and ratios of autogenous bone to bone additives in composite grafts analysed with an adequate histomorphometric technique. Part of this study was presented at the 15th ICOMS, Durban, South Africa, 19-24 May 2001.

Alveolar Ridge Augmentation↗

[Refinement of cytopathology of CT-guided fine needle aspiration biopsies with additional histologic examination of formalin-fixed blood-clots].

PURPOSE: To evaluate formalin-fixed blood-clot for diagnostic efficacy and safety in percutaneous CT-guided fine needle aspiration biopsy (FNAB) in addition to cytopathology. MATERIALS AND METHODS: 61 CT-guided FNABs were entered into a prospective trial. FNAB was performed in 22 female and 39 male patients (32 - 83 years, m = 62.8 +/- 10.9 y) using 20- (n = 7) and 22-gauge (n = 54) needles. After correct placement within the tumor, material for cytopathological work-up was harvested. Additional material was sampled by needling (stirring and aspirating) within the lesion. These blood-clots were fixed in buffered formalin and delivered for histopathological work-up along with the smears. All results were correlated with the clinical course of the patient; cases of negative biopsies underwent surgery or were followed clinically for a minimum of 13 months (m = 14.8 +/- 1.4 months). Finally, all puncture-related side-effects and complications were analyzed and compared with data from 108 transthoracic FNABs performed over a two-year period before using this technique. RESULTS: Tissue samples adequate for pathological diagnosis were obtained in 93.4 % (57 of 61 patients). Malignant cells were found in 50 samples, and 7 biopsy results were negative. The relevant pathological changes were depicted on both smear and blood-clot in 47 cases (82.4 %). In the remaining patients, the diagnoses were exclusively established by cytopathology (n = 6) and histopathology (n = 4). Altogether, additional information was obtained in 20 of the 57 FNABs (35.1 %). In the 47 cases with relevant findings obtained with both methods, the routine stain already led to the correct diagnosis in 9 cases by showing cohesive layers of malignant cells, and immunocytochemistry allowed subclassification of the biopsy material in additional 7 cases. Pneumothorax occurred in 12 of 38 transpleural punctures (31.6 %), hemoptysis in one patient (2.6 %). Four pneumothoraces required further treatment (3 thoracocenteses, 1 chest tube placement). Hemorrhagic complications requiring further treatment were not seen, but two minor hematomas were observed in the 19 abdominal punctures. The overall rate for pneumothorax was 38.9 % (42 of 108 interventions) for the FNAB performed in standard technique. CONCLUSION: Histological work-up of sampled blood-clots yielded a higher accuracy of CT-guided FNABs. Additional immunocytochemical studies allowed subclassification of tumor material. The complication rate of this technique was not higher than for FNAB alone.

Adult↗

[Frequency and costs of additional hospitalisations in the year after inpatient or day hospital detoxification treatment].

OBJECTIVE: We examined if the presumed reduction in costs of day hospital detoxification compared to inpatient treatment is neutralised by more frequent additional inpatient treatment episodes during a 1-year follow-up. METHOD: Randomised clinical trial with 1-year follow-ups. Calculation of costs for additional treatments is based on data from health insurances. RESULTS: Compared to inpatient treatment, day hospital treatment saved approximately 24 % of the costs of the initial detoxification. Overall, additional inpatient treatments during the follow-up period produced more costs than the initial treatments, but no significant difference emerged between the treatment groups. About 75 % of costs for additional treatments were caused by 25 % of the patients. CONCLUSIONS: Lower costs of day treatment detoxification treatment are not annilihated by increased costs of additional inpatient treatments during the first year after discharge. Under a health services perspective, research concerning a relatively small group of "heavy users" is especially important.

Adult↗

Recurrence rates after treatment of breast cancer with standard radiotherapy with or without additional radiation.

BACKGROUND: Radiotherapy prevents local recurrence of breast cancer after breast-conserving surgery. We evaluated the effect of a supplementary dose of radiation to the tumor bed on the rates of local recurrence among patients who received radiotherapy after breast-conserving surgery for early breast cancer. METHODS: After lumpectomy and axillary dissection, patients with stage I or II breast cancer received 50 Gy of radiation to the whole breast in 2-Gy fractions over a five-week period. Patients with a microscopically complete excision were randomly assigned to receive either no further local treatment (2657 patients) or an additional localized dose of 16 Gy, usually given in eight fractions by means of an external electron beam (2661 patients). RESULTS: During a median follow-up period of 5.1 years, local recurrences were observed in 182 of the 2657 patients in the standard-treatment group and 109 of the 2661 patients in the additional-radiation group. The five-year actuarial rates of local recurrence were 7.3 percent (95 percent confidence interval, 6.8 to 7.6 percent) and 4.3 percent (95 percent confidence interval, 3.8 to 4.7 percent), respectively (P<0.001), yielding a hazard ratio for local recurrence of 0.59 (99 percent confidence interval, 0.43 to 0.81) associated with an additional dose. Patients 40 years old or younger benefited most; at five years, their rate of local recurrence was 19.5 percent with standard treatment and 10.2 percent with additional radiation (hazard ratio, 0.46 [99 percent confidence interval, 0.23 to 0.89]; P=0.002). At five years in the age group 41 to 50 years old, no differences were found in rates of metastasis or overall survival (which were 87 and 91 percent, respectively). CONCLUSIONS: In patients with early breast cancer who undergo breast-conserving surgery and receive 50 Gy of radiation to the whole breast, an additional dose of 16 Gy of radiation to the tumor bed reduces the risk of local recurrence, especially in patients younger than 50 years of age.

Adult↗

Chromosome healing through terminal deletions generated by de novo telomere additions in Saccharomyces cerevisiae.

Broken chromosomes healed by de novo addition of a telomere are a major class of genome rearrangements seen in Saccharomyces cerevisiae and similar to rearrangements seen in human tumors. We have analyzed the sequences of 534 independent de novo telomere additions within a 12-kb region of chromosome V. The distribution of events mirrored that of four-base sequences consisting of the GG, GT, and TG dinucleotides, suggesting that de novo telomere additions occur at short regions of homology to the telomerase guide RNA. These chromosomal sequences restrict potential registrations of the added telomere sequence. The first 11 nucleotides of the addition sequences fell into common families that included 91% of the breakpoints. The observed registrations suggest that the 3' end of the TLC1 guide RNA is involved in annealing but not as a template for synthesis. Some families of added sequences can be accounted for by one cycle of annealing and extension, whereas others require a minimum of two. The same pattern emerges for sequences added onto the most common addition sequence, indicating that de novo telomeres are added and extended by the same process. Together, these data indicate that annealing is central to telomerase registration, which limits telomere heterogeneity and resolves the problem of synthesizing Rap1 binding sites by a nonprocessive telomerase with a low-complexity guide RNA sequence.

Chromosome Aberrations↗

tRNAHis guanylyltransferase catalyzes a 3'-5' polymerization reaction that is distinct from G-1 addition.

Yeast tRNA(His) guanylyltransferase, Thg1, is an essential protein that adds a single guanine to the 5' end (G(-1)) of tRNA(His). This G(-1) residue is required for aminoacylation of tRNA(His) by histidyl-tRNA synthetase, both in vitro and in vivo. The guanine nucleotide addition reaction catalyzed by Thg1 extends the polynucleotide chain in the reverse (3'-5') direction of other known polymerases, albeit by one nucleotide. Here, we show that alteration of the 3' end of the Thg1 substrate tRNA(His) unleashes an unexpected reverse polymerase activity of wild-type Thg1, resulting in the 3'-5' addition of multiple nucleotides to the tRNA, with efficiency comparable to the G(-1) addition reaction. The addition of G(-1) forms a mismatched G.A base pair at the 5' end of tRNA(His), and, with monophosphorylated tRNA substrates, it is absolutely specific for tRNA(His). By contrast, reverse polymerization forms multiple G.C or C.G base pairs, and, with preactivated tRNA species, it can initiate at positions other than -1 and is not specific for tRNA(His). Thus, wild-type Thg1 catalyzes a templated polymerization reaction acting in the reverse direction of that of canonical DNA and RNA polymerases. Surprisingly, Thg1 can also readily use dNTPs for nucleotide addition. These results suggest that 3'-5' polymerization represents either an uncharacterized role for Thg1 in RNA or DNA repair or metabolism, or it may be a remnant of an earlier catalytic strategy used in nature.

Biopolymers↗

Reducing gaseous nitrogen loss from stored laying hen manure by the addition of carbohydrates.

Three separate experiments were conducted to determine if the addition of carbohydrate sources directly to freshly-produced laying hen manure reduced the loss of gaseous nitrogen containing compounds during 7 d of storage. The addition of sucrose (8 g/kg) to the manure resulted in a greater increase in bacterial numbers, a greater loss of carbon and a trend for a reduced loss of nitrogen. Although glucose addition to the manure increased bacterial numbers and tended to increase carbon loss, nitrogen loss increased relative to the control. Addition of straw to the manure did not affect the change in bacterial numbers or rate of nitrogen loss compared to the control treatment. Experiment 2 indicated that, when either sucrose or maltose were mixed (8 g/kg) with laying hen manure, microbial numbers were increased and gaseous nitrogen losses were reduced. A combination of starch plus alpha-amylase did not affect the characteristics of the manure. Experiment 3 showed that increasing sucrose addition gave a non-linear reduction in nitrogen loss. Minimum nitrogen loss was obtained with 35 g/kg sucrose, though the maximum increase in bacterial numbers occurred at 20 g/kg of added sucrose.

Animals↗

Effects of cultivar, pelleting and enzyme addition on nutritive value of barley in poultry diets.

1. The effect of pelleting process and Trichoderma viride enzymes (TVE) addition on apparent metabolisable energy, corrected for nitrogen balance (AMEn) and on productive value of practical diets containing 40 and 45% of three different barley cultivars and one wheat were studied in poultry. 2. The effect of the pelleting process on AMEn was inconsistent and was dependent on the cereal included and the addition of enzyme. 3. The growth trial showed a significant effect of enzyme addition to pelleted diets over the whole growth period (0 to 42 d). Addition of TVE improved weight gain and food efficiency by 1.3% and 2.9%, respectively and decreased food intake by 1.6% between 0 and 22 d. In the finisher period (23 to 42 d) TVE improved efficiency by 2.8% and reduced food intake by 2.9%. 4. The incidence of sticky droppings was related to the viscosity of barley used, and enzyme supplementation reduced it. Both pelleting and enzyme addition increased dry matter content of excreta. 5. At the end of the experiment, 14 animals per treatment were slaughtered and carcass yield, viscera weight and abdominal fat were determined.

Animal Feed↗

Short-term recall of visually presented additive and nonadditive digital material by deaf and hearing subjects.

An attempt was made to examine the encoding of visually presented additive and nonadditive digital material and its processing by deaf and hearing Ss. A 2 X 3 X 4 within-Ss design consisting of groups (45 deaf and 45 hearing Ss), numeral sets (additive, lower additive, and additive random), and recall intervals (0, 3, 9, and 12 seconds) was used. Results showed better recall of the additive set in which the third digit was the sum of the first two (e.g., 5-3-8) than other sets. Although the hearing Ss recalled better than the deaf Ss at short delay, performance of both groups deteriorated with increase in retention intervals. Implications of this study are related to the problem of automatic processing in short-term recall and how it is sensitive to the structure of the sequence of a numeral set.

Cognition↗

Lamivudine and famciclovir combination therapy with or without addition of interferon-alpha-2b for HBeAg-positive chronic hepatitis B: a pilot study.

Lamivudine and famciclovir combination therapy has been used in patients with chronic HBeAg-positive hepatitis B to enhance the antiviral effect and reduce the risk of development of resistance. Interferon-alpha (IFN-alpha) can theoretically be added to the regimen to further improve the antiviral effect. Twenty patients with HBeAg-positive chronic hepatitis B were given lamivudine and famciclovir combination therapy for 24 weeks. After 12 weeks of treatment, patients were randomized on a 1:1 basis to either the addition of IFN-alpha 2b or no addition for the last 3 months of therapy. The decline in HBV DNA levels, the loss of HBeAg and the HBeAg seroconversion rate were assessed. Patients with loss of HBeAg and/or development of anti-HBe were followed up for at least 1 y after stopping treatment. Four of 19 patients (21%) had lost HBeAg and/or developed anti-HBe 24 weeks after stopping treatment, 1 of whom had received additional IFN-alpha. During long-term follow-up post-treatment, 2/19 patients (10.5%) had a durable HBeAg seroconversion. The mean HBV DNA level declined by 5 logs during the first 12 weeks of treatment. Addition of IFN-alpha during the last 3 months of treatment did not result in any further decline in HBV DNA levels compared with the non-IFN-alpha-treated group, nor in any increase in the HBeAg seroconversion rate. In conclusion, lamivudine and famciclovir combination treatment induced seroconversion from HBeAg to anti-HBe in 4/19 patients, 2 of whom became long-term responders. Addition of IFN-alpha did not improve the seroconversion rate.

2-Aminopurine↗

Polymer additive migration to foods--a direct comparison of experimental data and values calculated from migration models for high density polyethylene (HDPE).

To reduce the amount of compliance testing for food contact polymers the use of migration modelling has been proposed. This study was conducted to provide valid data for the independent evaluation of two such diffusion-based models using a range of different high density polyethylene (HDPE) polymers and plastics additives. Seventy-two experimental migration data have been obtained in triplicate and used to evaluate two Fickian-based migration models in the prediction of specific migration of four HDPE additives into olive oil. All tests were conducted using olive oil, representing the most severe case for fatty foods with test conditions of 2 h at 70 degrees C, 6 h at 70 degrees C, 10 days at 40 degrees C representing short term exposures at high temperatures and room temperature storage. Predicted migration values were calculated by inserting the measured initial concentration of additive in the polymers (Cp,0) into the equations together with known variables such as additive molecular weight, temperature and exposure time. The results indicate that both models predict migration values into olive oil close to, or in excess of, the experimental results. The Piringer migration model, using the 'exact' calculations of the Migratest Lite program, gave an overestimation for 83% of the migration values generated in this study. The highest overestimation was 3.7 times the measured value. For all measurements, the predicted migration from the Migratest Lite program was greater than 50% of the observed value. The FDA model was found more accurately to predict migration in most situations but underestimated migration more frequently. Differences in the polymer specification had little effect on specific migration of the additives investigated.

Chemical Phenomena↗

Stability testing of selected plastics additives for food contact in EU aqueous, fatty and alternative simulants.

Within the framework of the AIR3-CT94-2360 EU-project, the stability of three plastics additives in three EU aqueous and fatty food simulants and in two alternative simulants was studied under various time-temperature conditions. The additives tested were bis(2-ethylhexyl) adipate (DEHA), bis(2-ethylhexyl) phthalate (DEHP) and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (Irganox 1076). The various test conditions included exposures of 10 days at 40 degrees C, 1 h at reflux temperature for all aqueous simulants, 10 days at 40 degrees C and 1 h 175 degrees C for the olive oil and 2 days at 20 degrees C and 3 h at 60 degrees C for the isooctane simulant. Following the exposure, the additive samples were extracted from aqueous simulants with hexane. A sonication step was necessary to ensure maximum extraction of control samples. In the case of the isooctane simulant, the samples were analyzed directly from the simulant. The oil samples were extracted by acetonitrile. The extracts of samples exposed to various heat conditions as well as unexposed spiked controls and blanks were analysed by gas chromatography (GC) on a non-polar (5%--phenyl)-methylpolysiloxane capillary column with high temperature capabilities. The results showed that DEHA, DEHP and Irganox 1076 were stable at 40 degrees C and at reflux temperature in ethanolic or acidic aqueous simulants. The various additives were also stable in the organic isooctane simulant as well as in the fatty simulant olive oil. Studies on the stability of such additives used in food packaging are designed for regulatory purposes as an aid to decide whether the legislation should regulate limits for plasticizers based on a quantity in the food packaging itself or based on an ingested dose by the consumer.

Chromatography, Gas↗

Evaluation of organics leaching from solidified/stabilized hazardous wastes using a powder reactivated carbon additive.

Cement based stabilization/solidification systems have been widely used to minimize leaching of contaminants from hazardous wastes, particularly for stabilization of wastes that contain heavy metals or other inorganic materials. However, few researchers have demonstrated that stabilization/solidification systems can adequately trap and retain organics present in these wastes. Identification of additives that can be used with the inorganic binder to retain organics has attracted much interest. Activated carbon has been found to be the best additive for immobilizing organic contaminants, but it is generally too expensive for routine use. The use of powdered reactivated carbon was studied in this research to prevent organics from leaching from solidified/stabilized waste forms because it is effective and more economically competitive. The Shrinking Unreacted Core leach test method was employed in this study. Stabilization/solidification waste forms were prepared using five organic compounds--phenol, 2-chlorophenol, chlorobenzene, aniline and Methyl Ethyl Ketone (MEK)--that were spiked into the waste forms at two concentration levels each. Reactivated carbon amounts of 0% (as control), 1% and 2% (w/w) were added into each waste form batch to determine how effectively the reactivated carbon can immobilize those organics and the optimum dose of reactivated carbon addition required. Leachate samples were analyzed using gas chromatography. Results show that 1% reactivated carbon addition is generally enough to reduce leaching of all of the organic contaminants by more than 70%, while a 2% addition reduces leaching for most of the organics to less than 1%.

Carbon↗

The effect of additional physiotherapy to hospital inpatients outside of regular business hours: a systematic review.

Provision of out of regular business hours (OBH) physiotherapy to hospital inpatients is widespread in the hospital setting. This systematic review evaluated the effect of additional OBH physiotherapy services on patient length of stay (LOS), pulmonary complications, discharge destination, discharge mobility status, quality of life, cost saving, adverse events, and mortality compared with physiotherapy only within regular business hours. A literature search was completed on databases with citation tracking using key words. Two reviewers completed data extraction and quality assessment independently by using modified scales for historical cohorts and case control studies as well as the PEDro scale for randomized controlled trials and quasi-randomised controlled trials. This search identified nine articles of low to medium quality. Four reported a significant reduction in LOS associated with additional OBH physiotherapy, with two articles reporting overall significance and two reporting only for specific subgroups. Two studies reported significant reduction in pulmonary complications for two different patient groups in an intensive care unit (ICU) with additional OBH physiotherapy. Three studies accounted for discharge destination and/or discharge mobility status with no significant difference reported. Quality of life, adverse events, and mortality were not reported in any studies. Cost savings were considered in three studies, with two reporting a cost saving. This systematic review was unable to conclude that the provision of additional OBH physiotherapy made significant improvement to patient outcomes for all subgroups of inpatients. One study in critical care reported that overnight physiotherapy decreased LOS and reduced pulmonary complications of patients in the ICU. However, the studies in the area of orthopaedics, neurology, postcardiac surgery, and rheumatology, which all considered additional daytime weekend physiotherapy intervention, did not provide strong evidence to indicate effective reduction in patient LOS or improving patient discharge mobility status or discharge destination. Investigation should continue in this area, but future trials should ensure factors such as random allocation, groups equal at baseline, blinded investigators, and proven intervention are included in the study design.

Case-Control Studies↗

Use of 13C and 15N mass spectrometry to study the decomposition of Calamagrostis epigeios in soil column experiments with and without ash additions.

The dynamics of C and N in terrestrial ecosystems are not completely understood and the use of stable isotopes may be useful to gain further insight in the pathways of CO2 emissions and leaching of dissolved organic carbon (DOC) and nitrogen (DON) during decomposition of litter. Objectives were (i) to study the decomposition dynamics of Calamagrostis epigeios, a common grass species in forests, using 13C-depleted and 15N-enriched plants and (ii) to quantify the effect wood ash addition on the decomposition and leaching of DOC and DON. Decomposition was studied for 128 days under aerobic conditions at 8 degrees C and moisture close to field capacity in a spodic dystric Cambisol with mor-moder layer. Variants included control plots and additions of (i) Calamagrostis litter and (ii) Calamagrostis litter plus 4 kg ash m-2. (i) Decomposition of Calamagrostis resulted in a CO2 production of 76.2 g CO2-C m-2 (10% of added C) after 128 days and cumulative DOC production was 14.0 g C m-2 out of which 0.9 g C m-2 was Calamagrostis-derived (0.1% of added C). The specific CO2 formation and specific DOC production from Calamagrostis were 6 times higher (CO2) and 4 times smaller (DOC) than those from the organic layer. The amount of Calamagrostis-derived total N (NH4+, NO3-, DON) leached was 0.7 g N m-2 (4.8% of added N). Cumulative DON production was 0.8 g N m-2 which was slightly higher than for the control. During soil passage, much of the DOC and DON was removed due to sorption or decomposition. DOC and DON releases from the mineral soil (17 cm depth) were 6.3 g C m-2 and 0.5 g N m-2. (ii) Addition of ash resulted in a complete fixing of CO2 for 40 days due to carbonatisation. Afterwards, the CO2 production rates were similar to the variant without ash addition. Production of DOC (98.6 g C m-2) and DON (2.5 g N m-2) was marked, mainly owing to humus decay. However, Calamagrostis-derived DOC and Calamagrostis-derived total N were only 3.9 g C m-2 (0.5% of added C) and 0.5 g N m-2 (3.4% of added N). The specific DOC production rate from the organic layer was 6 times higher than that from Calamagrostis. The results suggest that with increasing humification from fresh plant residues to more decomposed material (OF and OH layers) the production ratio of DOC/CO2-C increases. Addition of alkaline substances to the forest floor can lead to a manifold increase in DOC production.

Carbon Isotopes↗