Preservation of root cementum: a comparative evaluation of power-driven versus hand instruments.

OBJECTIVES: The purpose of this study was to evaluate the effects of three distinct periodontal treatment methods in comparison with hand instrumentation on residual cementum of periodontal diseased teeth. Cementum can influence the activities of periodontal cells and may play an important regulatory role in periodontal treatment. The ideal method for periodontal therapy involves removal of biofilm, calculus and endotoxin while preserving root cementum. MATERIAL AND METHODS: Forty-eight caries free, single-rooted teeth in patients diagnosed with severe chronic periodontitis were treated using four different methods prior to extraction. The teeth were instrumented subgingivally at one approximal site either by hand curettes (HC), piezoelectric ultrasonic scalers (U), piezoelectric ultrasonic scalers following air polishing (U + AP) or air polishing (AP) alone. Following extraction of teeth, instrumented and non-instrumented sites were analysed with a dissecting microscope and SEM for measurement of the amount of and surface characteristics of residual cementum. RESULTS: The percentage of coronal cementum remaining following subgingival instrumentation was 84% for U, 80% for U + AP, 94% for AP and 65% for HC. Although subgingival instrumentation of apical portions of the cementum demonstrated 6% less retained cementum in comparison with coronal portions, the amount of retained cementum with AP was still significantly greater than with HC. SEM results found the smoothest root surfaces were produced by the HC followed by the AP, while root surfaces instrumented by U or U + AP presented grooves and scratches. CONCLUSIONS: This study demonstrated that AP was superior to U devices in preserving cementum, whereas HC were the most effective instruments in removing cementum.

Gender and cystectomy for bladder cancer: A high-volume tertiary urologic care center experience.

BACKGROUND: Differences have often been reported in the outcomes of bladder cancer (BC) patients according to gender. OBJECTIVE: This study aims to provide data on patients undergoing radical cystectomy (RC) in a high-volume tertiary urologic center and to assess whether gender discrepancies do exist in terms of surgical options and clinical outcomes. MATERIALS AND METHODS: Consecutive BC patients treated between 2016 and 2020 at a single center (Careggi University Hospital, Florence, Italy) were included in the study. The impact of gender on disease stage at diagnosis, overall survival (OS), and type of surgery was analyzed. RESULTS: The study series comprised 447 patients (85 females and 362 males). At a median follow-up of 28.3 months (IQR: 33.5), OS was 52.6% and cancer-specific survival was 67.6%. Significant differences in OS emerged for age, acute myocardial infarction (AMI), Charlson Comorbidity Index (CCI), pT, and pN. OS rates were higher in patients undergoing robot-assisted surgery and in those receiving open orthotopic neobladder (ONB) (p = 0.0001). No statistically significant differences were found between male and female patients regarding surgical offer in any age group, surgical time, early postoperative complications, pathologic stage, and OS. CONCLUSIONS: After adjustment for pathologic tumor stage and treatment modalities, female and male patients showed similar oncologic outcomes. Further studies should be undertaken to evaluate functional results in women subjected to RC.

[Heparin-induced thrombocytopenia: Update]. / La thrombopénie induite par héparine : mise au point.

Heparin-induced thrombocytopenia (HIT) is a serious complication of heparin therapy. It is due to the synthesis of antibodies most often directed against platelet factor 4 (FP4) modified by heparin (H). HIT is manifested by a platelet count fall, associated with a high risk of venous or arterial thrombosis. The diagnosis of HIT is based on the assessment of clinical probability (4Ts score or change in platelet count after cardiac surgery) and the demonstration of heparin-modified anti-FP4 antibodies (FP4/H). If the immunological tests are positive, functional tests should be performed. In case of suspicion of HIT, it is necessary to urgently stop heparin therapy, to perform a doppler ultrasound of the lower limbs, and to prescribe an alternative anticoagulation agent at a curative dose. Currently, danaparoid sodium and argatroban are authorized. The diagnosis and management of HIT remain complex and requires multidisciplinary collaboration.

Functional infrared imaging of paroxysmal ischemic events in patients with Raynaud's phenomenon.

The use of thermal infrared (IR) imaging together with the study of the thermal recovery from a controlled cold challenge has been proposed in the diagnosis and follow-up of therapeutic response of Raynaud's Phenomenon (RP) and Systemic Sclerosis (SSc). The controlled cold challenge test usually performed during IR investigations may induce a RP in patients with the latter condition. In our Institution we routinely perform capillaroscopy and thermal IR to follow-up SSc patients. In this paper, we describe the thermal recovery patterns shown by two SSc patients (a 40 year-old male with diffuse variant of SSc and a 71 year-old female with a limited variant of SSc) who presented ischemic and paroxysmal RP attack while recovering from the routine controlled cold challenge test. During RP attack, the cutaneous temperature of some fingers continued to decrease for some minutes even after the cessation of the cold stress. To the best of our knowledge, to date, no literature report has documented the thermal behaviour of SSc patients' fingers which occasionally present ischemic and paroxysmal response. Triggering of ischemic RP attack appears to not rely only on morphological and structural finger impairment, but also upon other aspects, like the emotional attitude of the subject and the possible discomfort experienced with the proceeding of the functional cold stress test.

Increase of renal resistive index and mineral metabolism disorder in patients with acute coronary syndrome with preserved renal function.

OBJECTIVE: Coronary artery disease is one of the first causes of death in the Western world; for this reason, it is essential to identify new, systemic, non-invasive and low-cost cardiovascular risk markers. The acute coronary syndrome includes ST-Elevation Myocardial Infarction (STEMI) and Non-ST-Elevation Myocardial Infarction (NSTEMI), based on ECG findings. We aimed to evaluate Renal Resistive Index (RRI) as a marker of cardiovascular risk and assess the associations with other cardiovascular risk factors (metabolic indexes, mineral metabolism disorders and endothelial dysfunction and atherosclerosis markers) in STEMI and NSTEMI patients. PATIENTS AND METHODS: Clinical, laboratory and instrumental examinations as metabolic and inflammation indexes, markers of atherosclerosis and endothelial dysfunction (renal function, mineral metabolism disorders, inflammation indexes, Intima Media Thickness (IMT), Ankle Brachial Pressure Index, Left Ventricular Mass Index, Relative Wall Thickness) were performed. RESULTS: Eighty-one patients with STEMI and NSTEMI were enrolled. We showed a significant positive correlation between RRI and age (p<0.01), intact parathyroid hormone (p<0.01) and IMT (p<0.01), as well as a significant negative correlation between RRI and body surface area (BSA) (p=0.02), estimated Glomerular Filtration Rate (eGFR) (p<0.01), serum calcium (p<0.01) and 25-hydroxy-vitamin D (p=0.03). Moreover, we found a significant correlation between RRI and male patients (p<0.01), coronary artery disease history (CAD) (p=0.049), hypertension (p=0.025) and left ventricular eccentric hypertrophy (LVEH) (p=0.047). CONCLUSIONS: Our study showed an association between RRI and the main traditional and non-traditional cardiovascular risk factors involved in atherosclerosis pathogenesis, such as age, BSA, hypertension, male sex, CAD history, mineral metabolism disorders and LVEH, in patients with preserved renal function. Moreover, we found a significant correlation between RRI and eGFR, suggesting that RRI could be useful in the evaluation of both renal function and progression of renal damage, even in an early stage with a conserved or only slightly reduced kidney function. We also showed a significant correlation with some markers of systemic atherosclerosis such as IMT and LVEH. For a more precise assessment of prognosis and cardiovascular risk in patients with high cardiovascular mortality, we suggest performing a systematic RRI evaluation, considering the non-invasive nature of the procedure, its reproducibility, easy execution, and low costs.

EGF-R signaling through Fyn kinase disrupts the function of integrin alpha6beta4 at hemidesmosomes: role in epithelial cell migration and carcinoma invasion.

We have examined the mechanism and functional significance of hemidesmosome disassembly during normal epithelial cell migration and squamous carcinoma invasion. Our findings indicate that a fraction of EGF receptor (EGF-R) combines with the hemidesmosomal integrin alpha6beta4 in both normal and neoplastic keratinocytes. Activation of the EGF-R causes tyrosine phosphorylation of the beta4 cytoplasmic domain and disruption of hemidesmosomes. The Src family kinase inhibitors PP1 and PP2 prevent tyrosine phosphorylation of beta4 and disassembly of hemidesmosomes without interfering with the activation of EGF-R. Coimmunoprecipitation experiments indicate that Fyn and, to a lesser extent, Yes combine with alpha6beta4. By contrast, Src and Lck do not associate with alpha6beta4 to a significant extent. A dominant negative form of Fyn, but not Src, prevents tyrosine phosphorylation of beta4 and disassembly of hemidesmosomes. These observations suggest that the EGF-R causes disassembly of hemidesmosomes by activating Fyn, which in turn phosphorylates the beta4 cytoplasmic domain. Neoplastic cells expressing dominant negative Fyn display increased hemidesmosomes and migrate poorly in vitro in response to EGF. Furthermore, dominant negative Fyn decreases the ability of squamous carcinoma cells to invade through Matrigel in vitro and to form lung metastases following intravenous injection in nude mice. These results suggest that disruption of hemidesmosomes mediated by Fyn is a prerequisite for normal keratinocyte migration and squamous carcinoma invasion.

Expression of CD133-1 and CD133-2 in ovarian cancer.

Cancer stem cells have been isolated from several solid tumors including prostate, colon, liver, breast, and ovarian cancer. Stem cells isolated from nervous system and prostate express CD133 antigen, which is widely used to isolate hematopoietic stem and progenitor cells. The aims of this study were to investigate the expression of the CD133-1 and CD133-2 epitopes in primary ovarian tumors and to biologically characterize CD133(+) ovarian cancer cells, also according to clinicopathologic parameters. Tissue specimens were obtained at primary surgery from 41 ovarian carcinomas; eight normal ovaries and five benign ovarian tumors were also collected. Flow cytometry with monoclonal antibodies against CD133-1 and CD133-2 epitopes was employed. FACS (fluorescence activated cell sorting) analysis enabled the selection of CD133(+) cells, whose epithelial origin was confirmed by immunofluorescence analysis with monoclonal anti-cytokeratin 7. CD133(+) cells gave rise to a 4.7 +/- 0.9-fold larger number of colonies than that documented in CD133(-) population (P < 0.001). Moreover, CD133(+) cells showed an enhanced proliferative potential compared to CD133(-) cells. The percentages of CD133-1- and CD133-2-expressing cells were significantly lower in normal ovaries/benign tumors with respect to those in ovarian carcinoma. Both the percentages of CD133-1- and CD133-2-expressing cells were significantly lower in omental metastases than in primary ovarian cancer (P = 0.009 and 0.007 for CD133-1- and CD133-2-expressing cells, respectively). There seems not to be any difference in the distribution of the percentage of CD133-1- and CD133-2-expressing cells according to clinicopathologic parameters and response to primary chemotherapy. CD133-1 and CD133-2 may be useful in order to select and enrich the population of CD133(+) ovarian tumor cells, which are characterized by a higher clonogenic efficiency and proliferative potential.

Tracing 2,4-D metabolism in Cupriavidus necator JMP134 with 13C-labelling technique and fatty acid profiling.

The use of stable isotope probing of fatty acid methyl esters (FAME-SIP) is a powerful tool to study the microorganisms involved in xenobiotic biodegradation in soil. Nevertheless, it is important to determine how representative these molecules are of microorganisms both qualitatively and quantitatively. Using Cupriavidus necator JMP134 as a simple experimental model, we showed that the (13)C-labelling technique can be used both at a global (here defined as cellular, medium and CO(2)) and molecular level to study the metabolism of 2,4-Dichlorophenoxyacetic acid (2,4-D). Although isotopic fractionation among substrate, biomass and FAME were observed, this technique could be used when using a highly (13)C-labelled substrate. Global (13)C analyses gave similar results to those obtained with traditional (14)C-labelling methods. After 10 days of incubation 59% of ring-C was mineralized and about 30% remained in the liquid medium. A maximum of 11% was incorporated into the biomass after 3 days. The assimilation yield of chain-C into the biomass was about half that of ring-C, suggesting a preferential use of chain-C for energy acquisition. Molecular analysis of the lipid fraction evidenced that the incorporation of the labelled 2,4-D did not correspond to a bioaccumulation of pesticide residues but to the metabolism of the 2,4-D carbons for FAME synthesis. Provided the labelling is located on the benzenic ring, the assessment of (13)C-FAME is a robust method to quantify the incorporation of (13)C into the whole microbial biomass. However, the variability of the (13)C incorporation among FAME due to physiological processes has to be considered in complex biological systems. The coupling of bulk and molecular studies with a simple model as C. necator JMP134 is a good approach for testing FAME-SIP.

Culture of human cell lines by a pathogen-inactivated human platelet lysate.

Alternatives to the use of fetal bovine serum (FBS) have been investigated to ensure xeno-free growth condition. In this study we evaluated the efficacy of human platelet lysate (PL) as a substitute of FBS for the in vitro culture of some human cell lines. PL was obtained by pools of pathogen inactivated human donor platelet (PLT) concentrates. Human leukemia cell lines (KG-1, K562, JURKAT, HL-60) and epithelial tumor cell lines (HeLa and MCF-7) were cultured with either FBS or PL. Changes in cell proliferation, viability, morphology, surface markers and cell cycle were evaluated for each cell line. Functional characteristics were analysed by drug sensitivity test and cytotoxicity assay. Our results demonstrated that PL can support growth and expansion of all cell lines, although the cells cultured in presence of PL experienced a less massive proliferation compared to those grown with FBS. We found a comparable percentage of viable specific marker-expressing cells in both conditions, confirming lineage fidelity in all cultures. Functionality assays showed that cells in both FBS- and PL-supported cultures maintained their normal responsiveness to adriamycin and NK cell-mediated lysis. Our findings indicate that PL is a feasible serum substitute for supporting growth and propagation of haematopoietic and epithelial cell lines with many advantages from a perspective of process standardization, ethicality and product safety.

Induction of apoptosis by p75 neurotrophin receptor in human neuroblastoma cells.

The low-affinity nerve growth factor receptor p75NTR belongs to a membrane receptor superfamily whose members, in certain cell types, are able to transduce an apoptotic signal. To investigate the effect of p75NTR expression in neuroblastoma cells, we transfected the p75NTR cDNA into SK-N-BE cells, a neuroblastoma cell line that lacks expression of both p75NTR and TrkA. Cell clones expressing elevated levels of p75NTR showed a high degree of cell death by apoptosis, even in serum-supplemented medium. Moreover, the level of apoptosis correlated directly with the expression level of the receptor, indicating that p75NTR could activate the cell death program by itself. Clones expressing p75NTR showed a dramatic increase of cell death when switched into serum-free medium; these cultures rapidly extinguished. This apoptotic effect was greatly inhibited by NGF treatment. Our results support the hypothesis that p75NTR, when it is not bound by NGF, may play a role in neuronal selection during embryonic development and suggest that neuroblastomas may arise from immature neuroblasts that escape programmed cell death. Therefore, the loss of p75NTR expression in developing neural crest cells might be a primary event in the genesis of neuroblastoma.

Immune reconstitution after autologous peripheral blood progenitor cell transplantation: effect of interleukin-15 on T-cell survival and effector functions.

OBJECTIVE: The aim of this study was to evaluate the occurrence of T-cell spontaneous apoptosis (A(spont)) and its modulation in vitro by the interleukin-2 receptor (IL-2R) gamma-chain (gammac)-signaling cytokine IL-15 in patients transplanted with autologous peripheral blood progenitor cells (PBPC) for hematologic malignancies. MATERIALS AND METHODS: Patients were examined on days 30-60, 60-90, and 90-120 after PBPC infusion. Dissipation of mitochondrial transmembrane potential, a hallmark of T-cell apoptosis, has been detected using the fluorescent probe 3,3'-dihexyloxacarbocyanine iodide, after short-term T-cell culture in the absence or presence of exogenous cytokines. Expression of Bcl-2 family members has been studied by flow cytometry and reverse transcriptase polymerase chain reaction. T-cell proliferative responses to recall antigens have been estimated in autologous mixed leukocyte cultures. RESULTS: A(spont) was seen in 45% +/- 6% of CD4(+) and 55% +/- 6% of CD8(+) T cells cultured in the absence of cytokines. Of interest, IL-15 and, to a lesser extent, its structural cousin IL-2 counteracted T-cell A(spont) by inhibiting the processing of caspase-3 and up-regulating Bcl-2 mRNA and protein levels. Cell division tracking confirmed that IL-15 did not rescue T cells from A(spont) by promoting proliferation but rather acted as a genuine survival factor. Addition of a gammac-blocking antibody to cytokine-conditioned cultures abrogated both apoptosis inhibition and Bcl-2 induction by IL-15, suggesting involvement of the IL-2Rgammac signal transduction pathway. Whereas cytokine-unprimed posttransplant T cells mounted inadequate responses to recall antigens, T cells conditioned with IL-15 expanded vigorously, indicating restoration of antigen-specific proliferation. CONCLUSIONS: T cells recovering after autologous PBPC transplantation are highly susceptible to spontaneous apoptosis in vitro. This phenomenon can be counteracted by the gammac-signaling cytokine IL-15. These findings suggest that IL-15 might be a promising immunomodulating agent to improve postgrafting T-cell function.

Protein-metabolism kinetics and energy-substrate utilization in infants fed parenteral solutions with different glucose-fat ratios.

The relative effect of glucose and lipids on whole-body protein-metabolism kinetics was assessed in seven infants undergoing parenteral feeding. Protein intake was kept constant and nonprotein energy was either provided as glucose alone or as an isoenergetic glucose-lipid mixture according to a randomized crossover trial. Protein metabolism and energy-substrate utilization were assessed by a primed, constant L-[13C]leucine infusion, combined with indirect calorimetry. There was a significant difference in the pattern of energy-substrate utilization according to regime. Protein turnover (11.3 +/- 0.7 vs 9.8 +/- 0.4 g.kg-1.d-1; P less than 0.05), protein breakdown (8.4 +/- 0.6 vs 7.1 +/- 0.4 g.kg-1.d-1; P less than 0.05), and amino acid oxidation rates (2.7 +/- 0.4 vs 1.4 +/- 0.5 g.kg-1.d-1; P less than 0.05) were higher for the glucose than the glucose-lipid treatment, whereas protein-synthesis rates did not significantly differ. These results suggest that the nature of energy substrates delivered to parenterally fed infants may affect protein metabolism.

Contribution of odd-chain fatty acid oxidation to propionate production in disorders of propionate metabolism.

Whole-body propionate and protein kinetics and energy substrate metabolism were studied in five metronidazole-treated patients with propionic or methylmalonic acidemias by the use of a primed, 4-h constant infusion of [1-13C]propionate and L-[O-2H5]phenylalanine combined with indirect calorimetry. Measurements were performed during fasting and carbohydrate feeding, successively, to assess the contribution of odd-chain fatty acid oxidation to total propionate production. Fat oxidation decreased from 490 +/- 179 to 57 +/- 49 mumol.kg-1.h-1 (P < 0.05) as a result of feeding. Propionate appearance rate was 38.6 +/- 8 mumol.kg-1.h-1 during fasting and decreased to 22.6 +/- 5 mumol.kg-1.h-1 (P < 0.05) on the carbohydrate diet. Precursor amino acid catabolism did not change significantly (22 +/- 5 vs 21.2 +/- 5 mumol.kg-1.h-1), suggesting that the 41% reduction in propionate production observed in response to feeding was related to the suppression of fatty acid oxidation. Therefore, significant therapeutic gains may be expected from the use of diets aimed at reducing lipid oxidation.

Experimental gingivitis in women using oral contraceptives.

Oral contraceptives (OC) have historically been considered a risk factor for gingival diseases. We set out to investigate this premise further, given that, over recent years, hormone concentrations in OC have been substantially reduced. Using a prospective, split-mouth, experimental gingivitis model, pre-menopausal women either taking (n 14) or not taking (n = 16) OC refrained from all oral hygiene practices in one maxillary (test) quadrant while continuing to perform normal oral hygiene activities in the contralateral (control) quadrant. Mean increases in plaque index (PI), gingival index (GI), and gingival crevicular fluid (GCF) volume from days 0 to 21 were significant in test quadrants (P < 0.05) but did not differ regardless of whether subjects received OC (P > 0.05). PI, GI, and GCF volume did not vary in control quadrants over the course of the study (P > 0.05). Analysis of these data suggests that current OC formulations do not affect the inflammatory response of the gingiva to dental plaque.

Combination of biomolecular and stable isotope techniques to determine the origin of organic matter used by bacterial communities: application to sediment.

Natural isotopic composition is a good tool to trace organic matter in ecosystems. Recent studies used a combination of molecular and stable isotope techniques to determine the origin of the organic carbon used by bacteria in the water column. In our study, we show that this procedure can be used for analysis of sediment bacterial communities with few modifications. In the water column, bacterial recovery is done before DNA extraction. In the sediment, we tested qualitatively and quantitatively a direct and indirect extraction of DNA. The direct extraction was the most efficient. It recovered between 3.1 and 15.8 microg DNA g(-1) dry sediment and the contamination of field samples by eucaryotic DNA was less than 13%. In this preliminary study of the salt marsh ecosystem, the delta(13)C values of DNA (-26 to - 24%) recovered from the sediment were close to the delta(13)C values of halophytic plants (-26.4 and - 25.3%) showing a relationship between plants and microorganisms. Thus, this procedure can be used to trace the flow of carbon through the sediment microbial biomass and to understand the variation of bacterial activity according to the inputs of allocthonous and autochtonous organic matter.

Recovery of [13C]-bicarbonate as respiratory 13CO2 in parenterally fed infants.

Ten infants on continuous total parenteral nutrition (TPN) were infused with NaH13CO3 for 6 h in order to assess the amount of 13C recovered as breath 13CO2. Protein intake was 2.8 +/- 0.3 g/kg/d and non-protein energy intake 107 +/- 4 kcal/kg/d (447 +/- 18 kJ/kg/d), provided either as glucose alone or as an isoenergetic glucose-lipid mixture. In the five infants receiving glucose as the sole non-protein energy source, total CO2 production (559 +/- 50 mumol/kg/min), natural 13C abundance of breath CO2 (-11.8 +/- 0.6 delta % versus PDB) and basal 13CO2 production (6.1 +/- 0.6 mumol/kg/min) were higher than in the five infants infused the glucose-lipid mixture (465 +/- 30 mumol/kg/min, P less than 0.02; -16.1 +/- 0.5 delta %, P less than 0.01 and 5.0 +/- 0.3 mumol/kg min, P less than 0.02, respectively). There was a good agreement, in the glucose-infused infants, between the net glucose oxidation rate measured by indirect calorimetry (25.6 +/- 2 g/kg/d) and the glucose oxidation rate estimated from the 13C natural abundances of breath CO2 and infused substrates (23.5 +/- 3 g/kg/d). Steady state 13C enrichment of breath CO2 was reached in all infants after 120 min infusion and ranged from 11.0 to 21.5 delta % over baseline. Steady state 13C enrichment was negatively related to total CO2 production (r = -0.72; P less than 0.02). In contrast, steady state 13CO2 production in excess of baseline was only correlated to bicarbonate infusion rate (r = 0.95; P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

A human umbilical cord stem cell rescue therapy in a murine model of toxic liver injury.

BACKGROUND: Several studies have demonstrated that bone marrow contains a subpopulation of stem cells capable of participating in the hepatic regenerative process, even if some reports indicate quite a low level of liver repopulation by human stem cells in the normal and transiently injured liver. AIMS: In order to overcome the low engraftment levels seen in previous models, we tried the direct intraperitoneal administration of human cord blood stem cells, using a model of hepatic damage induced by allyl alcohol in NOD/SCID mice. METHODS: We designed a protocol based on stem cell infusion following liver damage in the absence of irradiation. Flow cytometry, histology, immunohistochemistry and RT-PCR for human hepatic markers were performed to monitor human cell engraftment. RESULTS: Human stem cells were able to transdifferentiate into hepatocytes, to improve liver regeneration after damage and to reduce the mortality rate both in both protocols, even if with qualitative and quantitative differences in the transdifferentiation process. CONCLUSIONS: We demonstrated for the first time that the intraperitoneal administration of stem cells can guarantee a rapid liver engraftment. Moreover, the new protocol based on stem cell infusion following liver damage in the absence of irradiation may represent a step forward for the clinical application of stem cell transplantation.

Forest savanna ecotone dynamics in India as revealed by carbon isotope ratios of soil organic matter.

In India, the stability of the forest savanna boundary (ecotone) has been questioned. To investigate the possibility of vegetation change at this boundary, we used the natural difference in the stable carbon isotope ratio (13C/12C, expressed as δ13C) of C3 (forest) and C4 (savanna) plants, which is preserved in the isotopic composition of soil organic carbon. Past changes in the position of the ecotone can thus be documented by 13C/12C analysis of soil organic matter (SOM). Measurements were made on soil samples taken along a transect across the forest savanna boundary. In both ecosystems, δ13C values of SOM in upper soil layers appeared to be in equilibrium with the current plant community: SOM was near-14‰ under savanna cover, and near-28‰ under forest. By contrast, δ13C values of SOM from deep layers of soil profiles under forest cover near the ecotone, were less negative than would be expected for a C3-dominated community. These results indicate that a change in ecosystem dominance occurred recently, and that forest has invaded an area occupied previously by a C4 plant community (savanna and cultivated grassland).

Spatial partitioning of the soil water resource between grass and shrub components in a West African humid savanna.

Most savanna water balance models assume water partitioning between grasses and shrubs in a two-layer hypothesis, but this hypothesis has not been tested for humid savanna environments. Spatial partitioning of soil water between grasses and shrubs was investigated in a West African humid savanna by comparing the isotopic composition (oxygen-18 and deuterium) of soil water and plant stem water during rainy and dry conditions. Both grass and shrub species acquire most of their water from the top soil layer during both rainy and dry periods. A shift of water uptake pattern towards deeper horizons was observed only at the end of the dry season after shrub defoliation. The mean depth of water uptake, as determined by the isotopic signature of stem water, was consistent with grass and shrub root profiles and with changes in soil water content profiles as surveyed by a neutron probe. This provides evidence for potentially strong competition between shrubs and grasses for soil water in these humid savannas. Limited nutrient availability may explain these competitive interactions. These results enhance our understanding of shrub-grass interactions, and will contribute to models of ecosystem functioning in humid savannas.

Changes of the forest-savanna boundary in Brazilian Amazonia during the Holocene revealed by stable isotope ratios of soil organic carbon.

The possibility of ecosystem boundary changes in northern Brazilian Amazonia during the Holocene period was investigated using soil organic carbon isotope ratios. Determination of past and present fluctuations of the forest-savanna boundary involved the measurement of natural 13C isotope abundance, expressed as δ13C, in soil organic matter (SOM). SOM 13C analyses and radiocarbon dating of charcoal fragments were carried out on samples derived from soil profiles taken along transects perpendicular to the ecotonal boundary. SOM δ13C values in the upper soil horizons appeared to be in equilibrium with the overlying vegetation types and did not point to a movement of the boundary during the last decades. However, δ13C values obtained from deeper savanna and forest soil layers indicated that the vegetation type has changed in the past. In current savanna soil profiles, we observed the presence of mid-Holocene charcoals derived from forest species: fire frequency at that time was probably greater, and more extensive savanna may have resulted. Isotope data and the presence of these charcoals thus suggest that the forest-savanna boundary has shifted significantly in the recent Holocene period, forest being more extensive during the early Holocene than today. During the middle Holocene, the forest could have strongly regressed, and fires appeared, with a maximum development of the savanna vegetation. At the beginning of the late Holocene, the forest may have invaded a part of this savanna, and fires occurred again.