Soil C dynamics after deforestation and subsequent conversion of arable cropland to grassland in humid temperate areas

Land use and plant-soil management influence soil organic C stocks and soil properties. This study aimed to identify the main mechanisms by which these factors alter soil organic matter (SOM) dynamics and stocks. Changes in the organic C pools and biochemical quality in different OM compartments were assessed: a) after deforestation and intensive cultivation (SOM loss) and then, b) after the conversion of cropland to grassland (SOM replenishment) in a chronosequence of recovery (1-45 years). Topsoil samples were subjected to physical fractionation to assess the distribution of free particulate OM (POM) and mineral associated OM (MAOM). SOM quality was characterized by 13C NMR spectroscopy, thermal analysis (DSC/TG), and microbial activity was monitored by isothermal microcalorimetry. Deforestation and intensive cultivation led to the loss of 80 % of the C stored in the upper mineral soil (up to 30-35 cm). The POM was almost depleted, MAOM underwent significant losses (>40 %) and all OM compounds, including the aromatic C, were affected. The large and unexpected loss of MAOM can be attributed to the low specific surface soil area and also to the labile (biodegradable) nature of the OM in this fraction. After 45 years, conversion of cropland to grassland recovered 68 % of the C lost in the mineral soil (mainly as MAOM), at an annual rate of 1.25 Mg C ha-1. The present findings showed that the persistence of long-term OM depends on how strongly organic compounds are adsorbed onto mineral surfaces (i.e., the specific surface area) and the biochemical nature of OM compounds. Adequate plant-soil management favoured the replenishment of the MAOM under these experimental conditions, and this fraction was an active pool in terms of C storage and biochemical quality. This study served to test current theories about changes in soil C fractions due to land use changes and soil-plant management.

Revisiting the magnetic structure of Holmium at high pressure by using neutron diffraction

Low-temperature neutron diffraction experiments at [Formula: see text] GPa have been conducted to investigate the magnetic structures of metallic Holmium at high pressures by employing a long d-spacing high-flux diffractometer and a Paris-Edinburgh press cell inside a cryostat. We find that at [Formula: see text] GPa and [Formula: see text] K, no nuclear symmetry change is observed, keeping therefore the hexagonal closed packed (hcp) symmetry at high pressure. Our neutron diffraction data confirm that the ferromagnetic state does not exist. The magnetic structure corresponding to the helimagnetic order, which survives down to 5 K, is fully described by the magnetic superspace group formalism. These results are consistent with those previously published using magnetization experiments.

Inner bark vs sapwood is the main driver of nitrogen and phosphorus allocation in stems and roots across three tropical woody plant communities

Nutrient allocation is central to understanding plant ecological strategies and forest roles in biogeochemical cycles. Thought to be mainly driven by environmental conditions, nutrient allocation to woody organs, especially to living tissues, is poorly understood. To examine the role of differences in living tissues (sapwood, SW, vs inner bark, IB), organs, ecological strategies, and environmental conditions in driving nutrient allocation and scaling in woody plants, we quantified nitrogen and phosphorus in main stems and coarse roots of 45 species from three tropical ecosystems with contrasting precipitation, fire regime, and soil nutrients. Nutrient concentration variation was mostly explained by differences between IB and SW, followed by differences between species and, in the case of phosphorus, soil nutrient availability. IB nutrient concentrations were four times those of SW, with root tissues having slightly higher concentrations than stem tissues. Scaling between IB and SW, and between stems and roots, was generally isometric. In cross-sections, IB contributed half of total nutrients in roots and a third in stems. Our results highlight the important role of IB and SW for nutrient storage, the coordination in nutrient allocation across tissues and organs, and the need to differentiate between IB and SW to understand plant nutrient allocation.

Patterns of leaf trait variation underlie ecological differences among sympatric tree species of Damburneya in a tropical rainforest

PREMISE

Although ecological differentiation driven by altitude and soil is hypothesized to promote coexistence of sympatric tree species of Damburneya (Lauraceae), the mechanistic role of leaf functional variation on ecological differentiation among co-occurring species remains unexplored. We aimed to determine whether the patterns of leaf trait variation reflect ecological differences among sympatric Damburneya species. We tested whether trait correlations underlying functional strategies and average species traits vary in response to local soil heterogeneity along an altitudinal gradient, potentially affecting species distributions.

METHODS

At two contrasting altitudes (100, 1100 m a.s.l.) in a Mexican tropical rainforest, we characterized soil chemical and physical properties and sampled four Damburneya species to quantify five leaf functional traits. We used linear models to analyze paired and multivariate trait correlations, spatial and interspecific effects on trait variation, and trait response to local soil heterogeneity. Relative contributions of intra- and interspecific variation to local trait variability were quantified with an ANOVA.

RESULTS

Soil nutrient availability was higher at low altitude, but all species had a high leaf N:P ratio across altitudes suggesting a limited P supply for plants. Species distribution differed altitudinally, with some species constrained to low or high altitude, potentially reflecting soil nutrient availability. Leaf traits responded to altitude and local soil properties, suggesting interspecific differences in functional strategies according to the leaf economics spectrum (conservative vs. acquisitive).

CONCLUSIONS

The interspecific divergence in functional strategies in response to local environmental conditions suggests that trait variation could underlie ecological differentiation among Damburneya sympatric species.

Land-Use Change and Management Intensification Is Associated with Shifts in Composition of Soil Microbial Communities and Their Functional Diversity in Coffee Agroecosystems

Despite the central role of microorganisms in soil fertility, little understanding exists regarding the impact of management practices and soil microbial diversity on soil processes. Strong correlations among soil microbial composition, management practices, and microbially mediated processes have been previously shown. However, limited integration of the different parameters has hindered our understanding of agroecosystem functioning. Multivariate analyses of these systems allow simultaneous evaluation of the parameters and can lead to hypotheses on the microbial groups involved in specific nutrient transformations. In the present study, using a multivariate approach, we investigated the effect of microbial composition (16SrDNA sequencing) and soil properties in carbon mineralization (C_MIN) (BIOLOG™, Hayward, CA, USA) across different management categories on coffee agroecosystems in Mexico. Results showed that (i) changes in soil physicochemical variables were related to management, not to region, (ii) microbial composition was associated with changes in management intensity, (iii) specific bacterial groups were associated with different management categories, and (iv) there was a broader utilization range of carbon sources in non-managed plots. The identification of specific bacterial groups, management practices, and soil parameters, and their correlation with the utilization range of carbon sources, presents the possibility to experimentally test hypotheses on the interplay of all these components and further our understanding of agroecosystem functioning and sustainable management.

Assessment of above-ground biomass and carbon loss from a tropical dry forest in Mexico

Primary forests in seasonally dry tropical regions have undergone intense land-use/cover change, ranging from widespread shifting agriculture to land clearing for livestock production systems, and selective logging. Despite the importance of tropical dry forests (TDF), little is known about the implications of carbon (C) emissions from deforestation in local, national, and global scales. Therefore, the main objective of this study is to quantify and understand the processes that drive major C losses of this ecosystem in Mexico. Also, we evaluated the applicability of the already published above ground biomass (AGB) maps to quantify and allocate changes in C stocks. The results suggest that biomass maps can be used to capture the patterns of AGB distribution and to identify the driving forces of C emissions. The C losses are more related to socioeconomic drivers than biophysical characteristics like topography and climate. Besides, this study shows that published current AGB maps may be used for landscape management, including conservation and restoration areas.

Soil organic matter and phosphorus dynamics after low intensity prescribed burning in forests and shrubland

Various different factors have led to the accumulation of biomass in forest soils in the Mediterranean-climate region in the last few decades, thus exacerbating the effects of wildfires. Although prescribed burning is used to decrease the fuel load and reduce the currency of mega-wildfires, the impacts on soil organic matter (SOM) and nutrient cycling, and therefore on forest ecosystem sustainability, are uncertain. The present study was designed to cover a range of conditions and therefore to assess the variability in the responses in similar geographical areas. Three prescribed burning treatments producing different levels of soil burn severity were conducted in two different types of forests (Pinus nigra and Pinus pinaster) and one (previously treated by prescribed burning) shrubland ecosystem (Cytisus oromediterraneus), all characterized by different fuel loads and depths of soil organic layer, in Central Spain. After the treatments, the SOM content, its thermal properties, and the distribution of Phosphorus (P) forms (³¹P NMR spectroscopy) were measured in the soil organic layer and mineral soils (0-2 cm depth), and the results were related to the temperatures reached. The prescribed burning les to low-moderate perturbations in SOM quality and Carbon (C) and P dynamics. The organic P, which in the unburnt plots represented 70% of the extractable P, was greatly depleted (by 56 and 95% with respect the initials values). This effect was concurrent with decreases in the most thermolabile SOM fractions, suggesting that organic P is readily mineralized, even at relatively low temperatures. Release of large amounts of soluble orthophosphate may occur when the prescribed burning leads to a high level of soil burn severity. The findings show that prescribed burning treatments should be planned carefully in order to prevent long-term perturbation of C and P cycling.

Restoration planning to guide Aichi targets in a megadiverse country

Ecological restoration has become an important strategy to conserve biodiversity and ecosystems services. To restore 15% of degraded ecosystems as stipulated by the Convention on Biological Diversity Aichi target 15, we developed a prioritization framework to identify potential priority sites for restoration in Mexico, a megadiverse country. We used the most current biological and environmental data on Mexico to assess areas of biological importance and restoration feasibility at national scale and engaged stakeholders and experts throughout the process. We integrated 8 criteria into 2 components (i.e., biological importance and restoration feasibility) in a spatial multicriteria analysis and generated 11 scenarios to test the effect of assigning different component weights. The priority restoration sites were distributed across all terrestrial ecosystems of Mexico; 64.1% were in degraded natural vegetation and 6% were in protected areas. Our results provide a spatial guide to where restoration could enhance the persistence of species of conservation concern and vulnerable ecosystems while maximizing the likelihood of restoration success. Such spatial prioritization is a first step in informing policy makers and restoration planners where to focus local and large-scale restoration efforts, which should additionally incorporate social and monetary cost-benefit considerations.

Effect of initial soil properties on six-year growth of 15 tree species in tropical restoration plantings

In restoration plantings in degraded pastures, initial soil nutrient status may lead to differential growth of tropical tree species with diverse life history attributes and capacity for N₂ fixation. In 2006, we planted 1,440 seedlings of 15 native tree species in 16 fenced plots (30 × 30 m) in a 60‐year‐old pasture in Los Tuxtlas, Veracruz, Mexico, in two planting combinations. In the first year, we evaluated bulk density, pH, the concentration of organic carbon (C), total nitrogen (N), ammonia (NO3−), nitrate (NH4+), and total phosphorus (P) in the upper soil profile (0–20 cm in depth) of all plots. The first two axes of two principal component analyses explained more than 60% of the variation in soil variables: The axes were related to increasing bulk density, NO3−, NH4+, total N concentration, and pH. Average relative growth rates in diameter at the stem base of the juvenile trees after 6 years were higher for pioneer (45.7%) and N₂‐fixing species (47.6%) than for nonpioneer (34.7%) and nonfixing species (36.2%). Most N₂‐fixing species and those with the slowest growth rates did not respond to soil attributes. Tree species benefited from higher pH levels and existing litter biomass. The pioneers Ficus yoponensis, Cecropia obtusifolia, and Heliocarpus appendiculatus, and the N₂‐fixing nonpioneers Cojoba arborea, Inga sinacae, and Platymiscium dimorphandrum were promising for forest restoration on our site, given their high growth rates.

Enhancing single-wall carbon nanotube properties through controlled endohedral filling

Chemical control of the endohedral volume of single-wall carbon nanotubes (SWCNTs) via liquid-phase filling is established to be a facile strategy to controllably modify properties of SWCNTs in manners significant for processing and proposed applications. Encapsulation of over 20 different compounds with distinct chemical structures, functionalities, and effects is demonstrated in SWCNTs of multiple diameter ranges, with the ability to fill the endohedral volume based on the availability of the core volume and compatibility of the molecule's size with the cross-section of the nanotube's cavity. Through exclusion of ingested water and selection of the endohedral chemical environment, significant improvements to the optical properties of dispersed SWCNTs such as narrowed optical transition linewidths and enhanced fluorescence intensities are observed. Examples of tailoring modified properties towards applications or improved processing by endohedral passivation are discussed.

Variations in soil carbon sequestration and their determinants along a precipitation gradient in seasonally dry tropical forest ecosystems

The effect of precipitation regime on the C cycle of tropical forests is poorly understood, despite the existence of models that suggest a drier climate may substantially alter the source-sink function of these ecosystems. Along a precipitation regime gradient containing 12 mature seasonally dry tropical forests growing under otherwise similar conditions (similar annual temperature, rainfall seasonality, and geological substrate), we analyzed the influence of variation in annual precipitation (1240 to 642 mm) and duration of seasonal drought on soil C. We investigated litterfall, decomposition in the forest floor, and C storage in the mineral soil, and analyzed the dependence of these processes and pools on precipitation. Litterfall decreased slightly - about 10% - from stands with 1240 mm yr(-1) to those with 642 mm yr(-1), while the decomposition decreased by 56%. Reduced precipitation strongly affected C storage and basal respiration in the mineral soil. Higher soil C storage at the drier sites was also related to the higher chemical recalcitrance of litter (fine roots and forest floor) and the presence of charcoal across sites, suggesting an important indirect influence of climate on C sequestration. Basal respiration was controlled by the amount of recalcitrant organic matter in the mineral soil. We conclude that in these forest ecosystems, the long-term consequences of decreased precipitation would be an increase in organic layer and mineral soil C storage, mainly due to lower decomposition and higher chemical recalcitrance of organic matter, resulting from changes in litter composition and, likely also, wildfire patterns. This could turn these seasonally dry tropical forests into significant soil C sinks under the predicted longer drought periods if primary productivity is maintained.

A symmetric, triply interlaced 3-D anionic MOF that exhibits both magnetic order and SMM behaviour

Triply interpenetrated diamondoid nets of a Co citrate MOF, formed by SMM Co citrate cubanes bridged by six-coordinated Co(ii), preserve SMM behavior with magnetic blocking at 3.8 K, presenting magnetic order at 2.7 K.

Effects of Increased Nitrogen Availability on C and N Cycles in Tropical Forests: A Meta-Analysis

Atmospheric N deposition is predicted to increase four times over its current status in tropical forests by 2030. Our ability to understand the effects of N enrichment on C and N cycles is being challenged by the large heterogeneity of the tropical forest biome. The specific response will depend on the forest's nutrient status; however, few studies of N addition appear to incorporate the nutrient status in tropical forests, possibly due to difficulties in explaining how this status is maintained. We used a meta-analysis to explore the consequences of the N enrichment on C and N cycles in tropical montane and lowland forests. We tracked changes in aboveground and belowground plant C and N and in mineral soil in response to N addition. We found an increasing trend of plant biomass in montane forests, but not in lowland forests, as well as a greater increase in NO emission in montane forest compared with lowland forest. The N2O and NO emission increase in both forest; however, the N2O increase in lowland forest was significantly even at first time N addition. The NO emission increase showed be greater at first term compared with long term N addition. Moreover, the increase in total soil N, ammonium, microbial N, and dissolved N concentration under N enrichment indicates a rich N status of lowland forests. The available evidence of N addition experiments shows that the lowland forest is richer in N than montane forests. Finally, the greater increase in N leaching and N gas emission highlights the importance of study the N deposition effect on the global climate change.

Effects of precipitation regime and soil nitrogen on leaf traits in seasonally dry tropical forests of the Yucatan Peninsula, Mexico

Leaf traits are closely associated with nutrient use by plants and can be utilized as a proxy for nutrient cycling processes. However, open questions remain, in particular regarding the variability of leaf traits within and across seasonally dry tropical forests. To address this, we considered six leaf traits (specific area, thickness, dry matter content, N content, P content and natural abundance (15)N) of four co-occurring tree species (two that are not associated with N2-fixing bacteria and two that are associated with N2-fixing bacteria) and net N mineralization rates and inorganic N concentrations along a precipitation gradient (537-1036 mm per year) in the Yucatan Peninsula, Mexico. Specifically we sought to test the hypothesis that leaf traits of dominant plant species shift along a precipitation gradient, but are affected by soil N cycling. Although variation among different species within each site explains some leaf trait variation, there is also a high level of variability across sites, suggesting that factors other than precipitation regime more strongly influence leaf traits. Principal component analyses indicated that across sites and tree species, covariation in leaf traits is an indicator of soil N availability. Patterns of natural abundance (15)N in foliage and foliage minus soil suggest that variation in precipitation regime drives a shift in plant N acquisition and the openness of the N cycle. Overall, our study shows that both plant species and site are important determinants of leaf traits, and that the leaf trait spectrum is correlated with soil N cycling.

Discovery of blood transcriptomic markers for depression in animal models and pilot validation in subjects with early-onset major depression

Early-onset major depressive disorder (MDD) is a serious and prevalent psychiatric illness in adolescents and young adults. Current treatments are not optimally effective. Biological markers of early-onset MDD could increase diagnostic specificity, but no such biomarker exists. Our innovative approach to biomarker discovery for early-onset MDD combined results from genome-wide transcriptomic profiles in the blood of two animal models of depression, representing the genetic and the environmental, stress-related, etiology of MDD. We carried out unbiased analyses of this combined set of 26 candidate blood transcriptomic markers in a sample of 15-19-year-old subjects with MDD (N=14) and subjects with no disorder (ND, N=14). A panel of 11 blood markers differentiated participants with early-onset MDD from the ND group. Additionally, a separate but partially overlapping panel of 18 transcripts distinguished subjects with MDD with or without comorbid anxiety. Four transcripts, discovered from the chronic stress animal model, correlated with maltreatment scores in youths. These pilot data suggest that our approach can lead to clinically valid diagnostic panels of blood transcripts for early-onset MDD, which could reduce diagnostic heterogeneity in this population and has the potential to advance individualized treatment strategies.

Magnetic dipolar ordering and quantum phase transition in an Fe8 molecular magnet

We show that a crystal of mesoscopic Fe(8) single-molecule magnets is an experimental realization of the quantum Ising model in a transverse field, with dipolar interactions. Quantum annealing has enabled us to explore the quantum and classical phase transitions between the paramagnetic and ferromagnetic phases, at thermodynamical equilibrium. The phase diagram and critical exponents that we obtain agree with expectations for the mean-field universality class.

Oral complication risks after invasive and non-invasive dental procedures in HIV-positive patients

BACKGROUND

Limited published scientific evidence is available to provide guidance to clinicians on possible increased risks of invasive oral procedures associated with the human immunodeficiency virus (HIV) status of the patient. The aim of this study was to assess post-procedural complications in patients infected with HIV.

MATERIAL AND METHODS

This was a retrospective cross-sectional study of the records of 101 consecutive HIV patients treated at the School of Dentistry of Madrid Complutense University and Sandoval STD Clinic in Madrid between January 2003 and February 2005. Data were gathered by an experienced dental practitioner using a structured epidemiological questionnaire for information on gender, age, HIV transmission category, medical history, hepatitis B virus (HBV) or hepatitis C virus (HCV) coinfection and other diseases, TCD4+ and TCD8+ count, HIV viral load (VL), platelet count, neutrophil count, international normalized ratio and haemoglobin level; tobacco and alcohol intake, highly active antiretroviral treatment and presence of oral lesions. Information was also collected on complications related to dental treatment (invasive or non-invasive) during the previous 6 months. Chi-squared test and Fisher's exact test were used to establish statistical significance.

RESULTS

Data were gathered on 314 dental procedures in 101 patients. The overall complication rate was 2.2% (7/314); in 147 invasive procedures, seven complications (4.8%) were documented (one persistent pain, two prolonged bleeding, three infections, one bone sequestrum) including extractions, periodontal scaling, endodontic treatment and biopsy. No differences were found in TCD4+, TCD8+, platelet count, HBV or HCV co-infections or HIV VL between patients with and/or without complications. Patients with complications were mainly in B stage of HIV disease (P=0.020). Oral lesions and smoking habit>20 cig day-1 were documented in 83.3% (P=0.086) and 50% (P=0.060), respectively, of patients with complications.

CONCLUSIONS

The complication rate was 2.2% overall and 4.8% after invasive dental procedures. Presence of oral lesions, smoking habit or HIV clinical stage B may be predictive factors for oral complications in HIV patients. No relationship was found between complications and virological, immunological or other laboratory values. Studies with wider samples and negative control group are warranted to confirm the absence of an association between HIV positivity and higher risk of oral complications.

Oral transmission of HIV, reality or fiction? An update

Human immunodeficiency virus (HIV) and many other viruses can be isolated in blood and body fluids, including saliva, and can be transmitted by genital-genital and especially anal-genital sexual activity. The risk of transmission of HIV via oral sexual practices is very low. Unlike other mucosal areas of the body, the oral cavity appears to be an extremely uncommon transmission route for HIV. We present a review of available evidence on the oral-genital transmission of HIV and analyse the factors that act to protect oral tissues from infection, thereby reducing the risk of HIV transmission by oral sex. Among these factors we highlight the levels of HIV RNA in saliva, presence of fewer CD4+ target cells, presence of IgA antibodies in saliva, presence of other infections in the oral cavity and the endogenous salivary antiviral factors lysozyme, defensins, thrombospondin and secretory leucocyte protease inhibitor (SLPI).

Metal-insulator transition in Nd(1-x)Eu(x)NiO(3) compounds

Polycrystalline Nd(1-x)Eu(x)NiO(3) (0≤x≤0.5) compounds were synthesized in order to investigate the character of the metal-insulator (MI) phase transition in this series. Samples were prepared through the sol-gel route and subjected to heat treatments at ∼1000 °C under oxygen pressures as high as 80 bar. X-ray diffraction (XRD) and neutron powder diffraction (NPD), electrical resistivity ρ(T), and magnetization M(T) measurements were performed on these compounds. The NPD and XRD results indicated that the samples crystallize in an orthorhombic distorted perovskite structure, space group Pbnm. The analysis of the structural parameters revealed a sudden and small expansion of ∼0.2% of the unit cell volume when electronic localization occurs. This expansion was attributed to a small increase of ∼0.003 Å of the average Ni-O distance and a simultaneous decrease of ∼-0.5° of the Ni-O-Ni superexchange angle. The ρ(T) measurements revealed a MI transition occurring at temperatures ranging from T(MI)∼193 to 336 K for samples with x = 0 and 0.50, respectively. These measurements also show a large thermal hysteresis in NdNiO(3) during heating and cooling processes, suggesting a first-order character of the phase transition at T(MI). The width of this thermal hysteresis was found to decrease appreciably for the sample Nd(0.7)Eu(0.3)NiO(3). The results indicate that cation disorder associated with increasing substitution of Nd by Eu is responsible for changing the first-order character of the transition in NdNiO(3).

Synthesis of indole derivatives via isocyanides

Fast and convenient approaches to the indole nucleus from isocyanides are reviewed as a means for the tailored preparation of conveniently functionalized indoles by using the unique reactivity of isocyanides in one-pot multicomponent and cascade reactions.

Long-range ferromagnetism of Mn12 acetate single-molecule magnets under a transverse magnetic field

We use neutron diffraction to probe the magnetization components of a crystal of Mn12 single-molecule magnets. Each of these molecules behaves, at low temperatures, as a nanomagnet with spin S = 10 and strong anisotropy along the crystallographic c axis. The application of a magnetic field H(perpendicular) perpendicular to c induces quantum tunneling between opposite spin orientations, enabling the spins to attain thermal equilibrium. For T approximately < 0.9(1) K, this equilibrium state shows spontaneous magnetization, indicating the onset of ferromagnetism. These long-range magnetic correlations nearly disappear for mu0H(perpendicular) approximately > 5.5 T, possibly suggesting the existence of a quantum critical point.

Oral candidiasis as a clinical marker related to viral load, CD4 lymphocyte count and CD4 lymphocyte percentage in HIV-infected patients

BACKGROUND

High viral load is currently considered to be one of the main indicators of the progression of HIV-induced immunodepression, but few studies have analysed its relationship to the presence of oral candidiasis (OC). The aim of this cross-sectional study is to analyse the relationship between viral load, total CD4 lymphocyte count, and percentage of CD4 lymphocytes to the occurrence of OC.

METHODS

The present cross-sectional study included 156 HIV-infected patients seen at a clinic for sexually transmitted diseases and HIV. We assessed the presence or absence of OC, and microbiological samples were obtained from the palatine mucosa and dorsal tongue for a smear stained with KOH (potassium hydroxide) and culture on Sabouraud's dextrose agar in all patients. Viral load was determined by quantification of viral RNA in peripheral blood with a minimum detectable level of 500 RNA copies/ml. CD4+ counts/CD4+ percentage were categorized as <200/<14%, 200-499/14-28%, and >500/>29%, and HIV viral loads were categorized as <500, 500-10,000, >10,000 copies/ml.

RESULTS

Thirty-eight percent (37.8%) of the patients had OC. Patients with CD4+ lymphocyte counts below 200 x 10(6)/l and CD4+ percentages below 14% showed a significantly higher frequency of OC (57.9% and 48.0%, respectively). Patients with a viral load over 10,000 copies/ml also had OC more frequently (44.8%). In the multiple logistic regression analysis, OC showed a statistically significant association with high viral load [>10,000 vs <500, odds ratio (OR)=11.4], low percentage of CD4+ lymphocytes (<14% vs >28%, OR=5), and injection drug use (IDU vs heterosexual transmission, OR=10.2). In HIV-infected patients, high viral load was associated with more frequent OC, regardless of CD4+ lymphocyte level.

CONCLUSIONS

These findings suggest that oral candidiasis could be a useful clinical marker of patients with high viral load. In view of these results, emphasis should be placed on the importance of systematic examination of the oral cavity in all medical follow-up examinations of HIV-infected patients.

Pulses of soil phosphorus availability in a Mexican tropical dry forest: effects of seasonality and level of wetting

Intact cores from the upper soil profile and surface litter were collected at the peak of the dry season and during the rainy period in the tropical deciduous forest of the Chamela region, Jalisco, México, to (1) analyze upper soil phosphorus (P) movement and retention, (2) compare soil P dynamic pools (soluble, bicarbonate, and microbial) in dry and rainy seasons, and (3) determine the response of these P pools to wetting. Unperturbed litter-soil cores were treated in the laboratory with either 10 mm or 30 mm of simulated rain with carrier-free ³²P and compared to a control (no water addition) to determine the fate and retention of added P. ³¹P concentrations and pools in most litter and soil fractions were higher in the dry than in the rainy season. Soluble P was 0.306 g/m² and microbial P was 0.923 g/m² in the dry season (litter plus soil) versus 0.041 (soluble) and 0.526 (microbial) g P/m² in the rainy season. After water addition, rainy-season cores retained 99.9 and 94% of ³²P in the 10- and 30-mm treatments, respectively. Dry-season samples retained 98.9 and 80% of inputs in the same treatments. Retention after wetting occurred mostly in soil (bicarbonate and microbial fractions). Simulated rainfall on rainy-season soils increased P immobilization. On the other hand, simulated rainfall on dry-season soils released P through mineralization. The P release represents between 46 and 99% of the annual litterfall return. Our results suggest that both soluble and microbial P constitute important sources for initiation of plant growth at the onset of the rainy season in tropical dry forest.

Continent colostomy by means of a new one-piece disposable device. Preliminary report

A study was established concerning a continent colostomy system consisting of a new one-piece disposable plug. Twenty patients participated: 13 men and 7 women, who ranged in age from 35 to 87 years. All patients had an end colostomy located on the left lower quadrant. The colostomy age ranged from 2 months to 7 years. Of the 20 participants, 17 found the new procedure to be safer and more comfortable, as well as a considerable improvement for their quality of life. The other three patients found no advantage in its use. In no case was there any perception of local, secondary, or general adverse effects owing to its use. Taking into consideration that the use of this new device does not require any type of special conditioning, we consider that it can contribute to the better quality of life of a colostomy patient, the one best able to evaluate the worthiness of its use.