Eastern Canadian boreal forest soil and foliar chemistry show evidence of resilience to long-term nitrogen addition

The boreal forest is one of the world's largest terrestrial biome and plays crucial roles in global biogeochemical cycles, such as carbon (C) sequestration in vegetation and soil. However, the impacts of decades of N deposition on N-limited ecosystems, like the eastern Canadian boreal forest, remain unclear. For 13 years, N deposition was simulated by periodically adding ammonium nitrate on soils of two boreal coniferous forests (i.e., balsam fir and black spruce) of eastern Canada, at low (LN) and high (HN) rates, corresponding to 3 and 10 times the ambient N deposition, respectively. We show that more than a decade of N addition had no strong effects on mineral soil C, N, P, and cation concentrations and on foliar total Ca, K, Mg, and Mn concentrations. In organic soil, C stock was not affected by N addition while N stock increased, and exchangeable Ca2+ and Mg2+ decreased at the balsam fir site under HN treatment. At both sites, LN treatment had nearly no impact on foliage and soil chemistry but foliar N and N:P significantly increased under HN treatment, potentially leading to foliar nutrient imbalance. Overall, our work indicates that, in the eastern Canadian boreal forest, soil and foliar nutrient concentrations and stocks are resilient to increasing N deposition potentially because, in the context of N limitation, extra N would be rapidly immobilized by soil micro-organisms and vegetation. These findings could improve modeling future boreal forest soil C stocks and biomass growth and could help in planning forest management strategies in eastern Canada.

Evaluating the effect of moss functional traits and sampling on elemental concentrations in Pleurozium schreberi and Ptilium crista-castrensis in Eastern Canada (Québec) black spruce forest

Characterizing atmospheric depositions allows evaluating the impact of air pollution on ecosystems, human health, and the economy. It also informs decision-makers about the implementation of regulations improving environmental quality. Biomonitoring uses organisms, such as mosses, as proxies to assess the presence of atmospheric contaminants (e.g., metals). This approach is cost-efficient and does not require complicated infrastructure or scientific skills, making it suitable for large-scale monitoring initiatives and citizen-based campaigns. Therefore, precise sampling protocols are needed to limit bias. Biomonitoring data remains scarce in North America, compared to e.g., Europe, and there is a need to develop large-scale and long-term biomonitoring initiatives to record current and future atmospheric depositions. As there is no standardized international sampling protocol, this study assessed the impact of parameters known to affect the elemental concentration of mosses, using samples collected along a 1000-km transect in Eastern Canada (Quebec) from 2016 to 2022. We specifically examined the effects of species, stem color, canopy opening, time of sampling, and stem length on 18 elements. Non-parametric statistical tests indicate that these factors have significant effects on some metals, but differences are generally low (<30 %), except for stem length. These results suggest that sampling protocols can be flexible in terms of species, canopy opening, time of sampling, and stem color. However, normalizing the length of the stems analyzed is required to account for differences in growth rates between sites. Moreover, since no large-scale biomonitoring campaign using mosses has been conducted in Eastern Canada, this paper also provides the first elemental baseline for moss in the region.

Unraveling global and diazotrophic bacteriomes of boreal forest floor feather mosses and their environmental drivers at the ecosystem and at the plant scale in North America

Feather mosses are abundant cryptogams of the boreal forest floor and shelter a broad diversity of bacteria who have important ecological functions (e.g., decomposition, nutrient cycling). In particular, nitrogen (N₂-) fixation performed by feather moss-associated diazotrophs constitutes an important entry of nitrogen in the boreal forest ecosystem. However, the composition of the feather moss bacteriome and its environmental drivers are still unclear. Using cDNA amplicon sequencing of the 16S rRNA and nifH genes and cyanobacterial biomass quantification, we explored the active global and diazotrophic bacterial communities of two dominant feather moss species (i) at the ecosystem scale, along a 500-km climatic and nutrient deposition gradient in the North American boreal forest, and (ii) at the plant scale, along the moss shoot senescence gradient. We found that cyanobacteria were major actors of the feather moss bacteriome, accounting for 33% of global bacterial communities and 65% of diazotrophic communities, and that several cyanobacterial and methanotrophic genera were contributing to N₂-fixation. Moreover, we showed that bacteria were occupying ecological niches along the moss shoot, with phototrophs being dominant in the apical part and methanotrophs being dominant in the basal part. Finally, climate (temperature, precipitation), environmental variables (moss species, month, tree density) and nutrients (nitrogen, phosphorus, molybdenum, vanadium, iron) strongly shaped global and diazotrophic bacteriomes. In summary, this work presents evidence that the feather moss bacteriome plays crucial roles in supporting moss growth, health, and decomposition, as well as in the boreal forest carbon and nitrogen cycles. This study also highlights the substantial effects of climate and nutrients on the feather moss bacteriome, suggesting the importance of understanding the impacts of global change on moss-associated bacterial growth and activity.

Quantification of Moss-Associated Cyanobacteria Using Phycocyanin Pigment Extraction

In the boreal forest, cyanobacteria can establish associations with feather moss and realize the biological nitrogen fixation (BNF) reaction, consisting in the reduction of atmospheric dinitrogen into bioavailable ammonium. In this ecosystem, moss-associated cyanobacteria are the main contributors to BNF by contributing up to 50% of new N input. Current environmental changes driven by anthropogenic activities will likely affect cyanobacteria activity (i.e., BNF) and populations inhabiting mosses, leading to potential important consequences for the boreal forest. Several methods are available to efficiently measure BNF activity, but quantifying cyanobacteria biomass associated with moss is challenging because of the difficulty to separate bacteria colonies from the host plant. Attempts to separate cyanobacteria by shaking or sonicating in water were shown to be poorly efficient and repeatable. The techniques commonly used, microscopic counting and quantitative PCR (qPCR) are laborious and time-consuming. In aquatic and marine ecosystems, phycocyanin (PC), a photosynthesis pigment produced by cyanobacteria, is commonly used to monitor cyanobacteria biomass. In this study, we tested if PC extraction and quantification can be used to estimate cyanobacteria quantity inhabiting moss. We report that phycocyanin can be easily extracted from moss by freeze/thaw disturbance of cyanobacteria cells and can be quickly and efficiently measured by spectrofluorometry. We also report that phycocyanin extraction is efficient (high recovery), repeatable (relative SD < 13%) and that no significant matrix effects were observed. As for aquatic systems, the main limitation of cyanobacteria quantification using phycocyanin is the difference of cellular phycocyanin content between cyanobacteria strains, suggesting that quantification can be impacted by cyanobacteria community composition. Nonetheless, we conclude that phycocyanin extraction and quantification is an easy, rapid, and efficient tool to estimate moss-associated cyanobacteria number.

The coastal environment affects lead and sodium uptake by the moss Hypnum cupressiforme used as an air pollution biomonitor

Several studies suggest that potential competition exists between marine cations and heavy metals for binding sites on the cell wall of mosses. This competition would impact the heavy metal concentration measured in mosses by biomonitoring programs, which may underestimate air pollution by heavy metals in a coastal environment. In the present study, we aim to identify possible mechanisms affecting lead uptake by mosses in a coastal environment, specifically, the competition between lead (Pb²⁺) and sodium (Na⁺) for binding sites in Hypnum cupressiforme (Hc). We also compared the response of continental and coastal Hc populations to Pb²⁺ exposure by immersing the moss samples in artificial solutions that comprised six experimental treatments and subsequently locating and quantifying Pb²⁺ and Na⁺ using the sequential elution technique and X-ray microanalyses with a scanning electron microscope. We demonstrated that high concentrations of Pb²⁺ prevented Na⁺ from binding to the cell wall. We also examined the effect of the salt acclimation of Hc on Pb²⁺ and Na⁺ accumulation. Coastal Hc populations accumulated more Na and less Pb than continental Hc populations in all treatments. Moreover, our results showed treatment effects on the intra/extracellular distribution of Na⁺, as well as site. This feedback on the influence of salt stress tolerance on Pb²⁺ uptake by mosses requires further study and can be investigated for other heavy metals, leading to a better use of mosses as biomonitoring tools.

Urbanization drives the evolution of parallel clines in plant populations

Urban ecosystems are an increasingly dominant feature of terrestrial landscapes. While evidence that species can adapt to urban environments is accumulating, the mechanisms through which urbanization imposes natural selection on populations are poorly understood. The identification of adaptive phenotypic changes (i.e. clines) along urbanization gradients would facilitate our understanding of the selective factors driving adaptation in cities. Here, we test for phenotypic clines in urban ecosystems by sampling the frequency of a Mendelian-inherited trait-cyanogenesis-in white clover (Trifolium repens L.) populations along urbanization gradients in four cities. Cyanogenesis protects plants from herbivores, but reduces tolerance to freezing temperatures. We found that the frequency of cyanogenic plants within populations decreased towards the urban centre in three of four cities. A field experiment indicated that spatial variation in herbivory is unlikely to explain these clines. Rather, colder minimum winter ground temperatures in urban areas compared with non-urban areas, caused by reduced snow cover in cities, may select against cyanogenesis. In the city with no cline, high snow cover might protect plants from freezing damage in the city centre. Our study suggests that populations are adapting to urbanization gradients, but regional climatic patterns may ultimately determine whether adaptation occurs.

Risk factors of postoperative vomiting in children receiving continuous intravenous morphine

BACKGROUND

Risk factors of postoperative vomiting (POV) have been less extensively explored in children compared to adults. We analyzed the risk factors of POV in children receiving continuous intravenous (i.v.) morphine in a standardized manner without POV prophylaxis after major surgery.

METHODS

This observational retrospective study included 235 children aged from 2 to 216 months (91 F:144 M, 11.5% <6 months, 31.5% 6-11 months). The primary end point was the occurrence of at least one episode of POV recorded on the nursing chart. The independent predictors of POV were determined by univariate analysis followed by a multivariate analysis by logistic regression. The data are presented as either medians (25th-75th percentile) or as values with a 95% confidence interval.

RESULTS

Continuous i.v. morphine was administered over 42 (22-60) h with an initial infusion rate of 20 µg x kg(-1) x h(-1) in 63% of cases, which was increased in 31.5% of cases and was accompanied by an additional bolus in 39.2% of children. At least one episode of POV occurred in 22.6% of children. The following three independent factors were associated with POV: female gender (OR 3.324 [1.695-6.519], P=0.0005), urological surgery (OR 5.605 [1.291-24.340], P=0.0214) and age (OR 1.012 [1.006-1.018], P<0.0001). The discriminating characteristics of the model were good with an ROC curve AUC of 0.778, sensitivity of 71.7% and specificity of 71.4% for a 0.22 cut-off value of POV incidence. The positive predictive value was 42.2%, and the negative predictive value was 89.6%.

CONCLUSION

Female gender, which is usually considered a risk factor after puberty, should be taken into account independent of age to guide the POV prophylaxis in children receiving a postoperative continuous i.v. morphine infusion.

Asynchronous Relaxation of Morphological Operators: A Joint Algorithm-Architecture Perspective

Asynchronous dynamics are introduced for the iterative computation of morphological image filters. We propose a fine-grain asynchronous algorithmic- architectural model that exploits these new possibilities to improve the convergence efficiency of such operators over standard sequential-recursive or parallel-synchronous update modes. We conclude with VLSI design perspectives and show how asynchronism can be exploited both at functional and architectural levels.

Fluoride excretion in children after sevoflurane anaesthesia

BACKGROUND

Defluorination of sevoflurane is catalysed by the hepatic enzyme cytochrome P450 2E1 (CYP2E1). Data about the ontogenesis (developmental variations in activity) of this enzyme suggest a low metabolism of sevoflurane during the first months of life.

METHODS

To test this hypothesis, 45 children less than 48 months of age undergoing sevoflurane anaesthesia were enrolled in a prospective open clinical trial. The 24 h urine fluoride excretion was measured in five groups of children (A, <4 months; B, 4 to <8 months; C, 8-12 months; D, >12-24 months; and E, >24-48 months old). An index of sevoflurane metabolism (ISM) was calculated as the ratio of fluoride excretion, cumulative expiratory sevoflurane concentrations measured every minute during anaesthesia, and body surface area. ISM values were median (IQ 25-75%).

RESULTS

ISM was lower in group A (n=9, 18.9 (11.2-29.5) than group C (n=11, 44.2 (37.5-53.5), P<0.05), group D (n=7, 52.6 (45.8-68.4), P<0.01) and group E (n=9, 53.6 (50.7-85), P<0.001). Median ISM expressed as a function of median age, exponentially increased with a rapid increase during the first months of life, followed by a slower increase after 10 months of age.

CONCLUSION

These results suggest that, in children less than 48 months, sevoflurane metabolism parallels postnatal development of CYP2E1.

Does sevoflurane inhibit serum cholinesterase in children?

Serum cholinesterase activity was measured at induction, and following anaesthesia in 41 children aged between 4 and 30 months. The median exposure to sevoflurane was 273%.min. The results did not demonstrate any significant difference in cholinesterase activity, when expressed by gram of serum proteins following inhalation anaesthesia using sevoflurane or intravenous anaesthesia using propofol. The values (SD) obtained were 175 (42) UI.g(-1) before anaesthesia and 177 (43) UI.g(-1) following anaesthesia. The only change in cholinesterase activity detected was related to heamodilution. We conclude that plasma fluoride concentration following sevoflurane administration [13.8 (4.2) microm x l(-1)] is too low to exert an inhibiting effect on in vivo cholinesterase activity and that the previously reported decrease in mivacurium requirements during sevoflurane anaesthesia is unlikely to be due to inhibition by fluoride ions.

Postoperative epidural analgesia with bupivacaine and fentanyl: hourly pain assessment in 348 paediatric cases

BACKGROUND

The objective of this prospective study was the evaluation of the analgesia provided by an epidural infusion of bupivacaine and fentanyl after different types of surgery in children.

METHODS

Data were collected from 348 epidural analgesia in 87 children below 2 years of age, in 80 children between 2 and 6 years and 181 above 6 years of age, for a median duration of 43 postoperative hours. Bupivacaine (mean concentration 0.185%) and fentanyl (5 microg.kg-1.day-1) were administered on the surgical ward.

RESULTS

Pain control was considered excellent in 86% of the 11 072 pain hourly assessments. Analgesia was found to be better for children older than 2 years, and the overall quality of their night's sleep was better than that of older children. Higher pain scores were noted for Nissen fundoplication surgery and club foot repairs. Early discontinuation rarely occurred, and only because of technical problems with the epidural catheter (4%) or insufficient analgesia (6%). Complications were minor (nausea/vomiting 14%, pruritus 0.6%, urinary retention 17%) and easily reversed.

CONCLUSIONS

This combination of bupivacaine-fentanyl provides safe analgesia after major surgery in children with frequent clinical monitoring. Regular pain assessments of intensity and duration are useful to improve the quality of postoperative analgesia.

Midazolam for premedication in children: nasal vs. rectal administration

The authors compared the acceptance and efficacy of rectal and nasal administration of midazolam (MDZ) for premedication. Ninety-five ASA I and II paediatric patients (8 months to 12 years) scheduled for elective surgery were randomly allocated to two groups. Group R received 0.3 mg kg-1 of rectal midazolam (in 5 mL saline). Group N received 0.2 mg kg-1 of nasal midazolam (5 mg ml-1). Both groups were divided in two subgroups according to age (group RA (< or = 6 years, n = 33), group RB (> 6 years, n = 18), group NA (< or = 6 years, n = 28), group NB (> 6 years, n = 16)). At the time of premedication, tolerance to the administration was confirmed. Twenty min after rectal or 10 min after nasal administration the quality of sedation was recorded. The nasal midazolam, in commonly used dosages, induced a sedation similar to that following rectal administration with a shorter delay of onset. Nasal administration was more often painful than rectal administration. Swallowing (nasal midazolam) and concerns about modesty (rectal midazolam) were more frequent in older children. Because of its poor tolerance, nasal premedication should be reversed for cases where there is no alternative. Rectal premedication should be avoided in older children.

Real-time spike detection in EEG signals using the wavelet transform and a dedicated digital signal processor card

This paper describes a complete real-time system for EEG signal analysis. Specific software and hardware have been designed to provide biologists with an efficient tool, which allows a complete study of the different states of vigilance as well as the paroxysmal activities. The analysis method which is based on the wavelet transform is first presented and compared to the standard spectral approach. The dedicated digital signal processor card, based on the Motorola 96002 processor chip, that has been designed to support real-time acquisition and real-time processing of EEG signals is then presented. We finally illustrate the proposed method by processing real EEG signals of rats, and show that it opens up new prospects in the domain of EEG-based diagnosis. We propose a new representation, called globalization, that provides a global view and better detection of paroxysmal activities.