Photosynthesis, growth and resistance to extreme environments in lichens from polar and alpine regions

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Farmacia, Departamento de Biología Vegetal II, leída el 20/06/2013Los líquenes dominan alrededor de un 8% de los ecosistemas terrestres, siendo especialmente representativos en regiones polares y alpinas. Ambas regiones están consideradas como zonas de riesgo en posibles futuros escenarios de cambio ambiental, por lo que existe un creciente interés en entender los mecanismos que regulan la presencia de estos organismos en dichos ecosistemas. Esta tesis doctoral utiliza la fotosíntesis como hilo conductor para, a lo largo de cinco capítulos, aclarar las relaciones entre metabolismo y crecimiento y tratar de acotar la capacidad de resistencia de estos organismos a condiciones ambientales extremas. Los capítulos I, II, III y IV abordan sobre todo el primer aspecto, aportando información novedosa. Se incluyen relaciones entre biotipo y metabolismo en distintos líquenes alpinos, y se refuerza el uso de la liquenometría desde el punto de vista fisiológico, ya que no se han encontrado relaciones entre tamaño de talo y fotosíntesis en el género alpino Rhizocarpon. Los capítulos III y IV pasan de las regiones alpinas a las polares, con un estudio ecofisiológico global del género Placopsis en Tierra de Fuego y una comparativa de actividad metabólica y microclima entre distintas especies en dos extremos climáticos del continente antártico. Dicha comparativa explica las diferencias en tasas de crecimiento, biomasa y cobertura entre ambos lugares. El segundo objetivo, los límites de la resistencia de los líquenes a ambientes extremos, se aborda a lo largo de toda la memoria, pero especialmente en los capítulos IV y V. En ellos se explican los mecanismos de resistencia de dos especies distintas de líquenes a un desierto polar en la Antártida continental y se explican los resultados de la exposición real a condiciones espaciales del liquen Circinaria gyrosa. Los resultados demuestran que los límites de la capacidad de resistencia de los líquenes a condiciones extremas aún no han sido establecidos.Lichens are the most important organisms in the 8% of the terrestrial ecosystems, being especially relevant in polar and alpine regions. Both regions are considered under risk in possible future climate change scenarios and there is a rising interest in understanding the mechanisms controlling the distribution of these organisms in such ecosystems. This work uses photosynthesis as the main driver to clarify the relationships between growth and metabolism and to try to establish a limit for the resistance of lichens to extreme environments. The chapters I, II, III and IV are focused mainly in the first objective, showing new information about it. Relationships between biotype and metabolism are included in different alpine lichens, and the use of lichenometry is reinforced from a physiological perspective because no links have been found between photosynthesis and thallus size in the alpine crustose genus Rhizocarpon. The chapters III and IV change from alpine to polar regions, with a general ecophysiological study of the crustose tripartite genus Placopsis in Tierra de Fuego and a comparison of physiological and microclimatic activity of different lichen species between two climatic extremes in Antarctica. The second objective, the limits of the resistance to extreme environments, is studied trough the whole work but is present mainly in chapters IV and V. The resistance mechanisms of two different species in a Polar Desert in Contienetal Anatrctica are explained, and the resistance of the lichen Circinaria gyrosa to real space conditions is evaluated. The results show that the limits of the resistance of lichens to extreme environmental conditions are still open.Depto. de Farmacología, Farmacognosia y BotánicaFac. de FarmaciaTRUEunpu

Relative humidity predominantly determines long‐term biocrust‐forming lichen cover in drylands under climate change

1. Manipulative experiments typically show a decrease in dryland biocrust cover and altered species composition under climate change. Biocrust‐forming lichens, such as the globally distributed Diploschistes diacapsis, are particularly affected and show a decrease in cover with simulated climate change. However, the underlying mechanisms are not fully understood, and long‐term interacting effects of different drivers are largely unknown due to the short‐term nature of the experimental studies conducted so far. 2. We addressed this gap and successfully parameterised a process‐based model for D. diacapsis to quantify how changing atmospheric CO2, temperature, rainfall amount and relative humidity affect its photosynthetic activity and cover. We also mimicked a long‐term manipulative climate change experiment to understand the mechanisms underlying observed patterns in the field. 3. The model reproduced observed experimental findings: warming reduced lichen cover, whereas less rainfall had no effect on lichen performance. This warming effect was caused by the associated decrease in relative humidity and non‐rainfall water inputs, which are major water sources for biocrust‐forming lichens. Warming alone, however, increased cover because higher temperatures promoted photosynthesis during early morning hours with high lichen activity. When combined, climate variables showed non‐additive effects on lichen cover, and effects of increased CO2 levelled off with decreasing levels of relative humidity. 4. Synthesis. Our results show that a decrease in relative humidity, rather than an increase in temperature, may be the key factor for the survival of the lichen D. diacapsis under climate change and that effects of increased CO2 levels might be offset by a reduction in non‐rainfall water inputs in the future. Because of a global trend towards warmer and drier air and the widespread global distribution of D. diacapsis, this will affect lichen‐dominated dryland biocrust communities and their role in regulating ecosystem functions worldwide.This research was supported by the Collaborative Research Centre 973 (www.sfb973.de) of the German Research Foundation (DFG) and by the European Research Council (grant agreement no. 647038 (BIODESERT)). P. Porada appreciates funding by Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—408092731. F.T. Maestre acknowledges support from Generalitat Valenciana (CIDEGENT/2018/041) and the Alexander Von Humboldt Foundation. J. Raggio acknowledges the ERA-Net BiodivERsA program as Soil Crust InterNational (SCIN) and The Spanish Ministerio de Economía y Competitividad (MINECO) project numbers PRI-PIMBDV-2011-0874 and CRYPTOCOVER, CTM2015-64728-C21-R

Himantormia lugubris, an Antarctic endemic on the edge of the lichen symbiosis

Himantormia lugubris is an Antarctic endemic with a distribution restricted to the northwest tip of Antarctic Peninsula, adjacent islands and South Georgia Island. In this region H. lugubris is an important component of the epilithic lichen community. The species has a fruticose thallus with usually simple and flattened branches whose grey surface is often disrupted exposing the black and dominant chondroid axis. Because the photobiont cells are mainly restricted to the patchy grey areas, positive carbon balance seems to be rather difficult for this species. Therefore, the aim of this paper is to elucidate which functional strategy, possibly linked with thallus anatomy, is used by H. lugubris that enables it to be a successful species in the maritime Antarctic. To achieve this goal, we constructed a picture of the lichen’s physiological, anatomical and morphological characteristics by using a broad range of technologies, such as chlorophyll fluorescence, CO exchange and electron microscopy. We found that H. lugubris has a very low net photosynthesis, apparently restricted to the grey areas, but high respiratory rates. Therefore, positive net photosynthesis is only possible at low temperatures. Chlorophyll content is also low but is present in both gray and black areas. Our conclusion is that the only possibility for this species to achieve a positive carbon balance is to be active for long periods under optimal conditions, that means, wet, cold and with enough light, a common combination in this region of Antarctica. Given these constrains, we suggest that H. lugubris is likely to be especially sensitive species to predicted climate warming in the maritime Antarctic.Field work as well as most of the lab experiments were supported by the grant CTM2015-64728-C2-1-R (MINECO/FEDER, UE). Electron microscopy work wassupported by the grant CTM2015-64728-C2-2-R (MINECO/FEDER, UE)

Exploring environmental and physiological drivers of the annual carbon budget of biocrusts from various climatic zones with a mechanistic data-driven model

Biocrusts are a worldwide phenomenon, contributing substantially to ecosystem functioning. Their growth and survival depend on multiple environmental factors, including climatic ones, and the relations of these factors to physiological processes. Responses of biocrusts to individual environmental factors have been examined in a large number of field and laboratory experiments. These observational data, however, have rarely been assembled into a comprehensive, consistent framework that allows quantitative exploration of the roles of multiple environmental factors and physiological properties for the performance of biocrusts, in particular across climatic regions. Here we used a data-driven mechanistic modelling framework to simulate the carbon balance of biocrusts, a key measure of their growth and survival. We thereby assessed the relative importance of physiological and environmental factors for the carbon balance at six study sites that differ in climatic conditions. Moreover, we examined the role of seasonal acclimation of physiological properties using our framework, since the effects of this process on the carbon balance of biocrusts are poorly constrained so far. We found substantial effects of air temperature, CO2 concentration, and physiological parameters that are related to respiration on biocrust carbon balance, which differ, however, in their patterns across regions. The ambient CO2 concentration is the most important factor for biocrusts from drylands, while air temperature has the strongest impact at alpine and temperate sites. Metabolic respiration cost plays a more important role than optimum temperature for gross photosynthesis at the alpine site; this is not the case, however, in drylands and temperate regions. Moreover, we estimated a small annual carbon gain of 1.5 g m−2 yr−1 by lichen-dominated biocrust and 1.9 g m−2 yr−1 by moss-dominated biocrust at a dryland site, while the biocrusts lost a large amount of carbon at some of the temperate sites (e.g. −92.1 for lichen-dominated and −74.7 g m−2 yr−1 for moss-dominated biocrust). These strongly negative values contradict the observed survival of the organisms at the sites and may be caused by the uncertainty in environmental conditions and physiological parameters, which we assessed in a sensitivity analysis. Another potential explanation for this result may be the lack of acclimation in the modelling approach, since the carbon balance can increase substantially when testing for seasonally varying parameters in the sensitivity analysis. We conclude that the uncertainties in air temperature, CO2 concentration, respiration-related physiological parameters, and the absence of seasonal acclimation in the model for humid temperate and alpine regions may be a relevant source of error and should be taken into account in future approaches that aim at estimating the long-term biocrust carbon balance based on ecophysiological data.</p

Continuous monitoring of chlorophyll a fluorescence and microclimatic conditions reveals warming-induced physiological damage in biocrust-forming lichens

Purpose Biocrust communities, which are important regulators of multiple ecosystem functions in drylands, are highly sensitive to climate change. There is growing evidence of the negative impacts of warming on the performance of biocrust constituents like lichens in the field. Here, we aim to understand the physiological basis behind this pattern. Methods Using a unique manipulative climate change experiment, we monitored every 30 minutes and for 9 months the chlorophyll a fluorescence and microclimatic conditions (lichen surface temperature, relative moisture and photosynthetically active radiation) of Psora decipiens, a key biocrust constituent in drylands worldwide. This long-term monitoring resulted in 11,847 records at the thallus-level, which allowed us to evaluate the impacts of ~2.3 °C simulated warming treatment on the physiology of Psora at an unprecedented level of detail. Results Simulated warming and the associated decrease in relative moisture promoted by this treatment negatively impacted the physiology of Psora, especially during the diurnal period of the spring, when conditions are warmer and drier. These impacts were driven by a mechanism based on the reduction of the length of the periods allowing net photosynthesis, and by declines in Yield and Fv/Fm under simulated warming. Conclusion Our study reveals the physiological basis explaining observed negative impacts of ongoing global warming on biocrust-forming lichens in the field. The functional response observed could limit the growth and cover of biocrust-forming lichens in drylands in the long-term, negatively impacting in key soil attributes such as biogeochemical cycles, water balance, biological activity and ability of controlling erosion.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This research was funded by the European Research Council (ERC Grant Agreements 242658 [BIOCOM] and 647038 [BIODESERT] awarded to FTM). FTM and DSP also acknowledge support from Generalitat Valenciana (CIDEGENT/2018/041) and Comunidad de Madrid (REMEDINAL TE-CM, S2018/EMT-4338) respectively. JR, DSP and LGS acknowledge to research projects funded by the Spanish Government, CTM2015–64728-C2–1-R and PID2019-105469RB-C21 for providing financial support at different stages of the data analyses and manuscript development. EV was supported by the 2017 program for attracting and retaining talent of Comunidad de Madrid (no. 2017-T2/ AMB-5406)

Efeito da concentração de clorexidina na resistência de união à dentina em dentes decíduos

PURPOSE: To evaluate the effect of the use of 0.5% and 2% chlorhexidine digluconate on the immediate bond strength of a conventional adhesive system to dentin in primary teeth. METHODS: Twenty-one healthy primary molars were divided into three groups (n=7), being one control (A) and two experimental groups (B and C). After dentin exposure, in Group (A) the adhesive procedure was performed using 37% phosphoric acid gel (15 s); dentin was washed (15 s), air dried (30 s) and rehydrated with water. Groups B and C followed similar procedures but for re-hydration with 0.5% and 2% chlorhexidine, respectively, for 30 s. A resin composite block was built simulating a restoration, and the teeth were stored in distilled water at 37°C for 24 h before the microtensile bond strength test. The bond strength data were analyzed by analysis of variance. RESULTS: No statistically significant difference in bond strength was found among the tested groups (P>0.05) CONCLUSION: The 0.5% and 2% concentrations of chlorhexidine presented similar behavior and caused no adverse effects on the bond strength to dentin in primary teeth.OBJETIVO: Avaliar o efeito do uso de digluconato de clorexidina 0,5% e 2% na resistência de união imediata à dentina de dentes decíduos para um sistema adesivo convencional. METODOLOGIA: Vinte e um molares decíduos hígidos foram divididos em três grupos (n=7), sendo um controle e dois experimentais. Após a exposição da dentina, foi realizado no grupo controle (A) o procedimento adesivo utilizando ácido fosfórico gel a 37% (15 s); a superfície foi então lavada (15 s), seca com ar (30 s) e reidratada com água. Os grupos B e C foram idênticos ao grupo A, apenas com diferença no reumidecimento de clorexidina 0,5% e 2% respectivamente, por 30 s. Após a confecção do bloco de resina composta, os dentes foram armazenados em água destilada a 37°C por 24 h antes do teste de microtração. Os dados de resistência de união foram avaliados através de análise de variância. RESULTADOS: Os dados apresentaram distribuição homogênea, não havendo diferença estatisticamente significante entre os grupos (P>0,05). CONCLUSÃO: As concentrações de clorexidina a 0,5% e 2% apresentaram comportamentos similares e não causaram efeitos adversos na resistência de união em dentina de dentes decíduos, quando comparadas ao grupo controle

Effects of parenteral supplementation with minerals and vitamins on oxidative stress and humoral immune response of weaning calves

We aimed to evaluate the effects of injectable mineral and vitamin supplementation on weaning calves subjected to a low-stress (fence-line) weaning system. Seven-month-old Aberdeen Angus female calves (n = 40, 152 ± 11 kg body weight) from a selenium-deficient area of extensive cattle production on natural grass were randomly assigned to two groups (n = 20 each). One group received subcutaneous supplementation with copper, zinc, selenium, manganese and vitamins A and E (SG), and the other was given sterile saline solution (CG). The animals were supplemented twice, seven days before weaning (day −7) and on the day of weaning (day 0), and they were evaluated 30 (+30) and 60 (+60) days after weaning. Total antioxidant status (TAS), selenium-dependent glutathione peroxidase (GPx) activity, body weight, and average daily gain (ADG) were evaluated. Additionally, antibody titers were assessed prior to and after each immunization with a vaccine containing bovine herpes virus type 1 (BoHV-1). On day +30, body weight (p = 0.03) was higher in SG, whereas TAS (p = 0.02) and GPx (p = 0.0038) activity were lower in CG and remained constant in SG. Antibody titers increased in SG and CG following immunization, being higher in SG on days +30 and +60 (p < 0.05). In conclusion, parenteral supplementation of minerals and vitamins with antioxidant effects in a low-stress weaning system prevented the decrease in TAS and GPx activity, improved antibody response and had positive effects on body weight.Fil: Mattioli, Guillermo Alberto. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Departamento de Ciencias Básicas. Laboratorio de Nutrición Mineral y Fisiología Reproductiva; ArgentinaFil: Rosa, Diana Esther. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Departamento de Ciencias Básicas. Laboratorio de Nutrición Mineral y Fisiología Reproductiva; ArgentinaFil: Turic, Esteban. Biogénesis Bagó; ArgentinaFil: Picco, Sebastian Julio. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Departamento de Ciencias Básicas. Laboratorio de Nutrición Mineral y Fisiología Reproductiva; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico CONICET- La Plata. Instituto de Genética Veterinaria "Ing. Fernando Noel Dulout". Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Instituto de Genética Veterinaria; ArgentinaFil: Raggio, Santiago José. Biogénesis Bagó; ArgentinaFil: Hamad Minervino, Antonio Humberto. Universidade Federal do Oeste do Pará; BrasilFil: Fazzio, Luis Emilio. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Departamento de Ciencias Básicas. Laboratorio de Nutrición Mineral y Fisiología Reproductiva; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Departamento de Patología. Cátedra de Patología Especial Veterinaria; Argentin

ART restorations for occluso-proximal cavities in primary molars: a two-year survival and cost analysis of an RCT comparing two GIC brands

There are many glass ionomer cements available on the Brazilian market for Atraumatic Restorative Treatment (ART), however, there is still a gap in the literature regarding their cost-effectiveness. Objectives: To evaluate the influence of restorative materials (Ketac Molar, 3M ESPE; and Vitro Molar, Nova DFL) in the two-year survival rate and cost-effectiveness of occluso-proximal ART restorations in primary molars. Methodology: A total of 117 children (aged four to eight years) with at least one occluso-proximal carious lesion in primary molars were selected and randomly divided in treatment groups (KM or VM) in this parallel randomized controlled trial. Treatments followed ART premises and were conducted in public schools by trained operators in Barueri, Brazil. A trained, calibrated, and blinded examiner performed the evaluations after two, six, 12, and 24 months (k=0.92). Kaplan-Meier survival analysis was used to estimate restoration survival and Cox regression was used to test the association with clinical factors (α=5%). For cost analysis, material and professional costs were considered. Monte Carlo analysis was used to generate a cost-effectiveness plane and bootstrapping was used to compare material costs over the years. Results: The overall survival rate was 36.9% after two years (48.6% for KM and 25.4% for VM). Restorations with VM failed more than those with KM (HR=1.70; 95% CI=1.06–2.73; p=0.027). VM presented lower initial cost, but no difference was observed between groups considering the two-year incremental cost. Conclusion: After a two-year evaluation, KM proved to be a better option than VM for occluso-proximal ART restorations in primary molars. ClinicalTrials.gov: NCT0226772