Comparative Local Case Study of Coniferous Forest Litter of the "Pinus halepensis Mill" in Arid and Semi-arid Areas of Western Algeria

Forest tree species produce litter, which is the plant/soil interface that ensures the maintenance of soil fertility whose properties depend on the botanical species considered. The differences of properties are marked in the nature of the decomposition processes and the forms of humus which result from it. In this study, the physicochemical characteristics and biological activity of litter were compared in coniferous plots located in the semi-arid and the arid zones of western Algeria. The objective of this work was to characterize and compare the physical-chemical properties and microbiological characteristics of softwood forest litter in the semi-arid and arid areas of western Algeria. We analyzed the properties of 50 samples of Aleppo pine litter collected from five stations in each zone. Analysis results show a highly significant difference (p<0.05) in the physical-chemical properties between the semi-arid and arid zone: humidity (20.7% – 6.51%), pH (5.98 – 6.14), conductivity (0.42 mS/cm – 0.65 mS/cm), carbon (45.74% – 73.42%), nitrogen (1.17% - 0.86%) and C/N ratio (37.47 – 73.42). A comparison of the mean of microbial biomass and their efficacy reveals what is homogeneous in both zones, with a small difference in basal respiration. The heterogeneity of these results indicates that such observations still need to be made in other forests of the Algerian territory in order to better understand the functioning of forest ecosystems and the effect of climate on these compartments, especially soil

Ethanol induction of laccase depends on nitrogen conditions of Pycnoporus sanguineus

Background: Ethanol has been pointed out as a laccase inducer. However, there are controversial reports about its efficiencywith some fungi. In this study,we hypothesized that ethanol laccase induced in Pycnoporus sanguineus depends on nitrogen nutriment conditions. To prove this,we assessed laccase production in submerged cultures of P. sanguineus,with different nitrogen concentrations andwith, orwithout ethanol added in a factorial designed experiment. Results: In order to analyze the effects of factors on the response variables, a factorial ANOVA, and response-surface models were performed. It was found that the nitrogen source was the main factor that affected laccase production in P. sanguineus. The treatments with yeast extract (2 g/L) and ethanol (3 g/L) induced the highest laccase activity (31.01 \ub1 4.9 U/L), while the treatments with urea reached the lowest activity (less than 1.6 U/L). Ethanol had positive and synergic effects on laccase production, in accordance with the surface response model, as long as simple nitrogen sources (urea) were not available. Conclusions: We suggest that laccase in P. sanguineus is regulated by a catabolic nitrogen repressionmechanism; laccase activity is strongly inhibited by urea used as nitrogen source and it decreases when the amount of urea increases; contrarily, a synergic positive effect was observed between yeast extract and ethanol on laccase production

Valorisation de molécules extraites d essences méditerranéennes en cosmétologie

La flore méditerranéenne est une source de matières premières valorisables au sein de l industrie cosmétique. Elle contient un grand nombre de molécules, originales et potentiellement actives sur la peau. Dans ce contexte, l olivier (Olea europea L.) et le chêne liège (Quercus suber L.), deux espèces caractéristiques de ces écosystèmes, ont été étudiées dans l optique de produire un ou plusieurs principes actifs cosmétiques à partir de l huile d olive et du liège. L élaboration d une huile d olive enrichie en 1,2-dioléines par la lipase de Carica papaya a nécessité la caractérisation biochimique de cette enzyme sn3 stéréospécifique. Les paramètres physico-chimiques permettant d obtenir un rendement d hydrolyse enzymatique important ont été mis au point. Les valeurs expérimentales ainsi obtenues ont permis d élaborer un protocole industriel pour la production d un principe actif cosmétique. L extraction par voies chimique et biotechnologique de différentes molécules issues du liège (cires, phénols, monomères de la subérine) a également permis l obtention de molécules actives en cosmétologie. Les différentes méthodes de dépolymérisation chimiques testées ont mis en évidence la présence de trois fractions : monomères de la subérine, composés vraisemblablement issus de la dégradation des polymères du liège et molécules de haut poids moléculaire. Parmi ces méthodes, l hydrolyse du liège à la potasse aqueuse a été retenue et les paramètres physico-chimiques de cette réaction ont été testés à l aide de la méthodologie de la recherche expérimentale. Un protocole simple permettant d obtenir un rendement élevé d extraction de molécules de la subérine également satisfaisant en terme de faisabilité et de coûts a été obtenu.AIX-MARSEILLE3-BU Sc.St Jérô (130552102) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

How do microlocal environmental variations affect microbial activities of a Pinus halepensis litter in a Mediterranean coastal area?

International audienceMediterranean coastal ecosystems suffer many different types of natural and anthropogenic environmental pressure. Microbial communities, major conductors of organic matter decomposition are also subject to these environmental constraints. In this study, our aim was to understand how microbial activities vary at a small spatio-temporal scale in a Mediterranean coastal environment. Microbial activities were monitored in a Pinus halepensis litter collected from two areas, one close to (10 m) and one far from (300 m) the French Mediterranean coast. Litters were transferred from one area to the other using litterbags and studied via different microbial indicators after 2, 5 and 13 months. Microbial Basal Respiration, qCO2, certain enzyme activities (laccase, cellulase, β-glucosidase and acid phosphatase) and functional diversity via Biolog microplates were assayed in litterbags left in the area of origin as well as in litterbags transferred from one area to the other. Results highlight that microbial activities differ significantly in this short spatial scale over time. The influence of microlocal conditions more intensified for litters situated close to the sea, especially during summer seems to have a stressful effect on microbial communities, leading to less efficient functional activities. However, microbial activities were more strongly influenced by temporal variations linked to seasonality than by location

Environmental Drivers of Microbial Functioning in Mediterranean Forest Soils

International audienceMediterranean forests own distinct characteristics resulting from climate, soil, and vegetation that affect soil microbial communities’ assembly and their associated functions. We initiated a multi-scalar analysis of environmental drivers of soil functioning to (1) identify pertinent factorial scales and (2) determine the relative importance of soil, vegetation, and geoclimate influences in shaping soil microbial functions across the French Mediterranean forests. Soil samples (0–15 cm) were collected from 60 forest sites and soil physicochemical and microbiological properties were assessed across different factorial scales i.e., bioclimates, slope exposures, and forest stands. Patterns in microbial catabolic potential (i.e., extracellular enzymes and microbial respiration) and carbon (C) source utilization (i.e., catabolic-level physiological profiling) were partitioned between vegetation cover, soil characteristics, and geoclimate components. Our results reveal that the catabolic potential of soil microbes was strongly influenced by the forest stands and mainly relied on ammonium and nitrate contents. In contrast, variation in C source utilization was mainly explained by vegetation cover. Soil metabolic capacities of microorganisms and resulting C dynamics were largely constrained by climate parameters, which suggests potentially important consequences for soil C storage. Our study revealed diverse structuration patterns between the catabolic potential and the carbon source utilization of soil microbial communities, and gives insights into the underlying mechanisms of soil microbial functioning in Mediterranean forests

Distance from the sea as a driving force of microbial communities under water potential stresses in litters of two typical Mediterranean plant species

International audienceThough many studies have focused on the incidence of drought, little attention has been paid to osmotic stress and to how the interaction of the two stresses impacts microbial functioning. Moreover, deciphering how certain environmental factors such as distance from the sea or type of litter may shape microbial responses to these stresses is of huge importance. The objective of this study is to shed light on the impact of matric and osmotic stresses (combined or not) on litter microbial communities potentially shaped differently by either plant species or distance from the sea. Two Mediterranean plant species, Cistus albidus L. and Pistacia lentiscus L., collected from both inland and coastal areas, were used to set up a total of 72 mesocosms (4 mesocosms × 3 types of litters (pure or mixed) × 2 sites (coastal and inland) × 3 types of stress). A first set of twenty four mesocosms 'control' (4 mesocosms × 3 types of litters (pure or mixed) × 2 sites (coastal and inland)) were maintained under favourable conditions for 60 days (25 °C, 600 g·kg −1 water content). For matric stress, twenty four mesocosms were subjected to 5 drying/rewetting cycles (7 days at 25 °C/7 days at 600 g·kg −1 water content and 25 °C). For osmotic stress, twenty four mesocosms received 10 mg of chlorine ions per g of litter using NaCl and then were incubated at 600 g·kg −1 water content and 25 °C for 60 days. The last twenty four mesocosms were subjected to the combined drought and salt stresses for 60 days. Resistance to added osmotic stress was also tested. Catabolic diversity assessed via Biolog Ecoplates, was higher in coastal than in inland areas after drought and combined stresses. Moreover, catabolic profiles were shaped differently after stresses depending on the litter type. Basal respiration withstood an added severe drought stress better in microbial communities previously subjected to combined stresses. Resistance to an added osmotic stress was higher in inland litters previously subjected to salt stress. Microbial communities from the coastal area were more able to maintain their catabolic potential and thus to withstand these stresses. Combined stresses and osmotic stress reinforced resistance to added severe drought or osmotic stress respectively. Thus our findings reveal that microbial communities previously subjected to water potential stresses were more capable to overcome additional stresses of similar nature, suggesting adaptation mechanisms to such type of stresses

Effects of pollutants on laccase activities of Marasmius quercophilus, a white-rot fungus isolated from a Mediterranean schlerophyllous litter

International audienceMarasmius quercophilus is a white-rot fungus involved in carbon recycling in Mediterranean ecosystems because of its laccase production. Here we described the effect of metal ions and halide salts, on laccase activity in order to point out the action of such environmental pollutants on this enzyme of major importance. Furthermore we tested organic solvent effects on laccase reaction since reaction mixture including solvent can be used in the transformation of xenobiotics. In the case of metal ions, we found that chloride ions were responsible for inhibition while CuSO 4 and MnSO 4 enhanced laccase activity. When halides were tested, we showed the following degree of inhibition: F À > Cl À > Br À. Furthermore we found that I À was oxidized by laccase with I 2 as the product of the reaction. With ABTS, 50% of the laccase activity remains for solvent concentration ranging from 40% to 60% depending on the solvent used while with syringaldazine solvent concentration ranged from 50% to 70%. The organic solvent effects observed were probably a result of enzyme denaturation and of both enhancement of oxidised product solubilisation and of substrate solubilisation (for syringaldazine). These results show that lac-case from M. quercophilus is not rapidly inhibited by certain environmental pollutants which sustains its role in carbon turnover under pertubation. However the strong effect of chloride ion on laccase activity should be further investigated with in situ studies since this could drastically influence carbon recycling in litters from Mediterranean littoral locations

Genotypic variations among isolates of Marasmius quercophilus, a white-rot fungus isolated from evergreen oak litter

International audienceMarasmius quercophilus is a white-rot basidiomycete isolated from evergreen oak litter. This fungus plays an extensive role in litter degradation because of its cellulase, pectinase, and laccase production. Our objective was to investigate the potential genotypic polymorphism of this species using RAPD (random amplified polymorphic DNA) and the amplification and the sequencing of fragments ITS (internal transcribed spacer) from the rRNA repeat. An intraspecies polymorphism was observed for the M. quercophilus isolates studied as suggested by the tree found with RAPD data: seven subgroups were defined. The minimum similarity coefficient observed in these groups was 0.278. The sizes of fragments ITS 1 and ITS 2 were the same for each isolate (ITS 1: 320 bp and ITS 2: 450 bp), and the percentages of nucleotide variation were 1.25 and 1.11%, respectively. Few isolates from the studied population had the same RAPD pattern that would suggest a clonal development in some zones of the site of La Gardiole.Marasmius quercophilus est un basidiomycète de la pourriture blanche isolé de la litière de chêne vert. Ce champignon joue un rôle important dans la dégradation de la litière de par sa production de cellulase, pectinase et laccase. Notre objectif consiste en la recherche d'un éventuel polymorphisme génotypique chez cette espèce en utilisant la RAPD (« random amplified polymorphic DNA ») et l'amplification suivie du séquençage des fragments ITS (« internal transcribed spacer ») à partir du cluster codant pour les ARNr. Un polymorphisme intraspécifique a été observé chez les isolats de M. quercophilus étudiés comme le suggère le dendrogramme trouvé à partir des données RAPD : sept sous-groupes ont été définis. Le coefficient de similarité minimum observé dans ces groupes était de 0,278. Les tailles des fragments ITS 1 et ITS 2 étaient identiques pour chaque isolat testé (ITS 1 : 320 pb et ITS 2 : 450 pb) et le pourcentage de variation des nucleotides étaient de 1,25 et 1,11%, respectivement. Quelques souches de la population étudiée présentaient le même profil RAPD ce qui suggère le développement de clones dans certaines zones du site de La Gardiole. Mots clés : Marasmius quercophilus, variabilité intraspécifique, ITS, RAPD. Farnet et al. 89

The importance of water availability in the reaction equilibrium of hydrolases in forest litters from a Mediterranean area: a study on lipases

International audienceWater is one of the main variables affecting the carbon cycle (carbon storage or assimilation) in soils or litters from the Mediterranean area, though in most studies it has been considered via soil moisture measurements only. Here, we investigated the effect of water availability as characterized by water activity, a w , on the equilibrium of enzyme reactions (hydrolysis/synthesis) for litters from three species characteristic of the Mediterranean area (Quercus pubescens L, Q. ilex L. and Pinus halepensis L.). Lipases were used as models and an organic phase was used as the reaction medium to adjust water amount. We found that the activities of hydrolysis/transesterification increased with a w , showing that both can occur at the same a w in litter. Furthermore, these lipase activities in litter decreased for a w close to 1, which has been described with purified lipases in organic media, indicating potential enzyme aggregation. Variations in a w with moisture were studied with sorption isotherms, which were found to be similar (isotherm type 2) for all the studied litters. Water activity is a crucial indicator for soils under hydric stress at small water contents, which should be considered for describing more precisely enzyme functioning and giving valuable information about carbon dynamics in soils or litters