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L'Acacia noir (Acacia mearnsii De Wild) fait dorénavant partie intégrante du paysage de la région d'El Kala. Cinquante ans après son introduction, cette légumineuse australienne occupe plus de 3200 ha et constitue une menace majeure pour la biodiversité locale.Le présent travail a été entrepris, d'une part, afin d'assurer une gestion durable des ressources naturelles de la région et, d'autre part, afin de développer une meilleure compréhension des mécanismes déclencheurs de la propagation de l'espèce invasive.Cette étude a pour but d'évaluer les changements des types d'occupation du sol de 1959 à 2016, mais aussi d'examiner l'apparition, l'évolution et la répartition actuelle des taches d'Acacia mearnsii en deux sites, en utilisant les outils de la télédétection aéroportée et satellitaire.Les résultats obtenus montrent que sur les sites 1 (forêt de Boumalek, 1536 ha) et 2 (forêt de Tonga, 1679 ha), les formations végétales initiales, sans Acacia noir, ont perdu respectivement 708 et 581 ha. La subéraie avec sous-bois a subi une rétraction particulièrement remarquable (196 ha à Boumalek, 350 ha à Tonga). En presque 30 ans (de 1987 à 2016), les superficies de l'eucalyptaie et de la subéraie envahies par l'Acacia noir sont passées respectivement de 62 à 487 ha et de 0,2 à 188 ha à Boumalek, de 30 à 730 ha et de 1,6 à 120 ha à Tonga. Durant la période considérée, de presque 60 ans, les perturbations d'origines naturelle et surtout anthropique, ont constitué des facteurs aggravants de l'envahissement, par ouverture de fenêtres d'invasion et par déclenchement de la levée des semences d'Acacia mearnsii. The Black Wattle (Acacia mearnsii De Wild) is now an integral part of the landscape of the El Kala region. Fifty years after its introduction, this Australian legume occupies more than 3200 ha and represents a major threat to local biodiversity.The present work was undertaken on the one hand, in order to ensure a sustainable management of the natural resources of the region; on the other hand, in order to develop a better understanding of the triggering mechanisms for the spread of the invasive species.The purpose of this study is to assess changes in land cover from 1959 to 2016, but also to examine the appearance, evolution and current distribution of the spots of Acacia mearnsii in two sites, using the tools of the airborne and satellite remote sensing.The results obtained show that on sites 1 (forest of Boumalek, 1536 ha) and 2 (forest of Tonga, 1690 ha), the initial plant formations, without Black Acacia, lost 708 and 581 ha respectively. The cork oak forest with undergrowth has undergone a particularly remarkable retraction (196 ha in Boumalek, 350 ha in Tonga). In almost 30 years (from 1987 to 2016), the area of invaded eucalyptus and cork oak forests increased respectively from 62 ha to 487 ha and from 0.2 to 188 ha in Boumalek, from 30 ha to 730 ha and from 1.6 to 120 ha in Tonga.During the period considered, of almost 60 years, disturbances of natural and especially anthropic origin have been aggravating factors of the invasion, by opening invasion windows and by triggering the emergence of Acacia mearnsii seeds.

Dans la région d’El Kala (extrême Nord-Est algérien), Acacia mearnsii De Wild. a été introduit lors des reboisements de 1970, en mélange à 20 % avec l'eucalyptus. Or, depuis quelques décennies, il est constaté un développement de taches d’invasion par cette espèce australienne dans cette même contrée du pays. L’utilisation d’outils tels qu’un système d'information géographique (SIG), avec des informations spatiales à jour, est nécessaire pour mieux comprendre l'invasion et identifier les écosystèmes potentiels à haut risque. Ainsi, le présent travail a été orienté vers la cartographie afin de procéder à l’étude de la répartition de l’invasion de cette espèce. Deux approches ont été adoptées, la première faisant appel aux données collectées sur le terrain et la seconde aux techniques de télédétection, en appliquant la méthode de classification supervisée sur une image Landsat 8. Les résultats obtenus par les deux méthodes montrent que la superficie envahie avoisine les 3 200 ha, répartis en quatre sites. La quasi-totalité de la surface envahie est occupée par l’eucalyptaie et la suberaie (respectivement 65,0 % et 17,9 % de la superficie totale). La classification de l’image satellite n’a permis de détecter que les paysages fortement envahis, tandis que la méthode des relevés effectués sur le terrain a permis de cartographier sa répartition totale. Toutefois, la superposition des deux cartes montre qu’elles sont majoritairement identiques (0,90 ≤ R ≤ 1). Pour conclure, l’utilisation des données spatialisées, couplées à des données ponctuelles (relevés de terrain), a permis, d’une part, de réduire les contraintes liées à la résolution de l’image Landsat et, d’autre part, de montrer l’importance des méthodologies basées sur les travaux de terrain.

Desert truffles are hypogeous fungi, with an important role in the folklore and cuisine of many countries. They are mycorrhizal fungi belonging to the Ascomycetes and forming symbiotic associations with several species of the family Cistaceae. The plant-desert truffle association has been the subject of numerous studies. The main purpose of the present research was to characterise the mycorrhizal system between Tuberaria guttata (L.) Fourr and Terfezia arenaria (Moris) Trappe. Plants of T. guttata were grown in pots under greenhouse conditions. They were inoculated in vivo with a solution containing spores of T. arenaria. The mycorrhizal level was assessed after root staining. T. guttata roots were also collected from littoral dunes in northeastern Algeria in order to compare the mycorrhizal status under both natural and in vivo conditions. Two principal ectomycorrhizal morphotypes were observed: branched mycorrhizae and club-shaped mycorrhizae. Root staining and observations of semi-thin sections showed that the in vivo produced roots had an ectomycorrhiza with Hartig net and extracellular hyphae more or less organised in a “real” sheath. The less-developed sheath was seen in the branched mycorhhiza and the well-developed one in the club-shaped mycorrhiza. This is the first report of a sheathing ectomycorrhiza formed by a desert truffle species associated with herbaceous plant.

The present work examined the impact of increasing diesel concentrations (0.05, 0.1, 0.25, 0.5 and 1%) on the development of both partners of the arbuscular mycorrhizal symbiosis: Rhizophagus irregularis and chicory roots (Cichorium intybus L.) grown in vitro. Our findings showed that although the different diesel concentrations tested (0.05, 0.1, 0.25, 0.5%) affect negatively the main stages of R. irregularis development (germination, germinative hyphal elongation, root colonization rate, extraradical hyphae development, sporulation) and the chicory root growth, they are not completely inhibited, except at 1%. The arbuscular mycorrhizal fungus was able to fulfil its life cycle in the presence of the pollutant. No increase in malondialdehyde (MDA) production – a biomarker of lipid peroxidation – was detected in diesel-exposed mycorrhizal or non-mycorrhizal roots, suggesting that the negative effect of diesel on the chicory roots growth could not result from the alteration of membrane lipids. Moreover, our results pointed out that the diesel toxic effect on the growth of chicory roots is less noticeable when they are mycorrhized, indicating a protective effect of mycorrhization. This protection could be related to induction of antioxidant enzyme peroxidase activity, but not to superoxide dismutase activity. Taken together, our results demonstrated the toxic effect of diesel on the mycorrhizal symbiosis and suggest a probable involvement of the mycorrhizal fungus in the protection of chicory roots against oxidative stress induced by diesel.

In order to improve the production of olive (Olea europaea L.), plantlets of Variety Ferkani were inoculated with three arbuscular mycorrhizal fungal (AMF) spores (Glomus sp.1, Glomus sp.2, Septoglomus constrictum) isolated from a hot-arid zone in Algeria and three commercial AMF (Rhizophagus intraradices, Funneliformis mosseae, Gigaspora margarita). Mycorrhization parameters and nine growth traits were estimated in two-year-old plantlets, then the variation of growth traits following mycorrhizae parameters of various AMF inoculums was tested. The tested AMF species were all infective and effective for the mycorrhization of Ferkani variety. Native species Glomus sp.1 gave the best results for mycorrhizal colonization and growth parameters. Indeed, the highest colonization frequency (F%) was recorded in plantlets inoculated with Glomus sp.1 (58 ± 6.5 %), whereas the highest values of colonization intensity of in the root system (M%) were obtained with Rhizophagus intraradices (2.45 ± 1.46 %) and Glomus sp.1 (2.26 ± 0.76 %). Abundances of arbuscules were low for all AMF inoculums. The controlled inoculation improved the growth of all plantlets compared to the AMF-free plantlets. AMF-inoculated plantlets showed significantly higher growth in terms shoot height, fresh and dry weights of shoot and root, and number of leaves and nodes. Statistical models revealed that all the latter growth parameters including mycorrhizal responsiveness increased significantly when mycorrhizal parameters increased, and that F% was most strongly correlated with plant growth compared to other mycorrhizal parameters. Findings of this controlled inoculation research underline the importance of local AMF isolated from the rhizosphere of Ferkani variety in rapidly and extensively infecting the root system and then increasing growth of the host.

In arid and semi-arid lands, the spiny prickly pear (Opuntia ficus-indica) is an outstanding plant for soil conservation and restoration. To determine the role of Opuntia ficus-indica on vegetation recovery process in desertified areas of Southern Tebessa (Northeast Algeria), we investigated the effect of prickly pear plantation age and some soil properties (grain size, pH, electrical conductivity, organic matter, total nitrogen, available phosphorus, and CaCO3 equivalents) on native plant community. Vegetation cover and plant diversity were assessed by calculating the number of individual plants (N), species richness (S), their ratio (N/S), Shannon index, and Evenness in prickly pear plantation plots of different ages (control, 5 and 20 years). Even if surveyed soil parameters did not differ significantly among O. ficus-indica plantations, results of ANOVA testing the effect of Opuntia plantations on native vegetation traits revealed significant variation for plant abundance (P < 0.0001), N/S ratio (P = 0.003) and vegetation cover (P < 0.0001). Vegetation cover differed significantly with both prickly-pear plantation age (P = 0.031) and seasons (P = 0.019). Tukey's tests revealed that all vegetation traits were significantly higher on prickly pear plantations than in control plots. Multiple comparisons also showed that plant abundance, N/S ratio and vegetation cover were significantly different between both young and old plantations and the controls. Prickly pear cultures facilitated the colonization and development of herbaceous species by ameliorating the severe environmental conditions. In conclusion, the facilitative effect of O. ficus-indica has been clearly demonstrated for both abundance and cover of native vegetation.

This study aims to determine the spatiotemporal dynamics of root colonization and spore density of arbuscular mycorrhizal fungi (AMF) in the rhizosphere of olive trees (Olea europaea) with different plantation ages and under different climatic areas in Algeria. Soil and root samples were seasonally collected from three olive plantations of different ages. Other samples were carried out in productive olive orchards cultivated under a climatic gradient (desertic, semi-arid, subhumid, and humid). The olive varieties analysed in this study were Blanquette, Rougette, Chemlel and the wild-olive. Spore density, mycorrhization intensity (M%), spore diversity and the most probable number (MPN) were determined. Both the intensity of mycorrhizal colonization and spore density increased with the increase of seasonal precipitation and decreased with the increase of air temperature regardless of the climatic region or olive variety. The variety Rougette had the highest mycorrhizal levels in all plantation ages and climates. Spore community was composed of the genera Rhizophagus, Funneliformis, Glomus, Septoglomus, Gigaspora, Scutellospora and Entrophospora. The genus Glomus, with four species, predominated in all climate regions. Spores of Gigaspora sp. and Scutellospora sp. were the most abundant in desertic plantations. Statistical models indicated a positive relationship between spore density and M% during spring and winter in young seedlings and old plantations. A significant positive relationship was found between MPN and spore density under different climates. For a mycotrophic species, the rhizosphere of olive trees proved to be poor in mycorrhiza in terms of mycorrhizal colonization and numbers of the infective AMF propagules.

We analyzed the diversity and identity of the rhizobial populations nodulating an invasive Australian legume tree Acacia mearnsii in a natural Quercus suber forest in the El Kala National Park, Algeria. Soils from three different forest plots corresponding to non invaded original Q. suber stand, partially invaded by A. mearnsii , and totally invaded (monodominant) A. mearnsii stand were used to trap nodulating bacteria with the same tree species. Symbiotic nitrogen-fixing bacteria were isolated from root nodules and characterized by sequencing of the internal transcribed spacer region, then submitted to phylogenetic analyses. A total of 67 isolates was obtained, representing the 3 different forest plots, all renodulating A. mearnsii in monoxenic conditions. Phylogenetic analyses showed that all isolates belong to different Bradyrhizobium lineages, according to each of the three locations with little intermixing between forest plots. These results illustrate the adaptation of nodulating Bradyrhizobium populations to the new soil conditions induced by invasion. This symbiotic adaptability is presumed to be a key factor of the invasive character of this tree species.

Acacia mearnsii is one of the most planted Australian Acacia around the world but is known to be highly invasive, threatening native habitats by competing with indigenous vegetation. The introduction of this species in the Algerian El Kala Biosphere reserve led to the invasion of natural formations to the detriment of Quercus suber , a native tree species. We hypothesized that shifts in soil microbial functions and ectomycorrhizal (EcM) fungal community structure triggered by this exotic Acacia species might correlate with a decrease of the early growth of Q. suber . Soil samples were thus collected from 3 different sites where the exotic species was at different stages of invasion in the Algerian El Kala Biosphere reserve, (i) a Q. suber forest free of A. mearnsii (site S1), (ii) a Q. suber / A. mearnsii mixed forest where the Australian Acacia has been recently detected (site S2) and (iii) pure stands of A. mearnsii formed more than 20 years ago (site S3). Plant growth, EcM community structure associated with Q. suber roots and soil microbial functionalities were assessed for 6 month-old cultures of Q. suber in glasshouse conditions. The results clearly demonstrated a strong deleterious impact of A. mearnsii invasion level on soil chemical characteristics, microbial functions and EcM community structure and colonization, correlated to a decrease in the early growth of Q. suber seedlings. The current study gives new insights into both the negative impact of exotic species on soil functioning and their effect on indigenous vegetation growth. These results may be used as a basis for improving the conservation practices of native tree species in such degraded areas as a complement of ecological strategies using indigenous ectotrophic early-successional shrub species (eg. Cistus spp.) that our findings have shown to promote EcM multiplication and the early growth of native tree species.