Diverse salinity responses in Crithmum maritimum tissues at different salinities over time

Crithmum maritimum (sea fennel) withstands high salinity, and to better understand how different protective mechanisms against salinity are activated, young seedlings were exposed to increasing concentrations of NaCl (0 to 512 mM) over six weeks. Plant survival and chlorophyll content were reduced at >85 mM NaCl and growth was affected at > 341 mM NaCl. Relative water content fell and Na+ accumulated more in leaves than in roots. Induction of Na+/H+ antiporter expression reached a maximum at 427 mM NaCl in both tissues. Salinity induced the accumulation of proline, soluble sugars and glycine betaine. All three accumulated to higher levels in leaves than roots and greatest accumulation was after 6 weeks and the highest salt concentrations. Hydrogen peroxide levels fell with increasing salinity in leaves, while ascorbic acid and catalase activity rose. Overall, the most dramatic changes occurred after six weeks of saline stress but different mechanisms were activated at different salinity thresholds and in the two tissues. Key salinity thresholds in the response of Crithmum maritimum to salinity stress are identified activating different mechanisms. At 85 mM NaCl roots reach osmotic adjustment, at 171 mM further osmolyte protection mechanisms are activated, at 256 mM NaCl leaves reach osmotic adjustment, at 341 mM plant growth is affected and at the highest salinity tested, 512 mM, protective mechanisms are affected in leaves but not in roots

Multiple mechanisms mediate growth and survival in young seedlings of two populations of the halophyte Atriplex halimus (L) subjected to long single step salinity treatments

Understanding how halophytes survive high soil salinity in realistic long-term experiments is important for strategies to mitigate the effects of increasing soil salinity worldwide. Protective mechanisms in halophytes enabling survival include sequestration of salt via Na+/H+ antiporters, synthesis and accumulation of osmolytes, and activation of protective mechanisms against reactive oxygen species (ROS). Protective mechanisms elicited by a single step-up to a range of NaCl treatments (34–256 mM) in two populations of the halophyte Atriplex halimus L. from contrasting environments (arid steppe and saline coastline) were compared over 6 weeks. The coastal population survived significantly better at high salinity compared with the steppe population, although in both populations, salinity inhibited growth. Increased Na+ and K+ concentration was accompanied by higher induction of Na+/H+ antiporter gene expression in coastal than in steppe population leaves. Osmolytes increased more significantly in the coastal than in the steppe population with greater induction of choline mono-oxygenase gene expression. Activation of ROS scavenging mechanisms was greater in coastal than in steppe plants. Differential responses found through time, in different salt concentrations, and between leaves and roots indicate a finely tuned response. Sharp changes in responses at 171 mM NaCl indicate that different mechanisms may be invoked at different stress levels.</jats:p

Ecological response of Cedrus atlantica to climate variability in the Massif of Guetiane (Algeria)

Aim of the study: The study analyzes the long-term response of Atlas cedar, Cedrus atlantica (Manneti), to climate variability. Area of study: Atlas cedar forest of Guetiane (Batna, Algeria).Material and methods: The dendrochronological approach was adopted. An Atlas cedar tree-ring chronology was established from twenty trees. The response of the species to climate variability was assessed through the pointer years (PYs), the common climate signal among the individual chronologies, expressed by the first component (PC1), the mean sensitivity (msx), and response function and correlations analysis involving the tree-ring index and climate data (monthly mean temperature and total precipitation).Results: The highest growth variability was registered from the second half of the 20th century. The lower than the mean PYs, the PC1, and the msx increased markedly during the studied period. Dramatic increases in the PC1 and msx were detected at the end of the 1970s, reflecting a shift towards drier conditions enhancing an increasing trend towards more synchronous response of trees to climate conditions. The response function and correlations analysis showed that tree growth was mainly influenced by precipitation variability.Research highlights: Our findings provide baseline knowledge concerning the ecological response of Atlas cedar to climate variability in in its southern distribution limit, where a high level of tree mortality has been observed during recent decades, coinciding with the driest period Algeria has ever experienced. This information is vital to support ongoing ecosystem management efforts in the region. Keywords: Atlas cedar; annual growth variability; dieback; dendrochronology.

Les banques de semences : une stratégie de conservation EX SITU des plantes et endémiques

Le grand nombre d'espèces végétales rares ou endémiques existant en Algérie appelle à d'urgentes solutions de préservation de la flore. L'établissement d'un réseau de banques de semences pourrait fournir la solution la plus pratique à ce problème. L'installation des banques de semences de plantes sauvages n'est ni onéreuse, ni difficile à créer et ne nécessite aucun équipement spécial et aucune dépense élevée. Actuellement, il est techniquement possible de préserver à long terme des semences viables, en utilisant des méthodes de conservation relativement simples, basées sur trois principaux facteurs : les basses températures, les faibles humidités des graines et les faibles teneurs en oxygène de l'air. Il convient de conduire des tests de germination sur les semences avant leur stockage permanent. Ces tests serviront à détecter d'éventuelles dormances du matériel végétal qu'il faut lever grâce à certains procédés et traitements (refroidissement, gibbérelline...). Enfin, la création de ces banques de semences pour les plantes rares ou endémiques en Algérie est plus que souhaitable

Diverse salinity responses in Crithmum maritimum tissues at different salinities over time

Crithmum maritimum (sea fennel) withstands high salinity, and to better understand how different protective mechanisms against salinity are activated, young seedlings were exposed to increasing concentrations of NaCl (0 to 512 mM) over six weeks. Plant survival and chlorophyll content were reduced at >85 mM NaCl and growth was affected at > 341 mM NaCl. Relative water content fell and Na+ accumulated more in leaves than in roots. Induction of Na+/H+ antiporter expression reached a maximum at 427 mM NaCl in both tissues. Salinity induced the accumulation of proline, soluble sugars and glycine betaine. All three accumulated to higher levels in leaves than roots and greatest accumulation was after 6 weeks and the highest salt concentrations. Hydrogen peroxide levels fell with increasing salinity in leaves, while ascorbic acid and catalase activity rose. Overall, the most dramatic changes occurred after six weeks of saline stress but different mechanisms were activated at different salinity thresholds and in the two tissues. Key salinity thresholds in the response of Crithmum maritimum to salinity stress are identified activating different mechanisms. At 85 mM NaCl roots reach osmotic adjustment, at 171 mM further osmolyte protection mechanisms are activated, at 256 mM NaCl leaves reach osmotic adjustment, at 341 mM plant growth is affected and at the highest salinity tested, 512 mM, protective mechanisms are affected in leaves but not in roots

Bilan des incendies de forêt dans le bassin méditerranéen : Cas du Portugal, l’Espagne, la France, l’Italie et la Grèce, (Période 1986-2005)

Cet article à pour objectif l’étude de l'évolution des incendies de forêts dans le bassin méditerranéen (Portugal, l’Espagne, la France, l’Italie et la Grèce) sur une période de 20 ans (1986-2005).Au cours de ces deux décennies, les incendies de forêts y ont parcouru l'équivalent de 9,5 millions d’hectares de forêts et d’espaces naturel pour 1,1 million départs de feu.Les auteurs tenteront de mettre en exergue les connaissances acquises au niveau de chaque pays sur les incendies pour une meilleure prévention et gestion du phénomène des feux de forêts

On a new station of Damasonium alisma subsp. polyspermum (Coss.) Maire (Alismataceae) in Algeria: syntaxonomy and implications of conservation

Les auteurs décrivent une nouvelle station à Damasonium alisma subsp. polyspermum découverte récemment à Aïn Bessem dans la plaine des Arib. Ils analysent la flore et la végétation des mares temporaires de cette station et de celle de Tiaret (Sersou). L’étude phytosociologique, à l’aide de 12 relevés réalisés selon la méthode de Braun-Blanquet, des communautés végétales dominées physionomiquement par D. alisma subsp. polyspermum permet l’identification de deux associations, le Ranunculetum baudotii (Ranunculion aquatilis), qui se présente ici comme un groupement basal paucispécifique dominé par des renoncules (Ranunculus baudotii et R. trichophyllus), et le Damasonio polyspermi-Crypsidetum aculeati (Verbenion). L’insertion syntaxinomique de ces associations est précisée. L’aspect typique de l’Elatinetum macropodae (Isoetion), décrit il y a plus d’une cinquantaine d’années dans la mare de Tasselent à Tiaret, n’existe plus, suite à la disparition de cette mare. Les taxons rares n’ont pas été retrouvés (Marsilea strigosa, Antinoria agrostidea, Ranunculus batrachioides, Elatine macropoda, Isoetes velata subsp. dubia, Riella sersuensis), à l’exception de D. alisma subsp. polyspermum qui semble résistant aux facteurs de perturbation. Les résultats obtenus mettent en évidence la nécessité et l’urgence de la mise en place de mesures conservatoires, autant pour ces taxons que pour les mares qui abritent ces communautés hydrophytiques de grande valeur patrimoniale (valeur paysagère, valeur phytocénotique, richesse en taxons protégés et taxons rares), mais sérieusement menacées par les impacts anthropiques.The authors describe a new site of Damasonium alisma subsp. polyspermum recently discovered at Ain Bessem in the plain of Arib. They analyse the flora and vegetation of temporary pools of this site and of Tiaret (Sersou). The phytosociological study, with 12 relevés made by the Braun-Blanquet method, of plant communities dominated physiognomically by D. alisma subsp. polyspermum allows the identification of two associations, Ranunculetum baudotii (Ranunculion aquatilis), which is a poor basal group dominated by buttercup (Ranunculus baudotii and R. trichophyllus), and Damasonio polyspermi-Crypsidetum aculeati (Verbenion). The insertion in a syntaxonomic system of both associations is stated. The typical aspect of the Elatinetum macropodae (Isoetion), described more than fifty years ago in the pond of Tasselent at Tiaret, no longer exists, after the confirmed destruction of this pond. Rare taxa were not found (Marsilea strigosa, Antinoria agrostidea, Ranunculus batrachioides, Elatine macropoda, Isoetes velata subsp. dubia, Riella sersuensis), except D. alisma subsp. polyspermum which seems resilient to disturbance. The obtained results highlight the need for the establishment of protection measures for both these taxa and the ponds hosting these hydrophytic plant communities of great patrimonial value (landscape value, phytocoenotic value, richness in protected and rare taxa), but seriously threatened by human impacts