Influence de la taille de l’échantillon sur la variation des paramètres hydriques déterminés à partir des courbes-pression-volume

Le potentiel hydrique est utilise en tant que grandeur thermodynamique qui sfapplique a tous les compartiments du continuum sol-plante-atmosphere et qui reagit la circulation de lfeau entre le sol, les racines, les tiges, les feuilles et lfatmosphere. Il est determine par la methode de la chambre a pression de Scholander ; methode simple et rapide qui donne aussi acces a plusieurs parametres hydriques, decrivant lfetat de lfeau dans la plante, a travers une representation graphique ou courbe-pression-volume (CPV). Cependant, certaines procedures experimentales utilisees lors des mesures peuvent augmenter les risques des erreurs, au niveau des resultats, comme lfutilisation arbitraire dfechantillons de tailles variables. Le but de ce travail est dfetudier lfimpact de la variabilite de la taille des echantillons preleves sur les parametres hydriques et de trouver a la suite des solutions pouvant minimiser les erreurs experimentales induites. De ce fait, 12 CPV par jour ont ete effectuees sur des phyllodes (10}0,5 cm de longueur) et des rameaux de 16}0,5 cm de longueur (avec 5 a 6 phyllodes), de plants dfAcacia cyanlophylla Lindl., preleves a lfaube,sous conditions hydriques non limitantes, temoins, (ĵb.-0,2 } 0,1 Mpa) ou stressantes (ĵb = -1,80 } 0,20 Mpa) puis soumis immediatement a saturations (12h, 24h et 48h). Les resultats indiquent qufaussi bienpour les plants temoins que les stresses, la taille de lfechantillon influe significativement leurs parametres hydriques. Le prelevement des rameaux a lfaube, et leurs mises a saturation jusqufa 48h, permettraitdfavoir moins de variations dans le nombre et dans les valeurs des composantes hydriques determines.Mots-cles : taille de lfechantillon, Acacia cyanophylla Lindl., parametres hydriques, courbes pression volum

Drought effects on buds growth and dynamic of Tunisian cork oak populations

Forest species have adapted to their local climate by changing some of their phenological characteristics. Differential phenological responses may modify tree chance of survival by altering the competitive balance between them. The study of key phenological stages (budding, budburst, flowering, falling leaves ...) knew a renewed interest these last years for climate changes consequences researches. Characterizing the phenological variability response, of five Tunisian cork oak populations from contrasting climatic situations, in front to water deficit, has been the subject of this study. Large differences between populations from highest and coldest sites as well as those of lowest and warm sites were detected and adaptative responses specific to some populations were founded

Do volatile organic compound emissions of Tunisian cork oak populations originating from contrasting climatic conditions differ in their responses to summer drought ?

The intrinsic variability of volatile organic compound emissions and photosynthetic parameters in response to two drying cycles was investigated on Quercus suber L. saplings originating from three Tunisian populations native to contrasting climates. Emissions mainly included monoterpenes plus traces of sesquiterpenes and methylsalicylate that steadily decreased during the experiment unrelated to treatments. Instead, monoterpene emissions increased by 30% during a first moderate drought and remained enhanced after rewatering, while CO2-H2O gas exchange was reduced by 30%. A second severe drought decreased monoterpene emissions to about two third of controls, strongly inhibited gas exchange and photochemical efficiency, and caused a partial loss of chlorophyll. Rewatering led to only partial recovery of emissions and photosynthetic parameters of stressed plants whose biomasses and leaf nitrogen and chlorophyll contents were lower than in control plants. There was no clear difference among populations in volatile organic compound emissions or photosynthetic parameters. However, the population inhabiting the most arid region had intrinsically smaller leaves with lower specific leaf masses and higher drought-related leaf losses than populations native to less arid climates. These results indicate an adaptive shift from stress-tolerating towards stress-avoiding ecotypes under arid climates involving mainly morphological adaptations without apparent differentiation in volatile organic compound production, probably because of its high phenological plasticity

Transcriptome profiling the basal region of poplar stems during the early gravitropic response

Stems of angiosperm trees are affected by gravity. Young poplar stems show primary growth in the top internodes and differential cambium activity in the basal internodes after inclination with some tension wood formed after 45 min. This study was conducted in order to characterize the early changes in poplar gene expression during the early stages of the gravitropic response. Using microarray technology, the expression of 15 000 genes was examined. Approximately 3.1 % of these genes exhibited significant expression changes within the first 45 min of gravity stimulation. Approximately 73 % of the identified genes were found to have a known or predicted molecular function. Many of these genes were involved in secondary wall formation (cellulose synthesis and lignification), cytoskeleton development, signaling, and stress response. Some identified genes seem to play a role in sensing gravitational signals during tension wood formation. A large number of the identified arabinogalactan (AGP) and transcription factor genes were involved in cell wall biosynthesis suggesting that these genes are particularly active in the first phases of signal transduction during tension wood formation

Performance of LAI-MODIS and the influence on drought simulation in a Mediterranean forest

This study investigates the benefits and methodological issues to integrate weekly 1 km Leaf Area Index (LAI) Moderate Resolution Imaging Spectroradiometer (LAI-MODIS) (MOD15A2) satellite product in a distributed water budget model over a Mediterranean forested ecosystem of about 2553 km2 for drought assessment at regional scale. The high overestimation of LAI-MODIS compared to field measurements was corrected based on the calibration of high-resolution Satellites Pour l'Observation de la Terre (SPOT) images combined with ground measurements. The LAI-MODIS time series over the 2003 to 2009 period has been calibrated and integrated into a spatially explicit water budget model at the regional level using spatial information on vegetation, soil types and topoclimates. Actual LAI-MODIS scenario was tested against temporal and spatial null models to assess for the benefits of the regional heterogeneity from MODIS and its intra-annual and interannual variation in a water budget model. From water budget analyses at local and regional scales, we concluded that calibration of LAI-MODIS images was mandatory to enhance the correlation coefficient between measured and simulated daily actual transpiration. We estimated daily bias in the resulting ‘Water Stress Index’ to be slightly affected between constant and seasonally-varying LAI datasets. However, the interannual variability in LAI detected by MODIS followed LAI adjustments expected from the ecohydrological equilibrium hypothesis. This can significantly affect the simulated annual drought period features, so that integrating LAI-MODIS spatial and temporal variability into water budget models for evergreen Mediterranean vegetation can be a useful dataset when carbon allocation schemes in dynamic vegetation models are lacking, but should be carefully calibrated particularly in transitions towards semi-arid zones

Drought effects on buds growth and dynamic of Tunisian cork oak populations

Forest species have adapted to their local climate by changing some of their phenological characteristics. Differential phenological responses may modify tree chance of survival by altering the competitive balance between them. The study of key phenological stages (budding, budburst, flowering, falling leaves ...) knew a renewed interest these last years for climate changes consequences researches. Characterizing the phenological variability response, of five Tunisian cork oak populations from contrasting climatic situations, in front to water deficit, has been the subject of this study. Large differences between populations from highest and coldest sites as well as those of lowest and warm sites were detected and adaptative responses specific to some populations were founded

Phenolic profile, antioxidant capacity of five Z<i>iziphus spina</i>-<i>christi</i> (L.) Willd provenances and their allelopathic effects on <i>Trigonella foenum</i>-<i>graecum</i> L. and <i>Lens culinaris</i> L. seeds

<p>The aim of this work was to evaluate some secondary metabolites, antioxidant activity of methanolic leaf extracts of five <i>Ziziphus spina</i>-<i>christi</i> provenances (INRGREF, Tozeur, Degueche, Nafta and Kebelli) and their allelopathic effects on <i>Trigonella foenum</i>-<i>graecum</i> and <i>Lens culinaris</i>. Leaves were collected during 2013 and 2014. Total phenols, flavonoids, tannins and antioxidant activity were evaluated using the Folin ciocalteux, Aluminum trichloride, vanillin and scavenging activity on 22-diphenyl-1-picrylhydrazyl (DPPH) radical methods, respectively. Total phenols, tannins and flavonoids were present, at levels of 57.41 mg GAE/g DW, 31.98 mg RE/g DW and 14.68 μg CE/g DW, respectively. The high antioxidant activity (0.086 μg/mL) was noted in kebelli provenance (2013). The highest germination, plumule and radicle lengths of tested species were observed in INRGREF provenance. <i>Z. spina</i>-<i>christi</i> leaf extracts may be suggested in foods and pharmaceutical industries. Leaf extracts could also provide a natural herbicide with a positive impact on the environment.</p

Climate change‐induced ecosystem disturbance: a review on sclerophyllous and semi‐deciduous forests in Tunisia

International audienceAccording to the sixth assessment report of the Intergovernmental Panel on Climate Change (IPCC), global climate change is now unequivocal. Tunisia, like many other countries, has been affected by climate changes, including rising temperatures, intense heatwaves, and altered precipitation regimes. Tunisia's mean annual temperatures has risen about +1.4 °C in the twentieth century, with the most rapid warming taking place since the 1970s. Drought represents a primary contributing factor to tree decline and dieback. Long‐term drought can result in reduced growth and health of trees, thereby increasing their susceptibility to insect pests and pathogens. Reported increases in tree mortality point toward accelerating global forest vulnerability under hotter temperatures and longer, more intense droughts. In order to assess the effect of these climate changes on the current state of forest ecosystems in Tunisia and their evolution, an investigative study was required. Here, we review the current state of knowledge on the effects of climate change on sclerophyllous and semi‐deciduous forest ecosystems in Tunisia. Natural disturbance during recent years, as well as the adaptability and resilience of some forest species to climate change, were surveyed. The Standardized Precipitation Evapotranspiration Index (SPEI) is a multi‐scalar drought index based on climate data that has been used to analyse drought variability. The SPEI time scale analysis showed a negative trend over the 1955–2021 period in Tunisian forest regions. In 2021, Tunisia lost 280 km 2 of tree cover to fires, which is equivalent to 26% of the total lost area between 2008 and 2021. Changing climate conditions have also affected phenological parameters, with an advance in the start of the green season (SOS) of 9.4 days, a delay at the end of the green season (EOS) of 5 days, with a consequent extended duration of the green season (LOS) by an average of 14.2 days. All of these alarming findings invite us to seek adaptation strategies for forest ecosystems. Adapting forests to climate change is therefore a challenge for scientists as well as policymakers and managers