Réactions fonctionnelles des écosystèmes sclérophylles méditerranéens à l'impact du débrousaillement

Functional reactions of mediterranean sclerophyllous ecosystems to clearing impact. Clearing brings about disturbances with manifold effects on vegetation. The authors analyse the consequences of these disturbances on soil, and on the Quercus ilex and Arbutus unedo nutrients. On calcareous soils, these disturbances cause significant decreases in the carbon ratio, the humic compounds concentration, and the cation exchange capacity. On siliceous soils, only the humic compounds concentration decreases significantly. The nutrients concentrations and seasonal dynamics are disturbed differently according to the species and the substrate. Only a significant decrease of nitrogen is observed in Quercus ilex on siliceous soils, whereas Arbutus unedo shows, in addition, significant variations in phosphorus, magnesium and calcium on calcareous soils.Le débroussaillement constitue une perturbation aux effets multiples sur la végétation. Les auteurs étudient les conséquences sur le sol et sur les nutriments chez le chêne vert et l'arbousier. Au niveau du sol, la perturbation se traduit par une diminution significative du pourcentage de carbone, de la concentration en composés humiques totaux et de la capacité totale d'échange sur calcaire. Sur silice, seuls les composés humiques totaux varient significativement. Les concentrations et la dynamique saisonnière des nutriments sont perturbées différemment chez les deux essences et sur les deux substrats. Chez le chêne vert, seul l'azote diminue significativement sur silice alors que, chez l'arbousier, il y a en plus des variations significatives, sur calcaire, pour le phosphore, le magnésium et le calcium

Increased drought of the mediterranean climate and biotic interactions: functional consequences on plant communities in a shrubland ecosystem

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Can compost improve Quercus pubescens Willd establishment in a Mediterranean post-fire shrubland?

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The use of compost in afforestation of Mediterranean areas: Effects on soil properties and young tree seedlings

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Production and Diversity of Volatile Terpenes from Plants on Calcareous and Siliceous Soils: Effect of Soil Nutrients

International audienceFertilizer effects on terpene production have beennoted in numerous reports. In contrast, only a few studies havestudied the response of leaf terpene content to naturallydifferent soil fertility levels. Terpene content, as determinedby gas chromatography/mass spectrometry/flame ionizationdetector, and growth of Pinus halepensis, Rosmarinusofficinalis, and Cistus albidus were studied on calcareousand siliceous soils under field conditions. The effect ofnitrogen (N) and extractable phosphorus (PE) from thesesoils on terpenes was also investigated since calcareous soilsmainly differ from siliceous soils in their higher nutrientloadings. Rich terpene mixtures were detected. Twenty-oneterpenes appeared in leaf extracts of R. officinalis and C.albidus and 20 in P. halepensis. Growth of all species wasenhanced on calcareous soils, while terpene content showeda species-specific response to soil type. The total monoterpenecontent of P. halepensis and that of some major compounds(e.g., δ-terpinene) were higher on calcareous than onsiliceous soils. A significant and positive relationship wasfound between concentration of N and PE and leaf terpenecontent of this species. These findings suggest that P.halepensis may respond to an environment characterized byincreasing soil deposition, by allocating carbon resources tothe synthesis of terpene defense metabolites without growthreduction. Results obtained for R. officinalis showed highconcentrations of numerous major monoterpenes (e.g., myrcene,camphor) in plants growing on calcareous soils, whileα-pinene, β-caryophyllene, and the total sesquiterpene contentwere higher on siliceous soils. Finally, only alloaromadendreneand δ-cadinene of C. albidus showed higher concentrationson siliceous soils. Unlike P. halepensis, soil nutrientswere not involved in terpene variation in calcareous andsiliceous soils of these two shrub species. Possible ecologicalexplanations on the effect of soil type for these latter twospecies as well as the ecological explanation of rich terpenemixtures are discussed

Effect of organic amendment on soil fertility and plant nutrients in a post-fire Mediterranean ecosystem

International audienceBackgrounds and aims In Mediterranean frequentlyburnt areas, the decrease of soil fertility leads to regressivevegetation dynamics. Organic amendments couldhelp to accelerate post-fire ecosystem resilience, byimproving soil properties and plant nutrition. This studywas conducted to assess the potential of a compostedbiosolid to restore an early post-fire shrubland.Methods About 50Mg.ha−1 of fresh co-composted sewagesludge and green wastes were surface applied7 months after fire on a silty-clayey soil. We monitoredover a 2-year period organic matter and nutrient transfersto soil, nutrient responses of dominant plant species,and ecosystem contamination by potentially toxic traceelements.Results Over the experimental survey, compost rapidlyand durably improved soil P2O5,MgO and K2O content,and temporarily increased N-(NO3− + NO2−) content.Plant nutrition was improved more or less durably dependingspecies. The most positive compost effect wason plant and soil phosphorus content. Plant nutrientstorage was not improved 2 years after amendment,suggesting luxury consumption. No contamination bytrace elements was detected in soil and plant.Conclusions The use of compost after fire could helpfor rapidly restoring soil fertility and improving plantnutrition. The increase of soil nutrient pools afteramendment emphazised the diversity of plant nutritionaltraits. Eutrophication risk could occur from high compostand soil P2O5 content

Shrub species richness decreases negative impacts of drought in a Mediterranean ecosystem

International audienceAimsGlobal change projections predict biodiversity changes and increased drought intensity in the Mediterranean Basin in the decades to come. This will presumably affect plant performance, plant community composition and ecosystem functioning. Shrublands are widespread in the Mediterranean area, yet we have no clear understanding of shrubland responses to the combined effects of increased drought and changes in plant diversity. LocationNatural Mediterranean shrubland, Marseille, south France. MethodsA rainfall manipulation experiment was conducted to examine the performance of four dominant shrub species in response to increased drought. The study assemblages spanned a gradient of four shrub richness levels (mono-, bi-, tri- and tetra-specific plant mixtures) and 15 different shrub combinations. Throughout the 2yr of non-destructive experiments (2012-2014), we measured plant litter fall, stand necromass and plant cover of the four dominant plant species: Cistus albidus, Quercus coccifera, Rosmarinus officinalis and Ulex parviflorus. ResultsIncreasing shrub richness levels in the plant community led to higher litter production by all four species and a decrease in dry shoots for Quercus and Ulex. Shrub species responses were affected by the rain exclusion treatment, but the effects were mainly dependent on shrub richness level. In mono-specific plots, aggravated drought conditions led to a decrease in litter fall of Cistus, Rosmarinus and Ulex and an increase in necromass of all four species. In general, these negative drought effects disappeared as number of shrub species in the community increased. Under rain exclusion treatment, Rosmarinus cover decreased in mono-specific plots whereas Quercus cover increased in bi-specific plots and Rosmarinus cover increased in tetra-specific plots. We observed two drought tolerance patterns, with Quercus and Rosmarinus being more tolerant species and Ulex and Cistus less tolerant. ConclusionsThe magnitude of drought effects on shrub performance is species-specific, and plant species combination-dependent. High shrub richness levels modulate the negative impacts of aggravated drought conditions. Our results point to a probable shift of interspecific relationships in response to water shortage. As drought impacts are not mediated in low-diversity communities, species-specific responses to drier conditions could lead to shifts in plant community composition favouring the most drought-resistant species, i.e. Quercus and Rosmarinus. Maintaining high diversity appears critical to mediate drought effects for less resistant species (Cistus and Ulex in our study)

Restoration of a Mediterranean Postfire Shrubland: Plant Functional Responses to Organic Soil Amendment

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Short-term Effects of Sewage-Sludge Compost on a Degraded Mediterranean Soil

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Use of urban composts for the regeneration of a burnt Mediterranean soil: A laboratory approach

Supplement : "Environmental Risks and Problems, Strategies to reduce them through Biotechnology and Engineering"International audienceIn Mediterranean region, forest fires are a major problem leading to the desertification of the environment.Use of composts is considered as a solution for soil and vegetation rehabilitation. In this study, wedetermined under laboratory conditions the effects of three urban composts and their mode of application(laid on the soil surface or mixed into the soil) on soil restoration after fire: a municipal wastecompost (MWC), a compost of sewage sludge mixed with green waste (SSC) and a green waste compost(GWC). Carbon (C) and nitrogen (N) mineralisation, total microbial biomass, fungal biomass and soilcharacteristics were measured during 77-day incubations in microcosms. The impact of composts inputon hydrological behaviour related to erodibility was estimated by measuring runoff, retention andpercolation (i.e. infiltration) of water using a rainfall simulator under laboratory conditions. Input ofcomposts increased organic matter and soil nutrient content, and enhanced C and N mineralisation andtotal microbial biomass throughout the incubations, whereas it increased sporadically fungal biomass.For all these parameters, the MWC induced the highest improvement while GWC input had no significanteffect compared to the control. Composts mixed with soil weakly limited runoff and infiltration whereascomposts laid at the soil surface significantly reduced runoff and increased percolation and retention,particularly with the MWC