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International audience; The capacity of a Quercus pubescens forest to resist recurrent drought was assessed on an in situ experimental platform through the measurement of a large set of traits (ecophysiological and metabolic) studied under natural drought (ND) and amplified drought induced by partial rain exclusion (AD). This study was performed during the 3rd and 4th years of AD, which correspond to conditions of moderate AD in 2014 and harsher AD in 2015, respectively. Although water potential (Ψ) and net photosynthesis (Pn) were noticeably reduced under AD in 2015 compared to ND, trees showed similar growth and no oxidative stress. The absence of oxidative damage could be due to a strong accumulation of α-tocopherol, suggesting that this compound is a major component of the Q. pubescens antioxidant system. Other antioxidants were rather stable under AD in 2014, but slight changes started to be observed in 2015 (carotenoids and isoprene) due to harsher conditions. Our results indicate that Q. pubescens could be able to cope with AD, for at least 4 years, likely due to its antioxidant system. However, growth decrease was observed during the 5th year (2016) of AD, suggesting that this resistance could be threatened over longer periods of recurrent drought.

International audience

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; In contrast to plant-animal interactions, the conceptual framework regarding the impact of secondary metabolites in mediating plant-plant interference is currently less well defined. Here, we address hypotheses about the role of chemically-mediated plant-plant interference (i.e., allelopathy) as a driver of Mediterranean forest dynamics. Growth and defense abilities of a pioneer (Pinus halepensis) and a late-successional (Quercus pubescens) Mediterranean forest species were evaluated under three different plant interference conditions: (i) allelopathy simulated by application of aqueous needle extracts of Pinus, (ii) resource competition created by the physical presence of a neighboring species (Pinus or Quercus), and (iii) a combination of both allelopathy and competition. After 24 months of experimentation in simulated field conditions, Quercus was more affected by plant interference treatments than was Pinus, and a hierarchical response to biotic interference (allelopathy < competition < allelopathy + competition) was observed in terms of relative impact on growth and plant defense. Both species modulated their respective metabolic profiles according to plant interference treatment and thus their inherent chemical defense status, resulting in a physiological trade-off between plant growth and production of defense metabolites. For Quercus, an increase in secondary metabolite production and a decrease in plant growth were observed in all treatments. In contrast, this trade-off in Pinus was only observed in competition and allelopathy + competition treatments. Although Pinus and Quercus expressed differential responses when subjected to a single interference condition, either allelopathy or competition, species responses were similar or positively correlated when strong interference conditions (allelopathy + competition) were imposed.

National audience

This chapter presents the botanic characteristics and identification criteria of Aleppo pine, Ce chapitre présente les caractéristiques botaniques et les critères de reconnaissance du pin d'Alep

International audience; Cuticular hydrocarbon composition was determined for 18 populations of Avicennia germinans (Avicenniaceae) collected from West Africa, Florida, the Pacific coast of Mexico and French Guyana. Variation in covariance structure among the hydrocarbons was evaluated from correlations among the traits for each of the populations and from a hierarchical common principal components analysis. Principal components ordinations of populations based on the 171 z* transformed correlation coefficients, onto which a minimal spanning tree was superimposed, suggested a network in which French Guyanan populations formed a nexus from which African populations differentiated biochemically from Floridan and Mexican groups. Common principal components analysis provided further support for the differentiation in covariance structure among these biochemical traits of African populations. Pacific coast Mexican populations appeared to have diverged less in covariation among traits from Atlantic American sources than did the northern (Floridan) and southern (French Guyanan) Atlantic American populations from one another. The complete isolation of Pacific coast sources after emergence of the Central American isthmus during the Pliocene provides a reference for comparison of levels of differentiation among regions that suggests an underlying pattern of divergence in this species. Partial Mantel matrix tests revealed significant geographic effects, with no significant climatic effects. Our results provide support for recognition of a major differentiation between Old and New World sources within the taxon and indicate the need for a full revision of this species.

International audience

Concentrations of two iridoid glucosides (2′-cinnamoyl mussaenosidic acid and 2′-caffeoyl mussaenosidic acid) were measured in different populations of several Avicennia species. The results obtained for 2′-cinnamoyl mussaenosidic acid seem to confirm the recognition of infraspecific taxa in A. marina and also in A. germinans ( africana (palaeotropic) and germinans (neotropic)).

International audience; croses or growth and development disturbances (Im-pens and Delcarte, 1995; Manning et al., 2002), or the The aim of the present study is to assess whether certain ecophysio-occurrence of internal physiological alterations (Ross-logical responses (contents of total phenols, total proanthocyanidins, and total and simple flavonols), in the needles of Aleppo pines (Pinus bach et al., 1999). In the latter case, analysis involves halepensis Mill.) may be valid bioindicators for the assessment of the the measurement of certain chemical compounds con-air quality. Samples were taken at five natural sites polluted by various tained in the plants as revealing a particular environ-pollutants (NO, NO 2 , other NO x , SO 2 , and O 3). The results show a mental state. In particular, the impact of air pollutants decrease in total phenol concentrations with levels of nitrogen oxide is often studied on the basis of experimentation under pollutions (significant negative correlations between the total phenol controlled conditions, each pollutant being generally concentrations and concentrations of NO, NO 2 , and other NO x). Total tested in isolation (Peñ uelas et al., 1996; Rodrigues et flavonoids (total flavonols and proanthocyanidins) are useful bioindi-al., 1996). Studies performed under natural conditions cators for ozone pollution (significant negative correlations between are rare and sometimes only deal with the impact of a total proanthocyanidins and the concentrations of ozone and signifi-single type of pollutant (Karlsson et al., 1995; Oleksyn cant positive correlations between total flavonols and the ozone pollution). Sulfur dioxide pollution is distinguished by low concentrations et al., 1999; Chappelka et al., 1999). However, the valida-in quercetin, isorhamnetin, and kaempferol (significant negative cor-tion of a bioindicator requires the undertaking of experi-relations between these simple flavonols and the concentrations of ments under natural conditions. SO 2). This work confirms the strong interest of using the phenolic Among the chemical compounds in plants, secondary compounds of Pinus halepensis as biological indicators of air quality. metabolites are of great importance in plant–environ-ment relationships in particular the phenolic compounds (e.g., phenols and flavonoids; Haslam, 1989; Rhodes