Specialized metabolism of mangrove trees, implication for biotic interactions in coastal environment

Arbres inféodés aux mangroves, les palétuviers produisent de nombreux métabolites spécialisés pouvant jouer un rôle dans les interactions entre plantes (allélopathie), ou entre plantes et microorganismes (e.g. décomposition). Dans cette thèse, (i) l’impact de la distance à la mer sur la dynamique de décomposition des litières d’Avicennia germinans a été évalué in situ. Nos résultats montrent une perte de masse plus rapide en milieu estuarien quelle que soit l’origine des litières, bien que les fonctions et activités cataboliques microbiennes y soient réduites. (ii) Le potentiel allélopathique de plusieurs espèces de palétuviers sur des plantes cultivées et sur les palétuviers eux-mêmes a été évalué. L’effet d’extraits aqueux de feuilles de huit espèces a été testé sur la germination et la croissance du riz (Oryza sativa) et de son adventice (Echinochloa crus-galli). Aegiceras corniculatum et Sonneratia apetala ont montré des effets inhibiteurs pour E. crus-galli et stimulants ou neutres pour O. sativa. Leurs biomarqueurs ont été annotés. (ii) L’effet allélopathique des sols rhizosphériques (avec ou sans ajout de litière de feuilles) des espèces pionnières Avicennia marina et Sonneratia caseolaris a été évalué sur le succès d’installation de trois espèces de la succession Kandelia obovata, A. corniculatum et Rhizophora stylosa. Nos résultats montrent une inhibition de la survie de K. obovata ainsi qu’une stimulation de sa croissance en présence de sol issu du peuplement d’A. marina avec litière. Ces travaux évaluent l’implication du métabolisme spécialisé des palétuviers dans les interactions biotiques au sein du fonctionnement de l’écosystème mangroveMangrove trees produce many specialized metabolites that may play a role in plant-plant (allelopathy) or plant-microorganism (e.g. decomposition) interactions. In this work, (i) the impact of distance to the sea on the decomposition dynamics of Avicennia germinans litter was evaluated in situ. Our results show a more rapid mass loss in estuarine environment whatever the origin of the litter, although the microbial catabolic functions and activities were reduced. (ii) The allelopathic potential of several mangrove species on cultivated plants and on the mangroves themselves was evaluated. The effect of aqueous leaf extracts of eight species was tested on the germination and growth of rice (Oryza sativa) and its weed (Echinochloa crus-galli). Aegiceras corniculatum and Sonneratia apetala showed inhibitory effects for E. crus-galli and stimulating or neutral effects for O. sativa. Their biomarkers were annotated. (ii) The allelopathic effect of rhizospheric soils (with or without the addition of leaf litter) of the pioneer species Avicennia marina and Sonneratia caseolaris was evaluated on the establishment success of three successional species Kandelia obovata, A. corniculatum and Rhizophora stylosa. Our results show an inhibition of the survival of K. obovata as well as a stimulation of its growth in the presence of soil originating from A. marina soil with litter. This work assesses the involvement of mangrove specialized metabolism in biotic interactions within the functioning of the mangrove ecosyste

Comparison of leaf litter decomposition and microbial decomposer communities in fringe and riverine mangroves in French Guiana

International audienceMangroves are highly productive and changing forests located in the intertidal zone of tropical regions. Leaf litter decomposition represents a substantial part of their carbon sink abilities. Little is known about the potential effect of climate change on this key process of ecosystem functioning. This study compared leaf litter microbial decay between fringe and riverine Avicennia germinans stands. A direct and reciprocal transplant experiment using litterbags was setup in French Guiana to test 3 hypotheses: (i) the activities and abundance of microbial decomposers are lowest in the fringe mangroves due to exposure to saline water and tidal immersion; (ii) for these reasons, litter decomposes faster in riverine stands; and (iii) according to the home-field advantage hypothesis, litter decomposes more rapidly in the environment from which it originates. Remaining litter masses, abundance of litter microbial community (phospholipid fatty acid signatures (PLFA)), and their functional capability (enzyme activities and Biolog) were assessed. Litter directly transplanted in riverine stands showed higher enzymatic activity (+ 77%), catabolic diversity (+ 10%), and microbial biomass (+ 60%) than litter transplanted directly in fringe stands. In contrast, both riverine and fringe derived litter showed faster decay at the fringe (14% mass loss) than riverine site (4% mass loss) between 30 and 45 days. Here, environmental conditions associated with different distances from the sea such as salinity and inundation regimes, rather than microbial features are suggested as main factors affecting decomposition process. Expected sea level rise in the coastal Guianas may therefore modify the mangroves productivity in the coming decades

Allelopathic Potential of Mangroves from the Red River Estuary against the Rice Weed Echinochloa crus-galli and Variation in Their Leaf Metabolome

International audienceMangroves are the only forests located at the sea–land interface in tropical and subtropical regions. They are key elements of tropical coastal ecosystems, providing numerous ecosystem services. Among them is the production of specialized metabolites by mangroves and their potential use in agriculture to limit weed growth in cultures. We explored the in vitro allelopathic potential of eight mangrove species’ aqueous leaf extracts (Avicennia marina, Kandelia obovata, Bruguiera gymnorhiza, Sonneratia apetala, Sonneratia caseolaris, Aegiceras corniculatum, Lumnitzera racemosa and Rhizophora stylosa) on the germination and growth of Echinochloa crus-galli, a weed species associated with rice, Oryza sativa. Leaf methanolic extracts of mangrove species were also studied via UHPLC-ESI/qToF to compare their metabolite fingerprints. Our results highlight that A. corniculatum and S. apetala negatively affected E. crus-galli development with a stimulating effect or no effect on O. sativa. Phytochemical investigations of A. corniculatum allowed us to putatively annotate three flavonoids and two saponins. For S. apetala, three flavonoids, a tannin and two unusual sulfated ellagic acid derivatives were found. Some of these compounds are described for the first time in these species. Overall, A. corniculatum and S. apetala leaves are proposed as promising natural alternatives against E. crus-galli and should be further assessed under field conditions

Mangrove's species are weak isoprenoid emitters

International audienceMangroves are ecosystems interfacing terrestrial and marine environments submitted to extreme abiotic factors (e.g. anoxia, flooding, salinity) producing stress on vegetation. Due to these stresses, we hypothesized that mangroves potentially emit biogenic volatile organic compound (BVOC), particularly isoprenoids as they are defense compounds. Despite mangroves cover only about 5% of the forest areas of the world, their emissions could impact air quality at the continental-ocean interface. As a result, it is important to fill the gap in the knowledge about BVOC emissions from the canopy of the major mangrove trees. The aim of this study was thus to screen isoprenoid emissions of the mangrove species. In this study, we sampled isoprenoid emissions of 14 species foliage among the 38 core species existing in the Indo-West Pacific (IWP) and the Atlantic Est Pacific (AEP) regions. Sampling was performed using a branch-bag dynamic enclosure system and analyzed with gas chromatography coupled to mass spectrometry. Our analysis showed that mangrove tree species are very low emitters suggesting that mangrove ecosystems would not strongly influence atmospheric chemistry and air quality