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Poster communications

Mangrove soils: Who drives their recycling functions?

Abstract : The Amazon River is responsible of a huge discharge of sediments in Atlantic Ocean. A portion of 10 to 20 % of this suspended particulate matter is diverted and follows a north-western path under the influence of Guiana Current that results in a spectacular migration of 1 600 km of subtidal mud belt along the coastline of Guianas to the Orinoco Delta. In the intertidal zone, mud banks form extensive mud flats whose periodic dewatering by tide cycles progressively generates the establishment and stabilization of the upper intertidal part. Its colonization by biofilms and then by propagules imported from fringing mature mangroves, promotes extending of mangrove ecosystem. In such environment, highly constrained by a rapid and intensive hydro-sedimentary dynamic, the evolution of mangrove ecosystem gradually leads to the development of series of stages, from pioneers to matures and finally to senescents. The interactions between aboveground-belowground vegetation, organic matter and sediment are responsible of changes in ground characteristics and pore-water composition. These are to be linked with microbial community functionning which are a central component of biogeochemical processes and nutrient dynamics that take place in mangrove ecosystem. The study site corresponds to a mangrove of Avicennia germinans and Laguncularia racemosa located at Montabo (Cayenne, French Guiana). This mangrove results from silt bed colonization which has began to deposit since 2003. Our objectives were to understand which environmental factors were the main drivers of the expression of microbial functions in this intertidal sediment. With this aim, we distinguished several classes of environmental factors potentially involved in microbial function regulation: 1) vegetation successional steps defined by 4 stages, i.e. bare mud (BM), seedling (S, <1y), pioneer (P, <5y) and young (Y, <10y); 2) hydro-climatic conditions, i.e. two contrasted seasons: rainy (R) and dry (D); 3) hydro- and physico-chemical properties of sediment, including OM quality characterization by SS 13C CPMAS NMR spectroscopy; 4) rhizospheric effects. Microbial functions investigated were: basal respiration, bacterial catabolic diversity profiles (BiologTM ECO) and enzymatic activities in CNPS biogeochemical cycles, i.e. FDA, β-glucosidases, lipases, ureases, phosphomonoesterases and arylsulfatases. It appeared that the main structurating factor of microbial functions was related to vegetation successional stages and the subsequent OM enrichment of sediment, which resulted in an increase of enzymatic activities and respiration and a concomitant decrease of functional diversity. Thus, results demonstrated a progressive specialization of microbial functions constrained by mangrove productivity.
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Mathieu Luglia, Stéven Criquet, Max Sarrazin, Fabio Ziarelli, Daniel Guiral. Mangrove soils: Who drives their recycling functions?. 4th International Multidisciplinary Conference on Hydrology and Ecology : Emerging Patterns, Breakthroughs and Challenges, May 2013, Rennes, France. 2013. ⟨hal-01451642⟩

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