Molecular biogeography of planktonic and benthic diatoms in the Yangtze River

Background: Diatoms are of great significance to primary productivity in oceans, yet little is known about their biogeographic distribution in oligotrophic rivers. Results: With the help of metabarcoding analysis of 279 samples from the Yangtze River, we provided the first integral biogeographic pattern of planktonic and benthic diatoms over a 6030 km continuum along the world's third largest river. Our study revealed spatial dissimilarity of diatoms under varying landforms, including plateau, mountain, foothill, basin, foothill-mountain, and plain regions, from the river source to the estuary. Environmental drivers of diatom communities were interpreted in terms of photosynthetically active radiation, temperature, channel slope and nutrients, and human interference. Typical benthic diatoms, such as Pinnularia, Paralia, and Aulacoseira, experienced considerable reduction in relative abundance downstream of the Three Gorges Dam and the Xiluodu Dam, two of the world's largest dams. Conclusions: Our study revealed that benthic diatoms are of particular significance in characterizing motile guild in riverine environments, which provides insights into diatom biogeography and biogeochemical cycles in large river ecosystems

Growth form defines physiological photoprotective capacity in intertidal benthic diatoms

International audienceIn intertidal marine sediments, characterized by rapidly fluctuating and often extreme lightconditions, primary production is frequently dominated by diatoms. We performed a comparativeanalysis of photophysiological traits in 15 marine benthic diatom species belonging to the fourmajor morphological growth forms (epipelon (EPL), motile epipsammon (EPM-M) and non-motileepipsammon (EPM-NM) and tychoplankton (TYCHO)) found in these sediments. Our analysesrevealed a clear relationship between growth form and photoprotective capacity, and identified fastregulatory physiological photoprotective traits (that is, non-photochemical quenching (NPQ) and thexanthophyll cycle (XC)) as key traits defining the functional light response of these diatoms. EPMNMand motile EPL showed the highest and lowest NPQ, respectively, with EPM-M showingintermediate values. Like EPL, TYCHO had low NPQ, irrespective of whether they were grown inbenthic or planktonic conditions, reflecting an adaptation to a low light environment. Our resultsthus provide the first experimental evidence for the existence of a trade-off between behavioural(motility) and physiological photoprotective mechanisms (NPQ and the XC) in the four majorintertidal benthic diatoms growth forms using unialgal cultures. Remarkably, although motilityis restricted to the raphid pennate diatom clade, raphid pennate species, which have adopted anon-motile epipsammic or a tychoplanktonic life style, display the physiological photoprotectiveresponse typical of these growth forms. This observation underscores the importance of growthform and not phylogenetic relatedness as the prime determinant shaping the physiologicalphotoprotective capacity of benthic diatoms