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Molecular level responses to chronic versus pulse nutrient loading in the seagrass Posidonia oceanica undergoing herbivore pressure

  • Physiological ecology - original research
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Abstract

Seagrasses are key marine foundation species, currently declining due to the compounded action of global and regional anthropogenic stressors. Eutrophication has been associated with seagrass decline, while grazing has been traditionally considered to be a natural disturbance with a relatively low impact on seagrasses. In the recent years, this assumption has been revisited. Here, by means of a 16-month field-experiment, we investigated the molecular mechanisms driving the long-term response of Posidonia oceanica to the combination of nutrient enrichment, either as a chronic (press) or pulse disturbance, and herbivory. Changes in expression levels of 19 target genes involved in key steps of photosynthesis, nutrient assimilation, chlorophyll metabolism, oxidative-stress response and plant defense were evaluated through reverse transcription–quantitative polymerase chain reaction (RT-qPCR). High herbivore pressure affected the molecular response of P. oceanica more dramatically than did enhanced nutrient levels, altering the expression of genes involved in plant tolerance and resistance traits, such as photosynthesis and defense mechanisms. Genes involved in carbon fixation and N assimilation modulated the response of plants to high nutrient levels. Availability of resources seems to modify P. oceanica response to herbivory, where the upregulation of a nitrate transporter gene was accompanied by the decline in the expression of nitrate reductase in the leaves, suggesting a change in plant-nutrient allocation strategy. Finally, press and pulse fertilizations altered nitrate uptake and reduction-related genes in opposite ways, suggesting that taking into account the temporal regime of nutrient loading is important to assess the physiological response of seagrasses to eutrophication.

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Acknowledgements

MR was supported by a SZN Ph.D. fellowship via the Open University. The authors acknowledge financial supports from MIUR through the PRIN 2010-2011 grant 2010PBMAXP_003 project TETRIS and from the University of Pisa through the PRA 2015 project.

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Contributions

FB, CR, and GP conceived and designed the experiments. CR, FB, GP, and MR participated in the fieldwork. MR performed all the molecular analyses. MR and LMG analyzed the data. MR wrote the manuscript with the help of all other co-authors.

Corresponding author

Correspondence to Miriam Ruocco.

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The authors declare that they have no conflict of interest.

Additional information

Communicated by James Fourqurean.

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Supplementary material 1 (DOC 108 kb)

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Ruocco, M., Marín-Guirao, L., Ravaglioli, C. et al. Molecular level responses to chronic versus pulse nutrient loading in the seagrass Posidonia oceanica undergoing herbivore pressure. Oecologia 188, 23–39 (2018). https://doi.org/10.1007/s00442-018-4172-9

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  • DOI: https://doi.org/10.1007/s00442-018-4172-9

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