Data from: New insights into carbon acquisition and exchanges within the coral-dinoflagellate symbiosis under NH4+ and NO3- supply

Anthropogenic nutrient enrichment affects the biogeochemical cycles and
nutrient stoichiometry of coastal ecosystems and is often associated with
coral reef decline. However, the mechanisms by which dissolved inorganic
nutrients, and especially nitrogen forms (ammonium versus nitrate) can
disturb the association between corals and their symbiotic algae are
subject to controversial debate. Here, we investigated the coral response
to varying N : P ratios, with nitrate or ammonium as a nitrogen source. We
showed significant differences in the carbon acquisition by the symbionts
and its allocation within the symbiosis according to nutrient abundance,
type and stoichiometry. In particular, under low phosphate concentration
(0.05 µM), a 3 µM nitrate enrichment induced a significant decrease in
carbon fixation rate and low values of carbon translocation, compared with
control conditions (N : P = 0.5 : 0.05), while these processes were
significantly enhanced when nitrate was replaced by ammonium. A combined
enrichment in ammonium and phosphorus (N : P = 3 : 1) induced a shift in
nutrient allocation to the symbionts, at the detriment of the host.
Altogether, these results shed light into the effect of nutrient
enrichment on reef corals. More broadly, they improve our understanding of
the consequences of nutrient loading on reef ecosystems, which is urgently
required to refine risk management strategies.