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Seawater pH , and not inorganic nitrogen source, affects pH at the blade surface of Macrocystis pyrifera : implications for responses of the giant kelp to future oceanic conditions
Author(s) -
Fernández Pamela A.,
Roleda Michael Y.,
Leal Pablo P.,
Hurd Catriona L.
Publication year - 2017
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/ppl.12478
Subject(s) - macrocystis pyrifera , ocean acidification , seawater , photosynthesis , kelp , chemistry , thallus , environmental chemistry , biology , botany , ecology
Ocean acidification ( OA ), the ongoing decline in seawater pH , is predicted to have wide‐ranging effects on marine organisms and ecosystems. For seaweeds, the pH at the thallus surface, within the diffusion boundary layer ( DBL ), is one of the factors controlling their response to OA . Surface pH is controlled by both the pH of the bulk seawater and by the seaweeds' metabolism: photosynthesis and respiration increase and decrease pH within the DBL ( pH DBL ), respectively. However, other metabolic processes, especially the uptake of inorganic nitrogen (N i ; NO 3 − and NH 4 + ) may also affect the pH DBL . Using Macrocystis pyrifera , we hypothesized that (1) NO 3 − uptake will increase the pH DBL , whereas NH 4 + uptake will decrease it, (2) if NO 3 − is cotransported with H + , increases in pH DBL would be greater under an OA treatment ( pH = 7.65) than under an ambient treatment ( pH = 8.00), and (3) decreases in pH DBL will be smaller at pH 7.65 than at pH 8.00, as higher external [H + ] might affect the strength of the diffusion gradient. Overall, N i source did not affect the pH DBL . However, increases in pH DBL were greater at pH 7.65 than at pH 8.00. CO 2 uptake was higher at pH 7.65 than at pH 8.00, whereas HCO 3 − uptake was unaffected by pH . Photosynthesis and respiration control pH DBL rather than N i uptake. We suggest that under future OA , Macrocystis pyrifera will metabolically modify its surface microenvironment such that the physiological processes of photosynthesis and N i uptake will not be affected by a reduced pH .