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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

journal contribution
posted on 2023-05-18, 23:24 authored by Pamela Fernandez Subiabre, Roleda, MY, Leal, PP, Catriona HurdCatriona Hurd
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 (pHDBL), respectively. However, other metabolic processes, especially the uptake of inorganic nitrogen (Ni; NO3 and NH4+) may also affect the pHDBL. Using Macrocystis pyrifera, we hypothesized that (1) NO3 uptake will increase the pHDBL, whereas NH4+ uptake will decrease it, (2) if NO3 is cotransported with H+, increases in pHDBL would be greater under an OA treatment (pH = 7.65) than under an ambient treatment (pH = 8.00), and (3) decreases in pHDBL 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, Ni source did not affect the pHDBL. However, increases in pHDBL were greater at pH 7.65 than at pH 8.00. CO2 uptake was higher at pH 7.65 than at pH 8.00, whereas HCO3 uptake was unaffected by pH. Photosynthesis and respiration control pHDBL rather than Ni uptake. We suggest that under future OA, Macrocystis pyrifera will metabolically modify its surface microenvironment such that the physiological processes of photosynthesis and Ni uptake will not be affected by a reduced pH.

History

Publication title

Physiologia Plantarum

Volume

159

Pagination

107-119

ISSN

0031-9317

Department/School

Institute for Marine and Antarctic Studies

Publisher

Blackwell Munksgaard

Place of publication

35 Norre Sogade, Po Box 2148, Copenhagen, Denmark, Dk-1016

Rights statement

Copyright 2016 Scandinavian Plant Physiology Society

Repository Status

  • Restricted

Socio-economic Objectives

Ecosystem adaptation to climate change

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