Emersion induces nitrogen release and alteration of nitrogen metabolism in the intertidal genus Porphyra.
We investigated emersion-induced nitrogen (N) release from Porphyra umbilicalis Kütz. Thallus N concentration decreased during 4 h of emersion. Tissue N and soluble protein contents of P. umbilicalis were positively correlated and decreased during emersion. Growth of P. umbilicalis did not simply dilute the pre-emersion tissue N concentration. Rather, N was lost from tissues during emersion. We hypothesize that emersion-induced N release occurs when proteins are catabolized. While the δ(15)N value of tissues exposed to emersion was higher than that of continuously submerged tissues, further discrimination of stable N isotopes did not occur during the 4 h emersion. We conclude that N release from Porphyra during emersion did not result from bacterial denitrification, but possibly as a consequence of photorespiration. The release of N by P. umbilicalis into the environment during emersion suggests a novel role of intertidal seaweeds in the global N cycle. Emersion also altered the physiological function (nitrate uptake, nitrate reductase and glutamine synthetase activity, growth rate) of P. umbilicalis and the co-occurring upper intertidal species P. linearis Grev., though in a seasonally influenced manner. Individuals of the year round perennial species P. umbilicalis were more tolerant of emersion than ephemeral, cold temperate P. linearis in early winter. However, the mid-winter populations of both P. linearis and P. umbilicalis, had similar temporal physiological patterns during emersion.
Departments of Ecology and Evolutionary Biology and Marine Sciences, University of Connecticut, Stamford, Connecticut, United States of America. jang.kim@uconn.edu
Jang K
JK
Kim
George P
GP
Kraemer
Charles
C
Yarish
D020418:Algal Proteins / Q000378:metabolism; D000704:Analysis of Variance; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D050901:Nitrate Reductase / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes; D044664:Porphyra / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D012995:Solubility; D055871:Tidal Waves
D020418:Algal Proteins; D009566:Nitrates; D009587:Nitrogen Isotopes; D050901:Nitrate Reductase; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen