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Nitrogen Assimilation and Partitioning in the Mediterranean Seagrass Posidonia oceanica
Author(s) -
Kraemer G. P.,
Mazzella L.,
Alberte R. S.
Publication year - 1997
Publication title -
marine ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.668
H-Index - 58
eISSN - 1439-0485
pISSN - 0173-9565
DOI - 10.1111/j.1439-0485.1997.tb00435.x
Subject(s) - posidonia oceanica , seagrass , shoot , photosynthesis , potamogetonaceae , biology , botany , mediterranean climate , biomass (ecology) , horticulture , agronomy , ecology , ecosystem
. The supply of nitrogen (N) often limits the productivity of marine macrophytes. In vitro and in vivo assays of glutamine synthetase (GS) activity were employed to investigate patterns of N assimilation by the Mediterranean seagrass Posidonia oceanica (L.) DELILE. Biomass‐specific GS activity wa measured in root tissue, in leaves within a shoot, in shoots collected at two sites during two season and over a depth range of 5–33 m. Root tissue was less important than shoot tissue in assimilating inorganic N in P. oceanica , due both to the small roots' biomass (ca. 3% of total plant biomass and greatly lower (10‐ to 50‐fold) GS activities. While the GS activity and N assimilatory potentia (biomass × GS activity; μmol N‐h‐ ‐1 ) were greatest in leaf 2, leaves 1 and 3–5 assimilated N a significant rates. Shoots from a site characterized by elevated N availability in the winter water column and no significant sediment N reservoir exhibited GS activities that were 9‐times higher than shoot from a more oligotrophic site. Shoot GS activities in July increased linearly from 5 to 33 m and wer correlated with light availability as defined by H sat , (daily period during which photosynthetic reaction are light‐saturated). This may represent metabolic compensation by P. oceanica to maintain N influx. Factors contributing to the ecological success of P. oceanica include the ability to assimilate N under conditions of severe light limitation (< 35 μmol photons. m ‐2 . s ‐1 ), and metabolic plasticity to ensur the de novo generation of N‐containing organic compounds.