MACROALGAL RESPONSES TO NITROGEN SOURCE AND AVAILABILITY: AMINO ACID METABOLIC PROFILING AS A BIOINDICATOR USING <em>GRACILARIA EDULIS</em> (RHODOPHYTA).

Jones, Adrian B.; Dennison, William C.; Stewart, George R.

The use of macroalgae as biological indicators of dissolved nutrient source and availability in the water column was investigated. Total tissue nitrogen (N) content, pigments, and amino acids of the red alga Garacilaria edulis (Gmelin) Silva were compared to N source and availability in laboratory and field incubations to identify responses that would serve as bioindicators of N. Field-collected algae were preincubated (6-8 wk) in low-nutrient seawater to deplete their luxury reserves of N. Incubations were then conducted for periods of 3 d in laboratory aguaria (N-spiked seawater) and in the field using macyoalgal incubation chambers. After incubation in different N sources (NH[SUB4,SUP ], NO[SUB3,SUP-], and ura) in laboratory aquaria, photosynthetic pigments (phycoerythrin and chlorophyll a) and total tissue N increased in response to increasing [NH[SUB4, SUP ]] but not to [NO [SUB 3, SUP-]] or [urea]. Incubation in two ranges of [NH[sub4, sup ]], one from 0 to 80 μM and the other from 0 to 800 μM, in laboratory aquaria increased the total amino acid pool. Citrulline concentrations were the most responsive to [NH[sub4, sup ]] (r[sup2]= 0.84) NH[sub4, sup ] source treatments produced increases in citrulline, phenylalanine, serine, and free NH[SUB4, SUP ] and decreases in alanina; NO[sub3, sup-] treatments produced increases in glutamic acid, citrulline, and alanine, and urea treatments produced increases in free NH[SUN4, SUP ] and decreases in phenylalanine and serine. The observed variations in amino acid content facilitated the development of an index for each N source based ob relative concentrations of various amino acids (i.e. metabolic profiling). Gracilaria edulis was incubated along a field N gradient in the Brisbane river (three sites) and Moreton Bay (four sites), Queensland, Australia. Both phycoerythrin and tissue N appeared to respond equally to NH[SUB4, SUP ] and NO[sub3, sup-] availability in the field. N source indices, based on amino acid concentration, were effective predictors of both [NH[SUB4, SUP ]] and [NO[SUB3, SUP-]] over a wider range of concentration along the field gradient. Macroalgal physiological responses, particularly amino acid content, to changes in source and availability of N appear to be useful as sensitive bioindicators on N.

GRACILARIA; RED algae; GRACILARIACEAE; PHYTOPLANKTON; NITROGEN; AMINO acids; BIOINDICATORS

Journal of Phycology, 1996, Vol 32, Issue 5, p757

0022-3646

Academic Journal

10.1111/j.0022-3646.1996.00757.x