Effect of nutrient pulses on photosynthesis of Chaetomorpha linum from a shallow Mediterranean coastal lagoon

The influence of nitrogen and phosphorus pulses on Chaetomorpha linum (Muller) Kutzing growth and photosynthesis was studied in laboratory experiments. Photosynthesis and growth of C linum from Tancada lagoon seems limited by both nitrogen and phosphorus, as indicated by the high rate (4.7-11.6 mg O-2 g(-1) dry weight h(-1)) of light-saturated photosynthesis (P.) and growth rates observed under nitrogen plus phosphorus enrichment in relation to enrichment by nitrogen alone (2.9-7.6 mg O-2 g(-1) dry weight h(-1)). Significant increase in nitrogen and phosphorus content as percentage of dry weight was observed in C linum fertilized with a single nutrient or with nitrogen plus phosphorus. In Tancada lagoon, when availability of nitrogen to primary producers is by pulses, an increase of nitrate concentration in the water column (from 6 to 100 mu M) has a greater effect on growth of C linum (growth rate: 0.13 day(-1)) than an increase in ammonium concentration (from 20 to 100 mu M and growth rate: 0.11 day(-1)). For a given thallus nitrogen content (0.6-1.4% N), both P-m and the photosynthetic efficiency (alpha) normalized to dry weight were correlated (r(2) = 0.73, p < 0.005) indicating that variations in electron transport were coupled to variations in C-fixation capacity. Optimizing both a and Pm may be a general characteristic of thin-structured opportunistic algae in more variable estuarine environments. (c) 2005 Elsevier B.V. All rights reserved.