EFFECTS OF NUTRIENTS ON THE PHOTOSYNTHESIS OF SARGASSUM-THUNBERGII

Sargassum thunbergii plants growing on a coast facing the open sea showed NO3 — and PO4 3— imited photosynthetic activity. NO3 - and PO3— 4 -limited plants showed little improvement in photosynthetic rate with single NO3 - or PO3— 4enrichment. The plants showed increased photosynthetic activity correlated with increased chlorophyll content on a fresh weight basis during incubation in NO3 - and PO3— 4-enriched sea water for 3 to 7 days. Such increases in photosynthesis and chlorophyll content were related to increases in the size of the pools for NO3 - and PO3— 4 in the tissues. Sargassum thunbergii plants from an inner bay, the coastal water of which is rich in nitrate and phosphate, showed no increase in photosynthetic capacity during incubation in NO3 - and PO3— 4-enriched seawater. © 1990, Walter de Gruyter. All rights reserved.