Responses of the Microalga Dunaliella Salina to Sulfur Limitation

Abstract

Sulfur is an essential element for plant and algal growth since it is a key component of amino acids, proteins, sulfolipids, vitamins and FE/S-clusters of the electron transport pathways (1). Traditionally, sulfur is thought never to limit productivity in aquatic ecosystems. This is likely to be true in most marine situations where sulfate ions, the primary source of sulfur, are present at concentrations of 20 –30 mmol L−1 (2). However, in many freshwaters, particularly oligotrophic lakes and rivers in upland areas where the sulfur content of the rocks in the catchment is low, the concentration of sulfate can be about 0.03 mmol L−1 (3). Furthermore, in such sites deposition from ‘acid rain’ can be the major source of sulfur (4) and the sulfur deposition is declining in Europe as air pollution is reduced (5) and may decline further as a result of the Oslo Protocol of 1994. Long-term records of water-chemistry in small lakes in the English Lake District, an upland area of the UK, have shown that sulfate concentrations have declined in response to reduced atmospheric deposition (3). The aim of this work is to fmd out whether sulfur may limit algal growth where sulfate concentrations are low and how algae respond to S-limitation.