To date, research on adaptation of photosynthetic microorganisms to external stimuli such as nutrients and light has mainly focussed on full adaptation. The aim of this study is to understand the largely unknown constrains that determine the transition fro m one adaptive state to another. This is not a time invariant phenomenon, but proceeds in a historical context in that every adaptation is determined by previous adaptation of an organism. In this respect the cellular memory will be studied as response to a sequence pattern of phosphorus pulses varying in amplitude and frequency. The 32P-uptake experiments focus on the ecophysiological relevance of information processing in a P-pulsed environment. From this view, the P-uptake will be described phenomenologically as in thermodynamics.
P is favoured because it can limit both marine and freshwater algal growth and plays a central role in metabolic pathways. In the past, nutrients as P have often been treated as slowly varying in ecological studies. However, we know that P is often supplied in pulses when microscopic animals or fish excrete, or when storms mix P-rich deeper waters into P-poor surface waters. A key issue here is, to gain a better understanding how the adaptive uptake of P-pulses interact with the utilisation of light and other nutrients. The P-light-interactions will be analysed by photosynthetic properties of contrasting states, the `adapted state and the `non-adapted (adaptive) mode.
The study of cellular P-compounds as DNA, RNA and lipids will b e linked to ecological stoichiometry. We will prove the hypothesis that distinct P-uptake strategists confirm a recently discussed concept of ecological strategists. Practical issues are to develop field bioassays determining the P-availability in marine systems. Experiments will be undertaken with two marine algae Thalassiosira weissflogii and Emiliania huxleyi, which have contrasting P-light requirements and are representative of marine biochemical cycles.
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