Influence of phosphorus on morphology and physiology of freshwater Chaetophora, Draparnaldia and Stigeoclonium (Chaetophorales, Chlorophyta)

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Abstract
The influence of various element deficiencies was tested on 13 strains of Chaetophorales (1 Chaetophora, 2 Draparnaldia, 10 Stigeoclonium) isolated from sites in Belgium, N.E. England and Germany. Judged by the yield in batch culture, the relative response to each deficiency was quite similar in all strains: control > –P > –Fe > –Ca = –S > –Mg > –N. Judged by the extent of hair formation, the relative response was quite different: –P > –N > –Fe = –S > –Ca > –Mg > control. P- and N-limited cultures were the only ones to have typical hairs, and hair development was much greater in the former. It proved possible to maintain continued growth of a culture in a hairy condition by developing a continuous culture technique and using a medium with a high N:P ratio. Five strains were selected for more detailed study. N and P compositions, percentage hairiness and surface phosphatase activity were followed during growth in batch culture in medium leading to P-limitation. Although the maximum P composition ranged from 2.4 to 6.4% dry weight, hair formation commenced when P had fallen to about 1% dry weight; hairs started to form long before the culture had ceased to grow or started to appear unhealthy. The N: P ratio (by weight) at the time hairs were just starting to form ranged from 5.41 to 7.21 (x̄ = 6.35). There was a marked correlation between phosphatase activity and extent of hair formation, though the former became detectable slightly before the latter in some cases. In contrast, cultures with hairs formed under N- or other element deficiencies showed no phosphatase activity. All five strains showed moderate to good growth not only with orthophosphate, but also with polyphosphate, pyrophosphate, β-glycerophosphate and glucose-6-phosphate; all but one used DNA as a P source, but none used lecithin or phytate. All strains showed zoospore formation when subcultured to fresh medium and when P or N was added to P- or N-limited cultures, respectively. Almost all cells of one Stigeoclonium strain differentiated into akinetes under severely P-limited conditions. The significance of these observations on the influence of P-status on morphology for taxonomy of Chaetophorales and the use of Stigeoclonium as a monitor and bioassay organism are discussed.