Simultaneous Effects of Light Intensity and Phosphorus Supply on the Sterol Content of Phytoplankton

Abstract

Sterol profiles of microalgae and their change with environmental conditions are of great interest in ecological food web research and taxonomic studies alike. Here, we investigated effects of light intensity and phosphorus supply on the sterol content of phytoplankton and assessed potential interactive effects of these important environmental factors on the sterol composition of algae. We identified sterol contents of four common phytoplankton genera, Scenedesmus, Chlamydomonas, Cryptomonas and Cyclotella, and analysed the change in sterol content with varying light intensities in both a high-phosphorus and a low-phosphorus approach. Sterol contents increased significantly with increasing light in three out of four species. Phosphorus-limitation reversed the change of sterol content with light intensity, i.e., sterol content decreased with increasing light at low phosphorus supply. Generally sterol contents were lower in low-phosphorus cultures. In conclusion, both light and phosphorus conditions strongly affect the sterol composition of algae and hence should be considered in ecological and taxonomic studies investigating the biochemical composition of algae. Data suggest a possible sterol limitation of growth and reproduction of herbivorous crustacean zooplankton during summer when high light intensities and low phosphorus supply decrease sterol contents of algae.

Phytoplankton sterol contents vary with temperature, phosphorus and silicate supply: a study on three freshwater species

“…The lowest and the highest phosphorus level to which each species was exposed here correspond to the low-P and the high-P treatments in our earlier study (Piepho et al, 2010). Our new results confirm the effects of phosphorus found in the previous study.…”

“…We found interactive effects of temperature and phosphorus supply (the present study) as well as of light and phosphorus supply (Piepho et al, 2010). Thus, the effect of one of these environmental factors should not be described without the other and the analysis of interactions of various environmental factors is a very important approach in understanding the changes of sterol concentrations in phytoplankton.…”

“…The sterol composition of this alga appeared to be hardly affected by environmental conditions (see also Piepho et al, 2010), either temperature or phosphorus level. This might be due to the mixotrophic lifestyle of this alga (Tranvik et al, 1989) and associated differences in the adaptation response to changing environmental conditions as compared with exclusively phototrophic species.…”

“…In addition to temperature, other factors significantly affect the sterol composition and concentration in algae and hence possibly also the availability of sterols for higher trophic levels. In a previous study, we showed that the sterol concentrations of four common phytoplankton species changed significantly with increasing light intensity and that the reaction to light was influenced by phosphorus availability (Piepho et al, 2010). The results suggested that with high light intensities and a low phosphorus supply, which represents a common scenario in many lakes during summer, the sterol concentrations of algae are reduced.…”

“…The limit of sterol quantification was 20 ng. The C-24 stereochemistry and the cis-trans isomery of sterols could not be identified with certainty and thus, if procurable, was adopted from the literature (see also Piepho et al, 2010). Accordingly, since it has been reported that cryptophycean algae contain epibrassicasterol (IUPAC name: (22E)-campesta-5,22-dien-3-ol), which is the 24-epimer of brassicasterol ((22E)-ergosta-5,22-dien3-ol) (Goad et al, 1983;Gladu et al, 1990), the presence of epibrassicasterol rather than brassicasterol was assumed in C. ovata.…”