Negative Effects of P-Buffering and pH on Photosynthetic Activity of Planktonic Desmid Species

Abstract

The photosynthetic activities of three planktonic desmid species (Staurastrum brachiatum, Staurodesmus cuspidatus var. curvatus, and Staurastrum chaetoceras) were compared after adaptation to medium enriched with either a 20 mM Na +phosphate (P) or HEPES buffer. Incubations up to 2 d were carried out at pH 6 or 8 under normal air or air enriched with 5 % CO 2 . Gross maximum photosynthetic rate (P max ) and growth rate were decreased in both S. brachiatum and Std. cuspidatus at higher pH when using the HEPES buffer and this effect was independent of CO 2 concentration, indicating that pH had an inhibitory effect on photosynthesis and growth in these species. The P-buffer at pH 8 caused a large decrease in P max and quantum yield for charge separation in photosystem 2 (PS2), compared to HEPES-buffered algae. This effect was very large in both S. brachiatum and Std. cuspidatus, two species characteristic of soft water lakes, but also significant in S. chaetoceras, a species dominant in eutrophic, hard water lakes. The decreased P max in P-buffer could not be related to a significant increase in cellular P content known to be responsible for inhibition in isolated chloroplasts. Experiments at pH 6 and 8 showed that two conditions, high pH and high Na + concentration, both contributed to the decreased P max and quantum yield in the desmids. Effects of a P-buffer were less pronounced by using K + -P buffer. The use of P-buffer at pH 8 possibly resulted in high irradiance stress in all species, indicated by damage in the PS2 core complex. In the soft water species pH 8 resulted in increased non-photochemical quenching together with a high de-epoxidation state of the xanthophyll cycle pigments.

Carbon acquisition mechanisms by planktonic desmids and their link to ecological distribution

“…As the effect of pH on the physiology of an alga is largely unknown or assumed to be rather unimportant (Talling 1976), species characteristic of soft waters (low pH) have traditionally been considered CO 2 users, and species inhabiting alkaline sites are grouped as HCO 3 -users, ignoring pH as an important factor underlying species distribution. In contrast, a recent study has shown that pH has an effect on the photosynthesis of desmids independent of CO 2 availability (Spijkerman et al 2004). In the present study, the possible mechanisms of C i acquisition in planktonic desmid species characteristic of different types of lakes (ranging from oligotrophic, acidic to eutrophic, alkaline) are described.…”

“…Although Raven (1990) assumed the effect of external pH to be an insignificant factor in the physiology of algae, Williams and Colman (1996) underlined that a possible detrimental effect of high pH is not (only) a function of low CO 2 . Indeed, also in some desmid species an external pH value of 8 appeared to decrease photosynthesis and growth independent of CO 2 concentration, already after exposure times of about 8 h (Spijkerman et al 2004).…”

Growth and photosynthetic characteristics of several Cosmarium strains (Zygnematophyceae, Streptophyta) isolated from various geographic regions under a constant light-temperature regime

“…Previous ecophysiological studies on desmids revealed possible distribution patterns of desmid species and strains concerning the amount of nutrients and the chemical condition of habitats (Tassigny 1971;Soeder et al 1971;Coesel 1996a, b, 1998;Spijkerman et al 2004Spijkerman et al , 2005. These investigations considered the physiological behaviour of desmid isolates from areas belonging to the same climate zone.…”

“…However, desmids are known for a high number of exceptions to this general rule. Due to the fact that the majority of desmid taxa place high demands on environmental conditions and are regarded as K-strategists (Coesel and Kooijman-Van Blokland 1991;Spijkerman and Coesel 1998;Spijkerman et al 2004), general geographic distribution areas could be drawn for most of the desmid taxa that do not express a large morphological variability and/or synonymy with the other taxa. Coesel (1996) refined Krieger's classification system of desmid floral regions, revealing a high number of desmid taxa confined exclusively to certain climatic regions.…”

Substrate specificity of periphytic desmids in shallow softwater lakes in Belgium

“…These concerns are warranted as desmids occur primarily in oligotrophic softwater lakes, where the effect of host plants on periphyton community composition is considered to be more pronounced than in eutrophic environments (Eminson & Moss, 1980). Desmids have been shown to be sensitive to increases in pH and changes in CO 2 concentration (Moss, 1973;Spijkerman et al, 2004). Therefore, plants that influence concentrations of H + ions and CO 2 in their environment may harbour different desmid communities.…”