Differences in acclimation potential of photosynthesis in seven isolates of the tropical to warm temperate macrophyte Valonia utricularis (Chlorophyta)

A. Eggert, R.J.W. Visser, P.R. Van Hasselt and A.M. Breeman. 2006. Differences in acclimation potential of photosynthesis in seven isolates of the tropical to warm temperate macrophyte Valonia utricularis (Chlorophyta). Phycologia 45: 546–556. DOI: 10.2216/05-03.1 The potential to acclimate photosynthesis to sub- and supra-optimal temperatures was investigated in seven isolates of Valonia utricularis (Roth) C. Agardh, a green macrophyte with a tropical to warm-temperate distribution. Photosynthesis–light response curves were obtained by measuring chlorophyll a fluorescence characteristics of algae grown at optimal (25°C), sub- and supra-optimal temperatures. Suboptimal temperatures were chosen to support 30% of the maximum relative growth rate in each isolate. Thermal acclimation was investigated by comparing short-term and long-term temperature effects on the initial rate of increase of the relative electron transport rate (rETR) and the maximum rETR under light-saturating conditions. Isolates from the northeast Atlantic and the Mediterranean all showed a strong potential to acclimate maximum rETR to suboptimal growth temperatures, i.e. short-term temperature effects were diminished after acclimation. However, photoinhibition, measured as a decrease of the maximal quantum yield (Fᵥ/Fₘ), was found when plants were grown at 30°C. The isolates reduced light harvesting at 30°C by decreasing total chlorophyll content and by increasing the chlorophyll a/b ratio. Up-regulation of photoprotective processes by the xanthophyll cycle pigments was not observed. In contrast, isolates from the Indo-west Pacific were unable to acclimate photosynthesis to suboptimal growth temperatures and these temperatures were strongly photoinhibiting, even though adjustments on the pigment level were observed. All Indo-west Pacific isolates reached comparable maximum rETR values at 30° and 25°C. Thus, the Atlantic/Mediterranean isolates had a stronger potential to acclimate photosynthetic rates at suboptimal growth temperatures compared to the Indo-west Pacific isolates, which was accompanied by losses at 30°C. The results are discussed in a biogeographical context.