Recycling of wood-ash to boreal forests has been suggested to prevent depletion of essential soil nutrient or reduce the negative effects of acidification of surface waters. This study investigated the effects of different concentrations of wood-ash (5, 10 and 12.5 mg l-1 diluted in cultivating medium) on chlorophyll a fluorescence in Euglena gracilis and Chlamydomonas reinhardtii. The green alga C. reinhardtii was more susceptible to wood-ash solutions than the flagellate E. gracilis. Two different forms of wood-ash solutions were tested. In the first solution no adjustment of pH was made. In the second, the pH was adjusted to 7. Wood-ash forms a very strong alkaline reaction if no adjustment of pH is made. The results show that no negative effect on fluorescence yield, electron transport rate (ETR), photochemical quenching (qP) or non-photochemical quenching (NPQ) was observed in E. gracilis. In contrast, C. reinhardtii displayed strong inhibition at concentrations of 10 and 12.5 mg l-1 with non-adjusted pH. The negative effects of high pH on the photosynthetic capacity in C. reinhardtii could either be related to the destruction of the ∆pH across the thylakoid or other parts in the photosynthetic systems that are negatively affected by changing pH. Elevated pH levels in aquatic ecosystems constitute a major environmental stress factor to the phytoplankton community and may lead to loss of diversity among primary producers. If wood-ash application was to become general practice in or near aquatic ecosystems the ash may need to be treated accordingly to avoid rapid changes in pH.
VR-Biology