Effects of Dissolved Organic Matter in Soil Extracts on the Growth of Microalgae

In this study, three soil extracts and seven species of microalgae were prepared and the growth enhancing/inhibiting effects of the addition of the soil extract on microalgae were investigated. The microplate technique was applied for incubation under various conditions, and the specific growth rate of the microalgae was compared between the control medium (the incubated microalgae without the addition of the soil extract) and the soil-added media. In addition, we focused on the characteristics of dissolved organic matter as major factors affecting the microalgal growth effect, and examined which organic characteristics affect the microalgal growth. It was suggested that the soil extract conventionally used in the National Institute for Environmental Studies (SE-N) showed the most marked growth-enhancing effect on microalgae at 25 °C. In addition, the soil extract made from the soil from the Rajamusa Forest Reserve, Malaysia, showed the most marked growth-enhancing effect on microalgae at 30 °C. The characteristics of SE-N on the excitation emission matrix (EEM) of fluorescence analysis were very different from the others because the soil extract had a clear tryptophan-like peak not observed in the others. SE-N also had organic matter of larger molecular size than the others. These characteristics might affect the microalgal growth.