Influence of black Aspergillus-based soil amendments on 137Cs uptake by rice grown in Fukushima-contaminated soils

Black Aspergillus species produce several metabolites, including organic acids, that can facilitate the release of soil-attached elements. In Fukushima soils, radiocesium has been observed to adhere to soil particles. We hypothesized that Aspergillus-derived organic acids may function as weathering agents, potentially affecting the phyto-availability of radiocesium in soils. Therefore, new soil amendments, comprising fermented wheat bran by different Aspergillus strains, were formulated and evaluated on Fukushima soils to assess their effects on rice growth and radiocesium uptake. Two pot experiments were conducted. The initial experiment focused on evaluating the fermentation product of A. saitoi, while the subsequent experiment assessed the fermentation products of seven strains belonging to A. luchuensis (one strain), A. niger (five strains), and A. saitoi (one strain) under laboratory-controlled and open-air cultivation conditions in Fukushima. Both experiments examinated the effects of amendments on growth and radiocesium uptake by rice grown in different Fukushima soils.

In the first experiment, A. saitoi amendment considerably enhanced shoot biomass and radiocesium quantity in TAT-26 rice line, by nearly 100% and 400%, respectively. In the second experiment, amendments from different Aspergillus strains revealed positive and negative effects on growth and radiocesium uptake by TAT-26. These effects varied depending on soil types and climatic conditions in which plants were cultivated. In the brown forest soil, results showed that amendment-induced soil acidification may increase radiocesium phyto-availability. TAT-26 showed a considerable ability to accumulate radiocesium in its above-ground biomass, making it a candidate accumulator plant. However, this feature must be verified under field conditions.