Impacts of soil type and drought stress on growth and cesium accumulation in Napier grass

In our previous study, the decontamination efficiency of cesium-137 (¹³⁷Cs) by Napier grass (Pennisetum purpureum Schum.) in the field was shown to be variable and often influenced by natural environmental factors. To elucidate the factors influencing this variable ¹³⁷Cs-decontamination efficiency, we investigated the influences of soil type and drought stress on Cs accumulation using cesium-133 (¹³³Cs) in Napier grass grown in plastic containers. The experiment was performed using two soil types (Soil A and B) and three different soil moisture conditions: well-watered control (CL), slight drought stress (SD), and moderate drought stress (MD). Overall, our results indicate that soil type and drought have a significant impact on plant growth and ¹³³Cs accumulation in Napier grass. Plant height (PH), tiller number (TN), leaf width (W_leaf), and dry matter weight of aboveground parts (DW_above) and root parts (DW_root) in Soil B were greater than those in Soil A. Drought stress negatively affected chlorophyll fluorescence parameters (maximal quantum efficiency of photosystem (PS) II photochemistry and potential activity of PS II), PH, TN, W_leaf, DW_above, DW_root, and total ¹³³Cs content (TCs), but it had a positive effect on ¹³³Cs concentration. The ¹³³Cs concentration in the aboveground parts (Cs_above) was increased by MD approximately 1.62-fold in Soil A and 1.11-fold in Soil B compared to each CL counterpart. The TCs in the aboveground parts (TCs_above) decreased due to drought by approximately 19.9%-39.0% in Soil A and 49.9%-62.7% in Soil B; however, there was no significant effect on TCs_above due to soil type. The results of this study indicate that soil moisture is a key factor in maintaining Napier grass ¹³⁷Cs-decontamination efficiency.