Effect of litter removal five years after the Fukushima accident on 137Cs uptake by Japanese cedar.

Removal of litter-associated 137Cs from the forest floor (litter removal) can reduce the 137Cs uptake by plants; however, the proposed effective period for litter removal was 1-2 years after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. This is because the 137Cs in forest soil migrates rapidly from the litter to surface mineral soil layers in Japanese forests, and thus the effectiveness of litter removal will quickly become limited. However, it is unknown whether this approach can be applied to forests whose vertical migration of 137Cs in the forest soil is relatively slow. Herein, we compared the 137Cs activity concentration in the inner bark of the Japanese cedar (Cryptomeria japonica) between litter removal (conducted in September and October 2016, 5 years after the accident) and in control areas in Kawauchi Village, Fukushima Prefecture, where the vertical migration of 137Cs was relatively slow from the litter to surface mineral soil layers. Air dose rates (ambient dose equivalent) in the litter removal area were significantly lower than those in the control area in 2022, and the 137Cs inventory in the forest soil in litter removal area also tended to be lower than that in the control area. In Japanese cedars with similar levels of outer bark contamination, the 137Cs activity concentration in the inner bark in the litter removal area was significantly lower than that in the control area, and consistent trends were also found when comparing the 137Cs activity concentration in the leaves of Stephanandra incisa and Wisteria floribunda obtained from the same forest. Thus, the litter removal 5 years after the FDNPP accident may have reduced the 137Cs uptake in Japanese cedar in an evergreen coniferous forest where the vertical migration of 137Cs is relatively slow in the forest soil.

Efficient sampling of shiitake-inoculated oak logs to determine the log-to-mushroom transfer factor of stable cesium.

BACKGROUND: Stable cesium (133Cs) naturally exists in the environment whereas recently deposited radionuclides (e.g., 137Cs) are not at equilibrium. Stable cesium has been used to understand the long-term behavior of radionuclides in plants, trees and mushrooms. We are interested in using 133Cs to predict the future transfer factor (TF) of radiocesium from contaminated logs to shiitake mushrooms in Eastern Japan. However, the current methodology to obtain a representative wood sample for 133Cs analysis involves mechanically breaking and milling the entire log (excluding bark) to a powder prior to analysis. In the current study, we investigated if sawdust obtained from cutting a log along its length at eight points is as robust but a faster alternative to provide a representative wood sample to determine the TF of 133Cs between logs and shiitake. METHODS: Oak logs with ready-to-harvest shiitake fruiting bodies were cut into nine 10-cm discs and each disc was separated into bark, sapwood and heartwood and the concentration of 133Cs was measured in the bark, sapwood, heartwood, sawdust (generated from cutting each disc) and fruiting bodies (collected separately from each disc), and the wood-to-shiitake TF was calculated. RESULTS: We found that the sawdust-to-shiitake TF of 133Cs did not differ (P = 0.223) compared to either the sapwood-to-shiitake TF or heartwood-to-shiitake TF, but bark did have a higher concentration of 133Cs (P < 0.05) compared to sapwood and heartwood. Stable cesium concentration in sawdust and fruiting bodies collected along the length of the logs did not differ (P > 0.05). DISCUSSION: Sawdust can be used as an alternative to determine the log-to-shiitake TF of 133Cs. To satisfy the goals of different studies and professionals, we have described two sampling methodologies (Methods I and II) in this paper. In Method I, a composite of eight sawdust samples collected from a log can be used to provide a representative whole-log sample (i.e., wood and bark), whereas Method II allows for the simultaneous sampling of two sets of sawdust samples-one set representing the whole log and the other representing wood only. Both methodologies can greatly reduce the time required for sample collection and preparation.

Leaf senescence in rice due to magnesium deficiency mediated defect in transpiration rate before sugar accumulation and chlorosis.

Magnesium (Mg) is an essential macronutrient supporting various functions, including photosynthesis. However, the specific physiological responses to Mg deficiency remain elusive. In this study, 2-week-old rice seedlings (Oryza sativa. cv. Nipponbare) with three expanded leaves (L2-L4) were transferred to Mg-free nutrient solution for 8 days. In the absence of Mg, on day 8, L5 and L6 were completely developed, while L7 just emerged. We also studied several mineral deficiencies to identify specific responses to Mg deficiency. Each leaf was analyzed in terms of chlorophyll, starch, anthocyanin and carbohydrate metabolites, and only absence of Mg was found to cause irreversible senescence of L5. Resupply of Mg at various time points confirmed that the borderline of L5 death was between days 6 and 7 of Mg deficiency treatment. Decrease in chlorophyll concentration and starch accumulation occurred simultaneously in L5 and L6 blades on day 8. However, nutrient transport drastically decreased in L5 as early as day 6. These data suggest that the predominant response to Mg deficiency is a defect in transpiration flow. Furthermore, changes in myo-inositol and citrate concentrations were detected only in L5 when transpiration decreased, suggesting that they may constitute new biological markers of Mg deficiency.