Norwegian Radiation and Nuclear Safety Authority, Østerås, Norway.
Centre for Environmental Radioactivity (CERAD CoE), NMBU, Ås, Norway.
PLoS One. 2021 Mar 17;16(3):e0247793. doi: 10.1371/journal.pone.0247793. eCollection 2021.
Decomposition of litter and organic matter is a very important soil ecosystem function where soil fauna play an important role. Knowledge of the responses in decomposition and soil fauna to different stressors is therefore crucial. However, the extent to which radioactivity may affect soil fauna is not so well known. There are some results showing effects on soil fauna at uranium mines and near Chernobyl from relatively high levels of anthropogenic radionuclides. We hypothesize that naturally occurring radionuclides affect soil fauna and thus litter decomposition, which will covary with radionuclide levels when accounting for important soil parameters. We have therefore used standardised litterbags with two different mesh sizes filled with birch leaves (Betula pubescens) to assess litter decomposition in an area with enhanced levels of naturally occurring radionuclides in the thorium (232Th) and uranium (238U) decay chains while controlling for variation in important soil parameters like pH, organic matter content, moisture and large grain size. We show that decomposition rate is higher in litterbags with large mesh size compared to litterbags with a fine mesh size that excludes soil fauna. We also find that litter dried at room temperature is decomposed at a faster rate than litter dried in oven (60⁰C). This was surprising given the associated denaturation of proteins and anticipated increased nutritional level but may be explained by the increased stiffness of oven-dried litter. This result is important since different studies often use either oven-dried or room temperature-dried litter. Taking the above into account, we explore statistical models to show large and expected effects of soil parameters but also significant effects on litter decomposition of the naturally occurring radionuclide levels. We use the ERICA tool to estimate total dose rate per coarse litterbag for four different model organisms, and in subsequent different statistical models we identify that the model including the dose rates of a small tube-shape is the best statistical model. In another statistical model including soil parameters and radionuclide distributions, 226Ra (or uranium precursory radionuclides) explain variation in litter decomposition while 228Ra (and precursors) do not. This may hint to chemical toxicity effects of uranium. However, when combining this model with the best model, the resulting simplified model is equal to the tube-shape dose-rate model. There is thus a need for more research on how naturally occurring radionuclides affect soil fauna, but the study at hand show the importance of an ecosystem approach and the ecosystem parameter soil decomposition.
枯枝落叶和有机物的分解是土壤生态系统的一个非常重要的功能，土壤动物在其中起着重要作用。因此，了解不同胁迫因素对分解和土壤动物的反应至关重要。然而，放射性对土壤动物的影响程度还不是很清楚。有一些结果表明，在铀矿区和切尔诺贝利附近，相对较高水平的人为放射性核素对土壤动物有影响。我们假设，天然存在的放射性核素会影响土壤动物，从而影响枯枝落叶的分解，而当考虑到重要的土壤参数时，放射性核素水平会与之相关。因此，我们使用标准的带两个不同网眼大小的落叶袋，用桦树叶（Betula pubescens）填充，以评估在钍（232Th）和铀（238U）衰变链中天然放射性核素水平增强的区域内的落叶分解情况，同时控制重要的土壤参数，如 pH 值、有机质含量、水分和大粒径的变化。结果表明，大网眼落叶袋中的分解速度比小网眼落叶袋（排除土壤动物）中的分解速度快。我们还发现，室温下干燥的落叶比在烤箱（60°C）中干燥的落叶分解速度更快。这令人惊讶，因为这与蛋白质的变性和预期的营养水平增加有关，但可能是由于烤箱干燥的落叶硬度增加所致。这一结果很重要，因为不同的研究通常使用烤箱干燥或室温干燥的落叶。考虑到以上因素，我们探索了统计模型，以显示土壤参数的大而预期的影响，以及天然放射性核素水平对落叶分解的显著影响。我们使用 ERICA 工具来估算每个大落叶袋的总剂量率，对于四个不同的模型生物，在随后的不同统计模型中，我们确定包括小管形状剂量率的模型是最佳的统计模型。在另一个包括土壤参数和放射性核素分布的统计模型中，226Ra（或铀前体放射性核素）解释了落叶分解的变化，而 228Ra（和前体）则没有。这可能暗示了铀的化学毒性效应。然而，当将该模型与最佳模型结合时，简化的模型与管形剂量率模型相同。因此，需要更多的研究来了解天然放射性核素如何影响土壤动物，但目前的研究表明，需要采用生态系统方法和土壤分解等生态系统参数。
