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Although soil organisms are essential for ecosystem function, the impacts of radiation on soil biological activity at highly contaminated sites has been relatively poorly studied. In April-May 2016, we conducted the first largescale deployment of bait lamina to estimate soil organism (largely soil invertebrate) feeding activity in situ at study plots in the Chernobyl Exclusion Zone (CEZ). Across our 53 study plots, estimated weighted absorbed dose rates to soil organisms ranged from 0.7 μGy h-1 to 1753 μGy h-1. There was no significant relationship between soil organism feeding activity and estimated weighted absorbed dose rate. Soil biological activity did show significant relationships with soil moisture content, bulk density (used as a proxy for soil organic matter) and pH. At plots in the Red Forest (an area of coniferous plantation where trees died because of high radiation exposure in 1986) soil biological activity was low compared to plots elsewhere in the CEZ. It is possible that the lower biological activity observed in the Red Forest is a residual consequence of what was in effect an acute high exposure to radiation in 1986. [ABSTRACT FROM AUTHOR]

Anthropogenic releases of radiation are of ongoing importance for environmental protection, but the radiation doses at which natural systems begin to show effects are controversial. More certainty is required in this area to achieve optimal regulation for radioactive substances. We recently carried out a large survey (268 sampled animals and 20 sites) of the association between environmental radiation exposures and small mammal gut‐associated microbiomes (fungal and bacterial) in the Chornobyl Exclusion zone (CEZ). Using individual measurements of total absorbed dose rates and a study design and analyses that accounted for spatial non‐independence, we found no, or only limited, association.Watts et al. have criticised our study: for not filtering candidate non‐resident components prior to our fungal microbiome analyses, for our qualified speculations on the relative merits of faecal and gut samples, and for the design of our study which they felt lacked sufficient replication.The advantage of filtering non‐resident‐fungal taxa is not clear and it would not have changed the null (spatially adjusted) association we found between radioactive dose and mycobiome composition because the most discriminatory fungal taxa with regard to dose were non‐resident taxa.We maintain that it was legitimate for us to make qualified discussion comments on the differences in results between our faecal and gut microbiome analyses and on the relative merits of these sample types.Most importantly, the criticism of our study design by Watts et al. and the designs and analysis of their recent studies in the CEZ show a misunderstanding of the true nature of independent replication in field studies. Recognising the importance of spatial non‐independence is essential in the design and analysis of radioecological field surveys. [ABSTRACT FROM AUTHOR]

Environmental impacts of the 1986 Chernobyl Nuclear Power Plant accident are much debated, but the effects of radiation on host microbiomes have received little attention to date.We present the first analysis of small mammal gut microbiomes from the Chernobyl Exclusion Zone in relation to total absorbed dose rate, including both caecum and faeces samples.We provide novel evidence that host species determines fungal community composition, and that associations between microbiome (both bacterial and fungal) communities and radiation exposure vary between host species. Using ambient versus total weighted absorbed dose rates in analyses produced different results, with the latter more robust for interpreting microbiome changes at the individual level. We found considerable variation between results for faecal and gut samples of bank voles, suggesting faecal samples are not an accurate indicator of gut composition.Associations between radiation exposure and microbiome composition of gut samples were not robust against geographical variation, although we identified families of bacteria (Lachnospiraceae and Muribaculaceae) and fungi (Steccherinaceae and Strophariaceae) in the guts of bank voles that may serve as biomarkers of radiation exposure.Further studies considering a range of small mammal species are needed to establish the robustness of these potential biomarkers. [ABSTRACT FROM AUTHOR]