Abstract
Little is known of the effects of ionizing radiation exposure on soil biota. We exposed soil microcosms to weekly bursts of 60Co gamma radiation over six weeks, at three levels of exposure (0.1 kGy/hr/wk [low], 1 kGy/hr/wk [medium] and 3 kGy/hr/wk [high]). Soil DNA was extracted, and shotgun metagenomes were sequenced and characterised using MG-RAST. We hypothesized that with increasing radiation exposure there would be a decrease in both taxonomic and functional diversity. While bacterial diversity decreased, diversity of fungi and algae unexpectedly increased, perhaps because of release from competition. Despite the decrease in diversity of bacteria and of biota overall, functional gene diversity of algae, bacteria, fungi and total biota increased. Cycles of radiation exposure may increase the range of gene functional strategies viable in soil, a novel ecological example of the effects of stressors or disturbance events promoting some aspects of diversity. Moreover, repeated density-independent population crashes followed by population expansion may allow lottery effects, promoting coexistence. Radiation exposure produced large overall changes in community composition. Our study suggests several potential novel radiation-tolerant groups: in addition to Deinococcus-Thermus, which reached up to 20% relative abundance in the metagenome, the phyla Chloroflexi (bacteria), Chytridiomycota (fungi) and Nanoarcheota (archaea) may be considered as radiation-tolerant.
Highlights
The effects of ionizing radiation on humans and the ecosystems have been investigated since the 1950s1–7 driven by interest in understanding radiation effects on both natural and agricultural ecosystems
The study of irradiated soil communities may be approached from a generalized ecological point of view, as a system subject to stress and disturbance effects and recovery. This approach has the potential to provide clues to the processes that govern the assembly of communities in nature, including the mechanisms behind diversity and coexistence. We took this approach, focussing on a number of hypotheses regarding the effects on radiation on soil communities and their functional characteristics: Soils subjected to gamma irradiation will have a taxonomically distinct biota from control soils, and the diversity of this biota will differ according to the radiation dose received
The concentration of total nitrogen (TN) was highest in the pre-treatment samples and lowest in high radiation treated samples whereas total organic carbon (TOC) concentration, which was highest in the pre-treatment, was lowest in the low radiation treated samples
Summary
The effects of ionizing radiation on humans and the ecosystems have been investigated since the 1950s1–7 driven by interest in understanding radiation effects on both natural and agricultural ecosystems. Www.nature.com/scientificreports diversity consists of complex communities of organisms that are microscopic or near microscopic, and morphologically cryptic[24] Most of these microscopic life forms have neither been isolated nor studied[25,26], yet these microorganisms play key roles in the ecosystem[27,28]. The study of irradiated soil communities may be approached from a generalized ecological point of view, as a system subject to stress and disturbance effects and recovery. This approach has the potential to provide clues to the processes that govern the assembly of communities in nature, including the mechanisms behind diversity and coexistence. We took this approach, focussing on a number of hypotheses regarding the effects on radiation on soil communities and their functional characteristics: Soils subjected to gamma irradiation will have a taxonomically distinct biota from control soils, and the diversity of this biota will differ according to the radiation dose received
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