Understanding leaf litter fungal decomposition and their ecological impact under ionising radiation conditions

Overview

All organisms are constantly exposed to low doses of radiation from natural radiation sources such as the earth’s crust and cosmic radiation. In some cases, these radiation levels increase due to man-made events such as accidents (e.g. Chernobyl and Fukushima) which result in organisms being exposed at higher levels. Since the radiological fallout from the Chernobyl accident in 1986, there have been a number of studies into the effects of radiation on wildlife around the Chernobyl Nuclear Power Plant. One of the main concerns with the increase in radiation levels in the environment is the potential destabilisation of natural ecosystem processes. However, little is known about the specific effects on ecosystem processes such as plant production, the degradation of dead organic matter, and elemental cycling. Interestingly, in the last 5 years, there have been conflicting reports of the impact of radioactive contamination on litter decomposition and any mechanism of action still remains unexplored.

Leaf litter decomposition plays a pivotal role in the cycling of essential nutrients for forest plant growth and both the rate and process of decomposition is driven by a diversity of microorganisms. Therefore, the AIM of this proposal is to assess the extent to which radiation impacts on leaf decomposition by fungi, microbes and other organisms to identify the mechanisms by which this process occurs. The specific OBJECTIVES are to 1) Investigate rate and extent of leaf litter decomposition under controlled radiation conditions; 2) Dissect the mechanism(s), for example, in fungal cell function altered by radiation by using well established yeast strains and assays.

This exciting project will explore how leaf decomposition may be affected by radiation. The student will expose fallen leaves collected from woodlands local to Stirling in our radiation facility which can mimic the radiation levels seen in the Chernobyl Exclusion Zone. S/he will identify the mechanisms by which decomposition occurs by studying the growth and development of fungi and other micro-organisms under radioactive conditions.

Methodology

The project will utilise the specialist experimental facilities at the University of Stirling for radiation exposure experiments. The student will expose sterilised fallen leaves collected from woodlands local to Stirling to a chronic radiation at environmentally relevant dose rates for fixed periods of time. S/he will assess the rate and extent of leaf litter decomposition by, for example, challenging them with single or multiple cultures of a variety of saprotrophic fungi and determine both leaf and fungal biomass by measuring the dry/ash free dry weight and ergosterol concentration, respectively.

The student will also study how the regulation of specific genes is affected by the radiation exposure using transcriptomic techniques by extracting RNA from saprotrophic fungi isolated from decomposed leaves after the irradiation experiments. Any key genes that are up- or down- regulated will be analysed by western blots.

Finally the student will study the response of fungi to different radiation doses by measuring linear mycelial growth on solid substrates, and the ability of fungi to adhere to plastic and invade agar, as well as rates of spore germination and melanin production. S/he will also focus on changes in yeast cell wall components such as chitin, mannan and beta-glucans through the use of microscopy and biochemical assays.

Project Timeline

Year 1

Conduct a literature review and design an appropriate research strategy for work within the radiation facility and laboratory (microbiology/cell biology) studies;

Culturing and/or maintaining a variety of saprotrophic fungi such as Cladosporium sphaerospermum.

Undergo training in genomics & RNA-seq data analysis.

Attend and present at one local conference.

Year 2

Inoculating sterilised dead leaf samples with spores isolated from soil samples obtained from site of leaf sampling and/or single or mixed cultures of saprotrophic fungi to determine the rate and extent of leaf litter decomposition under control and radioactive conditions.

Characterise saprotrophic fungi in soil samples and determine the cellular impact of radiation on them using transcriptome analysis.

Attend and present at one local conference.

Year 3

Expose fungi to different radiation doses in our radiation facility and study rates of spore germination and melanin production, growth and cell wall integrity by measuring structures and components of fungi cell wall components such as chitin, mannan and beta-glucans through the use of dyes or biochemical assay kit, linear mycelial growth on solid substrates, and the ability of fungi to adhere to plastic and invade agar.

Attend and present at one local and one overseas conference.

Year 3.5

Thesis finalisation and paper writing (although it is anticipated that these activities will be ongoing throughout the PhD).

Training
& Skills

The analytical techniques required for this study are already established at the University of Stirling and include: SDS-PAGE, western blotting, microbiological / biochemical assays, using microscopy & plate readers. S/he will receive training in experimental design, data analysis, and radiological protection related to the project work. S/he will attend classes on Effective Research, Scientific Writing, Statistics for Environmental Evaluation (and use of R), Presentation Skills, and Radiological Environmental Protection. S/he will attend 2 external courses run by Edinburgh Genomics in Linux for Genomics & RNA-seq Data Analysis.

The student will also benefit from wider interaction within research groups at Stirling and CEH Lancaster. We will establish regular meetings via Skype between CEH and Stirling to allow discussions on the student’s work. S/he will be expected to present the results of their research annually at the BES student symposium and to attend the annual UK COGER meetings which have an emphasis on encouraging students to present their work. The student will also be expected to present their work at one conference. The student will have the opportunity to interact with wider student networks (and training opportunities) though the European Radioecology ALLIANCE.

References & further reading

Beresford, N.A., Copplestone, D. (2011) Effects of Ionizing Radiation on Wildlife: What Knowledge Have We Gained Between the Chernobyl and Fukushima Accidents? Integer. Environ. Ass. Manag., 7, 371-37.

Bonzom J-M. et al. (2016) Effects of radiation contamination on leaf litter decomposition in the Chernobyl exclusion zone. STOTEN 15: 596-603.

Copplestone, D., Beresford, N.A., Howard, B.J. (2010) EDITORIAL: Protection of the Environment from Ionising Radiation: developing criteria and evaluating approaches for use in regulation. J. Radiol. Prot., 30, 191-194.

Møller & Mousseau (2006) Biological consequences of Chernobyl: 20 years on. Trends Ecol Evol. 21:200-207.

Wardle (2002) Communities and ecosystems: linking the aboveground and belowground components.

Zaitsev et al (2014) Ionizing radiation effects on soil biota: Application of lessons learned from Chernobyl accident for radioecological monitoring. Pedobiologia. 57:5-14.

http://tiny.cc/0r1m6y

Further Information

Jenson Lim +44 (0) 1786 467821, Email: jenson.lim@stir.ac.uk

Nick Beresford +44 (0)1524 595856, Email: nab@ceh.ac.uk

David Copplestone +44 (0)1786 467852, Email: david.copplestone@stir.ac.uk

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