title: Effects of X-Ray Dose On Rhizosphere Studies Using X-Ray Computed Tomography.
abstract: X-ray Computed Tomography (CT) is a non-destructive imaging technique originally designed for diagnostic medicine, which was adopted for rhizosphere and soil science applications in the early 1980s. X-ray CT enables researchers to simultaneously visualise and quantify the heterogeneous soil matrix of mineral grains, organic matter, air-filled pores and water-filled pores. Additionally, X-ray CT allows visualisation of plant roots in situ without the need for traditional invasive methods such as root washing. However, one routinely unreported aspect of X-ray CT is the potential effect of X-ray dose on the soil-borne microorganisms and plants in rhizosphere investigations. Here we aimed to i) highlight the need for more consistent reporting of X-ray CT parameters for dose to sample, ii) to provide an overview of previously reported impacts of X-rays on soil microorganisms and plant roots and iii) present new data investigating the response of plant roots and microbial communities to X-ray exposure. Fewer than 5% of the 126 publications included in the literature review contained sufficient information to calculate dose and only 2.4% of the publications explicitly state an estimate of dose received by each sample. We conducted a study involving rice roots growing in soil, observing no significant difference between the numbers of root tips, root volume and total root length in scanned versus unscanned samples. In parallel, a soil microbe experiment scanning samples over a total of 24 weeks observed no significant difference between the scanned and unscanned microbial biomass values. We conclude from the literature review and our own experiments that X-ray CT does not impact plant growth or soil microbial populations when employing a low level of dose (<30 Gy). However, the call for higher throughput X-ray CT means that doses that biological samples receive are likely to increase and thus should be closely monitored.
authors.affiliation: Division of Agricultural and Environmental Sciences, University of Nottingham, Sutton Bonington, United Kingdom.
authors.forename: Susan
authors.initials: S
authors.lastname: Zappala
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Helliwell
authors.forename: Saoirse R
authors.initials: SR
authors.lastname: Tracy
authors.forename: Stefan
authors.initials: S
authors.lastname: Mairhofer
authors.forename: Craig J
authors.initials: CJ
authors.lastname: Sturrock
authors.forename: Tony
authors.initials: T
authors.lastname: Pridmore
authors.forename: Malcolm
authors.initials: M
authors.lastname: Bennett
authors.forename: Sacha J
authors.initials: SJ
authors.lastname: Mooney
mesh_terms: D018525:Germination / Q000528:radiation effects; D012275:Oryza / Q000254:growth & development / Q000528:radiation effects*; D011829:Radiation Dosage; D058441:Rhizosphere; D012988:Soil Microbiology; D014057:Tomography, X-Ray Computed; D014965:X-Rays / Q000009:adverse effects