The value of synchrotron radiation X-ray techniques to explore microscale chemistry for ecology and evolution research

Synchrotron radiation (SR) techniques, which use high-energy photon beams to create high- resolution images and spectra of a sample, are valuable analytical methods that have long benefited physical, geological and biochemical research. Recent developments of synchrotron infrastructure has allowed SR techniques to become a more accessible resource for studying ecological and evolutionary phenomena at the micro- or nano-scale. Here we provide a synthesis to SR techniques, how they compare with other analytical techniques, how they have been used, and then discuss how this technology has significant potential for future applications within ecology and evolution research. A literature review demonstrates the growing use of SR techniques within environmental and ecological research communities, alongside the variety of organisms and target elements that have been prioritized since 2000. Clear gaps still exist within the imaging of lighter, biologically relevant elements (e.g., C, N and P) for assessing their cycling within organisms, and also in the study of a wider range of microbial, vertebrate and invertebrate species. Whilst different organism types and target elements may require different sample preparation strategies, the selection of an appropriate elemental fixation method (chemical or cryogenic), embedding material, sample thickness and mounting material is particularly important. We demonstrate the opportunities that SR techniques present to those in the fields of environmental biology, ecology and evolutionary science who may be unfamiliar, whilst demystifying the caveats and sample preparation considerations that must be addressed to acquire high-quality data. While these techniques are currently mainly employed within the context of environmental pollution and ecotoxicology studies, we argue that elemental imaging, X-ray microscopy and spectroscopic analysis has a huge, largely untapped potential within agri- ecology, paleoclimatology and comparative and functional morphology studies.