In situ soil imaging, a tool for monitoring the hourly to monthly temporal dynamics of soil biota

The complexity of the opaque soil matrix is a major obstacle to studying the organisms that inhabit it. Fast technological progress now offers new possibilities for the monitoring of soil biodiversity and root growth, such as in situ soil imaging. This study presents the potential of soil imaging devices to investigate the temporal dynamics and spatial distribution of soil biological activity and their interactions. The soil imaging devices were buried in a truffle field located in the south of France and set up to capture images automatically every 6 h at 1200 dpi. For the first time, root growth, mycorrhizal colonization and invertebrate occurrences – for 16 taxa – were studied simultaneously on the images captured over 3 months (between May and July 2019). The peak in root growth occurred at the end of May and beginning of June, followed by a peak in ectomycorrhizal colonization in mid-June. For invertebrates, specific dynamics of activity were observed for each taxon, reflecting contrasting phenologies. The constructed network of co-occurrences between invertebrates shows a change in its structure over the period, with a reduction of connectance. At a fine scale, oak fine roots revealed temporally variable growth rates with higher values at night. This window on the opaque soil matrix addresses many methodological challenges by allowing the monitoring of soil biological activity in an integrative, dynamic and non-destructive way. This innovative in situ imaging tool opens new questions and new ways of answering long-standing questions in soil ecology.