An evaluation of inexpensive methods for root image acquisition when using rhizotrons
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Plant Methods Open Access
METHODOLOGY
An evaluation of inexpensive methods for root image acquisition when using rhizotrons Awaz Mohamed1* , Yogan Monnier1, Zhun Mao1, Guillaume Lobet2,3 , Jean‑Luc Maeght4, Merlin Ramel1 and Alexia Stokes1
Abstract Background: Belowground processes play an essential role in ecosystem nutrient cycling and the global carbon budget cycle. Quantifying fine root growth is crucial to the understanding of ecosystem structure and function and in predicting how ecosystems respond to climate variability. A better understanding of root system growth is neces‑ sary, but choosing the best method of observation is complex, especially in the natural soil environment. Here, we compare five methods of root image acquisition using inexpensive technology that is currently available on the mar‑ ket: flatbed scanner, handheld scanner, manual tracing, a smartphone application scanner and a time-lapse camera. Using the five methods, root elongation rate (RER) was measured for three months, on roots of hybrid walnut (Juglans nigra × Juglans regia L.) in rhizotrons installed in agroforests. Results: When all methods were compared together, there were no significant differences in relative cumulative root length. However, the time-lapse camera and the manual tracing method significantly overestimated the relative mean diameter of roots compared to the three scanning methods. The smartphone scanning application was found to perform best overall when considering image quality and ease of use in the field. The automatic time-lapse camera was useful for measuring RER over several months without any human intervention. Conclusion: Our results show that inexpensive scanning and automated methods provide correct measurements of root elongation and length (but not diameter when using the time-lapse camera). These methods are capable of detecting fine roots to a diameter of 0.1 mm and can therefore be selected by the user depending on the data required. Keywords: Fine root elongation rate, Flatbed scanner, Handheld scanner, Smartphone, Time-lapse camera Background Fine root growth, defined as apical elongation over time [1–3], plays an essential role in the cycling and allocation of carbon and nutrients in ecosystems [4]. Due to the inaccessibility of root systems, special techniques are required to investigate the distribution and dynamics of roots, as well as to estimate belowground carbon budgets [5, 6]. Today, a number of methods have been used to estimate root growth. These methods can *Correspondence: [email protected] 1 AMAP, INRA, CNRS, IRD, Université de Montpellier, Montpellier, France Full list of author information is available at the end of the article
be grouped into indirect and direct techniques [5, 7], both of which have advantages and drawbacks. Indirect methods include the use of empirical models [8], estimations of nitrogen budget and carbon budget [7]. Direct methods can be classified into (i) destructive techniques such as soil coring [9], sequential soil coring [5], in-growth cores
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