title: An evaluation of inexpensive methods for root image acquisition when using rhizotrons.
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 necessary, 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 market: 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 regiaL.) 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: AMAP, INRA, CNRS, IRD, Université de Montpellier, Montpellier, France.
authors.forename: Awaz
authors.identifier: 0000-0002-6130-9496
authors.initials: A
authors.lastname: Mohamed
authors.affiliation: AMAP, INRA, CNRS, IRD, Université de Montpellier, Montpellier, France.
authors.forename: Yogan
authors.initials: Y
authors.lastname: Monnier
authors.affiliation: AMAP, INRA, CNRS, IRD, Université de Montpellier, Montpellier, France.
authors.forename: Zhun
authors.initials: Z
authors.lastname: Mao
authors.affiliation: Earth and Life Institute, Université catholique de Louvain, 1348 Louvain-la-Neuve, Belgium.|Agrosphere-IBG3, Forschungszentrum Juelich GmbH, 52428 Juelich, Germany.
authors.forename: Guillaume
authors.identifier: 0000-0002-5883-4572
authors.initials: G
authors.lastname: Lobet
authors.affiliation: iEES-Paris (IRD, Sorbonne Universités, UPMC Univ Paris 06, CNRS, INRA, UPEC, Université Paris Diderot), Soils and Fertilizers Research Institute (SFRI), Duc Thang Ward, Bac Tu Liem District, IRD, Hanoi, Vietnam.
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Maeght
authors.affiliation: AMAP, INRA, CNRS, IRD, Université de Montpellier, Montpellier, France.
authors.forename: Merlin
authors.initials: M
authors.lastname: Ramel
authors.affiliation: AMAP, INRA, CNRS, IRD, Université de Montpellier, Montpellier, France.
authors.forename: Alexia
authors.initials: A
authors.lastname: Stokes
keywords: Fine root elongation rate; Flatbed scanner; Handheld scanner; Smartphone; Time-lapse camera