Simplifying data acquisition in plant canopies‐ Measurements of leaf angles with a cell phone

Abstract

Summary1. Canopies are complex multilayered structures comprising individual plant crowns exposing a multifaceted surface area to sunlight. Foliage arrangement and properties are the main mediators of canopy functions. The leaves act as light traps whose exposure to sunlight varies with time of the day, date and latitude in a trade-off between photosynthetic light harvesting and excessive or photoinhibitory light avoidance. To date, ecological research based upon leaf sampling has been limited by the available technology, with which data acquisition becomes labour intensive and time-consuming, given the overwhelming number of leaves involved. 2. In the present study, our goal involved developing a tool capable of measuring a sufficient number of leaves to enable analysis of leaf populations, tree crowns and canopies. We specifically tested whether a cell phone working as a 3D pointer could yield reliable, repeatable and valid leaf angle measurements with a simple gesture. We evaluated the accuracy of this method under controlled conditions, using a 3D digitizer, and we compared performance in the field with the methods commonly used. We presented an equation to estimate the potential proportion of the leaf exposed to direct sunlight (SAL) at any given time and compared the results with those obtained by means of a graphical method. 3. We found a strong and highly significant correlation between the graphical methods and the equation presented. The calibration process showed a strong correlation between the results derived from the two methods with a mean relative difference below 10%. The mean relative difference in calculation of instantaneous exposure was below 5%. Our device performed equally well in diverse locations, in which we characterized over 700 leaves in a single day. 4. The new method, involving the use of a cell phone, is much more effective than the traditional methods or digitizers when the goal is to scale up from leaf position to performance of leaf populations, tree crowns or canopies. Our methodology constitutes an affordable and valuable tool within which to frame a wide range of ecological hypotheses and to support canopy modelling approaches.

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“…Cell phone‐based and other techniques: This approach provides low‐cost, rapid, and reliable instruments for field phenotyping. To date, few such instruments have been developed and proposed as reliable measurement tools for extracting multiple parameters on canopy structure (Escribano‐Rocafort et al ; Confalonieri et al ). One example is PocketPlant3D, a newly developed cell phone‐based phenotyping instrument that can extract both LI (the first value at the proximal parts between the stem and the leaf, Figure A) and LIA (Figure F) (Confalonieri et al ).…”

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“…Field procedure was conducted as recommended in Escribano‐Rocafort et al . (). This methodology gives SAL values as a percentage of a generic surface (SAL % ), regardless of its real area.…”

“…To assess within‐plant variations in leaf position, we used the range of variation in two leaf position angles: the lamina inclination angle (the angle of the maximum slope of the leaf from the vertical, ρ ) and lamina course angle (the angle between the magnetic north and the horizontal projection of the normal vector to the leaf lamina, β ) (see eqn 1 for ρ and eqn 2 for β calculation details in Escribano‐Rocafort et al . ). We calculated ρ from leaf pitch and roll angles.…”

“…Here, SAL estimations did not consider self‐shading, thus representing the potential exposure of the leaf surface to direct light (Escribano‐Rocafort et al . , ). Nevertheless, the difference between potential and real SAL is minimal in this species, because it has relatively simple architecture (Pearcy et al .…”

“…To estimate SAL, we took in situ measurements of four leaf angles describing leaf position, namely pitch, roll, lamina course, and midrib azimuth, with an application (Ahmes 1.0) for smartphones (Nokia N86, Nokia Group, Espoo, Finland) (Escribano-Rocafort et al 2014). Field procedure was conducted as recommended in Escribano-Rocafort et al (2014). This methodology gives SAL values as a percentage of a generic surface (SAL % ), regardless of its real area.…”