Extending Hyperspectral Imaging for Plant Phenotyping to the UV-Range

Anna Brugger,Matheus Thomas Kuska,Anne-Katrin Mahlein,Hans-Georg Luigs,Jan Behmann,Kristian Kersting,Stefan Paulus,Patrick Schramowski,Ulrike Steiner

doi:10.3390/rs11121401

Abstract

Previous plant phenotyping studies have focused on the visible (VIS, 400–700 nm), near-infrared (NIR, 700–1000 nm) and short-wave infrared (SWIR, 1000–2500 nm) range. The ultraviolet range (UV, 200–380 nm) has not yet been used in plant phenotyping even though a number of plant molecules like flavones and phenol feature absorption maxima in this range. In this study an imaging UV line scanner in the range of 250–430 nm is introduced to investigate crop plants for plant phenotyping. Observing plants in the UV-range can provide information about important changes of plant substances. To record reliable and reproducible time series results, measurement conditions were defined that exclude phototoxic effects of UV-illumination in the plant tissue. The measurement quality of the UV-camera has been assessed by comparing it to a non-imaging UV-spectrometer by measuring six different plant-based substances. Given the findings of these preliminary studies, an experiment has been defined and performed monitoring the stress response of barley leaves to salt stress. The aim was to visualize the effects of abiotic stress within the UV-range to provide new insights into the stress response of plants. Our study demonstrated the first use of a hyperspectral sensor in the UV-range for stress detection in plant phenotyping.

Highlights

Plant phenotyping using hyperspectral imaging involves the acquisition of specific parts of the electromagnetic spectrum
To compare the non-imaging sensor Flame Spectrometer S with the imaging UV line scanner, six different pure substances were measured with both systems
All measurements of the UV line scanner displayed a higher reflectance of about 0.2 starting at 300 nm compared to measurements of the Flame Spectrometer S (Figure 2)

Summary

Introduction

Plant phenotyping using hyperspectral imaging involves the acquisition of specific parts of the electromagnetic spectrum. Previous studies using hyperspectral sensors focused on the visible (400–700 nm), near-infrared (700–1000 nm) and short-wave infrared (1000–2500 nm) range [1]. Reflectance in the visible range can be correlated to leaf pigment content since plants tend to reduce leaf chlorophyll concentration [3], while the near-infrared range is mostly influenced by the leaf structure (e.g., leaf trichome density or leaf thickness) and leaf water content [4]. In addition to the leaf water content, the short-wave infrared range is influenced by the chemical compositions of the leaf [5,6] like lignin or cellulose [7]. A number of plant molecules like flavonoids, amino acids, anthocyanins and nucleoside feature absorption maxima in the UV-range [8,9,10]. Previous studies show that saline stress in barley seedlings leads to an increase of flavonoids and total phenolic compounds [14]

Methods

Results

Discussion

Conclusion