## 2 Materials and Methods
### Plant Sampling and Chemical Analysis  
Plant samples were taken at the edges of the container to prevent disturbances of the subsequent measurements, considering that the spectral analysis was conducted in the central area. Samples were divided into sub-samples, one for the determination of photosynthetic pigments and the second one for polyphenol determination.  
Photosynthetic pigments: Chlorophyll \(a\) and \(b\), and carotenoids were determined according to [PERSON] (1977). About 100 mg of fresh plant material that was exactly weighted was ground and extracted with acetone (100%), whereby a pinch of CaCO\({}_{3}\) was added [PERSON] (1977). Samples were filled up with acetone to a final volume of 10 mL. The extracts were centrifuged for 5 min at 5900 rpm at room temperature. Afterwards, the absorption of the supernatant was measured at different wavelengths (645, 662, 470, 730 nm) using a UV-Vis spectrometer (Lambda-35, [PERSON], Rodgau, Germany). The measurement at 730 nm should be very low and was conducted as a quality control.  
The content of chlorophyll \(ab\) and carotenoids were calculated on a fresh matter basis from the measured absorption values according to Lichtenthaler and Wellburn [PERSON] and [PERSON] (1977) by the following equations:  
Chlorophyll \[a\] ( \[\mu\)g/mL plant extract) \[=11.75*A662-2.35*A645\] (1) Chlorophyll \[b\] ( \[\mu\)g/mL plant extract) \[=18.61*A645-3.96*A662\] (2) Carotenoids ( \[\mu\)g/mL plant extract) \[=\frac{1000*A470-2.27*\text{Chl}a-81.4*\text{Chl}b}{227}\] (3)  
Polyphenol determination: Fresh plant material was pestled to a fine powder under liquid nitrogen by a mortar. About 200 mg of the fine powder was exactly weight in Eppendorf tubes and extracted with 1 mL ethanol/water (1/1, \(v\)/\(v\)) in an ultrasonic bath for 30 min. Afterwards, the extracts were centrifuged for 15 min at 13,200 rpm and the supernatant was transferred into a tube. The extraction procedure was repeated three times and the three supernatants were combined and yielded approximately 3 mL of sample. From this sample, 1 mL was diluted with 4 mL of distilled water and from this dilution the staining was conducted in the following way:  
Figure 2: Experimental design to investigate the spectral signature of plants that die off by glyphosate treatment in comparison to control plants and vegetation dieback caused by drought. The picture on the left shows the laboratory setup with the field spectrometer.  
From the diluted sample 600 \(\upmu\)L was mixed with 3 mL of staining solution (Folin-Ciocalteu reagent (Sigma-Aldrich) which was diluted every day fresh 1:10 with distilled water) and were left for 2-4 min to react. Then 2.4 mL Na\({}_{2}\)CO\({}_{3}\) solution (7.5%) was added and the tubes were mixed by inversion and left for 2 h to react at room temperature. Afterwards, the absorption was measured at 765 nm using a UV-Vis spectrometer (Lambda-35, Perkin Elmer, Rodgau, Germany). A standard calibration curve was prepared from gallic acid dissolved in water in concentrations of 10, 20, 30, 40, 50, 60 and100 mg gallic acid/l, which was stained in the same way as the samples and was used for the quantification and the total phenol content as gallic acid equivalents.  
Additionally, from each plant sample, the dry matter content was determined after drying the plant material in a ventilated oven at 60 \({}^{\circ}\)C until constancy of weight. Therefore, it was possible to calculate the polyphenol and photosynthetic pigment content on a dry matter basis as well.