*2.1. Data Collection*

Ground data collection was carried out over a farmland area in Changchun, Jilin Province, China (44◦42- 27--N, 124◦53- 08--E), which is located in the temperate and monsoon climate zone with a typical continental climate. The field size was approximately 2 ha. During the peanut growing season in 2018, three field campaigns were conducted on 27 July (acicula forming stage), 19 August (bearing pod stage), and 19 September (maturity stage) to collect peanut leaves, respectively. In each campaign, 20 plots were randomly selected. One or two plants were selected at each plot, and leaves that were fully expanded, homogenous in color, and showing no visible signs of damage were detached from the top to the bottom of the canopy [30]. They were, immediately packed and sealed into plastic bags and placed inside a cooler (the interior temperature of the cooler was 0 ◦C) to avoid desiccation and decomposition of the chlorophyll by light. In each campaign, we collected 28 leaves. Thus, a total number of 84 leaves were used for spectral measurement and chlorophyll extraction. All the measurements, including the spectral measurements and chlorophyll extraction, were carried out within 4 h of leaf harvesting to minimize changes in chlorophyll content. Figure 1 illustrates the phenomenon of peanut leaves changing orientation under strong solar irradiance, making the view of the canopy a mixture of the adaxial and abaxial sides (Figure S1).

**Figure 1.** Photographs of the peanut canopy in the field. Only the adaxial surface is visible under low solar irradiance (**a**), while both the adaxial and abaxial surfaces are visible under high solar irradiance (**b**).

The reflectance of the adaxial and abaxial surfaces was measured using an ASD FieldSpec® 3 portable spectroradiometer (Analytical Spectral Devices, Boulder, CO, USA) and a contact probe, equipped with an internal halogen source and directly attached to the leaf surface using a leaf clip accessory. The spectrometer can collect data in the 350–2500 nm spectral region, with a sampling interval of 1.4 nm in the 350–1000 nm wavelength range and 2 nm in the 1000–2500 nm wavelength range. The average of 10 separate measurements from each sample was recorded. To reduce errors associated with variations in illumination geometry, the contact probe was pressed to the leaf surface, which was illuminated by the internal light source, ensuring a consistent illumination geometry.

The LCC was determined from the same leaf samples used for reflectance measurements. Circular discs with a diameter of 6 mm were cut from each leaf. Leaf discs were extracted in the dark at room temperature for 24 h with 95% ethanol and shaken repeatedly to ensure chlorophyll was completely extracted, as indicated by the completely white appearance of the disc [31]. The absorbance of each extract was measured at 663 nm and 645 nm using a UV757CRT ultraviolet-visible spectrophotometer (Shanghai Precision Scientific Instruments Corporation, Shanghai, China). The LCC (μg/cm2) was then calculated according to the equations provided by Arnon [32]. In total, measurements of LCC and reflectance were collected for 84 leaves. The LCC values ranged from 21.50 to 70.55 μg/cm<sup>2</sup> with a mean value of 40.78 μg/cm<sup>2</sup> and a standard deviation of 11.68 μg/cm2.
