Leaf reflectance spectra measurements

Leaf reflectance was measured shortly after completion of the gas exchange measurements (typically immediately after completion or within one hour) as described previously [30,38], using a full range spectrometer (PSR 3500+, Spectral Evolution, Inc., Lawrence, MA, USA; spectral range: 350–2500 nm; spectral resolution: 2.8 nm at 700 nm, 8 nm at 1500 nm, and 6 nm at 2100 nm) together with an LC-RP-Pro leaf clip foreoptic (Spectra Vista Corporation, Poughkeepsie, New York) containing an internal, full-spectrum calibrated light source. The integration time was set to 2 seconds at the lowest light intensity. A white reference was taken before measuring the leaf reflectance using a white Spectralon® standard. To account for potential heterogeneity of the leaf sample, 3–4 reflectance measurements were taken on different sections of the leaf. They were then averaged to provide one mean leaf spectrum for each leaf.