Chlorophyll content was determined following the method recommended by Arnon [45 (link)]. A clean mortar and pestle, acetone (10 mL at 80% v/v for each sample), and 0.2 g of fresh tissue was used to extract chlorophyll. After filtration, the optical densities of the filtrates (supernatants) were monitored at 663, 645, and 480 nm with a UV-120 spectrophotometer (Shimadzu Corp., Kyoto, Japan).
In the field, chlorophyll fluorescence was measured in the fresh leaves using a fluorometer (FMS-2, portable, pulse-modulated, Hansatech, Norfolk, UK). The upper fourth leaf on each plant was subjected to light for 2 min until a constant rate of photosynthesis was reached. Steady-state fluorescence (Fs), maximum light-adaptive fluorescence (Fm), variable fluorescence (Fv), and minimum-adaptive fluorescence (F0) were measured [46 (link)]. Fv/Fm (maximum quantum yield of photosystem II, PSII) was calculated [47 (link)].
The performance index (PI) of photosynthesis was estimated based on equal absorption (PIABS) following Clark et al. [48 (link)]. Additionally, single-photon avalanche diode (SPAD) was measured by a portable chlorophyll meter (SPAD-502, Konica Minolta Sensing, Inc., Osaka, Japan).
In the field, chlorophyll fluorescence was measured in the fresh leaves using a fluorometer (FMS-2, portable, pulse-modulated, Hansatech, Norfolk, UK). The upper fourth leaf on each plant was subjected to light for 2 min until a constant rate of photosynthesis was reached. Steady-state fluorescence (Fs), maximum light-adaptive fluorescence (Fm), variable fluorescence (Fv), and minimum-adaptive fluorescence (F0) were measured [46 (link)]. Fv/Fm (maximum quantum yield of photosystem II, PSII) was calculated [47 (link)].
The performance index (PI) of photosynthesis was estimated based on equal absorption (PIABS) following Clark et al. [48 (link)]. Additionally, single-photon avalanche diode (SPAD) was measured by a portable chlorophyll meter (SPAD-502, Konica Minolta Sensing, Inc., Osaka, Japan).