Measurements of electron transport rate (ETR), photochemical quenching (qP) and non-photochemical quenching (NPQ)

Leaves were harvested at about 1300 h on the 2nd, 7th and 21st weeks of the experimental period. Square cuts (1 cm by 1 cm) were made out of the leaves and placed on moist filter papers in Petri dishes. Leaf cuts were pre-darkened for 15 min prior to measurements. A comparison test among 10, 15, 20 and 30 min of dark adaptation was carried out on well-watered leaves before selecting a period of 15 min for dark adaptation. There were no significant differences in F_m and F_v/F_m ratio (data not shown) among 15, 20 and 30 min of dark-adapted leaves for all species. Thus, a darkness of 15 min was used for this study. Through the Imaging-PAM Chl Fluorometer (Walz, Effeltrich, Germany), images of fluorescence emission were digitized within the camera and transmitted via a Firewire interface (400 Mb/s) (Firewire-1394.com, Austin, TX, USA) to a computer for storage and analysis. Measurements and calculations of ETR, qP, and NPQ was determined according to He et al. (2011).