**2.2 Gas exchange parameters**

The measurements of diurnal gas exchange parameters were carried out according to the method described by Wang et al. (2004) with a portable photosynthesis system CIRAS-2 (PP Systems, UK). At each time point, from 6:00 am to 18:00 pm, the net photosynthetic rate (*Pn*), intercellular CO2 concentration (*Ci*) and stomata conductance (*Gs*) were measured simultaneously under the photon flux densities (PFD) from a built-in light source equal to the natural light intensities with the ambient temperatures. Each measurement was conducted at least 10 times, and the means were used to compare the ALA's effect.
