*5.4. Photosynthesis Parameters*

After 14 d of treatment, Li-6800 portable photosynthesis system (LI-COR Inc., Lincoln, NE, USA) was used for photosynthetic parameter measurement on the third fully expanded leaf of alfalfa seedlings. All parameters, including net photosynthetic rate (*P*n), transpiration rate (*T*r), intercellular CO<sup>2</sup> concentration (*C*<sup>i</sup> ) and stomatal conductance (*g*s), were measured under steady photosynthetic photon flux density in the leaf chamber, which was set to the same level as the relevant treatments. An Li-COR standard red–blue chamber set at 25 ◦C and a CO<sup>2</sup> concentration of 460 µmol mol−<sup>1</sup> were used.
