Measurement of photosynthesis One individual with healthy, fully-expanded, exterior leaves in each treatment was chosen to measure gas exchange and chlorophyll fluorescence characteristics. Leaf gas exchange rates were measured using LI-6400 portable photosynthesis system (Li-Cor Inc., Lincoln, NE, USA) with a standard LED leaf chamber (2 × 3 cm2). The measurement conditions were: leaf temperature of 28 °C; relative air humidity of 60%; CO2 concentration of 400 ± 5 μmol mol-1, and photosynthetic photon flux density (PPFD) of 1500 μmol m-2 s-1. Once steady-state gas exchange rates were observed at these conditions, light-saturated photosynthesis rate (A), stomatal conductance (gs), intercellular CO2 concentration (Ci) and transpiration (E) were recorded. The leaf dark respiration rate (Rd) was measured under the same conditions except for the absence of light after the leaves were darkened for at least 5 min before recording the rates (Dong et al. 2019).T