Li 6400 40 leaf chamber fluorimeter

Net photosynthesis rate (CO₂ assimilation rate), stomatal conductance, transpiration rate, maximum efficiency of photosystem II under light (Fv/Fm), and the actual photochemical efficiency of photosystem II (Φ PSII) were measured with a LI-6400XT photosynthesis system (Li-Cor, Inc., Lincoln, NE, USA) equipped with a LI-6400-40 Leaf Chamber Fluorimeter and a LICOR 6400-01 CO₂ injector [5 (link)]. Leaf gas exchange was measured in a 2 cm² leaf cuvette. During these measurements, air CO₂ concentration was controlled using the injection system and compressed CO₂ cylinders with a CO₂ concentration of 400 μmol mol⁻¹ CO₂. Measurements were taken at a saturating light of 1000 μmol·m⁻²·s⁻¹ and at ambient air temperature and relative humidity every week, with recording points at 0 days (before the stress treatment started), 7 days (one week after the stress treatment started) and 14 days (2 weeks after the stress treatment started). Data reported are the mean ± SE 6–8 biological replicates per treatment.

We measured A_max, g and E parameters using a LI-COR 6400XT infrared gas analyser (IRGA; LI-COR Biosciences, Lincoln, NE, USA). All measurements were conducted using six seedlings of each species under each treatment from 11:00 to 14:00 h on August 17, 2014, which was a sunny day. Light was supplied by an LED lamp (LI-6400-02B, LI-COR Biosciences), and the light levels were kept at 1500 μmol·m⁻² s⁻¹, which is above the light saturation point for all four species according to the light response curves before the measurements. The external CO₂ was provided by portable tanks containing a CO₂/air mixture with a concentration of 400 μmol·mol⁻¹. A CO₂ injector (LI-6400-01, LI-COR Biosciences) was used to control the output of the tanks. The temperature was maintained at 25–28 °C, and the relative humidity was kept at 25–30%. Then, we divided A_max by E to calculate the instantaneous water use efficiency (WUE_i).
We examined the chlorophyll fluorescence parameters of leaves that had been kept under dark conditions for 30 min in the morning between 05:00 and 06:00 h on August 17, 2014. We also measured the maximum quantum yield of photosystem II (PSII, F_v/F_m) with the formula (F_m − F_o)/F_m, using an LI-6400-40 leaf chamber fluorimeter (LI-COR Biosciences).

Intact leaves from common reed plants growing in a greenhouse were used to measure the photosynthetic rate. Leaf gas exchange was measured using an open gas-exchange system (LI-6400XT; LI-COR Inc., Lincoln, NE, USA) with an integrated fluorescence chamber head (LI-6400-40 leaf chamber fluorimeter; LI-COR Inc.). The CO₂ assimilation rate (μmol CO₂ m⁻²·s⁻¹) was measured using the stored program of the light-curve mode of LI-6400. Parameters were set as follows: TempR (relative temperature) = 20°C, CO₂R (relative CO₂ concentration) = 400 μmol m⁻²·s⁻¹, flow = 500 μmol·s⁻¹, and PQntm (light intensity and quality) = 500 μmol photon m⁻²·s⁻¹ (containing 10% blue light).