Lci portable photosynthesis system

Several parameters, two months after treatment application, were considered in relation to gas exchange (i.e., transpiration rate, photosynthesis rate, stomatal resistance to CO₂, and sub-stomatal CO₂). These factors were measured from 09:00 a.m. to 12:00 using an LCi Portable Photosynthesis System (ADC Bioscientific Ltd). All measurements were carried out at a PPFD value of 1,200 μmol m⁻² s⁻¹, when the temperature of leaf samples was 25°C. The photosynthetic activity of fully-expanded leaf samples was measured on 7 plants in each treatment group. The measurements were carried out from 10:00 a.m. until noon to measure the maximum values. A steady condition of measurable photosynthesis was reached in 3 to 4 min, so that data could be collected. The measurements were also considered on intercellular CO₂ concentrations (Ci), stomatal conductance to water-vapor, and transpiration rate (E). In practice, the LI-6400 chamber was maintained at an ambient temperature of 26 ± 0.4°C. Airflow occurred at 500 ml min⁻¹, while CO₂ regulation operated at 380 mg/L with the help of a CO₂ blender. Carboxylation efficiency was expressed as A/Ci protocol (Zhang et al., 2001 (link); Stinziano et al., 2017 (link); Zhou et al., 2019 (link))

For both light and drought experiments, gas exchange was measured on the youngest fully expanded leaves after 10 and 6 weeks, respectively, using a LCi Portable Photosynthesis System (ADC BioScientific Ltd., United Kingdom). The top part of the leaf was enclosed in a broad leaf chamber (6.25 cm²) and the incoming air was passed through a 20-l bottle to buffer short-term fluctuations in the CO₂ concentration. Gas exchange data were collected over a 24-h period with measurements obtained at 15-min intervals (n = 3 plants). By integrating specific areas under the CO₂ exchange curves, net gas exchange was calculated per phase as well as total net gas exchange during the 24-h time course. Nocturnal CO₂ uptake was also assessed by analyzing the nocturnal increase in titratable acidity (ΔH⁺) by titration of methanol extracts against 0.005 M NaOH with phenolphthalein as indicator.

The net photosynthetic rate, transpiration rate and stomatal conductance were determined in situ using an LCi Portable Photosynthesis System (ADC BioScientific, Hoddesdon, the United Kingdom) with the following conditions in the measurement chamber: air temperature at 25°C, ambient CO₂ concentration at 550±50 μL L^-1, air flow rate at 205±30 μmol s^-1, and irradiance at 300 μmol m^-2 s^-1 [25 (link)].
The polyphasic rise of the chlorophyll fluorescence transient (OJIP) was measured at the upper surface of the dark-adapted (20 min) leaves in situ with the portable fluorometer FluorPen FP100max (Photon System Instruments, Brno, Czech Republic) as described in [26 (link)]. The parameters of the JIP test (see S1 Table) were calculated according to the theory of energy flow in the photosynthetic electron-transport chain [29 , 30 ]. The relative variable fluorescences W_OI, W_OJ, W_OK and W_IP (i.e., normalizations of the whole fluorescence transients) and the difference kinetics ΔW_OJ and ΔW_OK (as the differences between the drought-stressed and control plants) were also calculated according to [31 ] and their graphical representation was utilised to obtain further information on the primary photosynthetic processes.
The chlorophyll a and b contents and total carotenoids were determined spectrophotometrically [32 ] in the N,N-dimethylformamide extracts prepared as described in [33 (link)].