Os 30p

Photosystem II (PSII) quantum efficiency photosynthetic measurements were taken between 7 am and 8 am on the first fully grown sheet using a portable fluorometer (Os30P+, Opti-Sciences Inc., Hudson, NH, USA) [34 (link)].

Leaf chlorophyll index (SPAD) was measured non-destructively with a portable Minolta SPAD 502 Chlorophyll Meter (Minolta Camera Co. Ltd., Osaka, Japan). The measurements were made in the middle part of fully expanded, randomly selected leaves of 40 plants per treatment (10 plants per plot x 4 blocks). SPAD measurements were carried out from 10 am until 2 pm (local time) on clear days five times for all crop-rotation plants (Table 5). Growth stages according to the BBCH scale were identified following Meier [42 (link)].
To obtain the maximum quantum efficiency of PSII photochemistry (Fv/Fm), a multi-functional pulse-modulated handheld chlorophyll fluorometer (model OS-30p; Opti-Sciences, Inc., Hudson, NH, USA) was used to measure chlorophyll-α fluorescence in vivo. Fv/Fm was read directly on the chlorophyll fluorometer after a short period of adaptation to the dark [43 (link)]. Leaves of plants were allowed to adapt to the darkness for 1 min using light-withholding clips. Fv/ Fm measurements were made on the 1st fully expanded and randomly selected leaves of 5 plants per plot × 3 blocks (15 plants per treatment), five times per growing season (Table 5).

At 9 and 16 dot, stomatal conductance and chlorophyll fluorescence were recorded. The measurements were conducted on the 4th or 5th leaf starting from the apical meristem on randomly chosen plants at mid-morning, 4 h after onset of light. The stomatal conductance to water vapor was measured on three to five plants using a transient state diffusion porometer (AP4; Delta-T Devices, Cambridge, UK). The chlorophyll fluorescence (F_v F_m⁻¹), an indicator of the maximum quantum efficiency of photosystem II, was monitored on three or four plants after exposure to darkness for 20 min with a dark adaptation pin using a chlorophyll fluorometer (OS-30p; Opti-Sciences, Hudson, NH, USA).

Chlorophyll fluorescence quantifications were performed using a hand-held chlorophyll fluorometer (OS30p+, Opti-Sciences. Inc., Hudson, NH, USA), on leaves previously adapted to the darkness (30 to 40 min). The fundamental state Fo (all reaction centers are open) and the maximum level of fluorescence Fm (all reaction centers are closed) were determined. Then, the maximum photochemical quantum yield of PSII (Y = Fv/Fm = (Fm − Fo)/Fm) was determined. The efficiency of quantum open centers (Φexc = Fv’/Fm′ = (Fm′ − Fo′)/Fm′) was measured just after the transfer of plants into continuous light. In order to estimate the proportion of reaction centers open in the PSII, the coefficient of the photochemical quenching (qP = (Fm′ − Fs)/(Fm′ − F0′)) was allowed. The non-photochemical quenching NPQ ((Fm−Fm’)/Fm’) estimates the dissipated energy in heat form. The quantum yield of electron transport of PSII (ɸPSII = (Fm′ − Fs)/Fm′) estimates the efficiency of all the reaction centers of PSII under light.

Relative water content in AZ and leaves harvested after 48 and 51 days of plant growth in drought (25% WHC) and soil with optimal moisture (70% WHC, control plants) was measured using the drying method. Plant material (2 g) was weighed (analytical weight PB221S, Sartorius, an accuracy of ± 0.0001 g), placed in zinc vessels, and dried (SUP200W, WAMED) (60 °C) for 24 h. Then, plant material was cooled down in desiccator and weighed again. The relative water content percent (RWC) was determined through the following equation: RWC [%] = (FW-DW)/SW × 100, where FW: Fresh gross weight [g]; DW: Dry gross weight [g]; and SW: Sample weight [g]. The dried material was also used for element content determination.
The influence of drought stress on flower abortion rate was presented as a percentage of separated flowers in relation to the flowers formed by the plant. Additionally, we determined the effect of drought on the number of leaves per plant and leaf area per plant using AM350 Portable Leaf Area Meter (ADC BioScientific Ltd., Hoddesdon, UK). The maximum quantum efficiency of PS II (Fv/Fm) as a reliable marker of photo-inhibition [92 (link)] was measured using an OS-30P (Opti-Sciences, Inc., Hudson, NH, USA) according to the methods described by Weng (2006) [93 (link)]. The results were presented as the mean of the sum of the areas of all leaves per plant.

To ensure the adaptation of the leaves to light, quantum yield of PSII was measured between 7 and 9 a.m., on the first fully developed leaf of each plant. Also, maximum variable fluorescence (Fv/Fm), which would be the maximum quantum efficiency of PSII, was determined using a portable fluorometer (Opti-sciences—Os30P)⁴⁶ .

The quantum efficiency of the PSII (variable fluorescence and maximum fluorescence ratio) of leaves was measured using a fluorometer (Opti-Sciences® – Os30p +).