Li 3000

The SPAD-502 (Minolta Camera Co., Osaka, Japan) chlorophyll meter was used to take SPAD readings from the three uppermost fully expanded leaves with the mean being the representative value [29 (link)]. In particular, three randomly selected plants from each field plot were measured. Three SPAD values per leaf, including one around the midpoint of the leaf blade and two 3 cm apart from the midpoint, were averaged as the mean SPAD value of each leaf [29 (link)]. The leaf chlorophyll content (LCC, μg/cm²) was calculated from the SPAD readings using the equation built with a subset of samples from this study as shown below:
$\mathrm{y}=1.4498\times \mathrm{x}-22.014$
where y and x are LCC and SPAD reading, respectively. Leaf area was measured with a leaf area meter LI-3000 (LI-COR, Inc., Lincoln, NE, USA) and divided by the corresponding ground area to determine the leaf area index (LAI, m²/m²). The canopy chlorophyll content (CCC, g/m²) was calculated as the product of LCC and LAI. A summary of the chlorophyll content data was provided in Table 2. Additionally, the temporal profiles of LCC and CCC were presented in Figure 3. LCC and CCC values exhibited a tendency to increase and then decrease in the whole season with the peak being observed at the heading stage for LCC but at booting stage for CCC (Figure 3). Specially, a local minimum of LCC value was found at the jointing stage.

Triplicate plants with intact roots were randomly and carefully dug via digging a monolith of 10 × 10 × 25 cm³ from OTCs under ambient and elevated O₃ exposures at 100 DAT (days after treatment). Several growth parameters such as root and shoot length, number of leaves, leaf area, root and shoot fresh weight and tillers were measured. Leaf area was measured using a portable leaf area meter (Model Li- 3100, Li-COR, Inc., Lincoln, NE, USA). For the estimation of dry weight, each plant was separated into the root, shoot and leaf and then kept in the oven (80 °C) until constant weights were achieved. Dry and fresh weight was determined, and the cumulative addition of all plant parts gave the total biomass as g plants⁻¹. For the measurement of foliar injury percentage (FIP), triplicate plants were collected at 100 DAT from all treatment and the total area of leaves was estimated for all plants, with or without symptoms measured using a portable leaf area meter (LI 3000, LICOR Inc., USA). According to Mishra et al. [40 (link)], FIP was calculated using the following formula: $$\mathrm{FIP}=\frac{\mathrm{Total} \mathrm{leaf} \mathrm{area} \mathrm{injured} \times 100}{\mathrm{Total} \mathrm{leaf} \mathrm{area}}$$

The treatment solutions were applied every two days for 15 days (36 DAS). Subsequently, the plants were demounted out of the plug tray and the medium was washed off (39 DAS). Whole-plant fresh weight (surface-blotted with absorbent paper) and dry weight (kept in an air-forced oven at 60 °C for 72 h) were measured with an electronic balance. Lengths of shoots and tap roots, as well as leaf lengths and widths, were measured with a metal ruler. The leaf area was determined with a leaf area analysis meter (Li-3000, Li Cor Inc., Lincoln, NE, USA). The two topmost true leaves from each plant were individually sampled, immediately frozen in liquid nitrogen, and preserved at −70 °C for further analysis.

During the heading stage, a leaf area meter (LI-3000, Li-Cor Inc., Lincoln, NE, USA) was used to measure the green leaf area of the plants and determine the leaf area index (LAI). The SPAD measurements were conducted using the SPAD-502 Chlorophyll Meter (Minolta Co. Ltd., Osaka, Japan). To present the source–sink relationship of rice, we used the grain–leaf area ratio, including three forms, spikelet-leaf area ratio (SNR), grain–leaf area ratio (GNR), and grain weight–leaf area ratio (GWR), which were calculated as follows:

The shoot, leaf, stem, and root fresh weights of sweet basil plants were measured on harvest day (20 days after transplanting). Then, they were oven-dried at 80 °C for 3 days to measure the dry weights. Six replicates were performed for each treatment.
The total leaf area was measured using a leaf area meter (LI–3000, Li-Cor, Lincoln, NE, USA). The leaf dry mass per area (LMA) was calculated as the leaf dry weight divided by leaf area. Six replicates were performed for each treatment.

A screening experiment with ten rapeseed genotypes was carried out in order to validate the linear models on the rapeseed genotype “DH5” from experiment 2. The experiment was carried out from 26 July to 19 August 2013 with greenhouse climate set points similar to those for Experiment 2. The seeds of ten rapeseed genotypes, 0. Chuosenshu, 1. Cobra, 2. Expert OSR, 3. Palu, 4. Olympiade, 5. Major, 6. S13, 7. Resyn HO48, 8. Markus and 9. DH5, were sown in 11 cm pots containing peat and placed directly in ten subfields on the table where the scanner was mounted. The distance between the pots was similar to that in experiment 2. Scanning measurements of each subfield were conducted every hour at a scan velocity of 20 mm·s⁻², as in experiment 2. At the final harvest 24 days after sowing (DAS), all plants from each subfield were harvested. For each plant, the leaves were counted (LN) and the total leaf area (LA) was determined using a leaf area meter (LI-3000, LI-COR, Lincoln, NE, USA). Plant fresh weight (FW) was determined, plant material was dried at 70 °C for 24 h and plant dry weight (DW) was determined. The linear models obtained in experiment 2 were used to calculate daily values for plant FW, DW and total leaf area, to generate growth curves for the 23 DAS until the 18 August, the day before harvest.

Measurements of fresh weight, dry weight, leaf area and leaf number were collected as previously described at Day 21 and Day 35 after germination for lettuce and at Day 30 for tomato (Ravishankar et al., 2021 (link)). The 21-day early harvest corresponds to the age when young lettuce is typically transplanted. Both fresh and dry weights are above ground measurements that do not include root tissue. Dry weight was measured after leaves were dried at 65°C for three days. Leaf area was measured by leaf meter (LI-3000, LI-COR, Inc., USA) and summed per plant. Leaf number was also summed by plant and excluded any emerging leaves less than 1 cm in length. Additional measurements were taken of the tomato plants. Height was measured from the top of the rockwool block to the highest point of the plant. Visible flower buds and open flower buds were recorded per plant after initiation of flowering and at harvest. The number of leaflets was counted per plant. Height and leaf number were collected for all eight plants in each treatment. All other biomass measurements were collected for the four tomato plants per treatment not used for tissue sampling.