Photosynthesis and stomata dynamically respond to transient changes in light intensity; however, information regarding their long-term responses to the light intensity is limited. In the current ...study, biophysical properties of photosynthetic apparatus and stomatal characteristics of lettuce plants were investigated in response to long-term exposure to different photosynthetic photon flux densities (PPFDs) 75, 150, 300, and 600 µmol m
−2
s
−1
. Contrary to leaf growth, SLA decreased with increasing light intensity (i.e., thicker leaves under higher light intensity). Improving effect of higher light intensity on leaf fresh and dry weights was time dependent, in a way that the largest difference in biomass gain was observed following 40 days of exposure to the light treatments. Depending on the leaf developmental stages, exposure to higher light intensities caused faster development of photosynthesis system in terms of improvement in the maximum quantum efficiency of photosystem II (PSII) and non-photochemical quenching (NPQ) compared to lower light intensities. PSII performance index on an absorption basis was the highest under 600 PPFD. Small-sized stomata with narrow pore apertures were observed in plants grown under 75 PPFD; however, due to improvement in photosynthetic capacity and also the growth of the plants, water use efficiency (WUE) increased in a light intensity-dependent manner and the highest WUE was detected in 600 PPFD-exposed plants. In conclusion, exposing lettuce plants to higher light intensities (non-stress threshold levels) results in higher accumulation of biomass, faster development of photosynthetic system, and improved WUE.
The accurate estimation of water productivity (WP) and plant production becomes imperative in planning and managing irrigation practices. Light intensity and CO2 concentration are among the most ...important determinants of growth and WP of crops. In this study, the adaptive neuro-fuzzy inference system (ANFIS) was used to model the changes in growth parameters, stomatal properties, and WP of lettuce due to various scenarios of light intensity and CO2 concentration. The lettuce plants were exposed to four levels of light intensity 75, 150, 300, and 600 µmol m−2 s−1 Photosynthetic Photon Flux Density (PPFD) and CO2 concentration (400, 800, 1200, and 1600 ppm). The results showed that growth parameters such as fresh weight, dry weight, and leaf area improved by increasing the PPFD and CO2 concentration from 75 to 300 µmol m−2 s−1 and 400–1200 ppm, respectively. Maximum fresh weight was recorded at 300 µmol m−2 s−1 PPFD and 1600 ppm CO2 concentration while the highest dry weight was obtained at 600 µmol m−2 s−1 PPFD and 1600 ppm CO2 concentration. Stomatal pore width and length decreased by increasing PPFD and CO2 concentration. Moreover, evapotranspiration increased when plants were exposed to higher PPFDs and CO2 concentrations. ANFIS predicted all growth parameters, stomatal properties, and WP with acceptable performance (R2 > 0.99, RMSE < 0.8 ×10−2). The findings provide agricultural engineers with an artificial intelligence-based model to predict the WP and production of lettuce by having the light intensity and CO2 concentration.
•ANFIS predicted water productivity reliably with R2 values more than 0.99.•Lettuce exhibited the best performance under 300 µmol m−2 s−1 light intensity and 1200 ppm CO2 concentration.•ANFIS can be used as a reliable model for agricultural water management and crop performance.•ANFIS predicted different growth parameters and stomatal characteristics with acceptable performance.
A field experiment was conducted for three growing seasons to study the effects of seasonal water use and applied N fertilizer on grain yield and water productivity indices of wheat in an arid ...region. The results revealed that the yield response to N was associated with water application levels. The water productivity indices were influenced by irrigation strategies, and deficit irrigation effectively boosted productivity of irrigation water (WPI). The highest WPI was obtained at a seasonal irrigation water of 156 mm for different levels of applied nitrogen. For levels of applications 70% of the required nitrogen, required nitrogen, and 120% of the required nitrogen, WPI ranged between 0.93 and 2.28, 1.30 and 2.75, and 0.98 and 2.47 kg m−3, respectively. The data generated here indicate that maximum water productivity (WPE) would be achieved when 98 kg N ha−1 is combined with 156 mm of supplemental irrigation (2.72 kg m−3). Consequently, when limited irrigation water is combined with N fertilizer appropriate management, water productivity can be substantially and consistently increased in arid regions.
An experiment was conducted in a persian walnut (Juglans regia) orchard in the north of Iran to evaluate the effects of zinc (Zn) as zinc sulfate and/or boron (B) as boric acid in foliar spray with ...different concentrations and combinations. Three B and three Zn concentrations (0, 174, and 348 mg·L–1 for B and 0, 1050, and 1750 mg·L–1 for Zn) were applied either independently or in combination. Leaf nutrient concentrations, pollen germination, fruit set, leaf chlorophyll index, nut and kernel characteristics, vegetative growth, nut weight, and nut yield were measured to assess the effects of treatments. The results showed that all B and Zn applications and combinations had a significant effect on all traits except nut and kernel diameter, shell percent, husk thickness, and pistillate flower abscission (PFA). Pollen germination, fruit set, vegetative growth, nut weight, kernel percent, nut and kernel length, and chlorophyll index were highest when B and Zn were applied simultaneously at 174 and 1050 mg·L–1 concentrations, respectively.
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