High Photosynthetic Photon Flux Research Articles

Light Environment and Photosynthetic Capacities of Leaves at Different Locations within Eggplant Canopies in a Greenhouse in Ontario, Canada

To effectively manage crop production in a greenhouse, it is essential to understand the natural light environment and physiological responses of the plants to light. This study investigated the dynamics of photosynthetic photon flux densities (PPFD) and light quality within the canopies of greenhouse-grown eggplant (Solanum melongena) and the photosynthetic capacities of leaves at different locations within the canopies. The light environment was quantified at 0.2-m intervals within (intra-canopy) and adjacent to (extra-canopy) the crop canopy on both sunny and cloudy days within a commercial greenhouse located in Leamington, Ontario, Canada. Our results indicated a linear decline in extra-canopy PPFD on both sunny and cloudy days, but an exponential decrease in intra-canopy PPFD. The intra-canopy PPFD decreased by 91% and 76% between 0 m and 0.4 m from the canopy apex on sunny and cloudy days, respectively. The lower canopy (0.6–1.2 m) light spectrum consisted largely of far-red light, equal amounts of red light and green light, with a lower percentage of blue light. Parameters derived from leaf-level light response curves indicated that the light-saturated net carbon exchange rate, light saturation point, and light compensation point decreased as the distance from canopy apex increased, whereas quantum yield was unaffected. Thus, leaves in the lower canopy were less efficient at using high PPFD, but they displayed no deterioration of photosynthetic machinery. Based solely on photosynthetic capabilities, leaves between 0 and 1.0 m from the canopy apex should not be removed to decrease the total plant sink strength.

Vertical farming for lettuce production in limited space: a case study in Northern Thailand.

Greenhouse vertical farming under natural sunlight is an alternative farming technique that grows crops in a stacking column and extends in a vertical direction. Sunlight availability is one of the crucial factors for crop development in vertical farming. Therefore, this investigation aimed to examine the effect of sunlight availability on lettuce growth and yields at different levels of vertical shelves. Six shelves were constructed with three levels: upper, middle and lower levels. Lettuces (Lactuca sativa L.) as 'Baby Cos' and 'Green Oak' at 14 days after sowing were planted on the three levels. The photosynthetic photon flux density (PPFD) was recorded, and the PPFD values were then converted to the daily light integral (DLI). Plant height and canopy width were measured three times at 14, 21 and 28 days after transplanting. At maturity, fresh weight (FW) was directly monitored after harvest. The results showed that the highest PPFD and DLI values were found at the upper level (PPFD 697 μmol m-2 s-1 and DLI 29 mol m-2 d-1) in comparison to the middle (PPFD 391 μmol m-2 s-1 and DLI 16 mol m-2 d-1) and lower (PPFD 322 μmol m-2 s-1 and DLI 13 mol m-2 d-1) levels. The lowest plant height and canopy width values were observed on the upper levels for both lettuce varieties during the three measurement dates. The middle ('Baby Cos' = 123.8 g plant-1 and 'Green Oak' = 190.7 g plant-1) and lower ('Baby Cos' = 92.9 g plant-1 and 'Green Oak' = 203.7 g plant-1) levels had the higher values of FW in comparison to the upper level ('Baby Cos' = 84.5 g plant-1 and 'Green Oak' = 97.3 g plant-1). The values of light use efficiency (LUE) showed an increased trend from the upper to lower levels in both varieties, with values of 'Baby Cos' of 0.10 g mol-1 in the upper level, 0.28 g mol-1 in the middle level and 0.26 g mol-1 in the lower level and 'Green Oak' of 0.12 g mol-1 in the upper level, 0.44 g mol-1 in the middle level and 0.57 g mol-1 in the lower level. The findings of the study indicated the viability of utilizing vertical shelves for lettuce production.

How does supplementary green light and UV-radiation affect biomass and rutin content in Levisticum officinale?

Due to several benefits regarding human health, the flavonoid rutin gains interest in nutrition and pharmaceutical industry. In order to satisfy high quality standards during cultivation and the final product, plants are grown increasingly in controlled environments with LED-technology as artificial light source. In this study the effect of various light settings on rutin content and biomass of Levisticum officinale was investigated. For continuous tracking of the biomass during cultivation, RGB-Images were taken. The actual biomass after harvest showed a strong positive correlation with the number of leaf-pixels detected via image processing (R2 = 0.937). Concerning the effect of UV-B radiation on rutin synthesis, time of synthesis was investigated. Two days after UV-B treatment a significant increase in rutin was observed. A short exposure time in combination with a high irradiance of 1 W m2 also showed positive effects on the rutin content in lovage. No significant effect of UV-B light on fresh weight was shown, but the combination of supplementary green light and high total photosynthetic photon flux density (PPFD) resulted in an increase of biomass.

Plant responses to UV-A1 radiation are genotype and background irradiance dependent

A large fraction of solar UV radiation that reaches the Earth’s surface is in the UV-A1 waveband (350–400 nm). Despite its prevalence, it is unknown how strongly plant genotypes differ in their response to UV-A1, and how their responses to UV-A1 depend on the photosynthetic photon flux density (PPFD). We grew several horticultural (tomato, cucumber, and two lettuce cultivars) and a model species (Arabidopsis thaliana) under low (LL; 150 μmol m−2 s−1) and high PPFD (HL; 550 μmol m−2 s−1), each of which was paired with UV-A1 (peaking at 365 nm) at irradiances of 0, 20, and 100 µmol m−2 s−1. Arabidopsis was the most strongly affected, as under LL, addition of UV-A1 resulted in early flowering, changes in leaf shape, and strong decreases in shoot dry weight (∼40%). In all species, UV-A1 exposure induced photoinhibition (low Fv/Fm) only under LL, but not under HL. Under HL, exposure to UV-A1 also induced strong decreases in the concentrations of UV-absorbing compounds and anthocyanins in arabidopsis (Columbia-0) and lettuce cv. Klee, but not in other genotypes. Altogether, we found that UV-A1 had only mild effects on the morphology of horticultural species (e.g., petiole angle, leaf shape and curvature), did not significantly alter biomass or leaf biochemical compound concentrations, and these effects were almost entirely unaffected by background PPFD. In contrast, these traits were strongly affected by UV-A1 in arabidopsis, highlighting the importance of not relying solely on model species when exploring environmental effects on plants. We conclude that plant responses to UV-A1 radiation depend on genotype and background irradiance.

Optimization of Photoautotrophic Growth Regimens of Scenedesmaceae alga: The Influence of Light Conditions and Carbon Dioxide Concentrations

Improving methods for landless production of bioproducts is considered an important stage in the development of the modern bioeconomy. In this context, microalgal biomass is one of the most promising sources of valuable substances due to its rich biochemical composition. Despite the high adaptability of microalgae to various environmental factors, the effectiveness of cultivation systems depends on precisely selected parameters. Both the light conditions and the supply of inorganic carbon sources are key in determining the efficiency of photoautotrophic cultivation. In this work, the effect of a high daily photosynthetic photon flux density (PPFD) ranging from 37.44 to 112.32 mol m−2 day−1 on the growth and productivity of a novel Scenedesmaceae alga, strain EZ-B1, was assessed. The next stage of cultivation consisted of selecting the optimal CO2 concentration. Improved performance of microalga during cultivation in a photobioreactor was achieved at 112.32 mol m−2 day−1 (24 h photoperiod) and by supplying 2% CO2, as evidenced by the high biomass productivity (0.69 g L−1 day−1), total biomass yield (5.23 g L−1), and ammonium nitrogen consumption rate. The data obtained suggest that a higher level of PPFD led to the highest growth rate of the novel strain and the highest biomass productivity, which, in practice, will increase production capacity.

Design Optimization of Agri‐Photovoltaic Systems in Different Climate Regions†

This paper examines the optimal design for agri‐photovoltaic (agri‐PV) systems. Agri‐PV systems should be evaluated on the total crop yield and power generation, and the balance is essential. Specifically, the amount of solar irradiance reaching the farmland and power generation by PV systems varies by panel separation and tilt angle, affecting crop yield. Quantitative analysis is essential for balancing. This study investigated the balance between the output of Agri‐PV installed on farmland and photosynthetic photon flux density (PPFD), a crucial indicator for crop growth, and discussed the optimal solutions for Agri‐PV systems installed in various regions. Simulations were conducted for Miyazaki (semi‐tropical) and Nagano (inland climate) to understand the changes in different climate regions. Miyazaki has higher PPFD and PV output than Nagano because Miyazaki has more solar irradiance and longer sunshine duration than Nagano. When the normalized panel pitch is small, PPFD changes significantly by the tilt angle. When the normalized panel pitch is large, the profit may be maximized by setting the panel tilt angle to maximize the PV output. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Fine adjustment of emission wavelength, light-conversion quality, photostability of blue-violet light conversion agents based on FRET effect

Single fluorescent chromophore is difficult to achieve efficient photoecological effect, meanwhile, the cost of light conversion agent should be more strictly controlled, thereby promoting the large-scale application of light conversion agricultural film. To solve the above problems, three carbazole derivatives CZ, TCZ and MCZ as donors of Förster resonance energy transfer, and the tris(carbazolyl) substituted triazine TPT as an acceptor of Förster resonance energy transfer, were designed and synthesized. Based on absorption and emission spectra, aggregation induced emission experiments, and light conversion quality tests, the best formulation of light conversion film are obtained. Among of them, TCZ@0.2TPT@EVAb and MCZ@0.2TPT@EVAb films (40% ethylene vinyl alcohol copolymer defined as EVAb film) show highest photosynthetic photon flux density at 400–500 nm, and matching fluorescence emission (458 nm and 461 nm). Under 20 h of intensified ultraviolet radiation (365 nm, 40 W), the emission intensity of TCZ@0.2TPT@EVAb and MCZ@0.2TPT@EVAb films can maintain over 94% of the initial value, showing excellent photostability. Compared with the blank EVAa/EVAb film, the transmittance of the doping films at 500–600 nm are up to 95.12%–99.64%, meaning excellent compatibility and dispersion of light conversion agent in doping films. It is worth mentioning that emission maxima of doping films can be continuously adjusted within the spectral range 430–480 nm, which is conducive to meet the photoecological needs of different crops. Finally, the doping films show low transmittance (1.78%–11.42%) at 200–350 nm, outlining excellent UV light conversion properties.

Evaluation of the enhancement of photosynthetic rate in a komatsuna (Brassica rapa L. var. perviridis) canopy with upward lighting using an optical simulation in a plant factory with artificial light.

In a plant factory with artificial light (PFAL), upward lighting is expected to prevent senescence and decrease in the photosynthetic capacity of the lower leaves in the canopy. Upward lighting may also increase the photosynthetic rate of a canopy by improving its photosynthetic photon flux density (PPFD) distribution. However, the net photosynthetic rate (Pn) of leaves is lower when the abaxial surface is irradiated than that when the adaxial surface is irradiated. The aim of this study was to estimate the PPFD in a PFAL and the Pn of plants using three-dimensional plant models and optical simulation. First, we measured the Pn of komatsuna (Brassica rapa L. var. perviridis) leaves under different conditions of the proportion (pad ) of PPFD on the adaxial surface to total PPFD on both surfaces and developed an equation for the light response curve of photosynthesis considering pad . When PPFD was low, except when it was 30 and 70 µmol m-2 s-1, Pn increased as pad increased, because the absorptance also increased with pad . Under high PPFD conditions, Pn was maximized at 67-83% of pad because the light would be distributed more efficiently for photosynthesis. Next, using optical simulation and the developed equation, we estimated the photosynthetic rate of a komatsuna canopy (CPn) under downward and upward lighting. The CPn increased by 1.08-1.13 times by combining downward and upward lighting due to the increase in the photosynthetic photon flux (PPF) of light incident on the canopy and the decrease in the spatial variation of PPFD on the leaves in the canopy. As the depreciation of lamps for upward lighting accounts for 7.5-9.0% of the production cost in a PFAL, even if the depreciation of lamps for upward lighting increased, enhancement of CPn by upward lighting would be cost-effective. We performed optical simulations under 220 conditions and evaluated them using CPn as an index. Moreover, we provided the proportion of PPF of upward lighting that improved CPn and discussed the reason for this improvement. The result shows that optical simulation is useful for evaluating the lighting design in a PFAL and analyzing the effects of the lighting design on the light environment and photosynthesis.

Productivity, photosynthetic light-use efficiency, nitrogen metabolism and nutritional quality of C4 halophyte Portulaca oleracea L. grown indoors under different light intensities and durations.

Portulaca oleracea L. (known as purslane), is a nutritious facultative C4 halophyte. Recently, it has been successfully grown indoors under LED lightings by our team. However, basic understanding about the impacts of light on purslanes are lacking. This study aimed to investigate the effects of light intensity and duration on productivity, photosynthetic light use efficiency, nitrogen metabolism and nutritional quality of indoor grown purslanes. All plants were grown in 10% artificial seawater hydroponically under different photosynthetic photon flux densities (PPFDs) and durations and thus different daily light integrals (DLI). They are, L1 (240 µmol photon m-2 s-1, 12h, DLI = 10.368mol m-2 day-1); L2 (320 µmol photon m-2 s-1, 18h, DLI = 20.736mol m-2 day-1); L3 (240 µmol photon m-2 s-1, 24h, DLI = 20.736mol m-2 day-1); L4 (480 µmol photon m-2 s-1, 12h, DLI = 20.736mol m-2 day-1), respectively. Compared to L1, higher DLI promoted root and shoot growth and thus increased shoot productivity by 2.63-,1.96-, 3.83-folds, respectively for purslane grown under L2, L3, L4. However, under the same DLI, L3 plants (continuous light, CL) had significantly lower shoot and root productivities compared those with higher PPFDs but shorter durations (L2 and L4). While all plants had similar total chlorophyll and carotenoid concentrations, CL (L3) plants had significantly lower light use efficiency (Fv/Fm ratio), electron transport rate, effective quantum yield of PSII, photochemical- and non-photochemical quenching. Compared to L1, higher DLI with higher PPFDs (L2 and L4) increased leaf maximum nitrate reductase activity while longer durations increased leaf concentrations and total reduced nitrogen. There were no significant differences in leaf total soluble protein, total soluble sugar and total ascorbic acid concentrations in both leaf and stem regardless of light conditions. However, L2 plants had the highest leaf proline concentration but leaf total phenolic compounds concentration was higher in L3 plants instead. Generally, L2 plants had the highest dietary minerals such as K, Ca, Mg and Fe among the four different light conditions. Overall, L2 condition is the most suitable lighting strategy in enhancing productivity and nutritional quality of purslane.

‘Miguang’ Grape Response to Pergola and Single-Curtain Training Systems

Background and Aims: Grapevine shoot growth and light utilization are typically adjusted through the use of canopy management strategies that are adapted to the local climate. In this study, we analyze the effects of a pergola (PER) and single-curtain training system (SCT) on the microclimate, light interception, photosynthetic capacity, and assimilate distribution of ‘Miguang’ grape in a rainy region of China. Methods and Results: We measured light interception, spectral absorptance, leaf area, chlorophyll content, photosynthetic rate, soluble sugar and starch content per cane, assimilate distribution berry weight, soluble solids, and titratable acid content. SCT produced a higher photosynthetic photon flux density in the cluster region, a canopy light absorptance in the 450–800 nm wavelength range, higher chlorophyll content, and larger leaf area of the middle node leaves. It produced lower basal and top leaves leaf areas. At berry expansion (E-L-31) and veraison (E-L-35), the net photosynthetic capacity of the leaves from the base to the middle nodes was higher with SCT than with the PER, and the net photosynthetic capacity of leaves near the top was reduced with SCT. At the harvest period, the net photosynthetic rate of the middle and top node leaves and the shoot photosynthetic rate were higher with SCT than with the PER. The distribution of assimilates to the fruit was higher with SCT. In addition, SCT produced a higher shoot soluble sugar and lower internode length from the fourth to sixth nodes, and it produced a higher shoot starch content and internode diameter in the fourth internode. Conclusions: SCT significantly improved photosynthetic photon flux density in the cluster, promoted assimilate distribution to fruit, decreased vegetative growth, increased chlorophyll content, increased the leaf size of the middle node on the primary shoot, and increased shoot soluble sugar from the fourth to sixth nodes. Significance of this Study: The results of this study can provide a relevant theoretical basis and technical support for grape canopy management.

Influence of Day and Night Temperature and Radiation Intensity on Growth, Quality, and Economics of Indoor Green Butterhead and Red Oakleaf Lettuce Production

Lettuce (Lactuca sativa) is among the most consumed vegetables worldwide and is primarily field-grown; however, indoor agriculture enables year-round, precise production. Through precise manipulation of the mean daily temperature (MDT) and photosynthetic photon flux density (PPFD), crop color, morphology, and yield can be altered. Therefore, we quantified how MDT and PPFD interact and developed models predicting yield and economic viability. Eleven days after sowing, green butterhead lettuce ‘Rex’ and red oakleaf lettuce ‘Rouxaï RZ’ were transplanted into six deep-flow hydroponic tanks with day/night and MDTs of 22/15 °C (20 °C), 25/18 °C (23 °C), or 28/21 °C (26 °C), under light-emitting diodes providing a low or high PPFD of 150 or 300 µmol·m−2·s−1 for 17-h·d−1. As PPFD increased, shoot fresh mass (SFM) of ‘Rex’ increased by 29% (33.4 g). SFM of ‘Rouxaï RZ’ and shoot dry mass (SDM) of both cultivars was influenced by the interaction of MDT and PPFD. The greatest ‘Rouxaï RZ’ SFM (158.8 g) and SDM (6.42 g) were recorded at >20 °C MDT under the high PPFD; the lowest SFM (76.0 g) and SDM (3.17 g) occurred at 20 °C under the low PPFD. Similarly, ‘Rex’ SDM was greatest (7.36 g) and lowest (3.78 g) under the aforementioned MDTs and PPFDs. Increasing from the low to high PPFD increased tipburn incidence on ‘Rouxaï RZ’ from 0 to 25% and ‘Rex’ from 47 to 100%. ‘Rouxaï RZ’ had darker yellow-red foliage at lower MDTs under the high PPFD. A high MDT and low PPFD resulted in a lighter green. Finally, for the greatest SFM, while reducing energy costs as interpreted from the economic analysis, we recommend growing ‘Rex’ and ‘Rouxaï RZ’ under a PPFD of 150 and 300 µmol·m−2·s−1, respectively, at an MDT of 23 to 26 °C depending on the cost of temperature control.

Photosynthetic responses of Eulophia dentata, Bletilla formosana, and Saccharum spontaneum under various photosynthetic photon flux density conditions

This study aimed to determine the photosynthetic performance and differences in chlorophyll fluorescence (ChlF) parameters between Eulophia dentata and its companion species Bletilla formosana and Saccharum spontaneum when subjected to different photosynthetic photon flux density (PPFDs). Leaf surfaces were then illuminated with 50, 100 (low PPFDs), 300, 500, 800 (moderate PPFDs); 1,000; 1,500; and 2,000 (high PPFDs) μmol m-2.s-1, and the ChlF parameters were measured during the whole process. Increasing nonphotochemical quenching of ChlF and decreasing potential quantum efficiency of PSII, actual quantum efficiency of PSII, and quantum efficiency ratio of PSII in dark recovery from 0-60 min were observed in all leaves. A significant and negative relationship was detected between energy-dependent quenching (qE) and photoinhibition percent in three species under specific PPFD conditions, whereas a significant and positive relationship was detected between photoinhibitory quenching (qI) and photoinhibition percent. The qE and qI can be easily measured in the field and provide useful ecological indexes for E. dentata species restoration, habitat creation, and monitoring.

Effects of supplementing green light to red and blue light on the growth and yield of lettuce in plant factories

Red and blue light-emitting diodes (LEDs) are widely used as light sources in plant factories. Plants grown under red and blue light only produces purplish-gray light environment where plant leaves look purplish-gray. Under that light condition, it makes difficulty to check health status of plants specially insect and disease infected leaves by human naked eye. But the leaf color turns green when inspected under full spectrum of light environment. In this regard, the use of green light to red and blue create a white light environment which is congenial for the grower. Likewise, CO2 assimilation of green light is usually lower compared to red and blue light because of its lower absorptance under low PPFD. But at higher PPFD (≥500 µmol m−2 s−1), green light shows higher CO2 assimilation rate compared to red and blue light through uniform distribution of full spectrum (red, green and blue) of light into the plant canopy and the lower leaves. In this study, optimal intensity of green light supplementation to the red and blue LEDs was evaluated for better growth, yield, and quality of lettuce. In experiment I and II, green light was added with red and blue light where total photosynthetic photon flux density (PPFD) was increased for the additional green light. In experiment III, 0, 10, 20, 30, 40, 50, 60, 70, 80 µmol m−² s−1 green (G) light was supplemented to 235 µmol m−² s−1 red (R) and 59 µmol m−² s−1 blue (B) light maintaining 294 µmol m−² s−1 total PPFD. Lettuce plants were cultivated hydroponically in three-step vertical grow beds using half-strength of Enshi nutrient solution. The temperature was maintained at 20 ± 2 °C at day and night and the day length was 16 h. In experiment I and II, the fresh mass of lettuce grown under the combination of R, B and G LEDs was found higher than those cultivated under R and B LEDs only. In experiment III, lettuce plants produced high fresh masses when 30 µmol m−² s−1 of G light was supplemented with R and B lights maintaining the ratio 211:30:53 (R:G:B). By supplementing excessive G light (≥50 µmol m−² s−1) with R and B lights, lettuce shoot fresh mass declined. The various combinations of irradiation of R, G and B LED did not significantly affect the contents of ascorbic acid and mineral nutrients. It is recommended to supplement 30 µmol m−2 s−1 of green light to red and blue light for a higher yield of lettuce. Therefore, the suitable LED (R:G:B) combination would be 72% of red, 10% of green and 18% of blue for lettuce cultivation following recycled hydroponics in plant factories.

Carbon flux variation and associated biomass energy storage economic value implications in the Dinghushan Biosphere Reserve

Subtropical forests are a major carbon (C) storage pool and are therefore rich in biomass energy reservoirs. However, there have been no studies that quantify the C storage economic value, especially in the region of the Dinghushan Biosphere Reserve. This study is the first attempt to apply the eddy covariance technique to measure biomass energy storage and the associated economic value and demonstrates that CO2 flux measurement is a viable method for quantifying the ecosystem biomass energy storage. CO2 flux and micro-meteorological data were collected and analyzed to calculate the daily C sequestration and establish their inter-relationship. In addition, we used the C price estimates of Guangdong Province in China to determine the capital value of the C sequestered. The measured average annual precipitation was 1459.4 mm, the average temperature was 22.9 °C and the highest photosynthetic photon flux density (PPFD) was 334.92 μmol m−2s−1. CO2 flux and biomass energy storage varied seasonally. Photosynthetic photon flux density (PPFD) was highly correlated with gross primary production (GPP) (r2 = 0.99, p < 0.0001). Soil temperature was correlated with net ecosystem exchange (NEE) (r2 = 0.84, p < 0.0001). There was a positive correlation (r2 = 0.49, p < 0.0001) between soil moisture and NEE. The Dinghushan Biosphere Reserve sequestered an average of 5300 tCy−1 equivalent to RMB 3.3 million (USD 530,000). We conclude that economically, the Dinghushan Biosphere Reserve is highly significant to China's Guangdong Province because of its rich biomass energy reserves via C sequestration and our findings will stimulate the formulation of more aggressive conservation policies that will inevitably lead to better management of the reserve.

Effects of Daily Light Integral on Compact Tomato Plants Grown for Indoor Gardening

Our objective was to characterize the growth, physiological responses, fruit yield, and quality of tomato (Solanum lycopersicum L.) plants grown under different daily light integrals (DLIs) and photoperiods. In experiment I, nine compact tomato cultivars were grown indoors using broadband white light-emitting diode (LED) fixtures. Plants were grown under low (10.4 mol·m−2·d−1) and high (18.4 mol·m−2·d−1) DLIs with 12 and 16 h photoperiods, respectively, and two intermediate DLIs of 13.8 mol·m−2·d−1 with either 12 or 16 h photoperiods. In experiment II, three compact tomato cultivars were grown under the same low DLI with either 8 or 12 h photoperiods, and the same high DLI with either 12 or 16 h photoperiods. Generally, higher DLIs decreased plant growth and increased the fruit yield. Changing the DLI delivery strategy by adjusting the photoperiod and photosynthetic photon flux density (PPFD) did not have major effects on the growth, yield, and fruit quality of the compact tomato plants evaluated in this study, even though net photosynthesis increased under higher PPFDs in experiment II. Although several cultivars were affected by intumescence, only two cultivars showed treatment responses, for which the severity was generally higher in lower PPFDs using the same DLI.

Spatiotemporally variable incident light, leaf photosynthesis, and yield across a greenhouse: fine-scale hemispherical photography and a photosynthesis model

Although greenhouse agriculture can generate high crop yields, they vary due to spatiotemporal differences in incident light and photosynthesis. To elucidate these dynamics, multipoint analysis of hemispheric images and a photosynthesis model were used to visualize the spatiotemporal distribution of photosynthetic photon flux density (PPFD) and leaf photosynthetic rate (A) and compared these with strawberry fruit yield in a greenhouse. This method enabled successful estimation of spatiotemporal variability in PPFD and A with relative root mean square errors of 4.4% and 11.0%, respectively. PPFD, captured at ca. 2 m resolution, varied diurnally and seasonally based on sun position and external light intensity. A showed less spatial variability, because it is reduced by physical and physiological mechanisms in the leaves at excessive leaf temperatures and becomes saturated at high PPFD. Yield spatial variability was better explained by A than by PPFD. The association between A and yield weakened over the cultivation period (R2 declined from 46% in winter to 12% in spring), thus suggesting that, over the cultivation period, factors such as photoassimilate availability replaced A as the primary limiting factor. The proposed method can be directly applied to other types of greenhouses, and the findings may facilitate spatiotemporal optimization in crop production, improving precision greenhouse agriculture.

Elevated light intensity compensates for nitrogen deficiency during chrysanthemum growth by improving water and nitrogen use efficiency

Identifying environmental factors that improve plant growth and development under nitrogen (N) constraint is essential for sustainable greenhouse production. In the present study, the role of light intensity and N concentrations on the biomass partitioning and physiology of chrysanthemum was investigated. Four light intensities [75, 150, 300, and 600 µmol m−2 s−1 photosynthetic photon flux density (PPFD)] and three N concentrations (5, 10, and 15 mM N L−1) were used. Vegetative and generative growth traits were improved by increase in PPFD and N concentration. High N supply reduced stomatal size and gs in plants under lowest PPFD. Under low PPFD, the share of biomass allocated to leaves and stem was higher than that of flower and roots while in plants grown under high PPFD, the share of biomass allocated to flower and root outweighed that of allocated to leaves and stem. As well, positive effects of high PPFD on chlorophyll content, photosynthesis, water use efficiency (WUE), Nitrogen use efficiency (NUE) were observed in N-deficient plants. Furthermore, photosynthetic functionality improved by raise in PPFD. In conclusion, high PPFD reduced the adverse effects of N deficiency by improving photosynthesis and stomatal functionality, NUE, WUE, and directing biomass partitioning toward the floral organs.

Effects of photo-selective netting in Summer Beefsteak Tomato (Solanum lycopersicum L.) cultivation on the environmental conditions under nets as well as growth and yield

Located in a subtropical zone, Taiwan has intense summer sunlight that affects beefsteak tomato cultivation. In this study, beefsteak tomatoes were grown net-house under photo-selective netting of different colors to investigate netting performance. A significantly higher photosynthetic photon flux density (PPFD) was observed under the 24-mesh white (W24) and 24-mesh pink (H24) netting. A difference between the four net-house was only observed for wavelengths of 500–599nm. In 32-mesh blue (B32), the red to blue (R/B) and red to far-red (R/FR) ratios were significantly lower across canopies. The photosynthetic capacity of photosystem II of leaves in W24 was the lowest among the four treatments. In all four, fruit growth was relatively low under the impact of high temperatures, with the lowest single fruit weight and the smallest number of fruits per plant observed in W24. In H24 and 24-mesh pink (HH24), the yield per plant was significantly higher. Significantly fewer whiteflies were observed in the netting houses in H24, HH24, and B32 than in W24. However, the netting still failed to prevent high temperatures at noon. In H24 and HH24, the amount of light retained in the canopies was greater, the photosynthesis capacity was unchanged, the fruit yield was greater and the number of whiteflies in the netting houses was significantly lower. Therefore, pink netting is recommended for beefsteak tomato cultivation.

Growth and metabolism of basil grown in a new-concept microcosm under different lighting conditions

To simulate a typical market-oriented cultivation in laboratory, plants of basil (Ocimum basilicum L.) were grown from seedling to flowering stages in a new-concept microcosm device that enables roots and aerial parts to grow as under real crop conditions. To test the device efficacy, two microcosms were used with the same lighting architecture, temperature and photoperiodic conditions and with two different light spectra, white (W) or blue-red (BR), displaying a similar spectral power in the blue region. Plant growth, biomass yield, photosynthetic efficiency and nutrient uptake were determined. An innovative analytical approach for secondary metabolic profile was also developed to determine basil quality. The plants grew vigorous and healthy for the whole cultivation period and under both the lighting regimes, giving a biomass yield similar to those of basil grown under conventional greenhouse and field conditions. The two lighting regimes differently affected plant growth and yield, with the BR light, that was characterized by a higher photosynthetic photon flux density (PPFD), associated to higher plants, earlier flowering and greater yield. In the average, fresh and dry aerial biomasses per plant were about 250 g and 41 g under BR and about 114 g and 9 g under W light. Higher concentrations of major nutrients were detected in plants under W light, thus indicating that yield levels and major nutrient concentrations are not necessarily related to each other. Similar Fv/Fm (0.76–0.78) and ETR values were observed under the two light regimes, possibly indicating that plants under long lasting cultivation can adapt to different light regimes to reach similar photosynthetic efficiency levels. Different secondary metabolic profiles were detected in tissues sampled at the end of cultivation period and previously unreported profiles for basil were also recorded, possibly indicating that the extent of plant growth affects secondary metabolism in basil, in addition to light spectrum and PPFD level. This is the first report of basil grown under microcosm conditions from seedlings to adult plants. Our results indicate that the microcosm based-technology is effective in simulating a typical market-oriented cultivation and that long lasting cultivation emphasizes the effects of different environmental conditions on plant growth and metabolism.

High photosynthetic photon flux density can attenuate effects of light quality

High photosynthetic photon flux density can attenuate effects of light quality