Different LED Light Wavelengths and Photosynthetic Photon Flux Density Effect on Colletotrichum acutatum Growth

The study aimed to evaluate the effect of different photon flux density (PFD) and light-emitting diodes (LED) wavelengths on strawberry Colletotrichum acutatum growth characteristics. The C. acutatum growth characteristics under the blue 450 nm (B), green 530 nm (G), red 660 nm (R), far-red 735 nm (FR), and white 5700 K (W) LEDs at PFD 50, 100 and 200 μmol m−2 s−1 were evaluated. The effect on C. acutatum mycelial growth evaluated by daily measuring until five days after inoculation (DAI). The presence of conidia and size (width and length) evaluated after 5 DAI. The results showed that the highest inhibition of fungus growth was achieved after 1 DAI under B and G at 50 μmol m−2 s−1 PFD. Additionally, after 1–4 DAI under B at 200 μmol m−2 s−1 PFD. The lowest conidia width was under FR at 50 μmol m−2 s−1 PFD and length under FR at 100 μmol m−2 s−1 PFD. Various LED light wavelengths influenced differences in C. acutatum colonies color. In conclusion, different photosynthetic photon flux densities and wavelengths influence C. acutatum growth characteristics. The changes in C. acutatum morphological and phenotypical characteristics could be related to its ability to spread and infect plant tissues. This study’s findings could potentially help to manage C. acutatum by LEDs in controlled environment conditions.

Optimization of Photosynthetic Photon Flux Density and Light Quality for Increasing Radiation-Use Efficiency in Dwarf Tomato under LED Light at the Vegetative Growth Stage

Dwarf tomatoes are advantageous when cultivated in a plant factory with artificial light because they can grow well in a small volume. However, few studies have been reported on cultivation in a controlled environment for improving productivity. We performed two experiments to investigate the effects of photosynthetic photon flux density (PPFD; 300, 500, and 700 μmol m−2 s−1) with white light and light quality (white, R3B1 (red:blue = 3:1), and R9B1) with a PPFD of 300 μmol m−2 s−1 on plant growth and radiation-use efficiency (RUE) of a dwarf tomato cultivar (‘Micro-Tom’) at the vegetative growth stage. The results clearly demonstrated that higher PPFD leads to higher dry mass and lower specific leaf area, but it does not affect the stem length. Furthermore, high PPFD increased the photosynthetic rate (Pn) of individual leaves but decreased RUE. A higher blue light proportion inhibited dry mass production with the same intercepted light because the leaves under high blue light proportion had low Pn and photosynthetic light-use efficiency. In conclusion, 300 μmol m−2 s−1 PPFD and R9B1 are the recommended proper PPFD and light quality, respectively, for ‘Micro-Tom’ cultivation at the vegetative growth stage to increase the RUE.

Growth and Flowering Characteristics of Oncidium Gower Ramsey Varieties under Various Fertilizer Management Treatments in Response to Light Intensities

Oncidium are grown worldwide and play important economic roles. The objective of this study was to investigate the pseudobulb growth and flowering characteristics of the two Oncidesa Gower Ramsey cultivars, ‘Honey Angel (HA)’ and ‘Golden Star (GS)’, cultivated under 3 kinds of fertilizer treatments in response to 40% light intensity (LI-40) and 30% light intensity (LI-30, as control) photosynthetic photon flux density over a 5-month period. The conventional-fertilizer (CF) treatment, as a control, consisted of a liquid manure solution of N:K = 1:1.12, mixed with 7.8% N, 0.8% P2O5, 0.3% K2O, and 57.3% of organic matter that was foliage-applied to plants twice weekly. The stage-fertilizer (SF) treatment consisted of N:P:K = 1:1:5 foliage-applied to plants in an unsheathing pseudobulb stage until reaching inflorescence, followed by N:P:K = 1:1:1 application until the end of the experiment. The fortnight-fertilizer (FF) treatment consisted of N:P:K = 1:1:5 and N:P:K = 1:1:1 with interval-rotate foliage-application to plants weekly until the end of the experiment. Pseudobulb length (PL), pseudobulb major axis (PW), and pseudobulb minor axis (PT), and inflorescence length (FL), number of pedicel (FB), and floret numbers (FN) per plant were recorded and calculated from two months after pseudobulb maturity until the end of the five-month experimental period. The GS variety significantly increased PL when treated with CF and FF compared to HA, and GS treated with CF under LI-30 exhibited the longest PL at 81.65 mm. PW increased as LI increased under FF treatment, and the largest PW was observed in GS treated with FF under LI-40. A maximal and significant increase in PT occurred in LI-40 compared to LI-30 under the CF treatment. GS had a significantly higher FL compared to HA treated with CF, and the longest FL was detected in GS under LI-30. HA had a significantly higher FB and FN under LI-40 than under LI-30, and the highest number of FB and FN in HA occurred when it was treated with CF and SF, respectively. Precision management of fertilization treatments in response to LI can maximize pseudobulb growth, development, and flowering quality in Oncidesa species.

Forecasting Photosynthetic Photon Flux Density Under Cloud Effects: Novel Predictive Model Using Convolutional Neural Network Integrated With Long Short-term Memory Network

Forecast models of solar radiation incorporating cloud effects are useful tools to evaluate the impact of stochastic behaviour of cloud movement, real-time integration of photovoltaic energy in power grids, skin cancer and eye disease risk minimisation through solar ultraviolet (UV) index prediction and bio-photosynthetic processes through the modelling of solar photosynthetic photon flux density (PPFD). This research has developed deep learning hybrid model (i.e., CNN-LSTM) to factor in role of cloud effects integrating the merits of convolutional neural networks with long short-term memory networks to forecast near real-time (i.e., 5-minute) PPFD in a sub-tropical region Queensland, Australia. The prescribed CLSTM model is trained with real-time sky images that depict stochastic cloud movements captured through a Total Sky Imager (TSI-440) utilising advanced sky image segmentation to reveal cloud chromatic features into their statistical values, and to purposely factor in the cloud variation to optimise the CLSTM model. The model, with its competing algorithms (i.e., CNN, LSTM, deep neural network, extreme learning machine and multivariate adaptive regression spline), are trained with 17 distinct cloud cover inputs considering the chromaticity of red, blue, thin, and opaque cloud statistics, supplemented by solar zenith angle (SZA) to predict short-term PPFD. The models developed with cloud inputs yield accurate results, outperforming the SZA-based models while the best testing performance is recorded by the objective method (i.e., CLSTM) tested over a 7-day measurement period. Specifically, CLSTM yields a testing performance with correlation coefficient r = 0.92, root mean square error RMSE = 210.31 μ mol of photons m-2 s-1, mean absolute error MAE = 150.24 μ mol of photons m-2 s-1, including a relative error of RRMSE = 24.92% MAPE = 38.01%, and Nash Sutcliffe’s coefficient ENS = 0.85, and Legate & McCabe’s Index LM = 0.68 using cloud cover in addition to the SZA as an input. The study shows the importance of cloud inclusion in forecasting solar radiation and evaluating the risk with practical implications in monitoring solar energy, greenhouses and high-value agricultural operations affected by stochastic behaviour of clouds. Additional methodological refinements such as retraining the CLSTM model for hourly and seasonal time scales may aid in the promotion of agricultural crop farming and environmental risk evaluation applications such as predicting the solar UV index and direct normal solar irradiance for renewable energy monitoring systems.

Radiation Intensity and Quality Affect Indoor Acclimation of Blueberry Transplants

The objectives were to characterize and compare shrinkage (i.e., transplant loss) and growth of tissue-cultured blueberry (Vaccinium corymbosum) transplants acclimated in greenhouses or indoors under 1) different photosynthetic photon flux densities (PPFDs) (Expt. 1); or 2) spectral changes over time using broad-spectrum white (W; 400 to 700 nm) light-emitting diodes (LEDs) without or with red or far-red (FR) radiation (Expt. 2). In Expt. 1, ‘Emerald’ and ‘Snowchaser’ transplants were acclimated for 8 weeks under PPFDs of 35, 70, 105, or 140 ± 5 µmol·m‒2·s‒1 provided by W LED fixtures for 20 h·d−1. In another treatment, PPFD was increased over time by moving transplants from treatment compartments providing 70 to 140 µmol·m‒2·s‒1 at the end of week 4. Transplants were also acclimated in either a research or a commercial greenhouse (RGH or CGH, respectively). Shrinkage was unaffected by PPFD, but all transplants acclimated indoors had lower shrinkage (≤4%) than those in the greenhouse (15% and 17% in RGH and CGH, respectively), and generally produced more shoot and root biomass, regardless of PPFD. Growth responses to increasing PPFD were linear in most cases, although treatment effects after finishing were generally not significant among PPFD treatments. In Expt. 2, ‘Emerald’ transplants were acclimated for 8 weeks under constant W, W + red (WR), or W + FR (WFR) radiation, all of which provided a PPFD of 70 ± 2 μmol·m−2·s−1 for 20 h·d−1. At the end of week 4, a group of transplants from WR and WFR were moved to treatment compartments with W (WRW or WFRW, respectively) or from W to a research greenhouse (WGH), where another group of transplants were also acclimated for 8 weeks (GH). Shrinkage of transplants acclimated indoors was also low in Expt. 2, ranging from 1% to 4%. In contrast, shrinkage of transplants acclimated in GH or under WGH was 37% or 14%, respectively. Growth of indoor-acclimated transplants was generally greater than that in GH or under WGH. Although growth responses were generally similar indoors, plants acclimated under WFR had a higher root dry mass (DM) and longer roots compared with GH and WGH.

Blue Light Monochromatic Irradiation for 12 Hours in Lighting Pattern with Combinations of Blue and Red Light Elongates Young Cos Lettuce Leaves and Promotes Growth under High Daily Light Integral

Cos lettuce was grown under different spectral photon flux density distribution (SPFD) change patterns with blue- and/or red light-emitting diode (LED) irradiation with a 24-hour cycle. Twelve treatments were designed with a combination of four relative SPFD (RSPFD) change patterns and three photosynthetic photon flux density (PPFD) levels. The RSPFD change patterns were as follows: BR/BR, simultaneous blue- and red-light irradiation (BR) for 24 h; R/BR, red-light monochromatic irradiation (R) for 12 h followed by 12 hours of BR; B/BR, blue-light monochromatic irradiation (B) for 12 hours followed by 12 hours of BR; and B/R, 12 hours of B followed by 12 hours of R. Each RSPFD change pattern was conducted at three daily average photosynthetic photon flux densities (PPFDave) of 50, 100, and 200 µmol·m−2·s−1. The RSPFD change patterns that included B (B/BR and B/R) resulted in elongated leaves. A low ratio of active phytochrome to total phytochrome under B was considered the reason for leaf elongation. Shoot dry weight was significantly greater under the RSPFD change patterns that included B when the PPFDave was 200 µmol·m−2·s−1. The leaf elongation caused by B would have increased the amount of light received and thereby promoted growth. However, excessive leaf elongation caused the plants to fall, and growth was not promoted under the RSPFD change patterns that included B when the PPFDave was 50 µmol·m−2·s−1. Thus, 12-hour B promoted growth under conditions in which leaf elongation leads to increases in the amount of light received.

Photosynthetic Responses of Anthurium × ‘Red’ under Different Light Conditions

Light is an essential energy source for plant photosynthesis, although it can also be a stress-causing element. Therefore, the current research was aimed to compare photosynthetic responses of Anthurium × ‘Red’ leaves at different positions (bottom old leaf, 1; center mature leaf, 2; top expanded leaf, 3) established under three photosynthetic photon flux densities (PPFDs): 550 μmol·m−2·s−1 as high (H), 350 μmol·m−2·s−1 as medium (M), and 255 μmol·m−2·s−1 as low (L). After six months, all the replicates were relocated to interior rooms with a PPFD of 30 μmol·m−2·s−1. There were no significant differences in chlorophyll concentration of the old leaf among treatments, before (Day 0) and after shifting the plants to interior rooms (Day 30). The total chlorophyll concentrations of the mature and top leaves increased significantly. In greenhouse conditions, H and M treatments did not show any significant change for net photosynthetic rate (Pn) at various leaf positions. However, M2 exhibited an improved Pn in the interior conditions. Plants grown under M treatment were greener and had bigger leaves compared to other treatments. Our study reveals that Anthurium × ‘Red’ photosynthesis responses to different light conditions varied distinctly. However, M treatment can keep the plants looking green by accumulating enough energy for indoor conditions, and middle and lower leaves may be triggered to restore photosynthetic activity under low light or indoor conditions.