Continuous monitoring of canopy photosynthetic rates in a naturally ventilated greenhouse requires a method of measuring ventilation rates that can record accurate short-term responses throughout the day. It is necessary to clarify the difference between the accuracy and operability of ventilation rate methods. This study evaluated the diurnal-change of ventilation rate measured by the heat balance (HB) and water vapor balance (WVB) methods in the summer and early autumn seasons and compared two methods with the tracer gas (TG) method as a reference. The ventilation rate was determined in a single-span type experimental greenhouse with mature-stage tomato crops under different ventilator configurations to assess the accuracy of the above two methods. The ventilation rates measured via the HB and WVB methods were slightly lower than that measured by the TG method in the greenhouse without crops. However, the ventilation rates obtained using both methods exhibited similar variation trends with time. It is difficult to maintain high concentrations of TG in a greenhouse with a large ventilation opening area. However, it was easy to continuously measure the ventilation rate even in such a greenhouse using the HB and WVB methods. Practically, the WVB system is simpler than the HB method, which utilizes numerous sensors.
The ventilation rate is an essential parameter for the continuous monitoring of the photosynthetic rate for greenhousecultivated plants via the CO2 balance method. Diurnal changes in the ventilation rate (G) according to window aperture (W) and solar radiation level were therefore measured using the heat balance (HB) and water vapor balance (WVB) methods during winter and spring in a naturally ventilated greenhouse cultivating tomatoes. The results were indirectly compared with those of the tracer gas (TG) method. The G obtained through both methods increased with increasing W. However, when W increased rapidly, the increase in G was delayed when using the HB method compared to the WVB method. The G obtained via the WVB method performed similarly to the TG method at small values of W, and similarly to the HB method at moderate values of W. Furthermore, when measured using the HB method, the value in G was sensitive to the change in solar radiation level. Meanwhile, the G measured using the WVB method exhibited a stable response to the changes in W and could permit continuous real-time monitoring of greenhouse ventilation rates, which is necessary to estimate the photosynthetic rate for the plants in a greenhouse.
Numerous studies in plant factories show that alternating irradiation of red and blue (R/B) light promotes growth of leafy lettuce compared with simultaneous R+B (RB) light or white (W) light, even under the same daily light integrals. Here we investigate why alternating R/B light enhances lettuce growth in terms of the anatomical and photosynthetic changes in leaves. At 16 days after sowing (DAS), plants under alternating R/B light for 12/12 hours (R12/B12) had higher leaf thickness, mesophyll cell density, and leaf mass per area than did plants under RB light for 24 hours (RB24) or W light for 24 hours (W24). At 35 DAS, these anatomical values of leaves and the daily carbon gain of leaves evaluated by gas exchange analysis were higher under R12/B12 than under W24, and were similar to RB24. The projected leaf area and maximum leaf length were highest under R12/B12 across all growth stages, which would promote light capture. Marketable fresh weight under R12/B12 at 35 DAS was highest among the treatments. These results indicate that leaf morphological changes affecting the light absorption efficiency and photosynthetic rate could be the primary factors of enhanced lettuce production under the alternating R/B light condition.
We investigated whether short-term thermal acclimation (growth temperature of 38 ℃ for 4 days) enhanced heat stress (leaf temperature of 45 ℃ for 10 minutes) tolerance of the CO2 fixation system of photosynthesis in cucumber leaves. We found that thermal acclimation did not influence the gross photosynthetic rate (PG) or the maximum quantum yield of photosystem II (Fv/Fm), but significantly increased the transpiration rate (TR) of the leaves. An increase in TR due to thermal acclimation increased the nitrogen and magnesium content of leaves, resulting in an increase in the content of RuBisCO. However, the activation state of RuBisCO was significantly decreased by thermal acclimation. Although the PG, Fv/Fm, and initial RuBisCO activity in non-acclimated leaves decreased significantly on heat stress, those of acclimated leaves recovered to 69, 88, and 89 % of those before heat stress, respectively. Thermal acclimation maintained a high level of content and total activity of RuBisCO after heat stress, but low levels in the ratio of initial to total activity of RuBisCO. These results suggest that the quantitative intensification of RuBisCO by thermal acclimation makes up for its decreased activation state and leads to the recovery of photosynthetic potential after inhibition from heat stress.
This study introduces an image processing method capable of performing real-time detection of two common diseases, leaf blast (LB) disease and bacterial blight (BB) disease, in the paddy fields of the Vietnamese Mekong Delta (VMD). The input images were recorded with an RGB camera. The discrimination of the diseases on rice leaves was obtained by an image processing method based on the extraction of texture and color features from disease lesions, in conjunction with either the Gaussian Naïve Bayes classifier or the K-Nearest Neighbors (KNN) algorithm, to classify the disease into various categories. Both methods perform real-time detection of LB and BB disease in the early stages of development with uncontrolled light conditions in rice fields. Our results show that Gaussian Naïve Bayes is simple but effective, with a shorter processing time and higher detection accuracy than KNN.
Short postharvest life of button mushroom (Agaricus bisporus L.) is a serious problem in the expansion of marketing and long-distance transportation of this product. Edible coating is an effective way to delay the browning process and mitigate the deterioration of button mushroom. In this study, the impact of Aloe vera gel alone and combined with basil oil as an edible coating on postharvest quality and browning of mushroom has been investigated. Surface morphology of the coated and uncoated mushrooms was studied by scanning electron microscopy (SEM). The results indicated that application of A. vera gel enriched with basil oil significantly alleviated weight loss, softening and respiration rate during the storage. In addition, coated samples delayed browning and color change compared to uncoated samples. Interestingly, total phenolic contents, antioxidant and phenylalanine ammonia lyase activity increased in samples coated by treatment of A. vera and basil oil. Relative electrolyte leakage, malondialdehyde content and polyphenol oxidase activity were also significantly lower in A. vera enriched with basil oil treated samples. These findings suggest that combination of A. vera with basil oil is a promising method to preserve the quality of the button mushrooms during cold storage.
The aim of this study was clarifying whether the strawberry plants used for forcing cultivation could be stored and continuously cultivated in a plant factory with artificial light (PFAL). Forced June-bearing strawberries were harvested from November to May in Japan. In this study, we transferred the forced June-bearing strawberries to a PFAL in late April, and examined the differences in flowering and yield, and the effects of lighting conditions on flowering, yield, and leaf photosynthesis. We observed continuous flowering and fruit development through August, in low-temperature (20℃ in light and 10℃ in dark) and short-day (8-hour day length) treatment, and medium-temperature (25℃ in light and 15℃ in dark) and medium-day (12-hour day length) treatment. The prolific“Benihoppe”and“Akihime”cultivars had high yields from May to October. Furthermore,“Benihoppe”showed significantly higher photosynthetic rate under strong light (Photosynthetic Photon Flux Density (PPFD) of 510±12 μmol m-2 s-1) than under weak light (PPFD of 301.5±30.5 μmol m-2 s-1). The study suggests that the productive lives of June-bearing strawberry plants, which were usually discarded in commercial farms in mid-May, could be extended for up to 5 months (Jun. – Oct.) by transferring them to a PFAL.