Relative spectral distributions of light during growth and for measurement do not only directly affect the net photosynthetic rate (Pn), but also affect the rate indirectly through their interaction. This letter explains a plausible mechanism of the interaction, some situations in which the interaction should be considered, and recommendations for selecting appropriate spectral distributions of measuring light to evaluate photosynthesis. A leaf adjusts the excitation energy distribution balance between photosystems in response to the relative spectral distribution of growth light. This adjustment modifies the response of Pn to the relative spectral distribution of measuring light. Therefore, evaluating the Pn of leaves of plants grown under different relative spectral distributions of growth light with a single spectral distribution of measuring light causes Pn overestimation or underestimation. The obtained results must be discussed in relation to the spectral distribution of measuring light to avoid producing biased evaluations. Depending on the study purpose, Pn should be evaluated under appropriate measuring light. For instance, in retrospective studies aimed at elucidating the causes of differences in growth brought about by the growth conditions, Pn should be measured under light with the same spectral distributions as those under which the plants were grown.
Stem elongation and capitulum formation in lettuce is promoted during warm conditions. These morphosis reactions pose a problem to lettuce cultivation as they result in a decreased commercial value. Therefore, the development of the convenient and effective growth control techniques is required to avoid this problem. In this study, night chilling treatment and end of day lighting treatment were examined as potential techniques to reduce the stem elongation and capitulum formation in lettuce. Red and yellow fluorescent lamp were used as light sources in this experiment. Lettuce seeds were sown on May 9, 2013. Seedlings were exposed to low temperature during the night from May 23 to June 6, and sequentially exposed to end of day lighting from June 7 to July 4, 2013. The stem elongation was inhibited by night chilling treatment and was inhibited by end of day lighting treatment remarkably. The capitulum formation was inhibited in the night chilling treatment. These results suggest that end of day lighting after night chilling treatment is effective in suppressing stem elongation and floral stage of lettuce plant.
In this paper, we identified and modelled the short-term response of leaf water content to water temperature in hydroponic tomato plants using a neural network. Leaf water content was estimated from leaf thickness using an eddy current-type displacement sensor. Dynamic changes in the leaf water content of the tomato plants, as affected by water temperatures, was identified and modelled using a neural network. A three-layered neural network with optimal system order and hidden neuron number allowed nonlinearity of this system to be successfully identified. The estimated responses obtained from model simulation were correlated closely with the observed responses. Leaf water content increased with water temperature up to 35°C in a short period of several hours. At a water temperature above 35°C, however, leaf water content decreased with increasing water temperature. Leaf water content, including root water uptake, of tomato plants is significantly suppressed by high water temperature. The relationship between water temperature and leaf water content over a short-term of several hours is represented by a hill-shaped curve (nonlinear curve) and reaches maximum value when the water temperature is about 35°C. These dynamic and static relationships between water temperature and leaf water content were successfully confirmed from model simulation.
Global warming is predicted to increase air temperatures. With the aim of ensuring future stable production of strawberry under high autumn air temperatures, we examined the effect of a crown-cooling treatment on flower bud differentiation, flowering characteristics and fruit yield in a June-bearing strawberry (Fragaria×ananassa Duch. cv. Fukuoka S6). We forced strawberries under high air temperature conditions (controlled day/night temperatures of 30/27°C) to simulate future global warming. For approximately 40 d after transplanting in August, strawberry crowns were cooled using a crown-cooling tube filled with water controlled to temperatures of 10, 15, 20 and 25°C. The crown-cooling treatments of 10, 15 and 20°C significantly (P‹0.05) promoted flower bud differentiation in the first inflorescence compared with controls. This earlier differentiation resulted in quicker anthesis, and led to an increase in marketable fruit yield in December. However, continuous cooling treatments of 10 and 15°C after flower bud differentiation negatively affected anthesis and fruit yield. These data suggest that crown-cooling treatment for an appropriate period may be able to stabilize strawberry production under high air temperatures.
The aim of this study was to apply the transpiration integrated model proposed by Sago et al. (2011c) to the simulation of the day-to-day dynamics of root ion absorption of tomato plants in soilless culture. Quantitative data on root ion absorption during the daytime and nighttime were obtained using a nutrient film technique (NFT) soilless culture system in which tomato plants were cultivated, and the data were analyzed using the transpiration integrated model. The identified model parameters could represent the characteristics of root ion absorption. The day-to-day dynamics of root ion absorption were simulated reliably in the daytime, but the simulation of the nighttime ion absorption was difficult. Nevertheless, the nighttime ion absorption accounted for a small portion of the daily ion absorption, and the transpiration integrated model was found to be effective for evaluating the root ion absorption over the entire day. This model is expected to be applicable to the simulation of root ion absorption in NFT soil-less culture for sustainable nutrient management.
For stable year-round production of greenhouse crops with sustainability and high profitability, it is essential to establish a system that encompasses energy-saving and year-round environmental control via the application of renewable energy resources. One such renewable energy resource is the constant soil temperature layer, which is widespread and easily accessible in agricultural fields. However, owing to the low heat capacity and conductivity of media such as soil and air, heat exchange with the constant soil temperature layer has been considered insufficient for temperature control of the entire air volume inside a greenhouse. Therefore, we utilized a novel local temperature control system based on heat exchange between the constant soil temperature layer and the ambient air surrounding greenhouse crops. In the present study, we applied this system to the elevated bed system of strawberry crops with no-heating culture during the winter season. The system, that control the ambient air temperature of strawberry crops, increased fruits yield compared with no-heating, and was estimated 45% reduction of heating load to maintain 8°C or more.
By combining a cell pressure probe and an Orbitrap mass spectrometer, quantitative snapshot profiles of metabolites of in situ plant single cells during development of blossom end rot in tomato (Solanum lycopersicum L.) fruit were analyzed while tomato plants were grown hydroponically in a greenhouse. By using the pressure probe, cell turgor, cell volume, cell wall elastic modulus, and hydraulic conductivity of plasma membrane were measured, followed by managed cytoplasm sampling, and osmotic and water potentials determination. It was found that the cell bursting results from alterations in water relations and cell wall properties accompanied with changes in metabolites of cells located at blossom end rot area in tomato fruit. From the water relations point of view, the loss of the elasticity and cell wall weakening, with decreased water potential and excess turgor resulted in mechanical rupture of membrane and cell wall. Abscisic acid was detected in damaged cells as a possible evidence of triggered precocious maturity. Simultaneously, a sharp rise in the concentration of phenols (coumarinate-glucoside and chlorogenic acid) and salicylic acid and decline in ascorbic acid reflected the activation of cell death process that would facilitate the deterioration of cell wall and plasma membrane.
In greenhouse production of strawberries (Fragaria×ananassa×Duch.) during winter season in Japan, unsuitable climate condition (low solar radiation, low temperature, etc.) for strawberry growth causes serious problems such as yield depression and low quality of fruits. For sustainable production with high profitability, it is keenly desired to establish a system for efficient environmental control based on physiological functions of crops. Translocation of photosynthate from leaves to fruits is a major physiological determinant for size and sugar content of strawberries. It is therefore essential to clarify the response of photosynthate loading to surrounding environment. In this study, we focused on light condition which strongly influences the photosynthesis, and analyzed effects of irradiation on dynamics of photosynthate loading. Furthermore, aiming at the estimation of dynamics of photostnthate loading in cultivation field, we simulated daily amount of photosynthate loading by kinetic model using a saturable Michaelis-Menten component in combination with an unsaturable component obeying first-order kinetics.