To achieve higher production in greenhouses, maximization of crop net photosynthesis is required; hence, CO2 enrichment and supplemental lighting equipment has been installed in many commercial greenhouses. In practice, appropriate profitability analysis should be performed before such installations. Crop growth and yield simulation models based on the environmental response of leaf photosynthesis are useful to evaluate the increase in profitability derived from the new equipment. Therefore, accurate and compatible data on the environmental response of leaf photosynthesis are necessary. In this study, we proposed a general protocol for the measurement of leaf photosynthesis environmental response, i.e., light response curve and CO2 response curve, that can be widely applied to the crops grown in greenhouses. Furthermore, the effects of stomatal opening/closure and phosphate limitation on the photosynthesis of tomato leaves through the proposed measurement protocol were investigated. The results demonstrated that the effects of stomatal opening/closure on the photosynthetic rate during light response curve measurement are small, particularly under high CO2 concentrations; however, the stomata tended to be closed when the measurement was performed on a cloudy day. Moreover, in the measurement of CO2 response curve, the stomatal response to CO2 concentration differs depending on PPFDs, i.e., stomata tended to close under high CO2 concentrations (> 400 μmol mol-1) at a PPFD of 500 μmol m-2s-1, but not at PPFDs of 1000 and 1500 μmol m-2s-1. Furthermore, a slight but significant decrease in photosynthetic rate, which might be caused by phosphate limitation, was observed at high PPFD and high CO2 concentration.
Photocatalytic decompositions of organic compounds in aqueous titanium dioxide (TiO2) suspensions with water evaporation were investigated both experimentally and theoretically using 2,4-dinitrophenol (DNP) and methylene blue as reactants. The experimental result indicated that the concentrations of these reactants decrease more quickly than without water evaporation. This is because the water evaporation increases the reactant concentration at the TiO2 surface, thereby increasing the rate of decomposition. This acceleration of photocatalytic reaction was successfully reproduced through simulation using a power-law type kinetic reaction model constructed for the DNP decomposition. In conclusion, the photocatalytic wastewater treatment in aqueous TiO2 suspensions with water evaporation is useful to shorten the treatment time.
A preparation method of zeolite-supporting carbonized rice husk (CRH) is studied to develop an adsorbent for removing low-concentration ammonium ion (NH4+) from water. The procedure of this method mainly consists of two steps; dissolving an aluminum supply source in an aqueous solution of NaOH and then autoclaving the NaOH solution where CRH is immersed to synthesize zeolite particles on the CRH surface by means of hydrothermal reaction. The favorable condition for this reaction is found to be 130 °C for the temperature, 0.5 mol/L for the NaOH concentration, 2 g per unit weight of CRH for the NaAlO2 concentration, and 12 h for the reaction time. It is also found that aluminum foil can be used instead of NaAlO2. An SEM observation reveals that the CRH surface is covered with a large amount of zeolite particles. The adsorption experimental result suggests that the prepared adsorbent is useful to remove NH4+ at a low concentration.
Batch anaerobic digestion (AD) of residual stems, fruits and leaves of tomato plants was carried out to assess potential methane (CH4) gas recovery from plant residues in tomato hydroponics. The cumulative CH4 gas yielded from the substrates for fifty days was around 300 mL CH4 g VS-1, which value is comparable to that from other substrates in practical use, indicating that the energy recovery from tomato residues through batch AD is feasible. Two different kinetic AD models for the generation of CH4 gas from tomato residues were compared and verified to characterize AD of each substrate and obtain knowledge about stable operation of a scaled-up AD plant. The result shows that a 2-pool, 2-step model is superior to a first-order kinetic model in better data fitting and more process information throughout the experimental period.
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