Makoto Kiyota

The effect of gravity on surface temperature and net photosynthetic rate of plant leaves.

To clarify the effects of gravity on heat/gas exchange between plant leaves and the ambient air, the leaf temperatures and net photosynthetic rates of plant leaves were evaluated at 0.01, 1.0, 1.5 and 2.0 G of 20 seconds each during a parabolic airplane flight. Thermal images of leaves were captured using infrared thermography at an air temperature of 26 degrees C, a relative humidity of 15% and an irradiance of 260 W m-2. The net photosynthetic rates were determined by using a chamber method with an infrared gas analyzer at an air temperature of 20 degrees C, a relative humidity of 50% and a photosynthetic photon flux of 0.5 mmol m-2 s-1. The mean leaf temperature increased by 1 degree C and the net photosynthetic rate decreased by 13% with decreasing gravity levels from 1.0 to 0.01 G. The leaf temperature decreased by 0.5 degree C and the net photosynthetic rate increased by 7% with increasing gravity levels from 1.0 to 2.0 G. Heat/gas exchanges between leaves and the ambient air were more retarded at lower gravity levels. A restricted free air convection under microgravity conditions in space would limit plant growth by retarding heat and gas exchanges between leaves and the ambient air.

Effects of Air Current on Transpiration and Net Photosynthetic Rates of Plants in a Closed Plant Production System

The effects of the air current speed less than 1 m s-1 on transpiration (Tr) and net photosynthetic rates (Pn) of sweetpotato leaves and on a canopy of rice plants were determined using a chamber method and a combination of micro-meteorological and weighing methods, respectively. The effects of vertically downward moving and horizontal air currents on the Tr were also compared using a model plant canopy made from wet papers. The Tr and Pn of sweetpotato leaves were doubled as the air current speed increased from 0.01 to 0.3 m s-1 and was almost constant at air current speeds 0.3–1.0 m s-1. The Tr and Pn of the rice plant canopy increased linearly by 2.5 and 2 times, respectively, as the horizontal air current speed increased from 0.01 to 0.8 m s-1. Horizontal air current speeds above lms-1 are necessary to obtain maximal Tr and Pn of the canopy. The Tr of the model plant canopy was 2–3 times greater with the vertically downward air current than in the horizontal air current in an air current speed of 0.15–0.3 m s-1. A vertically downward air current at 0.3 m s” around leaves would be adequate for promoting Tr and Pn and thus plant growth in a closed plant production system.

Effects of air current speed on gas exchange in plant leaves and plant canopies

To obtain basic data on adequate air circulation to enhance plant growth in a closed plant culture system in a controlled ecological life support system (CELSS), an investigation was made of the effects of the air current speed ranging from 0.01 to 1.0 m s-1 on photosynthesis and transpiration in sweetpotato leaves and photosynthesis in tomato seedlings canopies. The gas exchange rates in leaves and canopies were determined by using a chamber method with an infrared gas analyzer. The net photosynthetic rate and the transpiration rate increased significantly as the air current speeds increased from 0.01 to 0.2 m s-1. The transpiration rate increased gradually at air current speeds ranging from 0.2 to 1.0 m s-1 while the net photosynthetic rate was almost constant at air current speeds ranging from 0.5 to 1.0 m s-1. The increase in the net photosynthetic and transpiration rates were strongly dependent on decreased boundary-layer resistances against gas diffusion. The net photosynthetic rate of the plant canopy was doubled by an increased air current speed from 0.1 to 1.0 m s-1 above the plant canopy. The results demonstrate the importance of air movement around plants for enhancing the gas exchange in the leaf, especially in plant canopies in the CELSS.

Heat and Gas Exchanges between Plants and Atmosphere under Microgravity Conditions

Abstract:  Fundamental studies were conducted to develop a facility having an adequate air circulation system for growing healthy plants over a long term under microgravity conditions in space. To clarify the effects of gravity on heat and gas exchanges between plant leaves and the ambient air, surface temperatures and net photosynthetic rates of barley leaves were evaluated at gravity levels of 0.01, 1.0, and 2.0 g for 20 sec each during parabolic airplane flights. Thermal images were captured using infrared thermography at an air temperature of 22°C, a relative humidity of 18%, and an irradiance of 260 W/m2. The net photosynthetic rates were determined by means of a chamber method with an infrared gas analyzer at an air temperature of 20°C, a relative humidity of 50%, and photosynthetic photon fluxes (PPFDs) of 250 and 500 μmol/m2/sec. Mean leaf temperatures increased by 1.9°C with decreasing gravity levels from 1.0 to 0.01 g and decreased by 0.6°C with increasing gravity levels from 1.0 to 2.0 g. The increase in leaf temperatures was greater at the regions closer to the leaf tip and at most 2.5°C over 20 sec as gravity decreased from 1.0 to 0.01 g. The net photosynthetic rate decreased by 20% with decreasing gravity levels from 1.0 to 0.01 g and increased by 10% with increasing gravity levels from 1.0 to 2.0 g at a PPFD of 500 μmol/m2/sec. The heat and gas exchanges between leaves and the ambient air were suppressed more at the lower gravity levels. The retardation would be caused by heat and gas transfers with less heat convection. Restricted free air convection under microgravity conditions in space would limit plant growth by retarding heat and gas exchanges between leaves and the ambient air.

Growth characteristics and yield of carrots grown in a soil ridge with a porous tube for soil aeration in a wet lowland

The growth characteristics and yield of carrots grown in a soil ridge with an aeration treatment were compared with those of carrots grown in a conventional ridge as a control under wet lowland field conditions. For the aeration treatment, a plastic porous tube was placed in the soil ridge. Water depth between the ridges in the aeration treatment and the control was kept at 20 mm throughout the growing period in order to imitate the wet soil conditions in tropical and subtropical lowlands. The fresh and dry weights of the storage root were 1.9 and 1.7 times greater, respectively, in the aeration treatment than in the control. The maximum root length in the aeration treatment was 1.8 times greater than in the control. The length of the leaf lamina and the leaf area per plant were greater in the aeration treatment than in the control. The fresh and dry weights of the total phytomass per plant were approximately 1.6 times greater in the aeration treatment than in the control. The fresh weight of the above-ground part was 1.3 times greater in the aeration treatment than in the control. The net photosynthetic rate and edible biomass index were greater in the aeration treatment than in the control. Carrot production in wet lowlands is possible if adequate aeration of the soil ridges is provided.

Plant growth and gas balance in a plant and mushroom cultivation system

In order to obtain basic data for construction of a plant cultivation system incorporating a mushroom cultivation subsystem in the CELSS, plant growth and atmospheric CO2 balance in the system were investigated. The plant growth was promoted by a high level of CO2 which resulted from the respiration of the mushroom mycelium in the system. The atmospheric CO2 concentration inside the system changed significantly due to the slight change in the net photosynthetic rate of plants and/or the respiration rate of the mushroom when the plant cultivation system combined directly with the mushroom cultivation subsystem.

Carbon dioxide and oxygen budgets of a plant cultural system in a CELSS — A case of cultivation of lettuce and turnips

In order to collect basic data about CO2 and O2 budgets of a plant cultural system in a CELSS, the variation of the CO2 absorption rates of lettuce and turnips were observed during the growing period, under different conditions. The O2 release rates were deduced from the CO2 absorption rates multiplied by 32/44. As a result, when the light intensity, the photoperiod and the atmospheric CO2 concentration increased, the rates also increased. The effects on the turnips were more significant than those on the lettuce. Turnips at 310 micromoles/m2/s of PPFD, 24 hours of photoperiod and 1100 ppm of CO2 concentration grew most actively in the present experimental conditions. One turnip absorbed 32.3 g CO2 and released 23.5 g O2 for 6 days between 24 days and 30 days after sowing.

Effect of wind velocity on ethylene release from lettuce plants

Effect of wind velocity on ethylene release rate of intact lettuce plant was investigated. Lettuce plants were grown at wind velocities of 0.1, 0.4, 0.8, and 1.4 m s-1 for 25 to 33 days and then used for ethylene measurement. When ethylene release rate of the plants grown at a wind velocity of 0.1m s-1 was measured at wind velocities of 0.2, 0.6 and 1.0m s-1 the rate was not affected by wind velocity. This result indicates that ethylene diffusion from lettuce leaf to atmosphere is not affected by boundary layer conditions. When ethylene release rate of the plants grown at wind velocities of 0.1, 0.4, 0.8 and 1.4 m s-1 was measured at the same wind velocity as growing conditions, the rate was scarcely increased by high velocity of wind. A strong wind (4.0 m s-1), which induced wounding damage in small areas of the leaves, had no measurable effect on a ethylene release of the whole plant.

Effects of Temperature and Irrigation on Fruiting of Sawdust-Culture Lentinus edodes in Environmental Controlled Facilities

Effects of temperature and interval of watering time on the yield and the morphological characteristics of fruit-bodies of shiitake mushroom (Lentinus edodes) was studied with sawdust-culture method. Four treatments including two different temperatures (15°C constant and 23°C (0600-1800 hr) /15°C (1800-0600 hr) ) and two different intervals of watering time (every 24 and 48 hr) were applied to two different commercial sawdust-cultured shiitake mushrooms.When the medium was watered every 24 h, fresh yield of fruit-bodies was 1.3 times as much as that watered every 48 h. In addition, the fruit-bodies could be harvested earlier, the fresh weight per fruit-body and its water content was higher, its size was larger and its cap was thinner than those watered every 48 h.When the temperature was 23/15°C, the fresh weight per fruit-body and the number of harvested fruit-bodies tended to be larger than those at the temperature of 15°C constant. The start time of harvest was 5-10 days earlier than that at 15°C. The length of the stipe was longer and the cap was thinner than those at 15°C.It was obvious that the temperature and the interval of watering time affected the yield and the shape of the fruit-body of shiitake mushrooms using sawdust-culture method.