To understand long-term association between canopy-scale photosynthesis and growth, we continuously and simultaneously measured the net photosynthetic rate (Ac) and leaf area index (LAI) of a spinach canopy from transplantation to harvesting. This long-term measurement was enabled by combining an open-type flux chamber method and image analysis of top-of-view canopy photographs. The photosynthetic photon flux density (PPFD) was the major determinant of Ac during a short-term period, but the change in Ac was significantly amplified by an increase in LAI during a long-term period. LAI, measured with reliable accuracy from gap fractions (projected non-leaf areas) of top-of-view photographs, increased exponentially through the growth period. These results indicate a positive feedback loop between photosynthesis and growth (i.e., the growth of leaves amplifies photosynthesis, and the amplified photosynthesis further accelerates the growth of leaves). Consequently, a linearity was found between cumulative canopy net photosynthesis (∑Ac) and LAI, implying that throughout the growth period, a fixed proportion of dry matter was partitioned to the leaves and that the leaf area was expanded in proportion to the partitioned dry matter. This linearity between ∑Ac and LAI also suggests that growth of a leafy vegetable canopy can be predicted from canopy photosynthesis.
Temperature control, fertilization management and long-day treatments are commonly implemented to achieve optimal growth control in strawberry (Fragaria × ananassa Duch.). Control of these parameters has typically relied on visual evaluation of plants by producers. For advanced production control, it is necessary to continuously monitor growth and amounts of light received. In this study, we quantified the height of strawberry plants, and leaf area receiving direct sunlight in different leaf layers over time using Kinect, a depth sensor. Data from the sensor enabled evaluation of temporal changes in plant height and of the differences in the stratification of strawberry plants grown in greenhouses at two different low nighttime temperatures. The amount of light received by different layers of the entire plant community could be estimated from sensor measurements, and was directly correlated with yield and dry weight. Our results demonstrate that a depth sensor like Kinect can quantify essential information on strawberry growth and amounts of light received. Further improving the accuracy of measurement by sensors could lead to the development of effective cultivation management methods based on the amount of photosynthesis and growth of plants.
Sesame (Sesamum indicum) seedlings were cultured under regimes of differing air temperature and photoperiod in a plant factory under artificial light to evaluate these factors for inducing leaf browning. In experiment 1, plants were cultured under continuous lighting either at a constant air temperature of 28℃, or fluctuating air temperature of 28℃ with a 10℃ difference (06:00―18:00; 33℃, 18:00―06:00; 23℃), or with a 15℃ difference (06:00―18:00; 35.5℃, 18:00―06:00; 20.5℃). Leaf browning was induced intensively by constant 28℃ and avoided by air temperature fluctuation, especially with the 15℃ difference. Shoot fresh weight and number of nodes were not significantly different among all the treatments. In experiment 2, plants were cultured under continuous lighting or a 12-h photoperiod either at a constant (28℃) or a fluctuating temperature (28℃ with a 15℃ difference). Leaf browning was induced by constant 28℃ and avoided by air temperature fluctuation, regardless of photoperiod. Shoot fresh weight under a treatment with combination of temperature fluctuation with 15℃ difference and continuous lighting was significantly greater than that under the other treatments. These results suggest that leaf browning of sesame seedlings is induced by constant air temperature and can be prevented by air temperature fluctuation.
We investigated the effects of zinc (Zn) supplementation on the growth and Zn accumulation of the edible cactus Nopalea cochenillifera (L.) Salm-Dyck by exposing hydroponically grown cladodes of N. cochenillifera to 0 ppm, 50 ppm, or 200 ppm of Zn for 10 weeks and assessing their growth. Daughter cladodes emerged from the mother cladodes and continued to grow at all three concentrations of Zn but growth of the daughter cladodes was inhibited and the fresh weights of both the daughter and mother cladodes were lower with the 200 ppm treatment. A high Zn concentration in the nutrient solution greatly increased the Zn concentration in the plant parts, with the roots of plants that were treated with 50 ppm and 200 ppm surpassing the threshold levels of Zn hyperaccumulator plants. A larger amount of Zn accumulated in the daughter cladodes with the 50 ppm treatment than with the 200 ppm treatment but there was no significant difference between these treatments in the other plant parts. These results suggest that the supplementation of nutrient solution with Zn affects the growth of N. cochenillifera and that this plant has a high capacity for accumulating Zn.
We investigated the effect of air temperature on the growth of the medicinal plant Pinellia ternata Breit. collected from the four prefectures, Fukushima, Kyoto, Nagasaki, and Okinawa prefectures. Plants were grown for 15 weeks in phytotrons controlled at air temperatures of 20, 25, and 30°C. In the Kyoto lines, the highest corm yield was observed at 25°C, whereas the corm yields in Fukushima, Nagasaki, and Okinawa lines did not differ significantly with respect to yield among the three growth temperature conditions. Therefore, in this study, the temperature effects on the photosynthesis by P. ternata collected from the three prefectures of Kyoto, Nagasaki, and Okinawa were investigated. Obvious effects of air temperatures were not observed in the plant photosynthesis for all regions. Thus, air temperature does not affect the yield through the photosynthesis in the P. ternata.