Leafy vegetables cultivated in greenhouses during the winter are sometimes exposed to cold air from outside the greenhouse to enhance sugar and nutrient content. To analyze the possible involvement of photosynthetic and respiratory activities in this process, we evaluated the gas-exchange activity of spinach (Spinacia oleracea L.) plants cultivated in an unheated greenhouse in mid-winter in Sapporo, where the daily mean air and soil temperatures are approximately -5 and 0 °C, respectively. Shoot fresh weight showed little increase, whereas the net leaf photosynthetic rate (Pn) attained 20 µmol m-2 s-1 and the CO2 concentration in the greenhouse ([CO2]) was sometimes lower than 200 µmol mol-1, which was suggestive of active photosynthetic CO2 uptake. After its peak in the morning, Pn decreased in the afternoon, presumably owing to ‘midday depression’ caused by suppressed water uptake in the root zone. Observed diurnal [CO2] change was consistent with a significant CO2 uptake during the daytime. The change also suggested that respiration was active immediately after sunset and suppressed at night. In addition, we calculated the whole-greenhouse CO2 emission rate (R) as a measure of night respiration in the plants, taking into account the air ventilation of the greenhouse. The R value was positive under sub-zero air temperatures in the greenhouse and was positively correlated with the nighttime air and soil temperatures. These experimental data suggest active photosynthesis and respiration of winter-sweetened spinach in the greenhouse, despite the low air and soil temperatures and growth retardation, and implies their involvement in the sweetening process.
In cool climates, low temperature is critical for growth and yield of sweet potato (Ipomoea batatas L.). Despite its negative effects, few studies have quantified the impact. We evaluated effects of soil temperature (Ts) on growth and yield in sweet potato from 2-year field trials in northern Japan. Ts was controlled by three steps using plastic mulch at different colors (green, black and white) with different Ts ranged in 21~24°C especially at early growth before the surface of the mulch covered by plant canopy. Higher Ts significantly increased vine elongation, branching, and leaf appearance, and the magnitude of increased by higher Ts decreased with proceeding growth stages. Increasing Ts significantly increased leaf chlorophyll content and stomatal conductance. Across treatments and years, aboveground biomass was linearly and positively correlated with Ts, and 58 g m-2 increased in aboveground biomass was observed per 1°C increase in Ts. However, final storage root fresh yield was not significantly affected by high Ts over years. Increased individual storage root weight at high Ts was offset by decreased storage root number. The present quantitative study tested in northern Japan showed that, the enhanced aboveground growth in sweet potato at higher Ts especially during early growth did not contribute to increase of storage root yields in cool climates.
This study was conducted to analyze the effectiveness of using reflective mulch under the stands of oil palm plants of several ages on the intensity of solar radiation reflection, growth, chlorophyll content, and photosynthetic characteristics of soybeans. A nested design was used, with the first factor of oil palm age group consisting of open land and land under oil palm stands aged 4, 5, and 8 years. The second factor was the reflective mulch that included land without mulch, land with inorganic reflective mulch, and land with organic reflective mulch. The use of reflective mulch in the soybean-oil palm intercropping system was able to increase the reflection intensity of surface solar radiation, as well as increase the soybean solar radiation interception. The use of inorganic and organic reflective mulch significantly increased the leaf area, specific leaf weight, and soybean stomatal density. Organic reflective mulch led to significant reductions in the amount of chlorophyll A and B content. The photosynthetic rate of soybean in lower leaves was increased significantly. Inorganic reflective mulch resulted in significant reductions in the rate of transpiration, intercellular CO2 concentration, and conductance of soybean stomata in lower leaves. The use of reflective mulch contributed to improved soybean performance under oil palm stands. The use of organic reflective mulch for soybean grown under oil palm stands aged up to 5 years resulted in better growth rates due to the increased intensity of solar radiation reflected from the surface. However, the reflection effect could not meet the needs of soybean solar radiation on land under oil palm stands aged >5 years due to the very low transmission. Therefore, the use of organic reflective mulch is more effective and efficient in the soybean-oil palm intercropping system until the oil palm reaches the age of 5 years.
Rice is the most important cereal crop in Japan, and therefore the impact of projected climate change on its production and quality has been assessed using rice growth models accounting for the effects of rising temperature and atmospheric CO2 concentration ([CO2]) on important growth processes. Recent experimental studies, however, have shown some negative effects of interactions between [CO2] and temperature on yield and quality of rice which were not accounted for by previous impact assessments. This study examined the importance of [CO2]×temperature interactions in the nationwide impacts of climate change on grain yield and quality of rice in Japan by 2100. We introduced new functions accounting for the effects of interactions on yield. Then we adopted the acceleration by elevated [CO2] in the estimation of the occurrence of chalky grains, an indicator of appearance quality of rice. We applied the modified model to Japan at a spatial resolution of 1 km using 10 climate scenarios (5 Global Circulation Models×2 representative concentration pathways [RCPs]) from 1981 to 2100. The effects of the newly introduced negative effects of [CO2]×temperature were evaluated by comparing simulations with and without the interaction in each scenario. Nationwide production was estimated to decrease by up to 28% and the percentage of white chalky grains to increase up to 16% relative to the previous assessment results, especially in RCP8.5, in which larger increases were projected in both temperature and [CO2]. The result suggests that the positive effect of elevated [CO2], which had been expected to offset the negative effect of increased temperature on rice productivity, may be limited in the future, and rice quality degradation may be more severe than predicted previously.
The statistical characteristics of 1789 deaths, 1552 injuries and 1904 disasters caused by lightning based on the 2009 to 2018 National Lightning Disaster Compilation of mainland China were analyzed. The results showed that males accounted for 53% of casualties. Lightning disasters were more common in the east and south than in the west and north. The number of lightning disasters and casualties in the south accounted for 82.98% and 82.94% of the totals, respectively. May to August of each year is the intensive period of lightning disasters in China, and the number of deaths, injuries and disasters caused by lightning during these four months accounted for 84.80%, 79.45% and 82.77% of the total numbers per year, respectively. From 2009 to 2018, the annual injury and death rates per million people in China were 0.13 and 0.12, respectively. After population weighting, the high death rate of lightning disaster shows a certain trend of transferring from the concentrated area to the sparsely populated area, after area weighting, the casualty density was higher in small provinces and lower in large provinces . The analysis of the environments in which lightning disaster casualties occurred found that environments closely related to agriculture, such as farmland (35%) and paddy fields or ponds (4%), accounted for nearly 40% of the casualties; accordingly, rural farmers were the main victims, accounting for 80.96% of the total casualties. Lightning protection and disaster reduction measures in rural agricultural areas should be the focus of future work.
Manually operated closed-chamber methods have been used extensively to measure CH4 emissions from rice paddies, but the long chamber deployment time (e.g., 30 min), together with the labor required for gas sampling and subsequent analysis by gas chromatography severely limit their usefulness for multiple, high-throughput measurements. The objective of this study was to develop a modified closed-chamber method suitable for high-throughput measurements. The design of the modified system is based on a conventional method, but uses a portable spectroscopic gas analyzer and a newly developed dehumidification system. Results of a series of test operations showed that the use of a portable gas analyzer substantially reduced the time needed for each chamber deployment to as little as 4–5 min. A simple dehumidification system employing a selective water vapor-permeable tube was introduced to effectively dehumidify the sample gas so that the risk of water condensation was removed without attenuating the CH4 concentration signal. The chamber must be equipped with a fan to ensure that the chamber air is well mixed and to attain representative CH4 concentration values. The new method is suitable for high-throughput CH4 emission measurements and can also be used for studying bubbling CH4 emissions.