閉鎖型生態系実験施設での物質循環の概要

摘要

The Closed Ecology Experiment Facilities (CEEF) were installed to collect experimental data for realistic estimation of radiocarbon transfer in the environment. The CEEF are composed of the Closed Plant Experiment Facility (CPEF) and the Closed Animal& Habitation Experiment Facility (CAHEF). Connecting four Plant Chambers (PCs) of the Plant Module (PM) of the CPEF, where 23 crops were cultivated simultaneously in a staggered manner, and the Animal and Habitation Module (AHM) of the CAHEF, where two humans and two goats stayed, two-week closed habitation experiments were carried out three times. In addition to the circulation of food, feed and air constituents, water was also circulated in the facilities during the experiments. The human subjects stayed for two weeks in the CEEF. 92-95% of the humans' food and 79% of the goats' feed were supplied from crops harvested in the CEEF. The amount of CO_2 uptake of crops was iairly stable, with an average of 96 mold~(-1)for the whole habitation period. The production rate of carbon by crops, averaged for the whole harvesting period, was estimated as104 mol-C d~(-1)from harvest data. The assimilatory quotients (= CPO_2/O_2) of rice, soybean and all crops were 0.95, 0.87 and 0.90, respectively, and were all similar to those calculated from their nutritional content. The total amount of CO_2 discharged by respiration of the two humans and two goats was stable, with an average of 53 mold~(-1)for the whole habitation period, corresponding to 55% of the CO_2 absorbed by crop photosynthesis. The average amount of O_2 consumed by the humans and goats was olmol d~(-1), corresponding to 57% of the O_2 produced by the crops. These results were because waste material was not circulated in the system. The respiratory quotient (= CO_2/O_2) of the humans and goats was 0.86. The total amounts of water supplied to and discharged from the crops averaged for the whole habitation period were 2090 and 2080 L d~(-1)respectively. The difference between them corresponded to the amount of water contained in the harvested crops. The total amounts of water supplied to and discharged from the humans and goats averaged for the whole habitation period were 75.2 and 68.2 L d~(-1), respectively. The difference between them was attributed to the amount of withdrawn human urine and evaporation loss during pyrolysis of goat excrement. Only 0.5 kL of water was withdrawn during the 38-week cultivation period, including the 18-week harvesting period in 2006, whereas 46.5 kL of water was withdrawn during the 27-week cultivation period, including the 10-week harvesting period m 2005; however, crop production in 2006 was less than in 2005. It was considered that some constituents, such as those eluted from standing medium, were accumulated in the nutrient solution and an imbalance of minerals in the solution might influence the crop growth. As decreased rice seedling growth mainly led to total crop production, newly made nutrient solution is being used for rice during the only three weeks of seedling growth m 2007. The humans' body weight, which decreased in 2005, did not decrease in 2006. A1-week vegetarian diet for acclimation prior to the habitation experiments worked well to stabilize body weight.