Analysis of Photosynthesis and Biomass Allocation for Simulation of Edible and Inedible Biomass Production and Gas Exchange of Main Crops within Ceef 2002-01-2484

The plant system plays roles of edible biomass production, O₂ production, CO₂ removal, and so on, in bioregenerative life support systems. In order to simulate the edible and inedible biomass production and gas exchange of crops, it is necessary to construct reliable dynamic prediction models for each crop considering not only short-term environmental effects but also its long-term effects, because response of plant system is highly dependent on plant age, plant size, and environmental condition experienced by the plant.

Closed Plantation Experiment Facility (CPEF) of Closed Ecology Experiment Facilities (CEEF) has three plantation chambers with artificial lighting system, which has maximum capability for providing PPFD of approximately 1900 μmol·m^-2·s^-1 for crops at canopy top level in these chambers. Each even-aged population of rice and soybean was grown in each plantation chamber. Two experiments with rice and one experiment with soybean were conducted and the second experiment with soybean is to be conducted using these three chambers. In order to examine the long-term effects of CO₂ concentration and temperature on these crops, usual CO₂ concentration and air temperature were set to differ among the three chambers. Growth of different parts and leaf area were investigated at two-weeks interval throughout the whole growth period. The short-term responses of canopy net photosynthesis of rice and soybeans to PPFD, temperature and CO₂ concentration were also investigated in the short-term tests conducted at two-weeks interval.

In rice and soybeans, which are main crops for CEEF, it was elucidated that the long-term higher CO₂ concentration decreased the ratio of leaf area to total dry weight. Although, increasing CO₂ concentration from 350 μL·L^-1 to 700 μL·L^-1 resulted in approximately 30% increase of net canopy photosynthetic rate as the short-term response, the long-term high CO₂ concentration did result in the increase by less than 10% because of higher CO₂ compensation point in the case of rice. These results could be utilized for the construction of the dynamic crop models. As for O₂ production, usefulness of estimation from data on CO₂ uptake and nutritional analysis of crops was discussed.