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A simplified closed system consisting of a plant growth chamber coupled to a decomposition chamber was used to study carbon exchange dynamics. The CO2 produced via the decomposition of wheat straw was used for photosynthetic carbon uptake by wheat plants. The atmosphere of the two chambers was connected through a circuit of known flow rate. Thus, monitoring the CO2 concentrations in both compartments allowed measurement of the carbon exchange between the chambers, and estimation of the rate of respiration processes in the decomposition chamber and photosynthetic rate in the producer chamber. The objective for CELSS research was to simulate a system where a compartment producing food via photosynthesis, would be supplied by CO2 produced from respiration processes. The decomposition of biomass by the decomposer simulated both the metabolism of a crew and the result of a recycling system for inedible biomass. Concerning terrestrial ecosystems, the objective was to study organic matter decomposition in soil and other processes related to permanent grasslands.

An experiment of Artificial Ecosystem in closed growth chambers is described. It comprises a biomass producer compartment coupled with a decomposer compartment. A model of carbon cycle is presented, simulating the CO2 changes in atmosphere and the carbon status in plants and in the decomposer system. Results of variation in several parameters such as photoperiod, rate of photosynthesis, percentage of harvested biomass introduced in decomposer, kinetics of biomass decomposition, are presented. Positive conclusions are deduced about the feasability of real experiments without particular control of CO2 nor buffering system. Applications in studies on plant-soil-atmosphere ecosystems, for spatial and terrestrial researches, are discussed.

The present study investigates the relationships between nitrogen uptake, transpiration, and carbon assimilation. Plants growing on nutrient solution were enclosed for 10-16d in a growth chamber, where temperature, photon flux density, vapour saturation deficit and CO[SUB2] concentration were controlled. One of these factors was modified every 4 to 5 d. Shoot photosynthesis and root and shoot respiration were recorded every half-hour. Nitrogen uptake from the root medium and plant transpiration were measured daily. In most cases, an increase in photon flux density led to increases in transpiration, net daily carbon assimilation, and nitrogen uptake. By modifying transpiration rate without changing photosynthesis (varying vapour saturation deflcit), or by modifying transpiration and carbon assimilation in opposite ways (varying CO[SUB2] air concentration), it was shown that nitrogen uptake does not follow transpiration, but is linked to the carbon uptake of the plant. When light was increased from low to interrnediate levels, the N uptake/C assimilation fatio remained constant. At higher photon flux density, this ratio declined markedly. It is proposed that in the first case, growth is limited by carbohydrate availability, thus any increase in carbon assimilation leads to a proportional increase in nitrogen uptake, in contrast to the second situation where carbohydrates may accumulate in the plant without further nitrogen requirement. [ABSTRACT FROM AUTHOR]

A model for the distribution of radiation incident on leaves in an isolated apple tree is presented. The simulated area of shadow cast by a tree compared well with measured values. The radiation model is combined with leaf models of photosynthesis and stomatal behaviour to simulate diurnal variations in the exchanges of carbon dioxide and water by the tree. Satisfactory correspondence was obtained when observed rates of transpiration and photosynthesis were compared with simulations. Further simulations indicated the diurnal patterns of transpiration and photosynthesis to be expected for trees with various shapes and leaf areas. [ABSTRACT FROM AUTHOR]

A cheap CO2 enrichment system was designed to perform continuous gas exchange measurements of branches of mature European beech trees (Fagus sylvatica L.). Branches were grown at ambient (350 cm3 m-3) and elevated CO2 (700cm3 m-3) during the whole 1992 leafy period. Leaks resulting from airtightness defaults in the system appeared to be low enough to measure accurately net CO2 assimilation and transpiration rates during the day. However, the CO2 exchange rates during the night (respiration) were too low to allow accurate measurements. Elevated CO2 had a great effect on the net assimilation rate of branches via its influence on both the C3 photosynthetic pathway and the shade-tolerance of beech trees (85% increase). The A/Ca curves showed no acclimation effect to high CO2, both control and enriched branches increasing their net assimilation in the same way. The decrease of net assimilation rates in mature leaves was similar for both control and enriched branches, The pattern of daily transpiration rates remained the same for both control and enriched branches, hence we can assume that there was no visible CO2 effect on stomata. [ABSTRACT FROM AUTHOR]