A simple mathematical model for calculating the concentration of mobile carbon skeletons in the shoot of soya bean plants [Glycine max (L.) Merrill cv. Ransom] was built to examine the suitability of measured net photosynthetic rates (PN) for calculation of saccharide flux into the plant. The results suggest that either measurement of instantaneous PN overestimated saccharide influx or respiration rates utilized in the model were underestimated. If neither of these is the case, end-product inhibition of photosynthesis or waste respiration through the alternative pathway should be included in modelling of CH2O influx or efflux; and even if either of these is the case, the model output at a low coefficient of leaf activity indicates that PN still may be controlled by either end-product inhibition or alternative respiration.

A transparent, cylindrical chamber system was developed to allow measurement of gas-exchange by small crop canopies in the undisturbed plant growth environment. The system is an elaboration of the Minitron system developed previously to compare growth of small plants in different environments within the same general growth area. The Minitron II system described herein accommodates hydroponic culture and separate control of atmospheric composition in individual chambers. Root and shoot environments are compartmented separately to accommodate atmospheres of different flow rate and/or gaseous composition. A series of 0-rings and tension-adjustable springs allow carbon dioxide in the flowing atmosphere to be analyzed without cross-contamination between chamber compartments or from external gas sources. Carbon dioxide has been maintained at set point +/- 9 g m-3 over a range of CO2 concentrations from 382 to 2725 g m-3 and with an atmosphere turnover rate of 136.7 cm3 s-1 by computer-assisted mass flow controllers. Each chamber has dimensions large enough (61 cm internal diameter, 0.151 m3 internal volume) to allow adequate replication of individual plants for statistical purposes (e.g., up to 36 equally-spaced plant holders). No significant variation in growth or photosynthetic rate of leaf lettuce occurred between chambers for a given set of environmental conditions. Gas-exchange rates in different chambers changed to a similar extent as CO2 concentration in the flowing atmosphere or chamber temperature were varied by the same amount. When coupled with appropriate control systems, Minitron II chambers can provide separate controlled environments for multiple small plants with adequate precision and at relatively low cost.

The diurnal trends of gas exchange and chlorophyll fluorescence parameters in four species ( var. and ) were determined and compared with a portable photosynthesis analysis system. Our study revealed that had the lowest light compensation point (LCP), while the other three species had higher LCP (12.37-14.99 μmol m s); had the highest light saturation point (LSP) (1,189 μmol m s), and and had lower LSP with the values being 322 and 345 μmol m s, respectively, and var. showed the intermediate LSP. Both the species and exhibited a typical and obvious decline in net photosynthetic rate ( ) during midday, which was not observed in . This indicated a possible photoinhibition in and as the ratio of variable to maximum fluorescence (Fv/Fm) values were higher in these two species. The minimal fluorescence (F) values were lower in and var. . The diurnal changes of transpiration rate () in all four species presented only one peak, appearing between 11:00 h or 13:00 h. By using simple correlation analyses, it was observed that the environmental factors affecting were different among four species and the main factors were photosynthetic photon flux density (PPFD) and relative humidity especially for and . The results of studying indicated that the four species could be divided into two groups. The species var. and were more adapted to a relatively high irradiance, and and could be grown in moderate-shade environment in order to scale up their growth and productivity.