A computer controlled semiclosed net CO2 exchange measurement system, employing an infrared gas analyzer and mass flow controllers to inject pure CO2 at preset rates, has been developed for measuring whole plant net CO2 exchange and net C gain in a controlled environment (i.e. CO2, light, and temperature). Data Many gas-exchange systems based on infrared gas analysis of CO2 have been designed to measure photosynthesis, photorespiration, and dark respiration of single plant leaves (2, 9, 15). However, measurement of leaf photosynthesis does not necessarily predict plant growth and crop productivity (3), since individual leaves are not representative of the photosynthetic behavior of the entire canopy. Furthermore, analysis of the metabolism of a single leaf does not take into account dark respiration of the entire plant and ignores both the problem of partitioning of photoassimilates and the evaluation of crop quality (5,14). A positive correlation between leaf photosynthetic rate and crop productivity requires considerable sampling (3,12) and is most easily obtained when studying a crop for which the vegetative portion of the plant (e.g. leaves or roots) is harvested for market (8,14,17). In spite of the problems in correlating photosynthesis with yield it is well known that over 95% of the dry matter of a plant is derived from photosynthesis and further that carbon (C) obtained from photosynthesis comprises approximately 40% of the plant dry weight under most growth conditions (1, 7). Even so, CO2 analysis itself is rarely used as a means of measuring growth rate.Growth rate is frequently defined as an increase in the physical size of the plants expressed simply as an absolute increase in dry weight with time (e.g. g gained * week-1) or as a relative increase I

Two cultivars of Rosa hybrida L.—‘Samantha’ and ‘Gabriella’—budded on R. manetti rootstock were grown at root-zone temperatures of 13°C (control-ambient), 18°, and 23° at 13° air night temperature under natural light conditions or natural light plus 55 ± 5 µmol s−1m−2 HPS nightly. Stem length of ‘Samantha’ roses was increased at 23° and the quality index was reduced at 18° soil temperatures. An interaction between light and soil temperature occurred in ‘Gabriella’ roses, where stem length and diameter, fresh weight, quality index, and yield were improved with increased soil zone temperature under natural daylength conditions, but the reverse was the case with HPS supplementary irradiation. Scion cultivar differences on the identical rootstock influenced the response of the plants to root-zone heating and HPS lighting.

Three cultivars of Gerbera jamesonii H. Bolus ex Hook. f. planted in peat bags were grown in greenhouses at 16 °C/12.5 °C/12.5 °C or 16 °C/12.5 °C/22 °C day/night/root-zone temperatures. The yield and stem length of the three gerbera cultivars were substantially enhanced by root-zone heating (16 °C/12.5 °C/22 °C). Placing peat bags on heated soil was effective in maintaining the root-zone temperature for Gerbera production.Key words: Gerbera jamesonii, greenhouse production

Stock plants of Chrysanthemum morifolium Ramat. cv. Dramatic were grown in clear plastic chambers within a greenhouse to study the effects of CO2 enrichment at a commercial level (1375 ppm) and supplementary high pressure sodium (HPS) lighting on yield and quality of cuttings. Based on increases in the number of cuttings, stem length, leaf area, fresh weight, and dry weight, CO2 enrichment during the day period was beneficial, regardless of the use of HPS lighting. When HPS lighting was used for 24 hours, the most effective time to add C02 was during the day because the low light level of 60 µmol s−1m−2 provided solely by the lamps was insufficient to make night CO2 enrichment a beneficial practice.