Short-term temperature change affects the carbon exchange characteristics and growth of four bedding plant species

Bedding plants are exposed to a wide range of environmental conditions, both during production and in the landscape. This research compared the effect of short-term temperature changes on the CO2 exchange rates of four popular bedding plants species. Net photosynthesis (P-dark) and dark respiration (R-dark) of geranium (Pelargonium xhortorum L.H. Bail.), marigold (Tagetes patula L.), pansy (Viola xwittrockiana Gams.), and petunia (Petunia xhybrida Hort. Vilm.-Andr.) were measured at temperatures ranging from 8 to 38 degreesC (for P-net) and 6 to 36 degreesC (for R-dark). Net photosynthesis of all species was maximal at 14 to 15 degreesC, while R-dark of all four species increased exponentially with increasing temperature. Gross photosynthesis (P-gross) was estimated as the sum of P-net and R-dark, and was greater for petunia than for the other three species. Gross photosynthesis was less sensitive to temperature than either P-net or R-dark, suggesting that temperature effects on P-net were caused mainly by increased respiration at higher temperatures. Gas exchange-temperature response curves were not useful in determining the heat tolerance of these species. There were significant differences among species in the estimated R-dark at 0 degreesC and the Q(10) for R-dark. Differences in the Q(10) for R-dark were related to growth rate and plant size. Large plants had a greater Q(10) for R-dark, apparently because these plants had a higher ratio of maintenance to growth respiration than small plants. The Q(10) of the maintenance respiration coefficient was estimated from the correlation between the Q(10) and relative growth rate, and was found to be 2.5 to 2.6.