Day and night temperatures, daily light integral, and CO2 enrichment affect growth and ̄ower development of Campanula carpatica `Blue Clips'

Campanula carpatica Jacq. `Blue Clips' plants were grown in a greenhouse under nine combinations of day and night temperatures created by moving plants every 12 h among three day/ night temperatures (15, 20, and 258C). At each temperature, there were three daily light integrals (DLI; 4.2, 10.8, and 15.8 mol mÿ2 per day, averaged over the experimental period) created with varying supplemental light, and ambient ( 400 mmol molÿ1) and enriched ( 600 mmol molÿ1) CO2 concentrations. Time to ̄ower was closely related to average daily temperature (ADT), and was not signi®cantly affected by the day or night temperatures delivered to achieve a speci®c ADT. Time to ̄ower was not largely affected by DLI or CO2 enrichment. As plant ADT increased between 15 and 258C, ̄ower diameter decreased about 1 mm per degree and was not related to the difference between day and night temperatures (DIF). Flower diameter was smallest and least sensitive to changes in temperature at lower DLI and at ambient CO2 levels. There were 10 less ̄ower buds and 0.3 g less dry mass per plant at ®rst ̄ower for every 18 increase in plant ADT at high and medium DLIs. Flower bud number and dry mass were relatively low and less sensitive to changes in ADT at low DLI, and increased slightly with CO2 enrichment at medium and high but not at low DLI. Plant height was not related to ADT, but increased linearly as DIF increased from ÿ6 to 128C at all DLIs, but the response was stronger under low DLI than high and medium DLIs. Flower bud number and dry mass were correlated closely with the ratio of DLI to daily thermal time (base temperature of 08C). Flower bud number and dry mass were highest when C. carpatica plants Scientia Horticulturae 87 (2001) 93±105 * Corresponding author. Tel.: ‡1-517-353-6628; fax: ‡1-517-353-0890. E-mail addresses: [email protected] (G. Niu), [email protected] (R.D. Heins). 0304-4238/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 4 2 3 8 ( 0 0 ) 0 0 1 6 4 3 were grown at 158C with a DLI of 10±15 mol mÿ2 per day. # 2001 Elsevier Science B.V. All rights reserved.