INFLUENCE OF PHOTOPERIOD AND LIGHT INTENSITY ON UPTAKE OF RADIOPHOSPHORUS BY CHRYSANTHEMUM AND PELARGONIUM

The effects of daily photoperiod and light intensity on the uptake of radiophosphorus by Chrysanthemum morifolium ’Princess Anne’ and Pelargonium hortorum ’Irene’ were studied in controlled-environment rooms. The rate of P32 uptake by both species increased with increasing photoperiod over the range 9, 14, and 19 hr per day at an intensity of 1,000 ft-c. The rate of P32 uptake was higher when the 9- and 14-hr photoperiods were started 7 days prior to the application of P32 than when started concurrently with the application of P32. Plants of each species exposed to a 19-hr photoperiod had the same rate of P32 uptake regardless of when the photoperiod was started.There was a progressive increase in the rate of P32 uptake by both species with increasing light intensity over the range of 500, 1,000, and 1,500 ft-c at a daily photoperiod of 17 hr. It is suggested that increased P32 uptake with increased photoperiod and light intensity is related to increased supply of the photosynthate.At a time when normal flower bud initiation is known to occur in Chrysanthemum morifolium, the rate of P32 uptake increased.