ENHANCEMENT OF SHORT-TERM NITROGEN UPTAKE BY GREENHOUSE ROSES UNDER INTERMITTENT N-DEPRIVATION

A recirculating nutrient solution system was utilized to study the eff ect of intermittent N deprivation on N uptake by mature 'Royalty' rose over the course of one flowering cycle. Plants received a nutrient so lution lacking N for 4, 8 or 16 days, after which one containing NO3-N (0.75 mM) was supplied for 4 days. N-deprivation resulted in a 2-3 fo ld increase in N uptake rate compared to control plants supplied conti nuously with N. The magnitude of this deprivation-enhanced N uptake wa s not affected by either the duration of N-deprivation or the plant de velopmental stage. Over the course of the flowering cycle, the total c umulative N uptake by the plants was 95, 66, and 44% of the control pl ants in the 4, 8 and 16-day deprivation treatments, respectively. A ch aracteristic diurnal pattern of N uptake occurred in both N-starved an d control plants. Uptake oscillated between minimum rates in the morni ng and maximum rates in the evening, the latter occurring 4-6 hr after the maximum rate of transpiration.