SEASONAL CARBOHYDRATE AND TOTAL NITROGEN DISTRIBUTION IN ROSE PLANTS: DEVELOPMENTAL AND GROWTH IMPLICATIONS

Year round production of cut flowers in rose crops, demands a continuous supply of sugars for the growing flower bud, which competes with the need for sugar at the root level, in particular, at roots devoted to absorption processes. This led to the study of carbohydrate distribution in rose plants at the peak of their flower productive period. Rose plants, cv. Dallas, were grown in a greenhouse with a perlite hydroponic system. Growing practices were the usual in all-year-round commercial production, which included the application of the shoot bending technique. Flower production was registered throughout the year and a set of four plants was sampled in April, July, November and February. These were separated into three parts, roots, leaves and stems (photosynthetic compartment), and flowers. Each part was weighed and analysed for soluble sugars and starch and total nitrogen. The results showed that, compared to the other seasons, soluble sugars were highest in the aerial parts in the spring and the starch and the nitrogen contents were lower in the spring than in the winter. All this coincided with high levels of incident solar radiation on the canopy and intense flower production. In the summer the content of soluble sugars and starch decreased. The drop in sugars was most outstanding in the aerial parts in this period. This coincided with the use of a shading net over the canopy, which reduced the incident radiation and coupled this reduced radiation with high temperatures and saturation deficit. The result was the reduction of biomass production in this season. Thermal time in the autumn was similar to the spring and was lower than in the summer. This resulted in an increase in soluble sugars in the photosynthetic compartment with respect to the summer. Nitrogen contents reach their highest value in the aerial parts in this period. The increase of starch and soluble sugars in roots in the winter, suggests a notable change of sink strength, from the photosynthetic compartment to the roots. This seems to agree with a slow down in the plant activity in this season. These results suggest a relationship between the distribution of assimilates and nitrogen among the roots and aerial parts and plant growth. The demand for sugars by the different sinks can result in critical competition. More detailed studies are needed to better understand these processes and their link with nitrate uptake in order to apply them to the improvement of crop management.