Evaluation of photosynthate accumulation and distribution and radiation use efficiency in roses in relation to irradiance and night temperature

The optimum night temperature (NT) for assimilate accumulation and use efficiency in cut rose 'Rote Rose' changes according to daily irradiance conditions. Single stem rose plants (Rosa hybrida L. 'Rote Rose') were grown in separate growth chambers with combinations of two PAR conditions (407 μmol m^-2s^-1 and 143 μmol m^-2s^-1) and three NT conditions (10°C, 14°C, and 18°C). While PAR mainly influenced the growth of plants directly related to carbon assimilation, NT mainly affected the development of the plants. The number of days to bud break or harvest increased by 90% or 35%, respectively, as NT decreased from 18°C to 10°C, regardless of PAR. Shoot blindness was strongly dependent on PAR. Low PAR resulted in up to 57% of the shoots developing into blind shoots. Daily dry mass accumulation rate (DAR, mg/day) was influenced more by PAR than by NT. Under high PAR, the relation between DAR and NT was shown to be positively linear and the highest DAR was observed at 18°C NT. Under low PAR, however, a parabolic relation was found with the vertex at 14°C NT. Radiation use efficiency (RUE, mg DM mol^-1 m^-2 PAR) responded to NT similar to DAR and was higher at low PAR (8.6-11.4 mg mol^-1 m ^-2) than at high PAR (4.6-6.6 mg mol^-1 m^-2), and the highest RUE (11.4 mg mol^-1 m^-2) was observed at 14°C NT. Distribution of DAR to different parts of plants was not shown to be significant, except for floral buds to which distribution was inhibited to 9.3% of the total DAR at 10°C NT at low PAR compared to an average of 23% with other treatments. From the above results, regression models have been developed to predict DAR and RUE based on PAR and NT in different parts of plants.