Temperature and photoperiod effects on photosynthetic indices of radish (Raphanus sativus L.)

The experiments were performed in 2010 at the Institute of Horticulture, Lithuanian Research Center for Agriculture and Forestry in the phytotron chambers, under controlled environment conditions. The aim of this study was to investigate the effect of different temperatures and photoperiod conditions on photosynthetic pigments accumulation, carbohydrate distribution and assimilative indices of radish (Raphanus sativus L. 'Faraon'). The day/night temperature and photoperiod were maintained at 4 C and 8 hours (F1), 4 degrees C and 16 hours (F2) in freezer chambers and 18/14 degrees C and 8 hours (F3), 18/14 degrees C and 16 hours (F4) in phytotron chambers, respectively. Just after cotyledons formation radishes were transferred to freezer chambers F1 and F2 for low positive temperature further (low-temperature) treatment, other plants were treated under F3 and F4 conditions. 14 days later radishes were moved from F1, F2 and F3 to the F4 conditions till the end of experiment (29 days). Our investigation revealed that low-temperature (4 degrees C) influenced the development of radishes by increasing biomass accumulation in storage organs further (roots) and accelerating plant growth (relative growth rate, net assimilation rate). Increased shoot-to-root ratio and specific leaf area showed that under ordinary temperature conditions (18/14 degrees C) radish grew more leaves but accumulated less assimilative products in roots. The lowest photosynthetic pigments concentration was found under long-day photoperiod independent of temperature treatment (F2 and F4). After the 1(st) measurement, in F2 treatment the highest and in F3 the lowest content of all carbohydrates in roots and leaves further (shoots) were determined but after the 2(nd) measurement there were no big differences between all treatments, because in 29 days growing under ordinary temperature and long-day period the development level of differently treated radishes equalized. In summary, low temperature had the strongest effect on the carbohydrate accumulation in roots and shoots. At the maturity stage, there were no differences in carbohydrate contents. Moreover, the dry weight of roots increased due to carbohydrates allocation from shoots to roots. Under low-temperature and short-day photoperiod relative growth and net assimilation rates of radishes were higher during all experiment.