This study investigated the effects of drought, nitrogen fertilizer and elevated CO2 and its interaction with nitrogen fertilizer on the physiology, growth, and production of the oil crop safflower (Carthamus tinctorius L.) in a semi-controlled glasshouse environment. Three levels of water stress were imposed: rosette (mid-season drought), stem elongation (terminal drought) and rosette to maturity (mid-season + terminal drought). Results indicated that all drought treatments imposed reduced stomatal conductance, but after the relief of mid-season drought plants recovered and as a result there were no significant differences from control in terms of yield components (branch and capital number) and seed number. Terminal drought and mid–season + terminal drought induced significant reductions in branch number (48% and 50%), in capitula number (33% and 67%), in seed number (89% and 92%), in above ground dry weight (30% and 54%) and in individual fresh seed weight (90% and 94%) respectively. However, water stress treatments had no significant effect on the maximum quantum efficiency of PSII (Fv/Fm) in dark adapted leaves compared with the control. Levels nitrogen fertilizer was studied equivalent to 0, 25, 50, 75, 100, 125, 150, 175 kg N ha-1 were evaluated. Safflower responded incrementally to increasing nitrogen applied in a curvilinear asymptotic fashion. Assimilation rate (42%), transpiration rate (32%), stomatal conductance (52%) and LAI (42%) increased III up to 100 kg N ha-1 compared with the control. The above ground dry weight and seed yield associated with WUE continued to increase with each increment in nitrogen rate and above ground dry weight (42%), individual seed fresh weight (76%) and WUE (41%) increased up to 175 kg N ha-1 compared with the control. The effect of elevated CO2, (1000 μmol mol-1) significantly increased assimilation rate (27%) reduced stomatal conductance (29%) and transpiration rate (18%), increased LAI (28%) and above ground dry weight (51%) when measured at anthesis compared with ambient (400 μmol mol-1). At the same time plant organ N content was reduced. At harvest, elevated CO2 increased above ground dry weight (42%) and individual fresh seed weight (49%). The interaction effect of elevated CO2 with nitrogen input was investigated using four nitrogen levels equivalent to 25, 75,125 and 175 kg ha-1. The nitrogen response rate was raised by elevated CO2 equally at each nitrogen application rate so that there was no significant interaction effect between the two for most parameters measured. In this way both CO2 and nitrogen were acting as “fertilizers”. Overall the results showed that despite being put forward as a drought resistant crop for low input agricultural systems safflower is capable of responding positively to well irrigate and well fertilized conditions. Furthermore under conditions of elevated CO2 it can be expected to increase its yield potential but to achieve this will require a higher degree of nitrogen fertilization. CO2 is capable of substituting for up to 100 kg N ha-1 without a decline in yield and this shows that CO2 is the primary limiting factor in safflower assimilation. IV Seed oil content and its fatty acid profile appeared to be relatively stable and were not affected drastically by either nitrogen fertilization or elevated CO2.This demonstrated the integrity of the oil filling process during seed fill and emphasized that this is primarily under genetic control with relatively little influence from environmental parameters.

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