Effect of diurnal variation of atmospheric and elevated levels of carbon-di-oxide and photosynthetically active radiation on intercellular concentration and rate of photosynthesis in maize and safflower

Abstract

A field experiment was conducted during rabi 2003 to study the effect of elevated levels of CO2 and PAR on intercellular CO2 concentration (Ci), net photosynthetic rate and their interrelationship in maize and safflower at different growth stages. The highest concentration of intercellular CO2 was recorded at 1200 and 1400 hrs and lowest concentration of intercellular CO2 was found during early hours in the morning (08 00 hours) irrespective of levels of CO2 and PAR at all the stages of maize and sunflower. The higher rate of net photosynthetic rate was observed in active vegetative stage (11.7 to 49.1 μmol CO2 cm-2 sec-1) compared to knee high and flowering stages of maize and during late vegetative stage (21.6 to 47.2 μmol CO2 cm-2 sec-1) in safflower compared to early vegetative and flowering stage. The optimum levels of CO2 and PAR for maize were 650μmol CO2 mol-1 and 960 μmol m -2 s-1 respectively and for safflower were 650μmol CO2 mol-1 and 1100 μmol m-2 s-1 respectively. A combination of 650 μmol CO2 mol-1 and 960 μmol m-2 s-1 of PAR for maize and 650 μmol CO2 mol-1 and 1100 μmol m-2 s-1 of PAR for safflower were found optimum levels. A positive correlation between the intercellular CO2 concentration and net photosynthetic rate in maize and safflower was found throughout the crop growth period.

Keywords

• CO2
• PAR
• intercellular CO2 concentration
• net photosynthetic rate