Photosynthesis of spring wheat (Triticum aestivum) in rainfed ecology of Pakistan

The effect of planting window (PW) acting as changing temperature scenarios and water availability at critical stages of wheat (Zadok’s scale) on photosynthesis (A), stomatal conductance (gs) and transpiration rate (E) as well as their relationship with yield of spring wheat genotypes viz: Chakwal-50, Wafaq-2001 and GA-2002 was studied. The research was conducted at three locations of varying climatic conditions (National Agricultural Research Centre Islamabad (NARC), Barani Agriculture Research Institute Chakwal (BARI) and farmer’s field at Talagang, District Chakwal) in year 2008-09 and 2009-10. The results showed that photosynthesis, stomatal conductance and transpiration rate were significantly affected under three locations due to change in temperature and water availability. Photosynthesis (27.03, 24.64 and 22.66 μ mole/m2/second), stomatal conductance (0.78, 0.31 and 0.09 mole/m2/second) were recorded and transpiration rate (8.66, 8.17 and 2.07 mole/m2/s) were recorded at NARC, Chakwal and Talagang, respectively. The values of these attributes were highest in growing year 2008-09 due to optimum temperature and water availability. The results clearly indicated that CO2 reduction rate, transmission of stomata and water loss rate were dependent on optimum temperature and moisture availability. Reduction in moisture availability and increase in temperature lead to reduction in photosynthesis which ultimately reduces the biomass produced and accordingly, limit the yield. Grain yield was observed to be 3540, 2352 and 1938 kg ha-1 for NARC, Chakwal and Talagang, respectively, which showed a regular reduction under three different observed environments. These physiological results of wheat genotypes can be used to find adaptive and potential genotypes for changing environment.Keywords: Wheat, photosynthesis, stomatal conductance, transpiration, environment