Effects of haze on net photosynthetic rate, stomatal conductance and yield of Malaysian rice (Oryza sativa L.) varieties

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R. Mohd Aziz, A.G. Mohamad Zabawi, A.T. Shaidatul Azdawiyah and A. Fazlyzan

Abstract
The potential direct effects of haze on net photosynthetic rate and stomatal conductance of several Malaysian rice varieties were investigated during the haze event in March 2014. The haze was at moderate level with Air Pollution Index (API) readings between 50 and 200 (moderate to unhealthy air pollution levels) but it worsened to very unhealthy and hazardous levels at certain areas. The gas exchange measurements were conducted on 60 and 78 days after transplanting on hazy and sunny clear days, respectively. The mean API readings on a hazy day and a clear day were 141 and 47 respectively. Solar radiation showed an average of 22% reduction on a hazy day from 0800 to 1700 h and a 45%
reduction at 1430 h. Haze caused 12.9 – 53.2% and 26.1 – 73.8% reduction in net photosynthetic rate and stomatal conductance of rice throughout the day respectively. Net photosynthetic rate was highly correlated to Photosynthetically Active Radiation (PAR) with a regression coefficient (R2) of 0.77 and 0.89 on clear and hazy days respectively. Haze significantly reduced net photosynthetic rate and stomatal conductance of all rice varieties largely through its effects on solar radiation/PAR reduction. Both net photosynthetic rate and stomatal conductance of all rice varieties generally showed similar responses to haze and there was no outstanding variety that can be considered resistant to the haze and solar radiation reduction. The yield of all rice varieties also showed 10 – 19% reduction as compared to the potential yield. Results indicated that 5 weeks of moderate haze that occurred during the late vegetative and early flowering stage had affected the physiological performance and yield of rice. A longer duration of severe level of haze (API 300 – 800) at flowering, grain filling and ripening stages will probably have greater effects on plant physiological performance and yield of rice.

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