THAI AGRICULTURAL RESEARCH JOURNAL

Volume 38, No. 03, Month SEPTEMBER, Year 2020, Pages -

Leaf light response of cassava cv. huay bong 60 under normal and low o2 in combination with 3 co2 concentrations

Pornchai Paiboon, Suntaree Yingjajaval

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The light response functions of cassava cv. Huay Bong 60 were determined under 3 levels of CO2 concentration inside the leaf chamber (Ca) at 400, 800, and 1,200 μmolCO2 mol air-1 to enhance the carboxylation process in combination with 2 levels of O2 concentration at 21% and 2% to suppress the oxygenation process. Results showed that under ambient air (Ca 400 μmolCO2 mol air-1 with 21% O2) cassava leaf had maximum gross photosynthetic rate (Pmax) of 31 μmolCO2 m-2 s-1. The light saturation range was 1,100-1,300 µmolPPF m-2s-1. Maximum electron transport rate (Jmax) was as high as 289 µmol e- m-2 s-1 and maximum photorespiration, (Rp, max) was 12.4 μmolCO2 m-2 s-1. Elevation of Ca could increase Pmax (26-76% increase) more than the lowering of O2 concentration (6-33% increase), as higher Ca enhanced carboxylation as well as suppressed oxygenation. However, the combination of both enabled Pmax to reach 61.2 µmolCO2 m-2 s -1, or 97% increase, coupling with the reduction in Rp and J.

Keywords

Cassava, C3 photosynthesis, Light response, Light saturation, Photorespiration

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