Leaf Photosynthesis Potential in Pineapple (Ananas comosus L. Merr.) ‘Smooth Cayenne’, a Crassulacean Acid Metabolism Plant

Abstract

Light response ofpineapple ‘Smooth Cayenne’, a crassulacean acid metabolism (CAM) plant, was assessed by combining the measurements of leaf gas exchange, chlorophyll fluorescence and total acid content during each of the four carboxylation phases. Results showed that the gas exchange parameters, namely the net photosynthesis (A) and the stomatal conductance (g_s) did not correspond to the applied radiation intensity (PPF_i). It was clear that the procedure of gas exchange measurement was not applicable to assess CAM light response in all phases. The chlorophyll fluorescence measurement, on the other hand, provided data on the light–adapted quantum efficiency (φ_PSII) and the electron transport rate (ETR). ETR showed increase with PPF_i, thus could be fitted into a non–rectangular hyperbola function in all phases. The estimation showed that the maximum ETR was 143 μmol e^- m^–2 s ^–1 during Phase III (9-12 h), and the estimated maximum gross photosynthesis rate (P_g) was 35.8 μmolCO₂ m^–2 s ^–1, with the light saturation (I_sETR) of 750 μmolPPF m^–2 s ^–1. The measurement of the leaf total acid content (H⁺) showed that the levels were high during Phase I and II (dark to dawn). During daytime Phase III, H⁺ was reduced drastically, confirming the release of CO₂ into the process of photochemistry. In Phase IV, both ETR and H⁺ were spent and the levels became low. Our study showed that we needed 3 procedures together to assess the light response of CAM leaf of pineapple.