Variation of photosynthesis along the canopy profile of sugarcane and energy canes

Abstract Energy cane ( Saccharum spp. hybrid) is a sustainable feedstock for the sucroenergetic sector due to its capacity of producing more biomass than sugarcane ( Saccharum spp. hybrid). As biomass is formed by carbohydrates, photosynthesis is a key physiological process to understand the biomass production by plants. Herein, one sugarcane (IACSP95-5000) and two energy canes (Vertix 2 and Vertix 3) genotypes were cultivated under greenhouse conditions to evaluate the photosynthetic capacity of top leaves and to measure the actual photosynthesis of all green leaves of the main tiller. All genotypes showed similar maximum and actual photosynthesis in the top leaves, which was not correlated to their biomass production. In fact, the effects of leaf aging on canopy CO 2 uptake, differential tillering and respiration rate seem to explain biomass production. IACSP95-5000 showed a sharp decrease in several photosynthetic traits and in abundance of key photosynthetic enzymes along the canopy profile, resulting in the lowest biomass yield. Vertix 2 and Vertix 3 exhibited a canopy with higher photochemical activity and lower variation in abundance of key photosynthetic enzymes with leaf aging as well as more well-developed tillers as compared with IACSP95-5000. Moreover, Vertix 2 – bred for high fiber content – exhibited a more homogeneous photosynthesis with leaf aging and higher growth respiration rate, two physiological traits associated with the highest biomass production among genotypes evaluated.