Efeitos da temperatura do ar na fotossíntese da cana-de-açúcar na fase inicial do desenvolvimento Effects of air temperature on photosynthesis of sugarcane in the initial phase of its development

To understand climate changes effects on plants it is necessary not only to know the effects of air temperature on plant development, but also to know which physiological factors are related to reduction and / or increasing photosynthesis. The aim of this study was to evaluate the effect of air temperature on photosynthesis and development in the initial growth of sugarcane. The experiment was conducted in a climate chamber type Phytotron with controlled temperature, photoperiod and irradiance. The experimental design was completely randomized with eight replications and three temperature regimes: low temperature (19 °C day and 13 °C night), average temperatures (29 °C day and 23 °C night) and high temperatures (33 °C day and 27 °C night) for 150 days. At 120 days after planting (DAP) was performed in leaves +1 evaluations of physiological parameters related to photosynthesis. At 150 DAP was evaluated the number of leaves, height, diameter and mass of the stem. Low temperatures reduced photosynthetic efficiency of plants of sugarcane, as well as the development and growth (plant height, dry weight and stem diameter). The results indicated that the main cause for the reduction of plant photosynthesis was the limitation of biochemical enzymatic activity of Rubisco under low temperatures. High temperatures did not affect the photosynthetic efficiency of the plants, which showed an increase in height and a reduction in stem diameter.