Leaf nitrogen supply improves sugarcane photosynthesis under low temperature

This study aimed to test the hypothesis that increases in leaf nitrogen concentration would reduce the sensitivity of sugarcane photosynthesis to low temperature. IACSP95-5000 plants were grown inside a growth chamber at 30/20 degrees C (day/night) and we evaluated the effects of leaf nitrogen spraying (2.5% urea) on plants facing low temperature (22/12 degrees C) for eight days. The leaf nitrogen supply increased leaf nitrogen concentration and plants exhibited higher leaf gas exchange as compared to nonsprayed ones. We also found higher activity of the carboxylation enzymes, Rubisco and phosphoenolpyruvate carboxylase, as well as a higher chlorophyll content in plants sprayed with nitrogen. Such enhancement of photosynthetic performance was associated with an increase in number of leaves and in total leaf area. Our results suggest that the effects of low temperature on photosynthesis of field-grown sugarcane plants could be alleviated by leaf nitrogen supply, with likely consequences for biomass production and crop yield.