It is well established that mineral nitrogen negatively affects symbioses and molecular nitrogen utilization by crops. Nevertheless, symbiosis and nitrogen fixation of tree species, less studied, has been showed certain tolerance to nitrate. The aim of this work was to evaluated the nitrogen molecular use by nodulated Lonchocarpus muehlbergianus, a Cerrado legume tree, even supplied with mineral nitrogen as nitrate, important feature for symbiotic plants growing in soil where nitrate is the prominent source of nitrogen. For this purpose, the number and dry weight of nodules, shoot and roots, as well as content of xylem sap amino acids, nitrate and ureides, product of symbiotic nitrogen fixation, and nitrate reductase activity were determined. At the end of the experiment, it was observed that the number and dry weight of nodules was not affected by nitrate. Addictionally, it was verified a short increment in shoots and roots treated with nitrate. Similar results were found for amino acids and ureides content and foliar nitrate reductase activity. Our results suggest that Lonchocarpus muehlbergianus is able to utilize at the same time both mineral and molecular nitrogen since transport of ureides from roots to shoots was not reduced when nodulated plants was fed with nitrate.
plant growth; plant stress; nodulation; xylem transport; plant tolerance to abiotic stress
