Characterization of Nitrogen Use by Neotropical Myrtaceae in Dry and Wet Forests of Southeast Brazil

We hypothesized that neotropical Myrtaceae could be organized into groups that are naturally less or non-responsive to NO3−, and that use other N forms, such as amino acids, for internal N transport. Ecophysiological tests were conducted to measure nitrate reductase activity (NRA), NO3− content, total N, δ15N natural abundance, the C:N ratio in leaves, free amino acid, and NO3− transport via xylem sap. We showed that Myrtaceae tree species have a relatively low NRA, in addition to little NO3− in leaves and free NO3− in the xylem sap during the wet and dry seasons. We suggested a possible compartmentalization of N use, wherein plants derive their internal N from and use their transport mechanism to move N between below-ground and above-ground parts, assimilating and transporting more N and C through amino acids such as glutamine, arginine, and citrulline. Evidence of low NO3− availability in tropical soils is important when trying to understand forest species’ N-use strategies, given their importance to plant nutrition. Differences in the responses of some Myrtaceae species to the seasonality of environmental factors suggest the need for further studies concerning N in natural forests, for example, to help understand the problem of N deposition ecosystems.