The soil-plant relationship of nitrogen use in three tropical tree species

摘要

We characterized and compared the use of nitrate (N-NO₃−), inthree recognized pioneer and secondary tropical species, analyzing theirrelationships with the availability of inorganic nitrogen in the soil of ariparian forest. We tested the hypothesis that pioneer species of theecological succession (Cecropia glaziovi – Cgl)would be more responsive to N-NO₃−available and would have high nitrate reductase activity (NRA) in leaveswhile secondary species (Inga marginata –Ima and Hymenaea courbaril – Hco) would have less responsivenessand would have lower levels of this enzyme on its leaves. We evaluated, tested andcompared the NRA and N-NO₃− content in leaves and xylem sap ofeach species. We measured N-NO₃− and N-NH₄+ content inthe soil. The results for Cgl showed an N-NO₃− content of xylemsap that met the demand of NRA and were correlated with inorganic soilnitrogen, showing the responsiveness of species to N-NO₃−. Hcowas verified as less responsive to assimilation and high N-NO₃−content in leaves. The species Ima showed an intermediate behaviour, whichsuggests the possibility of use of other nitrogen forms. Theecophysiological behaviours of the plants were related to the seasonalvariation and indicate that these plants use strategies with differentresponsiveness to the use of soil N-NO₃−. In this sense andconsidering that these species are typically used in ecological restorationprojects in Brazil, the knowledge of a strategy for nitrogen use specific toeach of them can assist in choosing the species appropriate to the edaphicconditions of the environment.