Ecophysiology of nitrogen use in tree species of Araucaria Mixed Forest, State Park Campos do Jordao, Brazil

Abstract

The phytosociological and floristic research made in the Atlantic Forest were much enhanced during the last decade and shows a difference at the dispersion, structure and function of the various floristic formations that compose the Atlantic Forest. Forest succession researches indicate that the forests compose a physiognomy mosaic associated to the forest regeneration: gap phase, secondary and mature forests. These three phases show different environmental characteristics, mostly light availability and they are characterized by the occupation of species with distinct ecophysiological characteristics, or functional groups, in terms of regeneration strategies. Basically they are classified into three groups: pioneer species, early secondary and late secondary species. Nitrogen is available to terrestrial plants in different forms, which include mineral N (NO3- e NH4+), nitrogen oxides (NOx) and volatile ammonium (NH4+), N2 molecular (not symbiotic and symbiotic) and organic N (amino acids and peptides). The study on the relationship between the N use in the Atlantic Forest succession was initiated by Aidar et al (2003), and the authors establishe that the species conform a continuum of nitrogen use strategies in accordance with the regeneration guilds in an area of Dense Ombrophilous Forest. Other studies in areas of Atlantic Forest corroborate the proposed model (Sub-Montane and lowland Rain Forests). Recently it was observed that the trees of the Montana Rain Forest showed high nitrate reductase activity in winter compared to summer in all sucessional categories diverging from the concepts of the nitrogen use model proposed by Aidar et al (2003) that assumes a higher enzyme activity in the summer when there is greater availability of nitrate in soil and in pioneer species that are specialized in reducing foliar nitrate. This differentiation in leaf nitrate reduction was related to aspects associated with cold acclimation rather than nutritional use. The project aims to characterize the ecophysiology of nitrogen use in dominant tree species in Mixed Forest (Araucaria forest) at the Campos do Jordão State Park, Brazil. The expected results should contribute positively to validate the model on the use of N in the rainforest and also will contribute to better understanding of the functionality of the ecosystem and how tropical forest ecosystems could respond to global climate change. (AU)