Along with the increased concentration of CO2, the atmospheric deposition of nitrogen is currently considered one of the most important factors of change in the functioning of native ecosystems and has caused drastic changes in their floristic composition and nutrient cycling in the northern hemisphere. In tropical and subtropical systems, however, the largest holders of the plants diversity, little is known about the effects of the nitrogen enrichment via deposition on their performance. Understanding the magnitude and direction of the responses of the orchids to the increase of the concentration of available nitrogen might be helpful to modeling of rock outcrops population dynamics in response to global changes. We evaluated the responses of flowering and fruiting in plants of Habenaria caldensis Kraenzl. (Orchidaceae), a species widely distributed in Minas Gerais, as a result of increased nitrogen availability through fertilization with ammonium nitrate, in situ, by spraying. In response to the addition of N, anthesis occurred about 15 days earlier compared to individuals of the control group. The results of this study demonstrated that the increased availability of N via atmospheric deposition can affect in a short term the ecology of orchids and possibly other plants from rock outcrops by changing their phenological and allometric patterns. In a medium and long term, such changes can have an important impact on the dynamics of populations and communities of this vegetation type.
fertilization; rock outcrops; flowering and fruit development
