ISSN: 1659-2751



Dynamics of 15N in an Organic Cacao Agroforestry System in the Atlantic Region of Costa Rica


Agroforestry systems, in which N2-fixing plants are associated with non-N2-fixing plants, have been proposed to alleviate N deficits that occur in some tropical agroecosystems. The supply of N-rich litter by the N2-fixing plant that decomposes in soil is substantial. However, it is important to consider that around 50 % of the N of N2-fixing trees could be in the root zone. Thus, it is important to understand the N transfer processes from plant to plant through the roots. These processes can be studied using the 15N natural abundance technique. In this study, the variation in time of δ15N and N total concentration was determined for leafs, roots, and rhizospheric soil from the trees in an organic cacao agroforestry system located in the humid tropical region of Costa Rica. The studied trees were: Inga edulis, Cordia alliodora, Theobroma cacao near I. edulis, T. cacao far from I. edulis and T. cacao without contact with I. edulis. The δ15N value did not vary significantly in time within species. I. edulis had a significant effect on the δ15Nof roots of T. cacao, which may be evidence on direct N transfer from plant to plant.

Key words: 15N natural abundance, Cordia alliodora,Inga edulis15N,Theobroma cacao, N transfer.

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