Das Projekt "Functional significance of tree diversity for nutrient dynamics in a tropical plantation" wird vom Umweltbundesamt gefördert und von Eidgenössische Technische Hochschule Zürich, Institut für Agrarwissenschaften, Departement Biologie durchgeführt. The main objective of this project is to study effects of altered tree species richness on the functioning of ecosystems. As a model system, we use an experimental plantation in Panama, Central America, which has been established in 2001. A total number of 24 experimental tree stands ('plots') were planted with one, three or six native tree species. By comparing the performance of these different plots, we are aiming to quantify the consequences of varying species diversity. For further information, see also: http://biology.mcgill.ca/faculty/potvin/sardinilla.htm http://www.biotree.bgc-jena.mpg.de/ We concentrate on diversity effects on nutrient cycling with special emphasis on nitrogen (N) and phosphorus (P). We aim at quantification of the uptake of both N and P to plants, organic N mineralization in soil, and losses through leaching down the soil profile. More specifically, we want to understand the mechanisms underlying any diversity effects, such as complementarity in resource uptake, adopting isotope tracer studies. Because even basic information is lacking about occurrence of mycorrhizal associations in most tropical tree species, we are currently examining to what extent the trees establish mycorrhizal associations and of which types. We shall gather information on possible effects of tree species richness on both the diversity and community structure of mycorrhizal communities. Additionally, we will also address to what extent different tree species benefit from mycorrhizal associations. Our main hypothesis is that, in contrast to monocultures, plots with higher tree species richness show complementary uptake of soil nutrients, either because of different spatial or temporal pattern of nutrient acquisition, or association with specific mycorrhizal fungi of the different trees. The nutrient portioning that we expect in the mixed, more diverse stands will result in enhanced net flow of nutrients from soil to plants, as well as to lower N losses from the system. Since afforestations with fast-growing, often exotic tree species planted in monocultures are strongly increasing in the tropics, but may cause environmental problems, this project may help to design ecologically sustainable ways to establish new plantation forest.