A2.2 Nutrient limitation in tropical mountain forests [funded by Le 762/10-1]

Project staff:

Prof. Dr. Christoph Leuschner
Dr. Jürgen Homeier


The role of nutrient limitation for the carbon balance, nutrient economy and diversity of trees in Andean forests of South Ecuador: an experimental approach


Increasing fertilizer use, industrialisation and biomass burning will greatly increase atmospheric nitrogen deposition in tropical countries in the coming decades. It is not sufficiently understood how tropical forests will respond to the expected N addition. In tropical lowland forests, phosphorus is a major growth-limiting element, whereas tropical mountain forests seem to be limited primarily by N. This project combines experimental and descriptive studies along an elevational transect (1000 to 3000 m asl) of Andean mountain forests to investigate (a) the type of nutrient limitation at different elevations, (b) physiological and morphological responses of trees to N and/or P addition, (c) the relationship of tree diversity and stand productivity, respectively, to nutrient availability, and (d) the effect of elevation on the relationships in (b) and (c). Three research approaches at different spatial and temporal scales are combined: A) A comparative field study within an environmental matrix (60 plots) to analyse the relationship between N and P availability and tree species diversity and forest structure. B) A replicated N and P addition experiment (NUMEX) to study the effects of addition of N (50 kg ha-1 yr-1), P (10 kg ha-1 yr-1), and N+P on stem increment, litter production, fine root biomass and foliar and leaf litter nutrient concentrations. C) A mesocosm study with seedlings of light-demanding and shade-tolerant tree species that are treated with different N and P amounts to investigate above- and below-ground growth responses, leaf and root longevity, nutrient partitioning patterns, responses of photosynthesis and leaf and root respiration to nutrient addition, and in situ nitrogen uptake rates and preference of nitrate, ammonium or organic N sources. The project takes the lead in the NUMEX experiment (central organisation and synthesis).