Juliane Röder

Drivers of decomposition in the tropics: effects of climate and land-use on soil invertebrates

The decomposition of organic material is an important component of nutrient cycling and carbon fluxes and therefore a major ecosystem service. The progress of litter decomposition depends on temperature and moisture, characteristics of the litter and the diversity and composition of decomposer assemblages. Decomposition is influenced by invertebrates in a number of different ways. ‘Ecosystem engineers’ shape the structure and porosity of the soil as they tunnel through the ground and leave faecal pellets. ‘Litter transformers’ shredder organic material which increases the available surface for microorganisms. And fungi and bacteria can be sheltered, distributed and/or preyed upon by invertebrates with body sizes varying by as much as two orders of magnitude. The diversity and composition of soil invertebrate assemblages can thus affect the decomposition of organic material. However, the importance of soil fauna for decomposition may vary depending on climatic and land-use variables. Repercussions of global warming and an intensified agriculture will affect decomposition directly and indirectly via changes of the decomposer assemblages.

To disentangle the effects of biotic and abiotic interactions, the KiLi-project¹ works at the slopes of Mt. Kilimanjaro. The highest mountain of the African continent (5895m a.s.l.) provides a considerable elevation and therefore climate gradient, and its foothills have a long history of settlement. Today, forests at higher and higher elevations are converted into fields or logged for timber and fire wood, owed to a growing population. Around the borders of the national park, i.e. between 1500 and 1800 m a.s.l., undisturbed and disturbed forests can be compared to a local form of agroforestry and conventional plantations. The ‘homegardens’ of the Chagga people maintain the structural characteristics of a forest and might be able to conserve a large part of natural biodiversity. However, the suspected positive relationship between structural similarity and biodiversity might not apply to all taxonomical or functional groups, and there may be differences in the strength and direction of correlations, respectively.

My part in this project, and at the same time the aim of my doctoral thesis, is to assess the abundance and diversity of soil invertebrates, their influence on the decomposition of leaf litter, the overall activity of the soil fauna and the effects of litter quality and diversity on decomposition. I sample the decomposer fauna with a range of complementary methods to establish a baseline of arthropod diversity along both the elevation and the land-use gradient, which I will use to 1) evaluate the relative effect of invertebrate decomposer diversity on decomposition, and 2) relate the composition of soil arthropod assemblages to the composition of the plant community, (macro-) climate, land-use and properties of the soil. I will further assess the interactions of litter functional traits, litter diversity and decomposer diversity regarding decomposition. Most of this data will be collected at all of 60 plots which are shared by all members of the project. Therefore it will be possible to relate the results of my work directly to the data collected by other members of the KiLi-project.

And if there is any time left I am feeding ants² and fighting with R...

¹“Kilimanjaro ecosystems under global change: Linking biodiversity, biotic interactions and biogeochemical ecosystem processes” (DFG research unit FOR 1246), https://www.kilimanjaro.biozentrum.uni-wuerzburg.de/

² Global Ant Collaboration, http://www.antmacroecology.org/collaboration.html