B08 - Structure and functioning of the decomposer system in lowland rainforest transformation systems

The decomposer system forms an essential component of terrestrial ecosystems but its structure and functioning, in particular in tropical rainforests, is poorly understood. In tropical lowland rainforest and two major conversion systems, i.e. rubber and palm oil plantations in two landscapes of Jambi province (Sumatra, Indonesia) the structure and functioning of the decomposer food web will be investigated. The project aims at identifying changes in community structure of soil animal taxa with conversion of rainforest. In particular we investigate the role of spatial and temporal variations of the response of soil food webs to rainforest conversion including sites of different presumed conservation priority, i.e. sites with higher water table. Soil microorganisms, and micro-, meso- and macrofauna will be sampled quantitatively, and determined at high taxonomic resolution. Focal functional groups include fungal and bacterial feeding soil invertebrates represented by oribatid mites and testate amoebae, respectively. Selected dominant species will be analysed for natural variations in stable isotope ratios (¹⁵N/¹⁴N and ¹³C/¹²C ratios) and for closer understanding of their food relationships by fatty acid analysis to identify variations in trophic niches with the conversion of rainforest into agricultural production systems. As part of the core design of the CRC also variations in microorganisms and microbial consumers with management intensity of oil palm plantations will be investigated. As a start in developing tools for identifying species and traces of species by using molecular markers, mitochondrial (COI) and nuclear markers (18S rDNA) of dominant species of oribatid mites, collembolans and gamasid mites will be analysed. Further, following up experiments established in the first phase of CRC 990, the role of roots and mycorrhizal fungi for soil animal nutrition and soil animal food web structure will be studied. The study is expected to uncover major driving factors of the variability of soil animal communities in lowland tropical rainforests and major agricultural production systems. The project is closely linked to other projects investigating animal food webs, soil carbon dynamics and below- / aboveground interrelationships. By comparing results of the proposed project with those of studies in rainforests in South America (Ecuador) and in temperate forest ecosystems investigated with similar methodology, we expect to uncover generalities on the structure, driving forces and functioning of soil animal communities of forests on a global scale.