While the diversity and abundance of soil organisms are recognised to play an important role in determining soil structure and fertility, the nature of these roles and the mechanisms by which they occur are still poorly understood. Similarly, various soil abiotic properties are known to influence biological activities. Given the importance of understanding these processes, this session will concentrate on microbial activities that take part in the cycling of the key nutrients essential for life and on pedofauna diversity. Nutrient cycling involves a series of integrated processes: initial fixation of nutrients rendering them available to other organisms in the biosphere (biomass); turnover of organic and inorganic matter; and loss of available nutrients from the biosphere. Soil biota also contribute substantially to the resistance and resilience of ecosystems to abiotic stress. Natural resource management strategies and agronomic practices rapidly affect soil microbial nutrient cycling and microbial abundance, diversity and activity; therefore, microbial community dynamics are good indicators of changes caused by perturbations and land use changes. Plant growth-promoting microorganisms, including bacteria, cyanobacteria, actinomycetes, Arbuscular mycorrhizal fungi (AMF), have been targeted for their potential as biofertilisers, biostimulants and bioprotectants. The ecosystem stability is also highly affected by the soil pedofauna abundance and biodiversity. The spatial heterogeneity and the degree of aggregation of the pedofauna, as well as mobility and interactions with the microflora, contribute substantially to soil ontogenesis, chemical content and the rate of organic matter decomposition. The mesofauna - Enchytraeidae, Collembola, Diptera larvae, Acari, Diplopoda, Isopoda, Nematoda and others – are well known for their influence on organic matter humification and soil quality.

This session will examine important soil organisms, their key roles within the soil ecosystem and their potential as indicators of soil quality, as well as technological developments in the analysis of soil communities. The past decade has seen an increase in the number and efficiency of methods for determining microbial diversity, abundance and function. Community studies over the past 15 years have relied on molecular techniques based on the 16S and 18S rRNA encoding sequences (DGGE, TRFLP, OFRG, ARISA, SSCP) as well as techniques based on the cellular composition of the microbes (PLFA composition), with more recent major advances in microbial community analysis employing high-throughput sequencing and microarrays. While the diversity of microbes can be determined using DNA-based techniques, the activity of microbes under particular sets of conditions requires the analysis of the ribosomal rRNA. Similarly, bio-indicators are now widely used to detect how organisms react to environmental changes; indeed, it has become increasingly important to identify bio-indicators to measure soil quality, to be used as benchmarks in environmental remediation and to monitor soil quality in soils subjected to degradation risk. These various techniques and approaches will be a key focus of this session, with particular attention to the potential for each as well as their limitations.