Quantifying the impact of microbes on soil structural development and behaviour in wet soils

There is evidence that microbial populations play an important role in altering soil pore geometry, but a full understanding of how this affects subsequent soil behaviour and function is still unclear. In particular the role of microorganisms in soil structural evolution and its consequence for pore morphological development is lacking. Using a combination of bio-chemical measurements and X-ray Computed Tomography (CT) imaging, a temporal comparison of microscale soil structural development in contrasting soil environments was made. The aim was to quantify the effect of microbial activity in the absence of other features likely to cause soil deformation (e.g. earthworms, roots etc.) on soil structural development in wet soils, defined by changes in the soil porous architecture i.e. pore connectivity, pore shape and pore volume during a 24 week period. Three contrasting soil textures were examined and changes compared between field soil, sterilised soil and a glucose enhanced soil treatment. Our results indicate that soil biota can significantly alter their microhabitat by changing soil pore geometry and connectivity, primarily through localised gaseous release. This demonstrates the ability of microorganisms to modify soil structure, and may help reveal the scope by which the microbial-rich rhizosphere can locally influence water and nutrient delivery to plant roots

Soil aggregates as massively concurrent evolutionary incubators

Soil aggregation, a key component of soil structure, has mostly been examined from the perspective of soil management and the mediation of ecosystem processes such as soil carbon storage. However, soil aggregation is also a major factor to consider in terms of the fine-scale organization of the soil microbiome. For example, the physico-chemical conditions inside of aggregates usually differ from the conditions prevalent in the bulk soil and aggregates therefore increase the spatial heterogeneity of the soil. In addition, aggregates can provide a refuge for microbes against predation since their interior is not accessible to many predators. Soil aggregates are thus clearly important for microbial community ecology in soils (for example, Vos et al., 2013; Rillig et al., 2016) and for microbially driven biogeochemistry, and soil microbial ecologists are increasingly appreciating these aspects of soil aggregation. Soil aggregates have, however, so far been neglected when it comes to evolutionary considerations (Crawford et al., 2005) and we here propose that the process of soil aggregation should be considered as an important driver of evolution in the soil microbial community