Characteristics of soil structure such as aggregation develop as a result of numerous factors including wet-dry cycles, clay flocculation, root activity, burrowing by soil organisms, fungal hyphal activity and microbial exudation (Tisdall and Oades, 1982, Dexter, 1988, Kleinfelder et al., 1992, Czarnes et al., 2000, Bossuyt et al., 2001, Denef et al., 2002 and Scullion et al., 2002). Tisdall and Oades (1982) stated the importance of bacteria, fungi and roots as binding and

stabilising agents within the soil environment, with their temporal contribution ranging from weeks to years. Feeney et al. (2006) suggested that soil structure and water repellency can be influenced by root and microbial activity extremely quickly. Their investigation showed that the number of aggregates of >2000 μm and their water repellency both significantly increased over a 30 day period; this Akt inhibitor was attributed to increased fungal activity, particularly in the rhizosphere. These authors used X-ray micro-Computed Tomography (μCT) to show that micro-organisms have an impact on development of soil structure and in particular on pore size distribution within aggregates. PD0325901 mw It is widely acknowledged that soil microbes significantly contribute to many soil ecosystem functions.

What is not known however is how microbially Hydroxychloroquine clinical trial diverse the soil ecosystem needs to be in order to maintain such functions. Relatively few experiments have attempted to differentiate

between interacting organisms when considering the relative importance of biota on soil structure (Hallett et al. 2009). Investigations that have concentrated on microbial populations have either been field studies focussing on reclamation or intensification gradients (Gomez et al., 2004), or relatively short-term laboratory culture studies (Franklin and Mills 2006). The dilution method of modifying microbial diversity has been frequently used in mineral soils (Griffiths et al., 2001, Wertz et al., 2006 and Wertz et al., 2007), peat (Dimitriu et al. 2010) and sewage (Franklin and Mills 2006). It is primarily used as a means of lowering species richness so functional ability can be correlated with biodiversity. Rarely is the function studied in this context related to soil porosity and the development of soil structure. This investigation aimed to measure the relationship between microbial community structure and soil physical properties such as aggregate stability, pore size and pore distribution. Macrocosms of sieved sterile soil were inoculated with one of two dilutions of field soil to create microbial communities differing in species richness. Additional treatments included planting with Plantago lanceolata (± arbuscular mycorrhizal inoculum) or leaving the soil unplanted.