JS2-4:

Soil aggregate structure and its implications for microbial ecology: location and quality of substrates for heterotrophs

Physical characteristics of ecosystem (e.g., temperature, pH and redox regimes) exert a first-order control on biota including microbial community. In terrestrial ecosystem, vast majority of microbes are present in soil where roughly 2/3 of ecosystem carbon (C) is stored. Thus, soil physical structure has strong control on microbial ecology. Specifically, soil structure creates diverse physico-chemical environment for microbes by controlling the mobility (diffusion) of gas/water and the physical accessibility of substrate and among microbes. Soil structure is also tightly linked to key ecosystem functions such as the maintenance of biodiversity, gas/water exchange, and the storage and turnover of soil organic matter (SOM) which holds major portions of C and nutrients.

Our recent research has a focus on the most complex and probably most compartmentalized soil structure called aggregates which is found at the interface of plant and mineral soil (e.g., surface soil horizon). A variety of interactions among dead and live organic matter (i.e. SOM and microbes) and soil mineral particles occurring in soil lead to the formation of soil aggregate structure which exhibits hierarchical characteristics at submicron to millimeter space scales and the organic matter of different origins (plant vs. microbes) appear to act as glues at different levels of hierarchy.

Here we will present our recent findings on the linkage between organic matter and aggregate hierarchy based on the combination of microscopic, isotopic and spectroscopic methods including synchrotron-based X-ray spectroscopy. We will discuss microbial contribution to the development and loss of soil aggregate structure with an emphasis on microbially-driven turnover of soil organic matter, a fundamental ecosystem function.

keywords:carbon turnover,microbial habitat,soil structure,soil aggregate hierarchy,soil carbon seqestration