Heterogeneity and C dynamics in soil

Heterogeneity (spatial, temporal chemical and biological) is a fundamental property of soils. Although it is rarely explicitly accounted for in models of soil microbial functioning, it is a determinant of microbial access to substrate and therefore of microbial activity. Microbial adaptation to heterogeneity is also likely to play a significant role in determining microbial activity and therefore C persistence in soil. A more developed understanding of heterogeneity and how microbial communities interact with their heterogenous environment can help us better understand the mechanisms that regulate microbial activity and soil C dynamics, as well as offer potential avenues for upscaling. In this presentation I will show how microbial communities have adapted to spatial and molecular heterogeneity at the microbial scale and, through the use of a spatial explicit model, how spatial and molecular heterogeneity interact to reduce decomposition. Pore scale heterogeneity affects the distribution of both decomposers and organic matter. Using a stable isotope approach, I will show that, although there does not appear to be a clear relationship between microbial decomposer composition and pore size, a simple relationship emerges between pore size and microbial decomposition of organic substrate. As the pore size distribution of soils can be deduced from pedo-transfer functions, this relationship may provide a more mechanistic basis for the representation of moisture effects on C dynamics in larger scale models.