Soil pores and their contributions to soil carbon processes

Abstract It has been generally recognized that micro-scale heterogeneity in soil environments can have a substantial effect on many soil physical, chemical, and biological processes driving physical protection of soil carbon (C). However, only recently the development of tools for micro-scale soil analyses, including X-ray computed micro-tomography (μCT), enabled quantitative analyses of these effects. X-ray μCT application to soil science is arguably one of the newest and fastest growing areas of soil science research; and its methodology is still being actively developed. The large amount of spatially explicit data that μ-CT scanning generates coupled with specially designed experiments can open new avenues for improved understanding of soil functioning and soil-plant interactions. Pores are both drivers and products of a variety of soil processes that ultimately determine physical protection of organic matter in soil by influencing its accessibility to microorganisms. The μCT tools are well suited for providing information on characteristics of soil physical micro-environments, a.k.a. soil pores. Here we review the experimental approaches currently employed by research groups around the world in exploring the role of pore characteristics in soil C processes, with specific focus on soil C decomposition and protection at 5–1000 μm spatial scale. We discuss pore/C/microbe relationships with emphasis 1) on direct and indirect effects of pore characteristics on soil microorganisms and subsequent microbial effects on decomposition of organic inputs; 2) on presence of feed-back effects of microorganisms on soil pore architecture; and 3) on importance of pore characteristics for decomposition of freshly added organic inputs/plant residues. The pore-oriented perspective will contribute to better structuring of the research efforts in deciphering the mechanisms of soil C protection/sequestration by soils.