The reuse of root channels affects rhizosphere physical properties and therefore the fate of carbon

Carbon inputs into soil take place primarily through rhizodeposition and root decay. Spatial inaccessibility of organic matter to organisms, i.e., physical protection, is a key factor for stabilizing such carbon in soils. Protection is governed by soil structure, i.e., the spatial arrangement of solids and voids, thus, differences in root distribution and in their rhizosphere physical properties influence carbon sequestration. This structure, in turn, is affected by roots, which explore the soil by rearranging existing soil particles and thus may compact the rhizosphere, especially, when the soil does not contain a well connected macropore system. Here we conducted an experiment to determine how plants rearrange the spatial distribution patterns of pores with different sizes and how this affects the fate and distribution of SOM. Soil cores, with structure either intact or destroyed by sieving, from monoculture switchgrass and prairie systems were incorporated into containers planted with Panicum virgatum L. (Switchgrass) and Rudbeckia hirta L. (Black-eyed Susan), plants with contrasting root characteristics. The cores were X-ray µCT scanned before and after plant growth, enabling explorations of the feedback interactions between roots and soil structure through analysis of pore size distributions, root distributions, and rhizosphere physical properties. To assess the fate of the plant-derived C, the plants were labelled by 14CO2; and presence of 14C in roots, rhizosphere, and rhizoplanes was examined. The cores were incubated for 14 days and 14CO2 and CO2 respiration was measured on a weekly basis. Soil solution from pores of different sizes was collected by centrifugation and analyzed for 14C. This will enable to investigate the fate and distribution of carbon in correlation to the structural properties derived from image analysis. First results show that roots of both plants reused existing root channels more often than randomly, which led to increased porosity in the rhizosphere of roots growing in structured cores compared to sieved cores. This in turn affected carbon CO2 respiration. The study is founded in part by the NSF DEB Program (Award # 1904267) and by the Great Lakes Bioenergy Research Center (Award # DE-SC0018409).