Pore structure in detritusphere of soils under switchgrass and restored prairie vegetation community

Abstract

Root detritusphere, i.e., the soil in vicinity of decomposing root residues, plays an important role in soil microbial activity and C sequestration. Pore structure (size distributions and connectivity of soil pores) in the detritusphere serves as a major driver for these processes and, in turn, is influenced by physical characteristics of both soil and roots. This study compared pore structure characteristics in root detritusphere of soils of contrasting texture and mineralogy subjected to >6 years of contrasting vegetation: monoculture switchgrass and polyculture prairie systems. Soil samples were collected from five experimental sites in the US Midwest representing three soil types. Soil texture and mineralogy were measured using hydrometer and X-ray powder diffraction, respectively. The intact cores were scanned with X-ray computed micro-tomography to identify visible soil pores, biopores, and particulate organic matter (POM). We specifically focused on pore structure within the detritusphere around the POM of root origin. Results showed that detritusphere of coarser-textured soils, characterized by high sand and quartz contents, had lower porosity in the vicinity of POM compared to finer-textured soils. POM vicinities in finer soils had high proportions of large (>300 μm Ø) pores, and their pores were better connected than in coarser soils. Lower porosity in outer (>1 mm) parts of detritusphere of switchgrass than of prairie suggested soil compaction by roots, and the effect especially pronounced in coarser soils. The results demonstrated that soil texture and mineralogy played a major, while vegetation a more modest, role in defining the pore structure in root detritusphere.