Genotype contrasts in field-grown switchgrass root system architecture and soil carbon

R scripts to reproduce analyses in the manuscript. Abstract: Roots influence plant biomass, stress tolerance, and soil properties, but approaches to reliably measure root trait differences among field grown perennial grasses have not been systematically examined. Here, we measure in-field variation associated with coring depth and harvest position relative to the crown for two well-characterized genotypes of a perennial biomass crop, switchgrass (Panicum virgatum L.). Soil and root cores were taken from replicated plants of VS16 and AP13 genotypes, which represent morphologically distinct upland and lowland ecotypes, respectively. Total root mass inside the crown was over 3-times that outside of the crown, with outside roots being finer and more branched. For 29 root system architecture traits, the mean coefficient of variation was 52% greater outside of the crown than inside, with 20 statistically significant (P < 0.05) genotypic differences detected among in-crown samples, and only five genotypic differences detected out-crown. For these four-year-old plants, particulate and mineral-associated carbon and nitrogen stocks in the soil differed by coring depth (5-15 cm vs 45-60 cm). Differences in mineral associated organic matter between switchgrass and the adjacent mowed border were detected only when considering samples harvested inside the crown at the shallow depth. These results provide baseline data for expanding measurements to additional genotypes or other perennial species and suggest that sampling position relative to the crown is important to detect genotypic differences, particularly in root system architecture.