Root heterogeneity and production in Agropyron cristatum (crested wheatgrass) and native grassland

We asked whether invasive species alter the patchiness, as well as the amount, of root biomass by comparing stands of Agropyron cristatum (crested wheatgrass), a perennial tussock grass introduced to North America from Asia, and native grassland. Previous studies showed that root mass beneath A. cristatum was 30% less than that of native grassland in the top 10 cm of the soil. We examined root production and heterogeneity in the top 30 cm of soil using digital images taken with a minirhizotron camera. In contrast to previous studies, total root length did not significantly vary between A. cristatum and native grassland, suggesting similarity in potential carbon storage. Root length heterogeneity, however, was significantly lower beneath A. cristatum than native grassland, suggesting that A. cristatum roots occupy soil volume more evenly than those of native grasses. The relatively homogeneous occupation of soil by A. cristatum roots may be an important component of its ability to displace native grasses.