Rooting depth is an important factor in understanding tree throw, erosion rates, vertical macropores, weathering, and regolith depth in soils. The current understanding is that in the majority of terrestrial biomes 80% of roots are distributed in the top 20 cm of soil. We hypothesized that sandstone lithologies will cause roots to distribute deeper in soils when compared to shale due to greater water holding capacity, nitrogen and phosphorus availability, and cation exchange capacity in the surface soils of shale. To test this, pits were dug at 14 locations in Central Pennsylvania from both the Tuscarora State Forest and the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO) with 9 locations where soils were derived from primarily shale, and 5 locations where soils were derived from primarily sandstone. At these sites, pit walls were photographed to a depth of 120 cm in order to determine roots distribution. Roots from pit walls were also collected for determination of mycorrhizal colonization and tree species identity by DNA barcoding. Root distribution at shale sites confirmed previous reports. However, observations at sandstone sites found root distributions of ~25% at depths of 20-40 cm, compared to ~15% in shale, which is consistent with our hypothesis that roots in sandstone-derived soils would be more deeply distributed. Root distributions from all other depths were not statistically different between the sandstone and shale sites. Roots are now being processed to identify relative abundance of tree species at different depths. The barcoding analysis will help to determine the role of niche partitioning in root distribution across different lithologies. These results highlight the effect of abiotic environments on root distribution, and the changing role of roots on biogeochemical cycling processes.
Szink, I., Adams, T.S., Orr, A.S., Ruppel, M., Donnelly, S., Brazil, L.I., and Eissenstat, D.M. (2016): Comparing Rooting Depth and Niche Partitioning Between Shale and Sandstone Derived Soils in Central Pennsylvania Mixed Forests. 2016 Fall Meeting, American Geophysical Union, San Francisco, CA, 12-16 Dec..
This Paper/Book acknowledges NSF CZO grant support.