Geochemical Tracing of Ecosystem Consequences of Vegetation Change
We are using strontium isotopes to investigate the consequences of changes in rooting depth changes associated with shrub encroachment into grasslands. A combination of over-grazing and fire suppression has contributed to woody plants invading grasslands, and these woody plants are much more deeply rooted than grasses. As part of a broad field study, we have taken soil cores to 10m depth have been taken in adjacent grassland and shrubland communities at six sites in New Mexico, Colorado, Kansas, Oklahoma, and Texas. Above and below-ground plant samples were taken at each of the sites. Water, carbon, and soil microbiology analyses are underway.
Since Sr is a chemical analog for Ca, an essential plant nutrient, Sr isotopes could be useful in determining the depth of nutrient uptake by plant roots. We are measuring the 87Sr/86Sr values of plant leaves for comparison with values for shallow and deep soil layers. The strontium isotope variations will be used to assess differences between the depths at which the woody plants vs. the grasses access nutrients.
This research is detailed in the following publication:
Jackson, R. B., Banner, J. B., Jobbágy, E. G., Pockman, W. T., Diana H. Wall, D. H., 2002, Changes in carbon storage and ecosystem functioning with desertification and woody plant invasions, Nature 418, 623-626. (Article, News & Views, other links).