Soil biogeochemistry of Hesperidanthus suffrutescens (shrubby reed-mustard) habitat in the Uinta Basin, Utah

Background/Question/Methods

Hesperidanthus suffrutescens (shrubby reed-mustard), an endangered perennial shrub endemic to the Uinta Basin, Utah, faces habitat loss and fragmentation due to development of natural resources, including road construction and gas and oil drilling. Although shrubby reed-mustard (SRM) has been long been observed in a particular shale strata of the Green River formation (Eocene), little is known about the ideal range of soil chemical and physical properties required for successful establishment, growth, and survival of SRM populations.

Soils with (SRM) and without (Non-SRM) shrubby reed-mustard vegetation were sampled at three sites within the Uinta Basin: Johnson Draw, Big Pack Mountain, and Badland Cliffs. Vegetation in Non-SRM plots was typically Artemisia nova (black sagebrush). A total of 49 soil profiles were described and sampled by morphologic horizon in small, hand-dug excavations.  Soil samples were sieved to obtain the <2mm fraction and analyzed for particle size distribution, available phosphorus, inorganic and organic carbon, nitrogen, cation exchange capacity (CEC) and total elemental analysis. Electrical conductivity (EC), sodium adsorption ratio (SAR), pH, and elemental analysis were determined on water extracts (1:1 soil:water).

Results/Conclusions

We found that SRM grows exclusively on shale and in shallow soils. Average depth to bedrock for SRM soils was 23 cm, with only one soil deeper than 50 cm.  On a weighted-average pedon basis, SRM soils had siltier textures (silt or silt loam) whereas Non-SRM soils had sandier textures (loam, sandy loam, clay loam). Inorganic carbon, most likely in the form of carbonates, was higher in SRM plots (6.0% versus 4.2% for Non-SRM plots), but organic carbon and nitrogen were similar in both plots (1% C, 0.1% N). Organic carbon to nitrogen ratios (C:N) were higher for SRM soils (14) than for Non-SRM soils (10), indicating that the organic matter present in SRM soils is less highly decomposed than in Non-SRM soils. However, nitrate levels were higher in SRM versus Non-SRM soils; SRM may have low nitrogen requirements compared to other vegetation, or other sources of nitrate, including bedrock, may be available. Available phosphorus in the SRM plots (17.4 mg P/kg soil) was about half the levels found in Non-SRM plots (41.8 mg P/kg soil). SRM soils had slightly higher CEC, pH and SAR than Non-SRM soils, but lower concentrations of the potentially toxic heavy metals Ag, As, Co, Cr, Cu, Ni, Sn, and Zn.