Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 11, 2013
Publication Date: June 15, 2013
Citation: Blank, R.R., Morgan, T.A., Clements, C.D., Mackey, B.E. 2013. Bromus tectorum L. invasion: Changes in soil properties and rates of bioturbation. Soil Science Society of America Journal. 178:281-290. Interpretive Summary: Cheatgrass (Bromus tectorum) has been and is responsible for much environmental degradation of Western rangelands. To gage the long-term effects of cheatgrass on soil properties, we monitored an invasion of a native winterfat community for 12 years. The data suggest cheatgrass has increased the availability of soil nitrogen and phosphorus. The greatest change, however, was an increase in deep-burrowing rodents. These rodents have mixed calcareous underlying material to the soil surface thereby fundamentally changing its chemistry and physical properties.
Technical Abstract: Bromus tectorum (cheatgrass, downy brome), an exotic annual grass of Eurasian origin, has replaced native Artemisia/bunchgrass communities on millions of hectares throughout the Intermountain West. Using Jenny’s (1941) framework that specific vegetation can differentially affect soil development; we hypothesize that invasion by B. tectorum will alter soil physical and chemical properties and alter pedogenic trajectories. Hypothesis testing was done in the Honey Lake Valley of northeastern CA, by monitoring the invasion of a near pristine Krascheninnikovia lanata (winterfat) community by B. tectorum. In 1999, a 13-point transect, 50 m apart, was established extending from the invasion front to non-invaded areas. Several times throughout the year, soils were sampled randomly near each transect point, 0-20 cm, and analyzed for various soil attributes. In 2004, we also installed resin capsules to quantify nutrient availability. In 2000, only the first four transect points were invaded. By 2011, at which time the study was concluded, all 13 points were invaded. We analyzed trends over time and compared soil properties between invaded and non-invaded. Relative to non-invaded sites, B. tectorum sites had: greater mineral N concentration and greater molar proportion of NH4+ in that fraction; greater enzyme activities of amidase and phosphatase; greater solution-phase concentrations of ortho-P and molar proportion of NO2- in the NO2--N + NO3--N pool; greater micronutrient availability of Fe and Cu; higher soil pH; and greater resin available Mn and P. Significant trends with time, as B. tectorum assumed a greater proportion of the experiment plots, were: a decline in mineral N, phosphatase activity, and soil-solution concentrations of Ca+2 and K+; an increase in net N mineralization potential, molar proportion of NH4+ in the mineral fraction, soil pH; greater resin availability of Fe; and less resin availability of NO3--N. These data support the developing paradigm that invasive plants such as B. tectorum are able to “engineer” the soil to favor their invasiveness. We offer evidence that the decline in solution-phase Ca+2 and ortho-P and the increase in soil pH is due to an invasion-fostered increase in bioturbation from rodents, which mix carbonate-bearing soil from lower horizons to the soil surface. We conclude that changes in soil properties induced by B. tectorum invasion have potential long-term ramifications to soil and successional trajectories.