Friday, August 6, 2010

PS 103-114: Plant-soil feedbacks in cheatgrass-invaded sagebrush ecosystems

John M. Stark, Brittany Packer, D'Jenane Diaz, Brandon Chambers, Cade Kowallis, Toby D. Hooker, and Jeanette M. Norton. Utah State University


Following wildfire in western rangelands, cheatgrass (Bromus tectorum) frequently invades and forms nearly monospecific stands that resist re-colonization by native grasses or shrubs. One mechanism hypothesized to explain this persistence is that cheatgrass creates positive plant-soil feedbacks. We examined long-term restoration plots in a sagebrush ecosystem in NW Colorado that had been fumigated (with methyl bromide to sterilize soil) and revegetated (planted to either native perennials or weedy species such as cheatgrass) 25 years ago to determine if cheatgrass modifies soil chemical or biological properties in ways that promote its own persistence.


Reciprocal plantings of cheatgrass and bluebunch wheatgrass seedlings in the field showed that both cheatgrass and bluebunch wheatgrass grew significantly better on cheatgrass soil than on sagebrush-wheatgrass soil. Soil assays suggest that net N-mineralization is greater on cheatgrass soil, and thus differences in plant production may result from greater N availability on cheatgrass soil; however, other soil characteristics, such as nematode population size, differ as well. The potential role of soil biological and chemical characteristics in promoting cheatgrass persistence will be discussed.