PARENT SESSION
Oral Session # 60: Invasive Species V: Genetics; Chemical Cycling Effects.
Presiding: S Miao
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 204.
Cheatgrass (Bromus tectorum L.) and seasonal patterns of soil phosphorus availability in arid ecosystems.
Sanford, Robert*,1, Belnap, Jayne2, Gopalani, Sarah1, Wojcik, Nathan1, Richardson, Maxwell1, 1 University of Denver, Denver, CO2 USGS - Biological Resources, Moab, UT
ABSTRACT- Seasonal changes in soil phosphorus (P) availability are not yet known for many ecosystems. We report seasonal changes in several pools of soil phosphorus, including plant available P from the Mojave Desert and Colorado Plateau. In addition we show that cheatgrass changes soil P fractions in unexpected and ecologically significant ways. Monthly soil samples (0-10 cm) from four sites in Canyonlands National Park in southeast Utah, are analyzed for P with a modified Hedley P fractionation method. Labile P (plant available) peaks in spring and autumn with significant monthly variation. Surprisingly, HCl extractable P changes as well, with a pattern inverse to that of labile P. Each of these sites has considerable Bromus tectorum L. (cheatgrass) invasion. In a separate greenhouse study with four contrasting soils (0-10 cm) from the Mojave desert CA and NV, we grew cheatgrass for 100 days to test for soil P changes. Regardless of the soil type, cheatgrass causes large (2x) increases in labile P and large (90%) decreases in both NaOH and HCl extractable P. In addition, root biomass, root nitrogen (N) and P as well as shoot biomass and shoot N and P vary widely according to soil type. We propose that cheatgrass roots solubilize large amounts of soil phosphorus seasonally, from P pools that are considered unavailable to most plant species, and that this solubilized P becomes available for Broumus tectorum L. uptake. These results are discussed in the contexts of root exudates, mycorrhizae and root rhizosphere effects on desert soil P.
Key words: soil, seasonal, Bromus tectorum , phosphorus