Bromus Tectorum (cheatgrass): Monitoring An Invasion for 10 Years.

In a Krascheninnikovia lanata (winterfat) community in the Honey Lake Valley of northeastern, CA we have monitored the effect of B. tectorum (a Eurasian exotic annual grass) invasion on surface soil properties. In 1990 a transect of 13 plots, 50 m apart was established, at which time only plots 1-5 were invaded. In 2009 all plots had been invaded. Within 5 m of each plot center, 0-30 cm soil samples from interspace locations were collected multiple times per year and analyzed for availability of N, P, Ca, Mg, K, Fe and Mn and enzyme activities. Pooled over all sampling dates and relative to non-invaded plots, B. tectorum invasion fostered significant increases in available of N (0.20 vs. 0.16 mmol kg-1), net N mineralization potential (0.24 vs. 0.18 mmol kg-1), Solution P (6.9 vs. 5.1 µmol L-1), DTPA-Fe (0.031 vs. 0.025 mmol kg-1), Phosphatase activity (0.46 vs. 0.33 µmol g-1 hr-1), and amidase activity (8.3 vs. 5.8 µmol g-1 hr-1). For the plots initially invaded in 1990, unexpected trends over 10 years included decline in phosphatase activity (2000=0.51; 2010=0.10 µmol g-1 hr-1) and solution phase Ca+2 (2000=4.3; 2010=0.4 mmol L-1). We hypothesize that solution phase Ca+2 decreased because increased bioturbation, upon B. tectorum invasion, brought solid phase CaCO3 to the soil surface and controlled Ca+2 solubility to a lower level.