Appendix F. Soil cation ratios among microhabitats.
The ratios of available Potassium to other available soil cations were calculated to examine the biotic influence of shrubs on microhabitat soil fertility. As K is chemically similar to other soil cations but more coupled to biotic cycling, a higher abundance of K under shrubs (relative to other cations) may indicate selective biotic accumulation (Schlesinger et al. 1996). In addition to fully-replicated measurements of N, P, and K in April 2006, I ran a soil cation panel (U.C. Davis Analytical Laboratory) using one homogenized sample from each microhabitat (homogenized samples contained an equal amount of soil from each replicate plot). Although homogenization removes measures of variance for soil cations, it provides an excellent estimate of the mean (mean K from individually-analyzed plots = 213 ppm vs. mean K from the 3 homogenized samples = 214 ppm). I calculated ratios of available K to other available soil cations (Ca, Mg, Zn, Mn, Cu, and Fe) for each plot as that plot’s available K (ppm) divided by the mean panel cation (ppm) for the appropriate microhabitat.
|FIG. F1. Ratios of available Potassium to other soil cations. Values are means with 95% confidence intervals. Asterisks indicate a significant test of the hypothesis that shrub microhabitats differ from intershrub microhabitats (**P < 0.01, ***P < 0.001), whereas NS indicates nonsignificance.|
Schlesinger, W. H., J. A. Raikes, A. E. Hartley, and A. E. Cross. 1996. On the spatial pattern of soil nutrients in desert ecosystems. Ecology 77:364–374.