Effect of Temperature on Potassium and Sodium Exchange in a Sierra Nevada Riparian Soil

Abstract

In the course of investigating nutrient availability in a montane meadow ecosystem of the Sierra Nevada range, it was determined that resin availability of Na+ and K+ was significantly affected by season (winter vs. summer and fall). The underlying mechanism(s) controlling this seasonal effect was investigated in the laboratory. Four replicate A horizon samples of a Typic Humaquept (silty clay texture, kaolinitic mineralogy, 3% organic C, pH 5.10) were saturated with Mg2+ Using 5‐g subsamples from each replicate, soil was equilibrated for a period of 30 min with 30 mL of a 5.00 mmol solution of Na+ and K+ at 1, 15, 30, and 45°C. After centrifugation, the supernatant was analyzed for K+, Na+, and Mg2+ Exchanger sorption characteristics varied significantly with temperature. Overall, K+ was preferentially sorbed over Na+, but the proportional sorption of K+ decreased significantly at a temperature of 1°C. The temperature dependence of K+ and Na+ sorption partially explains seasonal differences in availability. Net sorption (K+ + Na+ − Mg2+) was statistically similar to 0 at temperatures of 15, 30, and 50°C, but significantly increased at 1°C. This increase in cation exchange capacity at low temperature may have special relevance to ecosystems during snowmelt when increased retention of certain cations could occur.