Soil CO2 Efflux Responses to Soil Loss on Two Rangeland Ecosystems

Abstract

A steady state in soil carbon (C) requires that the production of organic C compounds equal their losses through respiration and erosion. How accelerated rates of soil loss affect this balance in western rangelands, where rates of C accumulation without disturbance are relatively slow, is not well understood. The purpose of this study was to determine the effects of soil loss on total, bare soil, and plant respiration rates at shortgrass prairie and sagebrush steppe sites. The experimental design was a split- plot, randomized block, with a factorial arrangement of treatments. The factor levels consisted of 3 levels of soil removal (0, 11.2, and 22.4 t/ha) and 2 range condition classes (good and fair) with 3 replications each at the shortgrass site. Range condition class was not a factor considered at the sagebrush site. Soil CO2 efflux was measured at weekly intervals during the 1999 and 2000 growing seasons at the shortgrass site but only during the 2000 season at the sagebrush site. Total, bare soil, and plant respiration rates at the sagebrush site varied little (P > 0.10) among the 3 soil removal treatments. While total respiration at the shortgrass site increased significantly (P < 0.10) as soil removal level increased, bare soil respiration did not vary (P > 0.10) among the 3 soil removal levels. Plant respiration rates at the shortgrass site generally increased as soil removal level increased, but this response was affected by environmental factors that influenced plant productivity. Increased total respiration rates observed on the shortgrass prairie resulted primarily from increased plant respiration rather than from changes in bare soil respiration. Thus, changes in plant respiration following disturbance may be more important to total soil CO2 efflux than soil flora and faunal respiration that appeared to be more resistant to disturbance.