No abstract

Good management of rangelands promotes C sequestration and reduces the likelihood of these ecosystems becoming net sources of CO2 As part of an ongoing study, soil was sampled in 2003 to investigate the long‐term effects of different livestock grazing treatments on soil organic carbon (SOC), total nitrogen (TN), and microbial communities. The three treatments studied (no grazing, EX; continuously, lightly grazed [10% utilization], CL; and continuously, heavily grazed [50% utilization], CH) have been imposed on a northern mixed‐grass prairie near Cheyenne, WY, for 21 yr. In the 10 yr since treatments were last sampled in 1993, the study area has been subject to several years of drought. In the 0 to 60 cm depth there was little change in SOC in the EX or CL treatments between 1993 and 2003, whereas there was a 30% loss of SOC in the CH treatment. This loss is attributed to plant community changes (from a cool‐season [C3] to a warm‐season [C4] plant dominated community) resulting in organic C accumulating nearer the soil surface, making it more vulnerable to loss. Soil TN increased in the EX and CL treatments between 1993 and 2003, but declined in the CH treatment. Differences in plant community composition and subsequent changes in SOC and TN may have contributed to microbial biomass, respiration, and N‐mineralization rates generally being greatest in CL and least in the CH treatment. Although no significant differences were observed in any specific microbial group based on concentrations of phospholipid fatty acid (PLFA) biomarkers, multivariate analysis of PLFA data revealed that microbial community structure differed among treatments. The CH grazing rate during a drought period altered plant community and microbial composition which subsequently impacted biogeochemical C and N cycles.

No abstract

Reclaimed coal mine lands have the potential to sequester atmospheric carbon (C); however, limited information exists for the western USA coalfields. This study was carried out on two chronosequences (BA-C 3 grasses and DJ-shrubs) of reclaimed sites at two surface coal mines to determine the effects of vegetation, soil texture, and lignin content on soil total organic carbon (TOC) accumulations. In the BA chronosequence, TOC increased over 26 years at an average rate of 0Á52 Mg C ha À1 yr À1 in the 0-30 cm depth and was significantly correlated with clay content. Comparison between < 1 and 16-year-old stockpile soils indicated TOC content did not differ significantly. In the DJ chronosequence, TOC content in the 0-30 cm depth declined from 31Á3 Mg ha À1 in 5-year-old soils to 23Á4 Mg ha À1 in 16-year-old soils. The C:N ratios suggested that some (up to 2Á0 per cent) of the TOC was potentially derived from coal particles in these reclaimed soils. Soil total N (TN) contents followed a similar trend as TOC with TOC and TN concentrations strongly correlated. Lignin contents in TOC of all reclaimed soils and topsoil stockpiles (TSs) were higher than that of nearby undisturbed soils, indicating the recalcitrant nature of TOC in reclaimed soils and/or possibly the slow recovery of lignin degrading organism. Results indicated that TOC accumulations in DJ were largely controlled by its composition, particular lignin content. In BA sites TOC accumulation was strongly influenced by both clay and lignin contents.