Microorganisms are vital in mediating the earth’s biogeochemical cycles; yet, despite our rapidly increasing ability to explore complex environmental microbial communities, the relationship between microbial community structure and ecosystem processes remains poorly understood. Here, we address a fundamental and unanswered question in microbial ecology: ‘When do we need to understand microbial community structure to accurately predict function?’ We present a statistical analysis investigating the value of environmental data and microbial community structure independently and in combination for explaining rates of carbon and nitrogen cycling processes within 82 global datasets. Environmental variables were the strongest predictors of process rates but left 44% of variation unexplained on average, suggesting the potential for microbial data to increase model accuracy. Although only 29% of our datasets were significantly improved by adding information on microbial community structure, we observed improvement in models of processes mediated by narrow phylogenetic guilds via functional gene data, and conversely, improvement in models of facultative microbial processes via community diversity metrics. Our results also suggest that microbial diversity can strengthen predictions of respiration rates beyond microbial biomass parameters, as 53% of models were improved by incorporating both sets of predictors compared to 35% by microbial biomass alone. Our analysis represents the first comprehensive analysis of research examining links between microbial community structure and ecosystem function. Taken together, our results indicate that a greater understanding of microbial communities informed by ecological principles may enhance our ability to predict ecosystem process rates relative to assessments based on environmental variables and microbial physiology.

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.

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Recovery of belowground microbial community structure is important for reclamation success. In this study, the recovery of soil microbial community structure in cool‐season grass dominated and sagebrush dominated reclaimed sites were examined using chronosequences ranging in time following reclamation from <1 to 26 yr. Phospholipid fatty acid (PLFA) analysis was used to characterize changes in microbial community structure with time. Initial effects of surface mining resulted in reductions of total microbial biomass and diversity, with the greatest influence on saprophytic fungi and arbuscular mycorrhizal fungi relative to undisturbed soils. The total concentration of PLFA biomarkers increased after 14 yr in soils established under cool‐season grass communities and 5 yr in soils colonized by sagebrush communities. Canonical multivariate analysis of variance indicated that soil microbial communities under reestablished sagebrush were more similar to one another than those under cool‐season grasses. In general, microbial biomarkers of reclaimed soils recovered to predisturbance levels within 5 to 14 yr, which indicated that the most important phase of microbial community recovery occurs between 5 and 14 yr after reclamation.

ent on a reclaimed area will depend to a large degree on a range of soil physical, chemical, and biological vari-Soil quality and the ability of soil to sustain nutrient cycling in drasables (National Research Council, 1994) and the severe tically disturbed ecosystems will influence the establishment and maintenance of a permanent and stable plant community. We undertook perturbations that occur in the strip mining process can research to evaluate a recently developed method to assess soil quality severely impact these variables. and nutrient cycling potential in a series of reclaimed soils. The method Arid and semiarid soils are characteristically low in involves correlating the 3-d flush of microbial respiration after a soil SOM and nutrients (Jenny, 1930) and this inherently is rewetted against a range of soil biological parameters. Soils were low soil fertility is further reduced by the mining process. sampled from a number of reclaimed coal mines, a reclaimed uranium In this process, the surface layers of soil (typically the mine, and native, undisturbed prairie. All sites were located in semiarid A ϩ B horizons) are removed, potentially stored for a Wyoming. Soils were dried at 55؇C, rewetted, and microbial respiration period of time in large stockpiles where plant inputs are measured at 3 d (Cmin 0-3d ) and 21 d (Cmin 0-21d ). In addition, microbial often minimal (particularly at depth), and then respread biomass C (MBC), N mineralization (Nmin 0-21d ), soil organic C (SOC), over regraded spoil material on these reconstructed sites. and total N were also measured. Correlations between Cmin 0-3d and the measured soil parameters in reclaimed and native soils were generally Soils are further altered, especially physically, during strong (r 2 Ն 0.45) and highly significant (P ϭ 0.0001). Differences seedbed preparation. All of these operations result in the between reclaimed and native soils were observed, with native soils destruction of aggregates (Abdul-Kareem and McRae, exhibiting more variability, possibly due to: differences in soil homog-1984) leading to the rapid mineralization and subseeneity/heterogeneity, the relative lability of the substrates present; quent decline of SOC. This loss of soil C is further exdifferent microbial communities; and differences in soil structural propacerbated by the additional dilution of C and nutrients erties. Correlations between Cmin 0-3d and the measured soil paramwhen the soils are salvaged and respread, as the much eters in spoil material, while significant, were less well correlated. We greater concentration of C and nutrients present in the believe this method is a relatively fast, accurate, and economical means A horizon are mixed with the B horizon. There is little by which soil quality and nutrient cycling can be ascertained. We in the way of literature as to the amount of SOC/SOM estimated that a minimum concentration of 0.52% SOC or 0.89% soil organic matter (SOM) is necessary to sustain an adequate level of

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