Carbon cycling dynamics during succession in sagebrush steppe.

摘要

Fire in big sagebrush (Artemisia tridentata Nutt.) ecosystems is a natural phenomenon and a land management tool that is associated with large releases of carbon dioxide (CO2) to the atmosphere while burning, and potentially large uptake of CO2 from the atmosphere during recovery (succession). Because big sagebrush covers ∼11% of North America, this ecosystem is a potentially important influence on continental-scale carbon cycling. However, little is understood about how the balance between C sources and sinks change as sagebrush ecosystems shift from dominance by herbaceous plants to dominance by big sagebrush shrubs during succession.; Therefore, this study quantified successional changes of both above- and belowground C pools (biomass and soil C) and soil respiration fluxes (R S), and established predictive models of RS using soil gravimetric water content (thetaG) and temperature (T) to help understand mechanisms driving RS. Allometric relationships describing big sagebrush biomass using simple crown measurements provided evidence that simple field measurements may be used to estimate biomass over large regions and that universal scaling rules may be valid for semiarid shrubs. Quantification of belowground C pools suggested that sagebrush ecosystem root biomass does not change during succession after fire (0.43 +/- 0.03 kg m-2 ). Separation of the mineral associated soil C provided evidence that soil is sequestering C during succession and that the largest amount of labile soil C (1.0 +/- 0.33 g C kg soil-1) occurred during the peak of ecosystem productivity when herbaceous and shrub plants were co-dominant. Partitioning soil respiration into heterotrophic (RH, non-root associated) and autotrophic (RA, root-associated) provided strong evidence that RH contributes a greater proportion of the soil CO 2 flux than RA, which is highly variable and depends on plant photosynthetic substrates and successional stage. Regardless of successional stage, RS, RH, and RA responded similarly to environmental drivers, but only when T was > 10°C and theta G was > 10%. Peak C cycling rates, both uptake and release, occurred during co-dominance between herbaceous and shrub species. This study will support future land management decision-making and C cycle modeling at multiple scales for sagebrush ecosystems.