Stable isotope characteristics across narrow savanna/woodland ecotones in Wolfe Creek Meteorite Crater, Western Australia.

The stable isotopic composition (delta13C) of sediments from lakes are frequently analyzed to reconstruct the proportion of the regional vegetation that used either the C3 or C4 photosynthetic pathways, often without conducting a detailed survey of the current local vegetation. We performed a study on the modern vegetation composition within the Wolfe Creek Meteorite Crater to complement our future paleoecological investigation of the crater. A bull's-eye pattern exists where C4 grasses dominate an outer ring and salt tolerant species, including shrubs, herbs, chenopods, and halophytic algae, dominate the inner pan of the crater. The ecotone between the inner and outer zones is narrow and occupied by tall (>7 m) Acacia ampliceps, with some C4 grasses in the understory. Along with the highest water table and most saline soils the center of the crater has C3 plants present with the highest delta13C and delta15N values. The range of delta13C and delta15N values from the analysis of surface soil organic matter (OM) was much smaller compared with the range of values from plant materials implying that either: (1) the current plant OM has not yet been integrated into the soils, or (2) processes within the soil have acted to homogenize isotopic variability within the crater. The application of a two end member mixing model to calculate %C4 and %C3 biomass from the delta13C of surface soil OM was complicated by: (1) the crater containing both a dry habitat with C4 grasses and a central pan with C4 halophytic plants and, (2) the large variation in the delta13C of the plants and soil OM.