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

The stable isotopic composition (delta C-13) of sediments from lakes are frequently analyzed to reconstruct the proportion of the regional vegetation that used either the C-3 or C-4 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 C-4 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 C-4 grasses in the understory. Along with the highest water table and most saline soils the center of the crater has C-3 plants present with the highest delta C-13 and delta N-15 values. The range of delta C-13 and delta N-15 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 %C-4 and %C-3 biomass from the delta C-13 of surface soil OM was complicated by: (1) the crater containing both a dry habitat with C-4 grasses and a central pan with C-4 halophytic plants and, (2) the large variation in the delta C-13 of the plants and soil OM.