Stable isotope ratios of pedogenic carbonate and organic matter were measured in a prairie-transition-forest soil biosequence near Ames, Iowa to determine the vegetation succession. The modern vegetation is dominated by non-native C plants which have been introduced by agricultural practices. The δC values of soil organic matter from the prairie and forest endmembers indicate C and C dominated ecosystems, respectively, during the accumulation of soil organic matter. Pedogenic carbonate from all soils, including rare pedogenic carbonate from the forested soil, has an average δC of-2.0‰, indicating that the carbonate formed under a C vegetation. These results indicate that the ecosystem was a C-dominated prairie and therefore suggest a recent arrival of forests and other C plants in the area. This study also implies that the primary features of the transitional Lester soil series, which has soil properties intermediate between Alfisols and Molisolls, formed under prairie conditions and were overprinted by an invading forest.
Soil redistribution (erosion and deposition) can greatly affect the fate of soil organic carbon (SOC) in agroecosystems. Landscape topography is one of the key factors controlling erosion processes and creating spatial variability in SOC. We combined carbon (C) isoscape (isotopic landscape) analysis, historic orthophoto interpretation, cesium ( 137 Cs) inventory measurement, and digital terrain analysis to quantify SOC dynamics and soil redistribution relationship and their responses to landscape topography in an Iowa cropland field with soybean/maize (C3/C4) rotation. The historic orthophotos and 137 Cs were used to reflect soil redistribution before and after the 1960s, respectively. Topography-based models were developed to simulate 137 Cs inventory, SOC density, and C isotopes using stepwise principal component regression. Spatial patterns of SOC were similar to soil erosion/deposition patterns with high SOC density in depositional areas and low SOC density in eroded areas. Soil redistribution, SOC density, and isotopic signature of SOC (δ 13 C) were highly correlated with topographic metrics, suggesting that topographic heterogeneity drove the spatial variability in erosion and SOC dynamics. Considering the isotopic composition of SOC, C3-derived SOC density was strongly controlled by topographic metrics, but C4-derived SOC density showed weaker expression of spatial pattern and poor correlation to topographic parameters. The resulting topography-based stepwise principal component regression models captured more than 60% of the variability in SOC density, δ 13 C , and C3-derived SOC density but could not reliably predict C4-derived SOC density. Our results indicate that exploring C isotopes in response to soil erosion is important to understand the fate of eroded SOC within croplands under C3/C4 cultivation.Plain Language Summary Landscape topography that describes the shape and features of landforms is an important factor influencing soil redistribution in agricultural lands because it governs the gravity-driven soil movement by water flow and tillage operations. This redistribution affects spatial distribution patterns of soil organic carbon (SOC) due to the preferential transportation of fine soil particles enriched in SOC. This study examined how topography controlled soil erosion and affected SOC and its carbon (C) isotope composition ( 12 C to 13 C ratio) in a cropland under soybean/maize (C3/C4) cultivation. A set of topographic metrics were derived from a digital elevation model using light detection and ranging data. We found that more than 60% of the spatial variability in SOC and isotopic signature of SOC (δ 13 C) was related to soil redistribution patterns in the landscape. Topographic metrics were strongly correlated with soil redistribution, SOC, δ 13 C , and C3-derived SOC, and the resulting topography-based models showed high efficiencies in simulating the above variables. In contrast, C4-derived SOC showed a lower spatial pattern. This study highlights the importance of topography on soil er...
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