Variability in soil and foliar stable carbon and nitrogen isotope compositions in the winter rainfall biomes of South Africa
2022
Carr, Andrew S. | Chase, Brian M. | Boom, Arnoud | Meadows, Michael E. | Sanchez, Javier Medina
We present the stable carbon and nitrogen isotope compositions of 204 plants and 99 soils from South Africa's Fynbos and Succulent Karoo biomes, from which we assess variability in δ¹³C and δ¹⁵N within and between the biomes. Higher foliar δ¹³C in the Succulent Karoo (−22.4 ± 4.7‰) primarily reflects a greater abundance of CAM photosynthesis relative to Fynbos (−25.7 ± 3.5‰). For C₃ plants within the Fynbos Biome, there is no statistically significant relationship between δ¹³C and climate, suggesting that within the present sampling framework, local-scale variability masks expected climatic controls on C₃ plant δ¹³C. Soil and foliar δ¹⁵N are highly variable, but foliar δ¹⁵N is significantly higher in the Succulent Karoo (7.7 ± 3.9‰) compared to the Fynbos (4.4 ± 3.3‰). Soil and foliar δ¹⁵N correlate, with soils 3 ± 1‰ more enriched in ¹⁵N. Both soil and foliar δ¹⁵N show stronger correlations with climate than δ¹³C, and they accord with the previously observed tendency for higher δ¹⁵N with greater aridity. The relationship between δ¹⁵N and mean annual rainfall is, however, relatively steep (2.4 ± 0.6‰ per 100 mm rainfall), potentially implying additional controls on δ¹⁵N variability. These data provide a benchmarking of contemporary isotopic variability, anticipated to support future archaeological, palaeoenvironmental and C and N cycling research.
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