The δ13C values of plants and corresponding charred materials from wood, C3 and C4 grasses, deriv... more The δ13C values of plants and corresponding charred materials from wood, C3 and C4 grasses, derived from natural burning and laboratory combustion were obtained to determine whether there was a significant difference in δ13C of grass-derived char (C3 ...
The analyses of stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) of soil organic matter... more The analyses of stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) of soil organic matter (SOM) is an increasingly used tool to estimate soil carbon turnover, to assess degree of soil development, and to study historical C3/C4 vegetation changes. However, the exact processes that control 13C- and 15N-enrichment of SOM within a soil profile are still not clearly identified. To better understand the isotopic processes associated with decomposition of SOM, we studied two Vertisol profiles and one Oxisol profile from southern Queensland by radiogenic (14C), stable isotopic (δ13C, δ15N), and spectroscopic (13C-NMR and FTIR) methods. The findings of this study demonstrate that fundamental differences exist in δ13C and δ15N fractionation dynamics in different soil types and that isotopic fractionation is highly influenced by soil chemistry, mineralogy, and type of organic matter input. Stable isotopic analyses of the Oxisol show the typically observed increase in δ13C and δ15N in the subsurface horizon whereas the Vertisols show consistently decreasing values with depth. The high degree of 13C-enrichment in the Oxisol compared with the Vertisols cannot be simply explained with increased fractionation due to soil age, as the 14C age of the Vertisols is greater and increases more rapidly with depth, compared with that of the Oxisol.Data from 13C-NMR, XRF and IR data together with data on pH and clay content reveal a more complex picture of isotopic fractionation in soils. The Oxisol is dominated by O-alkyl carbon and aromatic material whereas the Vertisols contain higher amounts of alkyl carbon. Smectite and kaolinite are the dominant clay minerals in the Vertisols while the Oxisol is dominated by gibbsite, kaolinite, and Fe and Al-oxides.We suggest that the 13C- and 15N-depletion in the Vertisols is associated with low pH, which inhibits nitrification and promotes stabilization of 13C-depleted alkyl material by smectitic clays. The 13C-enrichment in the Oxisol correlates with a high abundance of relatively 13C-enriched O-alkyl carbon, which is a mix of primary materials (plant carbohydrates) as well as secondary (microbially synthesized) carbon. The abundance of relatively labile O-alkyl carbon even at depth is likely due to physico-chemical protection through complexation with Fe- and Al-oxides.
... and nitrogen (15N) signatures in soil organic matter in central Australia DMJS Bowman,1* Guy ... more ... and nitrogen (15N) signatures in soil organic matter in central Australia DMJS Bowman,1* Guy S. Boggs,2 Lynda D. Prior1 and Evelyn S. Krull3 ... The best palynological late Pleistocene Holocene record comes from Lake Eyre and Lake Frome (Luly, 2001). ...
Here we present d13C and dD data of C27-C31 n-alkanes from C3 (trees) and C4 (grasses) plants and... more Here we present d13C and dD data of C27-C31 n-alkanes from C3 (trees) and C4 (grasses) plants and from the corresponding soils from a grassland-woodland vegetation sequence in central Queensland, Australia. Our data show that C4 species (Iseilema and Astrebla) from the grassland were consistently 13C-enriched relative to C3 tree plant materials (Acacia leaves and seedpods and Atalaya leaves) from the woodland and woody grassland. However, n-alkanes from the C4 grasses were \deltaD depleted (-77\permil) relative to the Acacia leaves and seedpods, but showed no difference in dD values when compared with C3 Atalaya leaves. This is contradictory to data from previous studies, showing that C4 plants were enriched in \deltaD relative to C3 plants (the same direction as the d13C values). This past observation has been ascribed to C4 plants accessing the more evaporation-influenced (D-enriched) surface water and tree roots sourcing more D-depleted deeper soil water. Our data, on the other hand, indicate that ecosystem characteristics (woody versus grassy) have a greater influence on the dD values of the vegetation than the type of photosynthetic pathway. Specifically, the differences in dD values from "woodland" trees (Acacia) compared with "woody grassland" trees (Atalaya) suggest that the dD of soil water in semi-arid climates is ecosystem-dependent. This concept is supported by d13C and dD analysis of the C31 n-alkane, a grass-specific biomarker, from woodland and grassland soils. The similar d13C values in the woodland (-25.2±0.34\permil) and grassland soil (-25.1±0.03\permil) confirmed that the C31 n-alkane is grass-derived. The dD values of the C31 n-alkane, on the other hand, were by 12\permil enriched in the soil under the woodland compared with the one under grassland, supporting that the dD values of the soil water profile are governed by the hydrological characteristics of the ecosystem, not by photosynthetic pathway. The C27 and C29 n-alkanes (tree-specific biomarkers) from the woodland soil were more enriched in dD than the C31 n-alkane and were very similar to the values of the Acacia leaves. A crossplot of the d13C and dD values of the long-chained n-alkanes from plants and soil organic matter indicates that isotopic values from soil organic matter n-alkanes faithfully record recent changes in vegetation (in this case C4 to C3-dominated) as well as changes in water sources as the ecosystem changed from grassy to forested. Thus, the data from this study provide insight into soil-water-plant dynamics in semi-arid climate soils and caution against the assumption that d13C and dD differences in C3 and C4 plants are independent of climate and water stress.
... and nitrogen (15N) signatures in soil organic matter in central Australia DMJS Bowman,1* Guy ... more ... and nitrogen (15N) signatures in soil organic matter in central Australia DMJS Bowman,1* Guy S. Boggs,2 Lynda D. Prior1 and Evelyn S. Krull3 ... The best palynological late Pleistocene Holocene record comes from Lake Eyre and Lake Frome (Luly, 2001). ...
... 265 my) age for this formation (Kyle, 1977; Retallack, 1980; Kyle and Schopf, 1982). ... In c... more ... 265 my) age for this formation (Kyle, 1977; Retallack, 1980; Kyle and Schopf, 1982). ... In contrast, long freezing episodes in water-logged soils likely would destroy the chambered Vertebraria roots associated with Glossopteris trees (Hunt and Hobday, 1984; Martini and ...
The δ13C values of plants and corresponding charred materials from wood, C3 and C4 grasses, deriv... more The δ13C values of plants and corresponding charred materials from wood, C3 and C4 grasses, derived from natural burning and laboratory combustion were obtained to determine whether there was a significant difference in δ13C of grass-derived char (C3 ...
The analyses of stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) of soil organic matter... more The analyses of stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) of soil organic matter (SOM) is an increasingly used tool to estimate soil carbon turnover, to assess degree of soil development, and to study historical C3/C4 vegetation changes. However, the exact processes that control 13C- and 15N-enrichment of SOM within a soil profile are still not clearly identified. To better understand the isotopic processes associated with decomposition of SOM, we studied two Vertisol profiles and one Oxisol profile from southern Queensland by radiogenic (14C), stable isotopic (δ13C, δ15N), and spectroscopic (13C-NMR and FTIR) methods. The findings of this study demonstrate that fundamental differences exist in δ13C and δ15N fractionation dynamics in different soil types and that isotopic fractionation is highly influenced by soil chemistry, mineralogy, and type of organic matter input. Stable isotopic analyses of the Oxisol show the typically observed increase in δ13C and δ15N in the subsurface horizon whereas the Vertisols show consistently decreasing values with depth. The high degree of 13C-enrichment in the Oxisol compared with the Vertisols cannot be simply explained with increased fractionation due to soil age, as the 14C age of the Vertisols is greater and increases more rapidly with depth, compared with that of the Oxisol.Data from 13C-NMR, XRF and IR data together with data on pH and clay content reveal a more complex picture of isotopic fractionation in soils. The Oxisol is dominated by O-alkyl carbon and aromatic material whereas the Vertisols contain higher amounts of alkyl carbon. Smectite and kaolinite are the dominant clay minerals in the Vertisols while the Oxisol is dominated by gibbsite, kaolinite, and Fe and Al-oxides.We suggest that the 13C- and 15N-depletion in the Vertisols is associated with low pH, which inhibits nitrification and promotes stabilization of 13C-depleted alkyl material by smectitic clays. The 13C-enrichment in the Oxisol correlates with a high abundance of relatively 13C-enriched O-alkyl carbon, which is a mix of primary materials (plant carbohydrates) as well as secondary (microbially synthesized) carbon. The abundance of relatively labile O-alkyl carbon even at depth is likely due to physico-chemical protection through complexation with Fe- and Al-oxides.
... and nitrogen (15N) signatures in soil organic matter in central Australia DMJS Bowman,1* Guy ... more ... and nitrogen (15N) signatures in soil organic matter in central Australia DMJS Bowman,1* Guy S. Boggs,2 Lynda D. Prior1 and Evelyn S. Krull3 ... The best palynological late Pleistocene Holocene record comes from Lake Eyre and Lake Frome (Luly, 2001). ...
Here we present d13C and dD data of C27-C31 n-alkanes from C3 (trees) and C4 (grasses) plants and... more Here we present d13C and dD data of C27-C31 n-alkanes from C3 (trees) and C4 (grasses) plants and from the corresponding soils from a grassland-woodland vegetation sequence in central Queensland, Australia. Our data show that C4 species (Iseilema and Astrebla) from the grassland were consistently 13C-enriched relative to C3 tree plant materials (Acacia leaves and seedpods and Atalaya leaves) from the woodland and woody grassland. However, n-alkanes from the C4 grasses were \deltaD depleted (-77\permil) relative to the Acacia leaves and seedpods, but showed no difference in dD values when compared with C3 Atalaya leaves. This is contradictory to data from previous studies, showing that C4 plants were enriched in \deltaD relative to C3 plants (the same direction as the d13C values). This past observation has been ascribed to C4 plants accessing the more evaporation-influenced (D-enriched) surface water and tree roots sourcing more D-depleted deeper soil water. Our data, on the other hand, indicate that ecosystem characteristics (woody versus grassy) have a greater influence on the dD values of the vegetation than the type of photosynthetic pathway. Specifically, the differences in dD values from "woodland" trees (Acacia) compared with "woody grassland" trees (Atalaya) suggest that the dD of soil water in semi-arid climates is ecosystem-dependent. This concept is supported by d13C and dD analysis of the C31 n-alkane, a grass-specific biomarker, from woodland and grassland soils. The similar d13C values in the woodland (-25.2±0.34\permil) and grassland soil (-25.1±0.03\permil) confirmed that the C31 n-alkane is grass-derived. The dD values of the C31 n-alkane, on the other hand, were by 12\permil enriched in the soil under the woodland compared with the one under grassland, supporting that the dD values of the soil water profile are governed by the hydrological characteristics of the ecosystem, not by photosynthetic pathway. The C27 and C29 n-alkanes (tree-specific biomarkers) from the woodland soil were more enriched in dD than the C31 n-alkane and were very similar to the values of the Acacia leaves. A crossplot of the d13C and dD values of the long-chained n-alkanes from plants and soil organic matter indicates that isotopic values from soil organic matter n-alkanes faithfully record recent changes in vegetation (in this case C4 to C3-dominated) as well as changes in water sources as the ecosystem changed from grassy to forested. Thus, the data from this study provide insight into soil-water-plant dynamics in semi-arid climate soils and caution against the assumption that d13C and dD differences in C3 and C4 plants are independent of climate and water stress.
... and nitrogen (15N) signatures in soil organic matter in central Australia DMJS Bowman,1* Guy ... more ... and nitrogen (15N) signatures in soil organic matter in central Australia DMJS Bowman,1* Guy S. Boggs,2 Lynda D. Prior1 and Evelyn S. Krull3 ... The best palynological late Pleistocene Holocene record comes from Lake Eyre and Lake Frome (Luly, 2001). ...
... 265 my) age for this formation (Kyle, 1977; Retallack, 1980; Kyle and Schopf, 1982). ... In c... more ... 265 my) age for this formation (Kyle, 1977; Retallack, 1980; Kyle and Schopf, 1982). ... In contrast, long freezing episodes in water-logged soils likely would destroy the chambered Vertebraria roots associated with Glossopteris trees (Hunt and Hobday, 1984; Martini and ...
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