Aridity-driven decoupling of δ13C between pedogenic carbonate and soil organic matter

Geology ◽  
2020 ◽  
Vol 48 (10) ◽  
pp. 981-985 ◽  
Author(s):  
Jiawei Da ◽  
Yi Ge Zhang ◽  
Gen Li ◽  
Junfeng Ji
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Pore Space ◽  
C4 Plants ◽  
Atmospheric Co2 ◽  
Chinese Loess Plateau ◽  
Pedogenic Carbonate ◽  
Chinese Loess ◽  
Pedogenic Carbonates ◽  
Soil Pore Space

Abstract Pedogenic carbonate is an invaluable archive for reconstructing continental paleoclimate and paleoecology. The δ13C of pedogenic carbonate (δ13Cc) has been widely used to document the rise and expansion of C4 plants over the Cenozoic. This application requires a fundamental presumption that in soil pores, soil-respired CO2 dominates over atmospheric CO2 during the formation of pedogenic carbonates. However, the decoupling between δ13Cc and δ13C of soil organic matter (δ13CSOM) have been observed, particularly in arid regions, suggesting that this presumption is not always valid. To evaluate the influence of atmospheric CO2 on soil δ13Cc, here we performed systematic δ13C analyses of paleosols across the Chinese Loess Plateau, with the sample ages spanning three intervals: the Holocene, the Late Pleistocene, and the mid-Pliocene warm period. Our paired δ13Cc and δ13CSOM data reveal broadly divergent trending patterns. Using a two-component CO2-mixing model, we show substantial incorporations of atmospheric CO2 (up to 60%) into soil pore space during carbonate precipitation. This result readily explains the enrichment of δ13Cc and its divergence from δ13CSOM. As a consequence, δ13C of pedogenic carbonates formed under semiarid and/or arid conditions are largely driven by regional aridity through its control on soil CO2 composition, and thus cannot be used to evaluate the relative abundance of C3 versus C4 plants. Nonetheless, these carbonates can be applied for atmospheric CO2 reconstructions, even for periods with low CO2 levels.

scholarly journals Paleovegetation reconstruction using <i>δ</i><sup>13</sup>C of Soil Organic Matter

2008 ◽  
Vol 5 (2) ◽  
pp. 1795-1823 ◽  
Author(s):  
G. Wang ◽  
X. Feng ◽  
J. Han ◽  
L. Zhou ◽  
W. Tan ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Negative Relationship ◽  
C4 Plants ◽  
Chinese Loess Plateau ◽  
C3 Plants ◽  
Soil Profiles ◽  
Chinese Loess ◽  
Δ13c Value ◽  
Sample Reconstruction

Abstract. The relative contributions of C3 and C4 plants to vegetation at a given locality may be estimated by means of δ13C of soil organic matter. This approach holds great potential for paleoecological reconstruction using paleosols. However, two uncertainties exist, which limits the accuracy of this application. One is 13C enrichment as plant carbon becomes incorporated into soil organic matter. The other is due to environmental influences on δ13C of plants. Two types of data were collected and analyzed with an objective of narrowing the error of paleovegetation reconstruction. First, we investigated δ13C variations of 557 C3 and 136 C4 plants along a precipitation gradient in North China. A strong negative relationship is found between the δ13C value of C3 plants averaged for each site and the annual precipitation with a coefficient of −0.40‰/100 mm, while no significant coefficients were found for C4 plants. Second, we measured δ13C of soil organic matters for 14 soil profiles at three sites. The isotopic difference between vegetation and soil organic matter are evaluated to be 1.8‰ for the surface soil and 2.8‰ for the soil at the bottom of soil profiles. Using the new data we conducted a sample reconstruction of paleovegetation at the central Chinese Loess Plateau during the Holocene and the Last Glaciation, and conclude that, without corrections for 13C enrichment by decomposition, the C4 abundance would be overestimated. The importance and uncertainties of other corrections are also discussed.

scholarly journals Paleovegetation reconstruction using δ<sup>13</sup>C of Soil Organic Matter

2008 ◽  
Vol 5 (5) ◽  
pp. 1325-1337 ◽  
Author(s):  
G. Wang ◽  
X. Feng ◽  
J. Han ◽  
L. Zhou ◽  
W. Tan ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
C4 Plants ◽  
Chinese Loess Plateau ◽  
C3 Plants ◽  
Soil Profiles ◽  
Strong Negative Correlation ◽  
Chinese Loess ◽  
Δ13c Value ◽  
Sample Reconstruction

Abstract. The relative contributions of C3 and C4 plants to vegetation at a given locality may be estimated by means of δ13C of soil organic matter. This approach holds a great potential for paleoecological reconstruction using paleosols. However, two main uncertainties exist, which limits the accuracy of this application. One is δ13C-enrichment as the plant carbon becomes incorporated into soil organic matter. The other is due to environmental influences on δ13C of plants. Two types of data were collected and analyzed with an objective of narrowing the error of paleovegetation reconstruction. First, we investigated δ13C variations of 557 C3 and 136 C4 plants along a precipitation gradient in North China. A strong negative correlation is found between the δ13C value of C3 plants averaged for each site and the annual precipitation with a coefficient of −0.40‰/100mm, while no significant coefficients were found for C4 plants. Second, we measured δ13C of soil organic matters for 14 soil profiles at three sites. The isotopic difference between vegetation and soil organic matter are evaluated to be 1.8‰ for the surface soil and 2.8‰ for the soil at the bottom of soil profiles. We conducted a sample reconstruction of paleovegetation at the central Chinese Loess Plateau during the Holocene and the Last Glacial (LG), and conclude that, without corrections for δ13C-enrichment by decomposition, the C4 abundance would be overestimated. The importance and uncertainties of other corrections are also discussed.

Multi-scale spatial relationships between soil organic matter and influencing factors in basins of the Chinese Loess Plateau

2017 ◽  
Vol 37 (24) ◽  
Author(s):  
朱洪芬 ZHU Hongfen ◽  
南锋 NAN Feng ◽  
徐占军 XU Zhanjun ◽  
荆耀栋 JING Yaodong ◽  
段永红 DUAN Yonghong ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Influencing Factors ◽  
Loess Plateau ◽  
Chinese Loess Plateau ◽  
Spatial Relationships ◽  
Chinese Loess ◽  
Multi Scale ◽  
The Chinese Loess Plateau

scholarly journals Supplemental Material: Aridity-driven decoupling of δ13C between pedogenic carbonate and soil organic matter

2020 ◽  
Author(s):  
Jiawei Da ◽  
Junfeng Ji ◽  
et al.
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Analytical Methods ◽  
Pedogenic Carbonate

Descriptions of chronology and analytical methods, Figures S1–S5, and Tables S1–S3.<br>

scholarly journals Evidence of old soil carbon in grass biosilica particles

2015 ◽  
Vol 12 (18) ◽  
pp. 15369-15410 ◽  
Author(s):  
P. E. Reyerson ◽  
A. Alexandre ◽  
A. Harutyunyan ◽  
R. Corbineau ◽  
H. A. Martinez De La Torre ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Organic Carbon ◽  
Soil Carbon ◽  
Co2 Sequestration ◽  
State Of The Art ◽  
Atmospheric Co2 ◽  
Plant Tissues ◽  
Complex Chemical ◽  
Isotopic Measurements

Abstract. Plant biosilica particles (phytoliths) contain small amounts of carbon called phytC. Based on the assumptions that phytC is of photosynthetic origin and a closed system, claims were recently made that phytoliths from grasslands play a significant role in atmospheric CO2 sequestration. However, anomalous phytC radiocarbon (14C) dates suggested contributions from a non-photosynthetic source to phytC. Here we address this non-photosynthetic source hypothesis using comparative isotopic measurements (14C and δ13C) of phytC, plant tissues, atmospheric CO2, and soil organic matter. State-of-the-art methods assured phytolith purity, while sequential stepwise-combustion revealed complex chemical–thermal decomposability properties of phytC. Although photosynthesis is the main source of carbon in plant tissue, it is found that phytC is partially derived from soil carbon that can be several thousand years old. The accumulation of old soil organic matter derived carbon in plant biosilica suggests that Si absorption and phytolith production promote old soil organic carbon mobilization. Although the magnitude of this mechanism still needs to be properly assessed at plant and ecosystem scales, its confirmation alone argues against attempts to use phytC as a proxy of plant carbon and call for the reexamination of phytolith atmospheric CO2 biosequestration estimates.

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