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Oxalic acid is one of the most abundant organic acids produced by plants. Much of the global production of oxalic acid is deposited on soil surfaces in leaf litter to be oxidized by microorganisms, resulting in a pH increase and shifting the carbonate equilibria. In what is known as the oxalate-carbonate pathway, calcium oxalate metabolism results in CO2 being sequestered into soils as insoluble calcite (CaCO3). There is a growing appreciation that the global scale of this process is sufficiently large to be an important contribution to global carbon turnover budgets.

The microbiomics, genetics, and enzymology of oxalotrophy are all soundly established, although a more detailed understanding of the landscape-scale kinetics of the process would be needed to incorporate oxalotrophy as an element of process models informing the relevant Sustainable Development Goals. Here, we review the current state of knowledge of oxalotrophs and oxalotrophy and the role they play in terrestrial ecosystem services and functions in terms of carbon sequestration and nutrient cycling. We emphasize the relevance of these to the Sustainability Development Goals (SDGs) and highlight the importance of recognizing oxalotrophy, when accounting for the natural capital value of an ecosystem.

Quantitative isotopic paleoaltimetry has been applied in regions where Rayleigh distillation controls isotopic lapse rates. Air mass mixing and moisture recycling are viewed as complicating factors. We show here that, because of such effects, a cross‐Andean transect of meteoric water δD values precisely marks the geographic position of the Western Cordillera crest. This modern water signal is also recorded in Pliocene‐Pleistocene hydrated volcanic glass δD values. δD values between the Pacific coast and Western Cordillera exhibit no trend up to 2.5 km elevation and 100 km inboard, consistent with an arid climate in which Amazonian moisture is topographically blocked and Pacific moisture is efficiently recycled. The result is a large δD lapse rate (−98‰/km) and an abrupt horizontal δD shift (2‰/km) at the Western Cordillera crest. Therefore, we conclude that cross‐orogen δD transects could locate the ancient Western Cordillera crest.

The geological record encodes the relationship between climate and atmospheric carbon dioxide (CO₂) over long and short timescales, as well as potential drivers of evolutionary transitions. However, reconstructing CO₂beyond direct measurements requires the use of paleoproxies and herein lies the challenge, as proxies differ in their assumptions, degree of understanding, and even reconstructed values. In this study, we critically evaluated, categorized, and integrated available proxies to create a high-fidelity and transparently constructed atmospheric CO₂record spanning the past 66 million years. This newly constructed record provides clearer evidence for higher Earth system sensitivity in the past and for the role of CO₂thresholds in biological and cryosphere evolution.

Drylands occupy nearly 40% of the land surface and comprise a globally significant carbon reservoir. Dryland‐atmosphere carbon exchange may regulate interannual variability in atmospheric CO₂. Quantifying soil respiration rates in these environments is often complicated by the presence of calcium carbonates, which are a common feature of dryland soils. We show with high‐precision O₂measurements in a laboratory potted soil experiment that respiration rates after watering were similar in control and carbonate treatment soils. However, CO₂concentrations were up to 72% lower in the carbonate treatment soil because CO₂was initially consumed during calcite dissolution. Subsequently, CO₂concentrations were over 166% greater in the carbonate treatment soil as respiration slowed and calcite precipitated, releasing CO₂. Elevated δ¹³C values of soil CO₂(>6‰ higher in the treatment than control) confirm that observed differences were due to calcite dissolution. These findings demonstrate that calcite dissolution and precipitation can occur rapidly enough to affect soil gas compositions and that changes in soil CO₂are not always directly related to changes in soil respiration rates. Studies of local soil respiration rates and carbon exchange are likely to be influenced by dissolution and precipitation of calcium carbonates in soils. We estimate that one fifth of global soil respiration occurs in soils that contain some amount of soil carbonate, underscoring the need to account for its obscuring effects when trying to quantify soil respiration and net ecosystem exchange on a regional or global scale.

Paleosols preserved in the Red Clay depositional sequence of the Chinese Loess Plateau record information about vegetation and regional hydrology responses to global temperature variation throughout the late Miocene and Pliocene. Reconstructing spatial and temporal patterns of environmental change across the Loess Plateau from carbon isotopes of pedogenic carbonate (δ¹³C_carb) is complicated because multiple factors affect δ¹³C_carbvalues and higher resolution records do not exist along the northern margin of the Loess Plateau. To address these needs, we present paired carbon isotope records of pedogenic carbonate and occluded organic matter (δ¹³C_org) from 697 discrete nodules sampled from 119 different depths at the Jiaxian section, North Central China. Between 7.6 and 2.4 Ma, δ¹³C_carbvalues increase by nearly 5‰, while δ¹³C_orgvalues increase by 2.5‰. These increases are explained by a progressive decline in moisture availability through time, and there is no definitive evidence from these δ¹³C data for C₄vegetation at the Jiaxian site until after 3.6 Ma. Comparison of the Jiaxian record to other Loess Plateau sections reveals a consistent spatial gradient with δ¹³C_carbvalues becoming higher and more variable to the N‐NW. Additionally, an independent index of monsoonal precipitation from a southern site corresponds to fluctuations in δ¹³C_carbvalues at Jiaxian, while southern δ¹³C_carbrecords remain more stable. These spatial patterns are explained by a progressive decline in moisture availability across the Loess Plateau through the Late Miocene and Pliocene, with δ¹³C_carbvalues being more sensitive to moisture availability under consistently more arid conditions to the NW.