Soil radiocarbon (14C) measurements are crucial for understanding soil carbon cycling over timescales ranging from years to millennia. However, the global synthesis and comparison of radiocarbon data have been limited due to the variety of measurement methodologies and data formats. The International Soil Radiocarbon Database (ISRaD) is an open-access, community-driven archive designed to compile soil radiocarbon data and facilitate large-scale research on soil carbon dynamics. Here, we present ISRaD version 2 (v2), which has grown significantly since its initial release in 2020 (https://doi.org/10.5281/zenodo.17860507, Beem-Miller et al., 2025). It now contains data from 515 unique studies spanning 1669 sites globally, with over 20 000 radiocarbon observations across multiple hierarchical levels, including bulk soil layers, soil fractions, laboratory incubations, interstitial carbon in soil pores, and in situ fluxes of CO2 and CH4. Major updates include expanded metadata structures to capture emerging measurement techniques and an improved soil fractionation template to better capture diverse methods. There has also been a substantial increase in data from underrepresented ecosystems, including cultivated soils and wetlands. Despite this growth, significant geographic and data-type gaps persist. Tropical and arid regions, soils deeper than 100 cm, and certain types of measurements, including incubation, interstitial, and flux, are severely undersampled. We discuss the scientific advances enabled by ISRaD v1 and the major updates to the database and data representation. We also explore future opportunities for ISRaD and the soil radiocarbon community. ISRaD v2 continues to serve as a living archive and dynamic platform for the soil radiocarbon research community. It supports synthesis efforts that are critical for predicting how soil carbon will respond to environmental and climatic changes.

Soil microorganisms perform biogeochemical processes fundamental to soil functions. Bulk respiration, or microbial metabolic emission of CO2, is the classic indicator of soil biological activity. However, among the millions of microbes per gram of soil, only 0.1%-2.0% are metabolically active at any given time. Understanding the relationship between bulk soil respiration and microbial activity is complicated by microbes potentially awakening from quiescent states during incubation test periods. Here, we investigated this relationship through parallel measurements of substrate-induced respiration and translationally active cell counts using bioorthogonal non-canonical amino acid tagging (BONCAT). After a 6-h incubation of agricultural soil with glucose, galactose, or only water, active cell counts were positively correlated with respiration rates. As hypothesized, active cell numbers increased rapidly compared to total cell numbers after a 6-h incubation with glucose, suggesting newly activated cells. Additionally, carbon-amended soils respired more than water-only soils with similar active cell counts. This suggested that cells in carbon-rich environments were turning over freshly added carbon faster or metabolizing it less efficiently than those exposed to native substrates only. This study distinguishes for the first time microbial activation in the soil matrix using a translation signal, providing evidence that respiration rates reflect active cell numbers and varied metabolic responses, decoupled from cell growth upon soil wetting and carbon addition. We propose BONCAT as a useful tool to gain mechanistic insights into microbial activation and recommend combining it with tracking substrate incorporation and phylogenetics.IMPORTANCEMany critical ecosystem services provided by soils rely on active microbes, even though most soil microbes are known to be quiescent or dormant much of the time. This study demonstrates that microbes become translationally active within hours after substrate addition and that the correlation between active cell numbers and soil respiration rates varies with the type of substrate. Advancing knowledge in this area will enable better interpretation of bulk soil respiration tests by land managers and inform modeling efforts that relate soil microbial respiration to global carbon dynamics.

Deforestation for cropland expansion in tropical sloping landscapes causes severe soil erosion and thus the loss of fertile, organic rich topsoil. Whether there is variation in the effect of land degradation on tropical soils developed from different parent materials, which may influence soil fertility is still largely unknown. Here, we compared SOC and other soil fertility indicators in undisturbed tropical forest topsoils with cleared hillslope topsoils (cropland, abandoned cropland, and reforestation with Eucalyptus monocultures) along the East African rift system using soil chronosequences after deforestation on both mafic and felsic parent material. In the mafic region, we found a consistent decrease of SOC, nitrogen, and phosphorus content with time after deforestation (relative changes of contents up to -69 % SOC, -72 % nitrogen, and -92 % phosphorus). SOC was strongly stabilized by reactive metal phases with little to no benefits to general soil fertility. Consequently, cropland was frequently abandoned by farmers due to the combination of low pH, high Al3+ mobility, and low available nutrient status at a relatively high average SOC content of 14-29 gkg-1 in topsoils. In the felsic region, the ameliorating effect of mid-Holocene carbonate volcanism mitigated soil degradation to some extent. In both geochemical regions, SOC content did not or only weakly positively correlate with clay content and cation exchange capacity. These results emphasize that soil organic matter, as well as clay content, appears to be unreliable indicators for soil fertility in degraded tropical cropland soils. Additionally, no significant improvement of soil fertility or SOC stocks was observed after replanting degraded fields with Eucalyptus monocultures. The estimated lifespan of croplands on hillslopes in our study area, approximately 145 +/- 56 years, underscores the severity of soil degradation for food production and forest protection in the upcoming decades, especially considering that many soils are already approaching the end of this estimated lifespan.

Soil organic carbon (SOC) can persist from days to millennia but remains vulnerable to carbon (C) loss upon disturbances, depending on environmental conditions and mode of stabilization. Understanding drivers of persistence and vulnerability is crucial to assess soil C sequestration as well as potential SOC losses due to changes in climate and land use. Here, we investigate SOC persistence and vulnerability in five land-use types by combining radiocarbon-derived estimates of SOC age (system age) and age of respired CO2 (transit time) with indicators of biological (SOC decomposability) and thermal stability (residual oxidisable carbon content, ROC). Based on this, we developed a vulnerability index for SOC and applied it across soil profiles from 19 sites representing temperate and alpine grasslands, forests, croplands, and managed peatlands. Transit times and system ages ranged from 2 years in the organic layer of forests to 5760 years in subsoils of managed peatlands and varied significantly across land-use types and soil depth. Transit times were generally shorter than system ages, indicating that soil-respired CO2 is dominated by more recent inputs, while bulk SOC contains more persistent C. In forests, temperate grasslands, and croplands, system ages were positively linked to thermal stability and mineral reactivity, indicating higher SOC persistence through organo-mineral stabilization. In contrast, alpine grasslands and managed peatlands showed centennial to millennial system ages despite low thermal stability (< 10%-ROC), reflecting inhibited microbial decomposition due to cold and/or anaerobic conditions in these ecosystems. In combination with high SOC stocks (> 90 kg m(-2) in managed peatlands), this implies a high vulnerability of these soils to environmental disturbances that alleviate these constraints. Our findings demonstrate that combining metrics of biological and thermal stability with radiocarbon data provides a powerful framework to assess SOC vulnerability to disturbances induced by environmental change.

Soil microbial growth and respiration are critical for soil organic carbon dynamics. Yet, we lack understanding of the main controls of soil microbial carbon metabolism at large scales (regional to global). Here we investigated if and how the chemical composition of extractable organic matter affects soil microbial carbon metabolism across soil systems along a gradient of 33 temperate grassland soils. We show that biomass-normalized rates of growth and respiration are primarily positively linked to aliphatics such as carbohydrate-, proteinaceous- and amino sugar-like compounds, and secondarily to unsaturated lignin-like compounds. Biomass-normalized respiration is positively linked to compounds with carbon in a reduced oxidation state, suggesting carbon-conserving catabolism. Biomass-normalized growth appears unrelated to the oxidation state of carbon, suggesting that other mechanisms than mere energetic constraints control microbial growth in aerobic soils. Our findings demonstrate that information on the chemical composition of bioavailable organic matter can provide insights into the processes that govern the fate of carbon across different ecosystems. Soil microbial growth and respiration rates across temperate grassland soils are positively linked to aliphatic and unsaturated compounds in extractable organic matter, according to an analysis along a geoclimatic gradient of 33 temperate grasslands soils from Chile.

Coastal alluvial plains in river deltas can store significant carbon by burying upland sediments and former topsoil. The Yellow River Delta, shaped by continuous upstream sediment deposition and shifting river courses, offers a unique case to study this. We collected five 2 m soil cores along a sediment sequence reflecting 80 years of deposition and river course changes. Our analysis of soil organic carbon (SOC) stocks and sources revealed that older river courses hold less SOC than newer ones. SOC was generally low, except near the surface. Upstream-derived organic carbon contributed more to SOC stocks than local vegetation, especially in younger sediments. All sediments showed high inorganic carbon and alkaline conditions, pointing to loess-derived subsoils from the uplands as the primary sediment source. These subsoils, low in organic carbon and weathering, indicate rapid erosion and a degraded terrestrial carbon cycle upstream. Although deltaic settings could protect deposited carbon, our findings highlight the limited increase in SOC due to the input of C-depleted materials. Therefore, soil conservation is critical not only in the delta but also in its erosion-prone upland sources.

Soil organic matter (SOM) quantity drives soil bacterial community composition from the regional to global scale. Qualitative characteristics of SOM are known to affect soil bacterial communities in manipulation experiments. However, it remains unresolved how strongly SOM characteristics affect soil bacterial community composition at the macroscale. Here, we investigated how quantity versus qualitative characteristics of SOM shape community composition along a biogeochemical gradient of grassland soils. We assessed relative abundance patterns of soil bacteria and characterised SOM based on scalable methods. Soils with higher SOM content (along a continuum between 0.6% and 18.7% SOC) and acidic pH (along a continuum between pH 4.1-6.7) hosted fewer narrowly distributed taxa (i.e., taxa occurring in few sites) and therefore had lower bacterial alpha diversity. We could explain a larger fraction of bacterial community composition (up to 59.6% of 16S rRNA reads) in these soils. Consequently, we understand community composition in low-SOM soils less than in high-SOM soils, because the drivers of narrowly distributed taxa remain poorly understood. Qualitative SOM characteristics did not strongly affect biogeographical patterns of widely distributed soil bacterial taxa. This suggests that broad aspects of SOM quality do not dominate soil bacterial community composition at the investigated macroscale.

Deforestation for cropland expansion in the sloping landscapes along the East African Rift system causes severe soil erosion and thus the loss of fertile, organic rich topsoil. However, the varying effect of land degradation in the region on soils developed from different parent material - which may influence soil fertility and carbon stabilization - are still largely unknown. To examine these factors, we compared soil organic carbon (SOC) and soil fertility indicators in undisturbed forest topsoils with cropland hillslope topsoils along a chronosequence after deforestation (2–7, 10–20, 20–40, > 60 years of cropping, land abandonment) on mafic (South Kivu, Democratic Republic of Congo) and felsic parent material (western Uganda). From previous studies, we expected higher soil fertility and SOC contents and therefore slower degradation on mafic soils due to the higher amounts of clay and pedogenic metal phases which stabilize SOM and thus further maintain soil fertility. However, we found similar SOC contents on both parent materials and a consistent decrease with time after deforestation. SOC values were significantly lower in soils that were cleared more than 60 years ago, compared to cropland which was cleared 2–7 years ago and nearby undisturbed forest topsoils (0–10 cm soil depth). While the effective cation exchange capacity (ECEC) positively correlated with SOC in soils on felsic parent material, this was not observed in soils with mafic parent material, where it correlated with mineralogical proxies (total reserves in bases). In both regions, SOC did not correlate with clay content. Mid-Holocene carbonate volcanism appears to have offset soil degradation in the felsic region, contributing to higher pH and ECEC and impeding land abandonment due to the maintenance of acceptable soil fertility levels. Surprisingly, abandoned cropland sites in the mafic region still had an average SOC content of 14–29 g kg-1 in topsoils, likely due to strong fixation of SOC with reactive metal phases; however, they were characterized by extremely low pH values and high Al3+ mobility, combined with low available nutrient status. Our results emphasize that soil fertility and carbon stabilization are reliant on the mineral composition of the underlying parent material, even in deeply weathered soils of the humid tropics. Soil organic matter in degraded tropical cropland soils does not appear to be a reliable indicator of soil fertility.

Soil microbes perform important functions in the soil organic carbon (SOC) cycle and soil microbial decomposition activity is a major determinant of the carbon budget of a soil. It is well-established that soil microbial physiology is directly affected by temperature and moisture. However, it is less clear to what extent the environmental setting (i.e. long-term climatic conditions, soil physicochemistry) vs. the microbial actors (i.e. soil bacterial and fungal community composition) control the cycling of SOC in the absence of strong direct physiological constraints such as temperature and moisture limitation.To address this knowledge gap, we used 35 grassland topsoils (0 – 10 cm) from 10 WRB major soil groups along a north-south transect in Chile, which ranged from arid steppe to tundra. We compiled climatic data and relevant physicochemical soil properties, together with an in depth characterization of OM quality. We then incubated the soils for 1 week in conditions favorable for microbial activity (20 °C, 50 % of water holding capacity). After incubation, we quantified soil microbial carbon and nitrogen, enzyme kinetics of three groups of relevant extracellular enzymes, basal heterotrophic respiration as well as microbial growth rates and carbon use efficiencies by incorporation of 18O into DNA. In addition, we characterized the microbial actors by DNA extraction and Illumina barcoding of a region of the 16S rRNA gene (bacteria) and a section of the ITS region (fungi). Finally, to investigate how strongly the measured microbial SOC functions were linked with the environmental setting vs. the microbial actors, we applied three different cross-validated regression approaches.The resulting data highlights the links between environment, microbial community composition and SOC cycle functions under conditions without direct temperature and moisture limitation. Our findings show that the environmental setting controlled the amount of microbial biomass, and in extension biomass dependent SOC cycle functions such as heterotrophic respiration. In contrast, microbial community composition was a better predictor of SOC cycle functions that are independent of microbial biomass such as carbon use efficiency and relative microbial growth rates. These insights help to disentangle the roles of the environmental setting and the microbial actors in the context of microbial SOC cycle functions.

Soil microorganisms carry out many processes that are fundamental to soil functions. Among the millions of microbial cells present in a gram of soil, however, less than 2% are commonly estimated to be active at any point in time. Because the respiratory response of a bulk soil to carbon substrate addition would be expected to reflect the number of active cells, we hypothesized a positive correlation between active cells and soil respiration rates during substrate-induced respiration (SIR) assays. To test this, we monitored respiration and active cell counts during 24-h incubations of agricultural soil subsamples after treating with two carbon substrates or a water-only control. We enumerated active cells with the Bioorthogonal Non-canonical Amino Acid Tagging (BONCAT) method. BONCAT provides a labeled amino acid for active cells to incorporate into newly synthesized proteins, which can then be tagged with a fluorescent dye to enable enumeration by flow cytometry. Both respiration rates and active cell counts increased over time and were positively correlated with each other after 6 h of incubation. After 24 h, increases in active cells were proportionally greater than increases in respiration. Additionally, carbon-amended soils had higher respiration rates than water-only soils with similar active cell counts, suggesting differences in carbon use efficiency. Our study documents for the first time the respiratory response from in-situ microbial activation induced by substrate amendment of soil within 6 h, a short enough timescale to exclude most cell replication. This study also demonstrates that the correlation between active cell numbers and respiration is substrate-dependent. IMPORTANCE While many critical ecosystem services provided by soil are known to rely on microbial activity, the soil microbial community largely remains a black box. While respiration is a common indicator of bulk soil microbial activity, this study demonstrates that the relationship between respiration and the number of active cells differs based on available carbon substrates. Advancing knowledge in this area will both enable better interpretation of biological soil tests by land managers and inform researchers modeling contributions of soil microbial respiration to global carbon dynamics. ### Competing Interest Statement The authors have declared no competing interest.

Soil microbial traits and functions play a central role in soil organic carbon (SOC) dynamics. However, at the macroscale (regional to global) it is still unresolved whether (i) specific environmental attributes (e.g., climate, geology, soil types) or (ii) microbial community composition drive key microbial traits and functions directly. To address this knowledge gap, we used 33 grassland topsoils (0-10 cm) from a geoclimatic gradient in Chile. First, we incubated the soils for 1 week in favorable standardized conditions and quantified a wide range of soil microbial traits and functions such as microbial biomass carbon (MBC), enzyme kinetics, microbial respiration, growth rates as well as carbon use efficiency (CUE). Second, we characterized climatic and physicochemical properties as well as bacterial and fungal community composition of the soils. We then applied regression analysis to investigate how strongly the measured microbial traits and functions were linked with the environmental setting versus microbial community composition. We show that environmental attributes (predominantly the amount of soil organic matter) determined patterns of MBC along the gradient, which in turn explained microbial respiration and growth rates. However, respiration and growth normalized for MBC (i.e., specific respiration and growth) were more linked to microbial community composition than environmental attributes. Notably, both specific respiration and growth followed distinct trends and were related to different parts of the microbial community, which in turn resulted in strong effects on microbial CUE. We conclude that even at the macroscale, CUE is the result of physiologically decoupled aspects of microbial metabolism, which in turn is partially determined by microbial community composition. The environmental setting and microbial community composition affect different microbial traits and functions, and therefore both factors need to be considered in the context of macroscale SOC dynamics. Soil microbial traits and functions are central for soil organic carbon (SOC) dynamics. However, at regional to global scales it is still unresolved whether the environment (climate, geology, soil types) or microbial community composition drive key microbial traits and functions directly. Using 33 soils from a temperate grassland gradient, we show that the environment determined the biomass and absolute respiration and growth of microbes. However, microbial carbon use efficiency was best explained by microbial community composition. The environment and the microbiome affect different microbial traits and functions, and therefore both factors need to be considered in macroscale SOC dynamics.image

Soil microbial growth rate and microbial carbon use efficiency (CUE) are critical parameters of soil microbial carbon metabolism, moderating soil organic carbon (SOC) dynamics. However, global patterns of soil microbial growth rate and microbial CUE are still unresolved. Here, we show that the metabolic theory of ecology (MTE) can be applied to model soil microbial growth rate at the global scale as a function of microbial biomass, temperature, and SOC contents. Rates of soil microbial growth were modeled at depths of 0-30 cm and calibrated against rates measured with the 18O-labeled H2O incubation method. The modeled soil microbial growth rates were strongly driven by temperature. They decreased with latitude and had greater seasonal variations in tundra and boreal forest compared to tropical biomes. Soil microbial CUE (0-30 cm) ranged from 0.25 to 0.63 among global biomes, averaging at 0.43. Modeled annual soil microbial growth rates followed the same global patterns and were on the same order of magnitude as other key ecosystem C fluxes such as net primary productivity, litterfall, and heterotrophic respiration. This indicates a strong functional linkage of aboveground and belowground communities at the global scale. Our MTE-based approach provides the first estimates of global patterns for soil microbial growth rate and microbial CUE and potentially provides a powerful mechanistic framework to incorporate soil microbes into Earth System Models.

Organic matter accumulation in soil is understood as the result of the dynamics between mineral-associated (more decomposed, microbial derived) organic matter and free particulate (less decomposed, plant derived) organic matter. However, from regional to global scales, patterns and drivers behind main soil organic carbon (SOC) fractions are not well understood and remain poorly linked to the pedogenetic variation across soil types. Here, we separated SOC associated with silt- and clay-sized particles (S + C), stable aggregates (>63 mu m, SA) and particulate organic matter (POM) from a diverse range of grassland topsoils sampled along a geoclimatic gradient. The relative contribution of the two mineral-associated fractions (S + C & SA) to SOC differed significantly across the gradient, while POM was never the dominant SOC fraction. Stable aggregates (>63 mu m) emerged as the major SOC fraction in carbon-rich soils. The degree of decomposition of carbon in stable aggregates (>63 mu m) was consistently between that of the S + C and POM fractions and did not change along the investigated gradient. In contrast, carbon associated with the S + C fraction was less microbially decomposed in carbon-rich soils than in carbon-poor soils. The amount of SOC in the S + C fraction was positively correlated to pedogenic oxide contents and texture, whereas the amount of SOC associated with stable aggregates (>63 mu m) was positively correlated to pedogenic oxide contents and negatively to temperature. We present a conceptual summary of our findings, which integrates the role of stable aggregates (>63 mu m) with other major SOC fractions and illustrates their changing importance across (soil-)environmental gradients.

In the nutrient-limited Antarctic terrestrial habitat, penguins transfer a significant amount of nutrients from the marine to the terrestrial ecosystem through their depositions (i.e., guano). This guano influences soil physicochemical properties, leading to the formation of ornithogenic soil rich in nutrients and organic matter. We hypothesize that soil prokaryotic communities will be strongly influenced by the contribution of nitrogenous nutrients from penguin rookeries, maintaining the influence over long distances. The objective was to establish how the soil prokaryotic diversity and community structure change with distance from a penguin colony, which provides large amounts of guano and nitrogenous compounds, and to study the effects of these nutrients on the functional role of these communities. Methods include volcanic soil sampling along a 1200 m transect from the penguin active rookery and the characterization of soil nutrient content and soil prokaryotic communities using 16S rRNA high-throughput amplicon sequencing. In contrast to our hypothesis, the results showed that the impact of guano from the penguin colony was restricted to the first 300 m. Probably because the penguin rookery was sheltered, strong wind and wind direction did not affect the transport of nutrients from the penguin rookery. Areas close to the penguin rookery were dominated by Proteobacteria and Bacteroidetes, while areas situated further away were dominated by Acidobacteria, Actinobacteria, Chloroflexi, Gemmatimonadetes, Nitrospirae, and Planctomycetes. Beta diversity analysis among the soil prokaryotic communities revealed a high degree of community heterogeneity, strongly associated with N compound characteristics (NH4, NO3, and

Introduction: Organic phosphorus (Po) compounds constitute an important pool in soil P cycling, but their decomposition dynamics are poorly understood. Further, it has never been directly tested whether low molecular weight Po compounds are taken up by soil microbes in an intact form, which reduces the dependence of their P acquisition on extracellular phosphatases.Methods: We investigated the short-term fate (24 h) of five 33P-labelled Po compounds (teichoic acids, phospholipids, DNA, RNA and soluble organophosphates) and 33P-labelled inorganic P (Pi) in two soils.Results: We found indications that soil microbial breakdown of phosphodiesters was limited by the depolymerization step, and that direct microbial uptake of Po occurred to a substantial extent.Discussion: We postulate a trade-off between direct Po uptake and complete extracellular Po mineralization. These findings have profound consequences for our understanding of microbial P cycling in soils.

ABSTRACTSoil microorganisms carry out many biological functions that are fundamental to soil ecosystems; however, less than 2% of soil bacterial cells are commonly estimated to be active at any point in time. Substrate-induced respiration (SIR) measures community-level microbial activity as the bulk soil response to carbon substrate addition. We hypothesized that this bulk respiration rate is dependent on changes in the number of active cells. We incubated subsamples of an agricultural soil with 2 carbon substrate treatments and a third water-only treatment, and we periodically monitored respiration and active cell counts for 24 h. To enumerate active bacterial cells, we applied the novel Bioorthogonal Non-canonical Amino Acid Tagging (BONCAT) method. BONCAT provides a labeled amino acid for active cells to incorporate into newly synthesized proteins, and then a fluorescent dye enables enumeration of labeled cells by flow cytometry. Both respiration rates and active cell counts increased over time and were positively correlated with each other after 6 h of incubation. After 24 h, however, increases in active cells were more than proportional to increases in respiration. Additionally, carbon-amended soils had higher respiration rates than water-only soils with similar active cell counts, suggesting differences in carbon use efficiency. Our results indicate that number of translationally active bacteria is an important but not singular contributor to observed bulk soil respiration.IMPORTANCEWhile many critical ecosystem services provided by soil are known to fundamentally rely on microbial activity, the soil microbial community largely remains a black box. This study demonstrates that substrate-induced respiration is linked to the number of active cells. Advancing knowledge in this area will both enable better interpretation of biological soil tests by land managers and inform researchers modeling contributions of soil microbial respiration to global carbon dynamics.

Abstract Organic matter accumulation in soil is understood as the result of the dynamics between mineral-associated (often more decomposed, microbial derived) organic matter and free particulate (often less decomposed, plant derived) organic matter. However, at global scales, the patterns and drivers behind main SOC reservoirs are not well understood and remain poorly linked to the pedogenetic variation across soil types that may impact SOC stabilization. Here, we separated soil organic carbon (SOC) associated with silt- and clay-sized particles (S + C), stable microaggregates (> 63 µm, SA) and free particulate organic matter (POM) from a diverse range of grassland topsoils sampled along a geo-climatic gradient. The relative contribution of the two predominantly mineral-associated fractions (S + C & SA) differed significantly across the gradient while free POM was never the dominant SOC reservoir. Rather, stable microaggregates emerged as the major SOC reservoir in soils with high SOC content. The SOC content in the two mineral-associated reservoirs was related to distinct climatic and mineralogic proxies that followed predictable patterns across the gradient. Furthermore, carbon quality in stable microaggregates was clearly distinct from carbon associated with silt- and clay-sized particles and free particulate organic matter. We summarize our findings in a conceptual framework, which integrates the role of stable microaggregates with other major SOC reservoirs and illustrates their changing importance across (soil) environmental gradients.

Carbon (C) mineralization and turnover in soil rely on complex interactions among environmental variables that differ along latitudinal gradients. This study aims to quantify the relationship between the variation in δ 13 C signature with soil depth (∆δ 13 C) and soil C turnover across a large geo-climatic gradient. Thirteen grassland sites were sampled along a 4000 km latitudinal gradient in Chile. Maximizing climatic and physicochemical soil’s diversity to test the index with the widest range of application. We used near-infrared spectroscopy (NIRS) to estimate δ 13 C of SOC at several soil depths. To assess soil C mineralization rates (CMR) and specific potential respiration (SPR) as proxies for C mineralization and turnover, using ∆δ 13 C, soil incubations were performed. Highest 13 C isotope abundance was found at low latitude (− 22.57‰, 35.5°S) and lowest at high latitude (− 27.43‰, 53.2°S). Our results show 13 C’s enrichment in parallel with decreasing C content with depth. The analysis of the relationship between ∆δ 13 C values versus CMR and SPR showed a significant positive relationship across all data points ( p < 0.0001, R 2 = 0.62; p < 0.01, R 2 = 0.29, respectively). Partial correlation analysis of control variables indicates a relationship between ∆δ 13 C with CMR and SPR when controlling for climatic and soil physicochemical variables. ∆δ 13 C calculated from NIRSs may serve as a proxy to research the potential degradability of SOM and its interaction with soil geochemistry. Uncertainty and variability in the prediction power of our model reveals the importance of considering the latitudinal changeability in soil types as a control on properties controlling ∆δ 13 C.