Predicting Soil Organic Carbon Mineralization Rates Using δ 13 C, Assessed by Near-Infrared Spectroscopy, in Depth Profiles Under Permanent Grassland Along a Latitudinal Transect in Chile

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.