Predicting Soil Organic Carbon Mineralization Rates Using δ13C, Assessed by Near-Infrared Spectroscopy, in Depth Profiles Under Permanent Grassland Along a Latitudinal Transect in Chile

Abstract

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 δ13C signature with soil depth (∆δ13C) 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 δ13C 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 ∆δ13C, soil incubations were performed. Highest 13C 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 13C’s enrichment in parallel with decreasing C content with depth. The analysis of the relationship between ∆δ13C values versus CMR and SPR showed a significant positive relationship across all data points (p < 0.0001, R2 = 0.62; p < 0.01, R2 = 0.29, respectively). Partial correlation analysis of control variables indicates a relationship between ∆δ13C with CMR and SPR when controlling for climatic and soil physicochemical variables. ∆δ13C 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 ∆δ13C.