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 delta C-13 signature with soil depth (Delta delta C-13) 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 delta C-13 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 Delta delta C-13, soil incubations were performed. Highest C-13 isotope abundance was found at low latitude (-22.57 parts per thousand, 35.5 degrees S) and lowest at high latitude (-27.43 parts per thousand, 53.2 degrees S). Our results show C-13's enrichment in parallel with decreasing C content with depth. The analysis of the relationship between Delta delta C-13 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 Delta delta C-13 with CMR and SPR when controlling for climatic and soil physicochemical variables. increment delta C-13 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 Delta delta C-13.