Coupling of δ 13 C and δ 15 N to understand soil organic matter sources and C and N cycling under different land-uses and management: a review and data analysis

This review analyzes the data on co-variations in δ 13 C and δ 15 N of soils with land-use types, management, and disturbance obtained from literature to explore potential implications of the dual isotopes in the study of soil organic matter (SOM) sources and C and N processes. Overall, croplands (δ 13 C and δ 15 N were − 20.3 ± 4.4‰ and + 7.6 ± 4.4‰, respectively) had greater isotopic values than grasslands (‒26.3 ± 3.0‰ and + 5.4 ± 1.1‰, respectively) and forests (− 26.0 ± 1.1‰ and + 4.3 ± 2.2‰, respectively). For intensively managed lands such as croplands and grasslands, application of organic inputs such as manure and compost of which isotopic signatures differed from the indigenous SOM was the main driver of co-variations in the δ 13 C and δ 15 N of SOM. For natural forests, both δ 13 C and δ 15 N of SOM co-increased with soil depth, reflecting heavy isotope enrichment during microbial stabilization of SOM and the potential influence of 13 C-depleted atmospheric CO 2 and 15 N-depleted N deposition on the upper soils. Such vertical co-enrichments of 13 C and 15 N were disturbed by a land-use conversion to other lands including croplands. Though there were indications that land management practices such as tillage in croplands and grazing in grasslands, land-use changes, and land disturbance including forest fire might also affect both δ 13 C and δ 15 N, more data need to be accumulated to find a general trend of the isotopic variations of SOM. Analysis of both δ 13 C and δ 15 N may enlarge understanding of changes in SOM sources and soil C and N cycling by land-use types, management, change, and disturbance.