Soil inorganic carbon: A review of global research trends, analytical techniques, ecosystem functions and critical knowledge gaps

Soil inorganic carbon (SIC) is a crucial component of the global carbon cycle, especially in drylands, and it plays critical roles in ecosystem functioning. The last two decades have witnessed a global surge in SIC research. As a result, the analytical methods have become many and research themes, broader. This can create confusion for researchers in identifying contemporary SIC research hotspots and the choice of suitable analytical techniques. In this review, a bibliometric analysis spanning the last twenty years (2003-2022) was used to provide insight into global research trends, analytical techniques, ecosystem functions, and research gaps in SIC research. Five research hotspots were identified: formation processes and morphological characterization of SIC, quantitative measurement of SIC, storage and SIC dynamics, modelling and mapping of SIC stock, and the environmental and ecosystem implications of SIC including, ecosystem management, past environment and climate reconstruction, geochronology, and archaeology. The characterisation of SICs requires the use of a range of complementary methods, but the choice must be made according to the objectives pursued, financial resources, and technical and environmental advantages. For quantitative measurements, dry combustion seems to give good results in terms of accuracy; however, it is less environmentally friendly, more expensive, and slower than spectroscopic methods, which are suitable for large-scale studies. This study has highlighted the need for further research into the role of SIC as a key soil property influencing ecosystem services. It also calls for more in-depth analysis of the long-term effects of land management regimes on SIC dynamics. This review provides reference topics for an indepth study of SICs to improve understanding of their role in the global carbon cycle and ecosystem services.