Carbonate Bedrock Shapes Soil Health: metal enrichment, nutrient limitation, and carbon sequestration in karst soil

Southwest China hosts the world's largest karst landscape, with karst soil derived from carbonate bedrock being widespread. Meanwhile, non-karst soil developed from silicate-rich clastic rocks is intermixed in this region. Unlike clastic rocks, carbonate rocks have unique lithological characteristics including abundant easily-soluble CaCO3 and MgCO3, and high weathering rates, which may shape different soil properties. Based on 1053 observations from 87 articles, we compared soil health between karst and non-karst soil to study the impacts of bedrock lithology, with heavy metals and nutrient elements being the main indicators. Our meta-analyses indicate that, compared to non-karst soil, karst soil had 433% higher Ca contents and 37−117% greater Fe/Mn contents on average. The abundant CaCO3 contributed to 25−28% higher pH and macroaggregate in karst soil. The secondary enrichment by Fe/Mn oxides likely contributes to 110–398% greater Cd, As, Cr, Pb, and Hg contents in karst soil, with limited phytoavailability. Additionally, the abundant CaCO3, Fe/Mn minerals, and macroaggregates provided critical physical barriers to protect organic matters from decomposing, resulting in 41–70% increase in total C, N and P, accompanied by 87–149% higher microbial C, N and P, but 27–36% lower DOC, NH4+-N, and available P in karst soil. Collectively, the higher enrichment of toxic metals and lower nutrient availability potentially pose negative impacts on plant growth, while the greater C sequestration, aggregate stability, and microbial diversity may have positive effects on karst soil health. Our work revealed the linkage of bedrock lithology to soil health in karst and non-karst soil and assessed the characteristics of karst soil from multiple perspectives. This review helps to better understand karst soil health and provides critical insights for their sustainable development.