Divergence in soil particulate and mineral-associated organic carbon reshapes carbon stabilization along an elevational gradient

Abstract

Variations in climates and vegetation types along elevations in mountain ecosystems strongly reshape soil organic matter (SOM) stabilization. However, soil carbon (C) stabilization pathways from litter to SOM and potential mechanisms along elevations in the subalpine area remain unclear. Here, we investigated the C stabilization pathway from litter to particulate and mineral-associated organic matter (POM and MAOM) and associated drivers along elevational gradients in the Hengduan Mountains, China, based on δ13C signatures. Our results showed C stabilization pathways from litter to POM to MAOM, irrespective of elevation. Unexpectedly, the δ13C values of SOM and its fractions (POM and MAOM) were not significantly related to litter δ13C across elevations although litter was the main source of SOM, suggesting that other potential drivers could weaken the coordination of δ13C among litter and SOM fractions. We observed that the△13CLitter→POM (△13C between litter and POM) was more dependent on the direct effect of soil texture (i.e., sand, silt and clay). However, the △13CPOM→MAOM (△13C between POM and MAOM) was more related to microbial attributes (i.e., microbial community and enzyme activities).These results emphasizing the different stabilization procedures between POM and MAOM. Particularly, soil temperature dominantly determined △13CLitter→POM, but soil pH was the primary factor regulating the △13CPOM→MAOM. Overall, our results suggested that POM and MAOM formation occurred with different regulation processes, the POM formation was primarily via more physical pathways and MAOM formation mainly via more microbial pathways, thus providing novel insights into the better understanding of SOM formation and stabilization mechanisms in mountain ecosystems.