Hierarchical drivers shaping the global patterns of soil organic carbon

Recent advancements in observational data and experimental research have
significantly enhanced our understanding of the mechanisms governing the
magnitude, distribution, and dynamics of soil organic carbon (SOC).
However, few studies have systematically explored the hierarchical drivers
of SOC. This study addresses this gap by integrating multiple independent
datasets—covering productivity, carbon allocation, carbon turnover, and
carbon fractions—to construct a comprehensive framework for the
hierarchical drivers shaping global SOC patterns. Using this framework, we
examine the impact pathways and contributions of primary drivers. Our
findings show that climate, as the fundamental primary driver, mainly
influences SOC through carbon input pathways, while soil properties, as a
secondary driver, predominantly affect SOC via carbon output pathways.
Further analysis reveals that carbon input plays a key role in shaping
topsoil SOC distribution, while carbon output is more influential in
regulating subsoil SOC. In both cases, these drivers exert their effects
primarily through stable organic carbon fractions, particularly
mineral-associated organic carbon (MAOC), whose influence on particulate
organic carbon (POC) is the opposite. This study provides the first
quantification of the impact pathways and relative strengths of the
hierarchical drivers shaping global SOC. It also underscores the need to
consider the hierarchical structure of these drivers when assessing the
magnitude, distribution, and dynamics of SOC, particularly in relation to
its fractions.