<b>Biological Invasions Enhance Soil Carbon Content in Terrestrial Ecosystems</b>

While biological invasions are acknowledged as a major driver of global environmental change, a systematic quantification of their impacts on soil carbon dynamics across different ecosystems and functional groups is still lacking. Our global meta-analysis of 1419 observations from 213 studies indicates that biological invasion leads to a 15% increase in soil carbon density in terrestrial ecosystems, although the magnitude of increase varied substantially across ecosystems. The most pronounced carbon accumulation occurs in urban ecosystems (+85.9%) and anaerobic wetlands (+47.7%), followed by forests (+23.4%) and grasslands (+20.9%), while tundra systems show no significant response. There is also significant variability among different functional groups, reflecting the fundamental differences in the functional strategies of the invaders. Annual herbaceous invaders exerted the strongest stimulatory effect on carbon content (+68.2%), markedly exceeding that of shrubs (+35.0%) and perennial herbs (+37.7%). In contrast, perennial climbing vines were associated with a reduction in carbon content (–12.2%). Trees, ferns, mammals, and soil macrofauna showed no significant effects. Climate exerted a stronger influence on SOC variation than biological traits, with mean annual temperature and precipitation alone explaining 28% of the observed changes. In fact, these overall patterns can be explained by a trait-environment matching process: the success and impact of an invader depend on how its growth strategy interacts with ecosystem-specific filters, like the disturbance regimes in urban systems or oxygen limitations in wetlands. Our study thus offers a mechanistic understanding essential for informing forecasts of global carbon cycling in an era of biological invasions.