The Role of Continuous Living Roots in Soil Carbon Sequestration Efficiency: A Meta-Analysis of Carbon Stocks and Inputs in Contrasting Agricultural Systems

Recent soil science research highlights that roots are a key source of soil organic C (SOC) in agricultural systems because root inputs are more efficiently transformed into soil organic matter than shoot inputs. We conducted a systematic meta-analysis of cropping system studies to evaluate the effect of enhanced living root continuity on SOC sequestration efficiency (i.e., SOC stock per unit C input) across diverse environments. Our analysis included 21 studies and 57 observations that measured C inputs and SOC stocks in paired systems of enhanced living root continuity and control systems. The paired systems included: continuous crop systems vs. fallow-inclusive systems, cover crop vs. no cover crop systems, and perennial-inclusive rotations vs. annual-only rotations. We analyzed the effect of enhanced living root continuity on average annual C inputs, C stocks, and SOC sequestration efficiency. Average annual C inputs were 51% and 21% greater in perennial systems and continuous cropping systems, respectively, relative to their corresponding control systems, whereas cover crop-inclusive systems did not differ significantly from no-cover-crop systems. The SOC stocks were 15% and 8% greater in perennial systems and continuous cropping systems, respectively, and tended to be greater in cover crop-inclusive systems than in no-cover-crop systems (p = 0.095). Because perennial and continuous cropping systems increased C inputs proportionally more than SOC stocks, they exhibited lower SOC sequestration efficiency than their respective control systems. Thus, our study found that cropping systems with enhanced living root continuity improve SOC storage primarily by increasing total C inputs rather than by enhancing the efficiency of C sequestration.