Increasing carbon sequestration in irrigated and rainfed agroecosystems: A global analysis of trend characteristics and driving mechanisms

Abstract

Agroecosystems have significant potential for carbon sequestration and are highly influenced by anthropogenic factors. However, the differences in carbon sink capacities between irrigated and rainfed agroecosystems, along with their underlying driving mechanisms, remain poorly understood. This study employed Innovative Trend Analysis and Breaks for Additive Seasonal and Trend to examine the trend characteristics and disparities in Net Ecosystem Productivity (NEP) across various global classifications of irrigated and rainfed agriculture. Advanced multi-model coupling techniques, such as Extreme Gradient Boosting, SHapley Additive exPlanations, and Generalized Additive Models, were utilized to explore the non-linear relationships between Net Primary Productivity (NPP), Heterotrophic Respiration (R_h), and NEP with crucial explanatory variables. These models also helped identify positive and negative influence threshold effects and potential driving mechanisms. The results revealed an overall increasing trend (0.38 gC·m⁻²·year⁻¹) in NEP across cropland in most regions (68.6%) globally from 1981 to 2019. On average, rainfed cropland exhibited higher NEP than irrigated cropland, although the annual rate of NEP increase was more significant for irrigated cropland. Notably, the largest abrupt changes in NEP across many cropland regions (65.0%) affected the asymptotic trends in subsequent years but did not reverse the direction of the preceding trends. The relationship between NEP and explanatory variables is predominantly non-linear, varying significantly across seasons and cropland types. Irrigation modifies the thresholds for both positive and negative effects of driving drivers on NEP. The intrinsic indicators, NPP and R_h, contribute 62.1% and −37.9%, respectively, to changes in NEP. Human activities (73.2%) emerged as the primary influence on NEP, followed by atmospheric CO₂ concentrations (18.1%), with climate change (−3.3%) and vegetation dynamics (5.3%) having a lesser impact. This study advances our understanding of the disparities in carbon sink capacities between various irrigated and rainfed agroecosystem types on a global scale, shedding light on the underlying mechanisms that drive these differences.