Global change and China's terrestrial carbon sink: A quantitative review of 30 years' ecosystem manipulative experiments

Quantifying terrestrial carbon (C) sequestration potential is crucial for climate change mitigation and achieving C neutrality. Ecosystem manipulative experiments (EMEs) provide valuable in situ assessments of terrestrial C dynamics under global change. Although EMEs have expanded rapidly in China, their current state and role in elucidating spatial drivers of the country's terrestrial C sink and responses to major global change factors remain underexplored. This study systematically reviewed 1140 publications on Chinese EMEs, compiling a dataset of net primary productivity (NPP) and net ecosystem productivity (NEP). We identified 558 EMEs in China since 1991, marked by two phases: (1) a preliminary stage (1991–2004) and (2) exponential growth (2005–present). Most EMEs focused on grasslands, with limited emphasis on CO₂ enrichment and studies in Northwest China. Our findings revealed that China's terrestrial ecosystems serve as a significant C sink (positive NEP), with sink strength positively associated with temperature, soil clay, silt, and nitrogen (N) contents, and negatively with soil sand content and bulk density. Optimal conditions for NPP and NEP were observed at precipitation levels of 850–1176 mm and soil pH between 6.5 and 7.0. Elevated CO₂ levels stimulated NPP and NEP when combined with N addition, particularly organic N, and effects varied with temperature and soil texture (clay, silt, and sand contents). Warming impacts differed by ecosystem and facility type, reducing NPP in wetlands and NEP in open-top chambers. Combined warming with water or N addition generally increased NPP and NEP, while coupling it with reduced precipitation caused declines. Warming above 1.5°C often had adverse impacts. Both NPP and NEP responded nonlinearly to precipitation, exhibiting negative asymmetry in their responses to anomalies. Nitrogen addition consistently stimulated NPP and NEP, with responses influenced by application rates, frequency, duration, and soil texture and pH. Additive effects of combined global change factors on NPP and NEP were common. To improve our understanding of terrestrial C feedbacks to anthropogenic changes, future research should focus on long-term, multifactor studies in mature forests and wetlands, aiding in the pursuit of net-zero targets.